DC-DC UPS?

[Guest]

| Believe whatever you like, but typically it's just a bridge
| rectifier, then a voltage doubler in 110VAC locations, so
| it's 2 x diode drop of about 0.7V. You still have to have a
| capacitor, though perhaps a smaller capacity would suffice
| if the power were already DC. That combined with removal of
| the bridge rectifier isn't much cost or space savings. Some
| AC filtration circuitry could also be reduced or removed but
| not all of it. These parts are only a small % occupancy of
| the real-estate in a PSU.

Sure, it's not a great deal of advantage to remove them. But
it's definitely more than 1% of the wasted power.


|>Where there's dissipation, there is efficiency gained if that part can be
|>eliminated without incurring that cost elsewhere (but that may be an issue
|>in the data center to convert its incoming 3 phase 480VAC to 400VDC and
|>managing the paralleling with the battery banks).
|
| yes but only a minimal amount of efficiency gained. There
| are lots of other ways to reduce power consumption so it is
| stretching a point too far.

There are lots of things that can be done with minimal efficiency
improvements. Do them all and you get a lot.


|>| Further, commodity grade electrical supply line wire is not
|>| very expensive relative to most other components, the loss
|>| on the (existing AC, or per your idea going to DC) supply
|>| wiring is also negligible.
|>
|>It's not too bad at 120VAC, though a it better at 240VAC (which I would
|>prefer to use). But a design around 12VDC would be some very big wires.
|
| ??? Who suggested using a 12VDC whole-site supply? It's
| non-applicable.

It has been suggested as a means to make use of car or golf cart
batteries. At least 12VDC is interruptible by circuit breaker
reasonably easy.


| The topic was using existing mains supply infrastructure or
| moving to something proprietary for a supposed gain. Also,
| you are ignoring that converting from the mains AC to this
| HV, ~ 400VDC is not without losses. It still has to be
| rectified, did you propose using synchronous rectification
| (which has more benefit vs cost in lower voltage
| applications) or continuing to use a bridge rectifier? If a
| bridge, you have lower power loss with individual bridge
| rectifiers in each system PSU than only one for the entire
| site HD DC, since voltage drop rises with a current
| increase.

I'm not suggesting any of these things specifically. I'm just
pointing out the various aspects people who want to look into
the things they can do should take a look at (or not).

My own plans for a better electrical system for my computers is
to use a 240VAC system.


|>|>But such a setup would be far too hazardous for typical home use
|>|>(that is, not something sold commercially for a consumer market, even
|>|>though an engineer hobbyist might have no problem with it).
|>|
|>|
|>| It would be impractical and expensive, but the hazard not
|>| significantly different than present 110/220V AC delivery
|>| systems. All that to save a trivial amount of power.
|>
|>Such a system can be made safe by competent electricians. But for homes,
|>the standards have to consider do-it-yourself-ers doing the wiring.
|
| It would not be more hazardous to any significant extent,
| it's not as though a DIYer doesn't have to use same methods
| for 110/220V.

If things are kept entirely in a metal box and properly constructed,
the hazard is under control. But running high voltage DC through the
building poses serious hazard issues that need to be designed very
carefully (especially with respect to electrical code compliance).


|>DC is not as easy to interrupt as AC. And your fault current from a central
|>PSU might not have enough to work the breakers properly.
|
| The current isn't THAT much lower, if all these proprietary
| supply parts were being installed it would simply be a
| matter of also sourcing suitable breakers.

The types of breakers needed for equipment supplementary protection are
quite different than those needed for structural wiring. If you keep
all the DC wiring out of the structure, then you can use cheaper circuit
breakers.

Try checking the UL listed voltage ratings of breakers for AC vs. DC.


|>Even common DC to 120VAC inverters are dangerous for homes because such
|>inverters can't properly trip circuit breakers when there is a short on
|>the AC side.
|
| There's no need for them to trip a home circuit breaker
| until the current exceeds a safe level to that inverter.
| Instead they have internal fuses, it is shutting off the
| device with a problem instead of the entire AC circuit,
| exactly the solution you'd want.
|
| Not dangerous, optimal.

I'm referring to inverters that produce AC output feeding the structural
wiring of a building like a home. A short circuit in the wiring will not
produce anywhere near the current flow that would happen if you shorted
the same wiring when fed by utility power. In the case of utility power,
when you cross the wires together, you get a nice blue flash that quits
instantly as the breaker's magnetic trip kicks it off within a half cycle
(and the arc breaks at the zero crossing, if not before). The current
would be a low hundreds to low thousands of amps, depending of many factors
like transformer capacity, wire length, etc. Magnetric trips in circuit
breakers are set to at high levels like 80 amps and up. If they were set
lower, then starting motors would be tripping breakers all the time. In
industrial settings, breakers are even adjustable. Cheap home breakers
have fixed settings for the magnetic trip (the one that works fast). If
there is a low level of overload, the thermal trip will eventually get it,
but it takes time to warm up and bend metal enough to release teh spring
energy to open the circuit. Inverters cannot deliver the high current
levels to start bit motors or trip magnetic elements of circuit breakers.
So if you cross the wires when an inverter is in use, instead of that
bright blue flash, your get a small sizzling arc that keeps on going for
a minute or two. Shorts caused by wiring damage would end up starting a
fire given the time involved. Arc-fault breakers might be usable to solve
this issue (and they are being more widely required in the 2008 electrical
code).

 

[kony]

Neither of us really knows what size cells, but of course theyll be
sized for the job. However given that D cells can knock out 60A
there doesnt seem much doubt that it'll all fit in a standard 5.25"
case.

With Sub-C yes, but I am not convinced you could get enough
D cells plus supportive circuitry including the connectors,
wiring harness, etc, in that space (not just volume but also
the form factor dimensions.

Maybe it simply uses two drive bays instead, if the case has
the bays that isn't a problem. If it were important to have
this internal I would just as soon select a case with two
bays available so as to be able to reach higher capacity.

I'd look at NiFe rather than NiCd though. With their very high
current ability they can be made smaller and more V stable.

It'll drive the price up even more when it seems cost
prohibitive already vs a standard external UPS.

those other parts are fairly small volume-wise.

Each alone, yes, but they'll all have to be on a circuit
board isolated and/or mounted to the casing in the rear, and
all these low volume parts add up, as well as requiring
fairly beefy wiring or traces to keep voltage drop to a
minimum since it is already a large concern by extending the
primary PSU harness to this circuit, through it and away
from it. Maybe it's not impossible but to know for sure
with a given battery cell size you will have to make a
prototype or at least a detailed model.

I'm not planning any extra wiring required inside the PC. Why do you
think there would need to be? V_drop too high?

Yes, as well as degradation of the wiring and connectors.
You can't just push multiple times as much current through
these connectors and wiring for more than a few seconds
without it causing a problem and even for a few seconds
there is definitely going to be a voltage drop. Given brief
enough runtime that these parts stay within thermal
thresholds, you could just factor for the lower delivered
voltage and start out with a higher supply voltage, but this
current supplied will vary per system so it becomes more
complex to calculate or not a universal solution because you
have multiple variable factors effecting whether your
battery supply remains within the upper and lower limits the
system needs, particularly for 3.3 and 5V. You could make
it all easier by just using a regulated (switching) supply
after the battery, but this also raises the cost and size.

Why would a business user choose an inbuilt miniups?
1. Because they dont want to fork out on a large whole site UPS, nor
have loads of mains plugin UPSes cluttering up the place.

As I'd stated previously, there is no new technology
suddenly making this possible where it wasn't before. I
have not heard of any demand for such a product except this
one thread on usenet.

2. Lower cost than an external plugin UPS

.... but it's not, I guarantee this won't sell for less than
a $30 UPS. I'm thinking due to low volume the retail price
would be closer to $200. Remember, it's not just bare parts
costs, there's construction, development, advertising,
distribution, etc, and then there's the profit that has to
be made off the product.

3. Ease: just tick the box on the form and you get a data-safe PC.
4. Any company PCs used offsite will always be UPS protected
this way

Maybe I'm wrong and your idea puts you one step away from
millions in profit... but I doubt it. Build a prototype and
try it with multiple varying platforms. Keep a BOM and then
take a poll of who will pay $X for Y performing internal
UPS.

main psu doesnt go through the batt pack, the wiring in the pc is
not affected, the miniups just plugs into a molex connector, end of
job.

It has to have the main psu running through it.

Remember, the computer has to get power from both supplies.
They both have to be wired to the (motherboard for example)
part powered to deliver the power to it, BUT you can't just
use a splitter, because the output from the battery pack
being commonly connected to the main PSU would result in
high current into the battery pack or vice versa, depending
on which had a higher actual voltage level. With more
sophisticated electronics this could be overcome but not as
you'd described it. The cheapest solution would be to just
use isolation diodes, but once again the volume of the parts
goes up, towards being too big to fit in the bay space.

If running the Pc's original wiring loom proves too high a
V_drop
to set the batt pack out a little higher and run it open loop, then
there would also need to be an exrta sense wire tagged on. Very
easy.

As I mentioned above, you can't just connect it to the PSU
wiring harness, because you have two supplies with
inevitably, slightly different voltage levels. With an
isolation method you could use the PSU wiring harness but
you still have to break that wiring harness by splicing into
it before it gets to the components from the PSU, or have an
inbuilt circuit on the internal UPS to do this.

You're way overcomplicating this. The battery pack output stays
connected via a relay whenever the machine is on.

You mean disconnected, right? If so, ok BUT this is yet
another part taking up space that had not been mentioned
yet, and multi-pole or multiple relays capable of this much
DC current aren't particularly small, and further PCB space
and traces continue to add to the volume required.

At power down
it senses that and continues supplying power for 15s (ie it doesnt
distinguish mains failure from normal power down) then cuts out.

15 seconds is not long enough to make this product worth
buying/owning/etc, IMO.

It may also need to distinguish mains failure from normal
power down.

A possible way to control charging is to connect the half way point
on the batt pack to each rail (0v or 12v) via a basic reg, thus
charging each half of the pack alternately. Doide & R ensures the
pack and its halves can discharge very fast but only charge at a
trickle.

?? What do you mean connect the half way point?

Yes you could get a usable result with resistors and diodes,
providing all parts are suitably spec'd. It still may not
be a univeral solution since different systems have
different current requirements and the voltage will vary
based on current. IMO, it really needs to stay within ATX
specs which is 5%. I suspect a difference in current from
one system to the next, alone will exceed this 5% meaning it
would have to be custom designed for each system...
something an OEM could do but would eliminate it from being
an aftermarket product unless the system integrator knows
exactly how to spec the current requirement and there were
multiple models of this internal UPS to meet each different
system requirement.

It would be much easier to just use a DC-DC switching
regulator supply after the battery pack. That makes it
nearly universal (within the current capability it can
handle as a max. amount).

Do you know what the R or range of R is? I've not measured it. The
ATX Vspec allows a fair amount of swing IIRC

If the system has enough power interruptions to make this
UPS viable, we're talking about a continual overcurrent
which will degrade the connectors (first, and then wiring).
The ATX spec allows 5% but with battery voltage dropping
while discharging, battery voltage dropping with changes
(increases) in current, and the wiring plus connectors
causing further drop with increases in current, very quickly
the UPS needs matched to a system within a certain current
usage, and this also greatly depends on what that system is
doing at the moment the power goes out since it is very easy
for modern processors/GPU/etc to have changes in current
over 30% if not a lot more.

trying to avoid any such switching if poss. If we switched the batt
pack between charge and out, a power failure would mess with the
pc before the relay clicked in.

Well... for the purposes of what I wrote, a relay is a
switch.

yeah. If too much R and load variation we could resort to an extra
sense wire to fix it. That would require a high current reg though,
best avoided if poss.

The sense wire would need to be from the load to the
feedback in the main PSU, meaning the system as it started
can't remain intact, it has to have the PSU wiring modified
regardless of whether that went to the UPS before the
components.

As for a sense wire from the UPS to the load, that too would
be a good approach to take to keep the voltage right, as a
feedback to the UPS which has a regulation stage on the
output. This is really the only universal solution to
ensure compatibility, the way it needs to be done to work
well. As for high current regulator, you want a switching
regulator circuit anyway not a linear because linear is too
lossy. A typical voltage drop across one might be roughly
1.5 to 2.5V, which times at least a dozen amps total as a
sum of all power rails to power the system, is 18W+ loss,
reducing the battery pack's runtime. An LDO linear could be
used instead with lower loss but still it's a significant
loss when running from battery power and with the battery
capacity constrained by available space in a drive bay.

The current isn't necessarily much of a problem for the
regulator though, as I'd mentioned in a past rely all one
would have to do is put a pass transistor into the regulator
subcircuit. Examples of this can be found in some linear
regulator datasheets, for example I think National's LM317
datasheet has one.

http://www.national.com/ds.cgi/LM/LM117.pdf
pg 16, but using pass transistor(s) capable of the current
instead of the default 3 * LM195 shown.

I went off on a tangent there, a switching supply output
from the pack is really the best alternative.

They do things proprietary ways mainly because they can save
money. 20p off 10,000 units is £200, os if they can do it non
standardly for a few p less they will. But I dont see proprietary vs
not having a big effect on viability.

Proprietary vs univeral means the OEM can determine the
current consumption per rail of the target system, and match
the DC ups to it. Without having the target system's
current requirement there is another variable in whether the
UPS' DC output stays in spec, unless it has the regulation
stage following it before the load and ideally the feedback
remote sense lead.

One PC mfr would only capture
part of the market, but people buying new systems are an attractive
target for addons, especially if they promise to safeguard against
business data corruption or loss, and do it at lower cost than
anyone else's UPS, and with less hassle..

yes, and that is exactly why it needs the regulation stage
to make it universal instead of just running straight from
the pack to the load, which is basically the same reason why
a switching main PSU also needs (already has) a feedback
loop so it can adjust for differing loads.

 

[Noozer]

Might be a dumb question, but the expensive part of a UPS is converting
the AC to DC for storage, then back to AC for use.

Why not put the UPS *after* the PSU... three (?) mini UPS's actually - 5v,
12v and 3.3v... and the -5v, etc if necessary. It could possibly even
mount into a 5.25" drive bay.

Just jumping in here for a second...

I posted this, not to produce a cheaper UPS, but a form of power backup that
is safer for the PC.

Have you seen the waveforms that come out of some of the lower end UPS's?

If you consider the cost of a REAL UPS that puts out a TRUE sinewave, 100%
of the time (not just when the power goes out) then you have a lot more room
to develop an inbuilt UPS.

Also, I can understand that this device may not be something that will work
in every PC, but as new cases are developed a standard could emerge that
would allow for an inboard DC UPS.

Think about it... laptops already do this. They are fed DC and charge their
own battery pack and can run for hours. How hard could it be to duplicate
this for a normal PC and get 5 minutes runtime, so you can get a safe
hibernation?

 

[kony]

| Believe whatever you like, but typically it's just a bridge
| rectifier, then a voltage doubler in 110VAC locations, so
| it's 2 x diode drop of about 0.7V. You still have to have a
| capacitor, though perhaps a smaller capacity would suffice
| if the power were already DC. That combined with removal of
| the bridge rectifier isn't much cost or space savings. Some
| AC filtration circuitry could also be reduced or removed but
| not all of it. These parts are only a small % occupancy of
| the real-estate in a PSU.

Sure, it's not a great deal of advantage to remove them. But
it's definitely more than 1% of the wasted power.

Nope, you're only talking about conversion to DC first,
which as I already mentioned means necessarily elimination
of the rectifier, a (roughly) 1.4V drop on a 110 or 220V AC
supply, which is about 1%.

|>Where there's dissipation, there is efficiency gained if that part can be
|>eliminated without incurring that cost elsewhere (but that may be an issue
|>in the data center to convert its incoming 3 phase 480VAC to 400VDC and
|>managing the paralleling with the battery banks).
|
| yes but only a minimal amount of efficiency gained. There
| are lots of other ways to reduce power consumption so it is
| stretching a point too far.

There are lots of things that can be done with minimal efficiency
improvements. Do them all and you get a lot.

Do them all and you have an obscene expense, a lot of time,
manufacturing and delivery costs to offset the trivial gain.
If you are serious about power conservation it is not the
answer, the answer is more energy efficient PSU and powered
hardware, which make these tiny power savings quite trivial
in comparison. The numbers don't lie.

|>| Further, commodity grade electrical supply line wire is not
|>| very expensive relative to most other components, the loss
|>| on the (existing AC, or per your idea going to DC) supply
|>| wiring is also negligible.
|>
|>It's not too bad at 120VAC, though a it better at 240VAC (which I would
|>prefer to use). But a design around 12VDC would be some very big wires.
|
| ??? Who suggested using a 12VDC whole-site supply? It's
| non-applicable.

It has been suggested as a means to make use of car or golf cart
batteries. At least 12VDC is interruptible by circuit breaker
reasonably easy.

There is no problem designing a circuit breaker for the
current it would use, the only issue is that the rarity of
the implemention means fewer units sold = higher cost per
unit.

If things are kept entirely in a metal box and properly constructed,
the hazard is under control. But running high voltage DC through the
building poses serious hazard issues that need to be designed very
carefully (especially with respect to electrical code compliance).

Wrong. It's not a significant jump from 220AC to 340DC.
Yes it has to be designed carefully, but so does 220VAC.

| The current isn't THAT much lower, if all these proprietary
| supply parts were being installed it would simply be a
| matter of also sourcing suitable breakers.

The types of breakers needed for equipment supplementary protection are
quite different than those needed for structural wiring. If you keep
all the DC wiring out of the structure, then you can use cheaper circuit
breakers.

It's not a hard thing, every device needs independant cutoff
anyway, so the same rules apply per site circuit when
choosing a breaker designed for the purpose.

Try checking the UL listed voltage ratings of breakers for AC vs. DC.

We dont' have to care, the manufacturer of the breaker is
the one to use the spec to design it, all you have to do is
purchase and install it.

|>Even common DC to 120VAC inverters are dangerous for homes because such
|>inverters can't properly trip circuit breakers when there is a short on
|>the AC side.
|
| There's no need for them to trip a home circuit breaker
| until the current exceeds a safe level to that inverter.
| Instead they have internal fuses, it is shutting off the
| device with a problem instead of the entire AC circuit,
| exactly the solution you'd want.
|
| Not dangerous, optimal.

What you wrote that was snipped doesn't matter.

If the AC supply to the DC-AC invertor is not exceeding the
capacity of that AC circuit, that AC circuit should NOT
trip. The trip point is always needing to be where the
device with the excessive current lies and no further
problems upstream of that point by cutting breakers which
effect other devices, before that point.

 

[kony]

Just jumping in here for a second...

I posted this, not to produce a cheaper UPS, but a form of power backup that
is safer for the PC.

Have you seen the waveforms that come out of some of the lower end UPS's?

Keep in mind, a switching PSU doesn't need any particular
waveform, all it needs is for the high side bulk caps to
maintain a high enough voltage level. Switching PC PSU are
far more tolerant of AC power waveform deviations than other
devices... until that odd waveform produces too much current
for the circuit to handle, but such is not the case with a
typical consumer grade ups powering one computer rather than
a larger UPS powering many systems.

If you consider the cost of a REAL UPS that puts out a TRUE sinewave, 100%
of the time (not just when the power goes out) then you have a lot more room
to develop an inbuilt UPS.

Granted, cost is not always the limit. Even so, describe
this system that will not run (using a standard ATX 2.x
revision) from a non-sine ups. Any decent PSU will run from
a non-sine wave ups. To this extend, those selling
since-wave ups for switching psu use are selling an ideal
more than a benefit. Actually, on a sine wave ups, it can
actually create MORE of a current rush than not, because
there is shorter duration at the peak voltage above that of
the charged capacitors. I mean on average, there might
still be a very momentary higher rush with non-sine UPS, but
really the important factor is if that surge current exceeds
the capacity of the PSU or ups, not just an ideal onto
itself. Since plenty of systems do run fine from non-sine
ups, we should assume the ideal is less useful than the
reality of it working without needing to be a sine-wave for
a computer PSU load.

Also, I can understand that this device may not be something that will work
in every PC, but as new cases are developed a standard could emerge that
would allow for an inboard DC UPS.

yes, a standard could emerge, it would be possible.
My prior comments about it being problematic were in the
context of it being directly battery powered, not that it
being internal was a problem per se (for shorter duration
power since being internal limits the capacity of it). IOW,
a good universal solution will have a DC-DC switching
converter after the battery pack, which can regulate output
regardless of changing input voltage from the battery pack.
Once there is a regulated output and a defined input current
and voltage range, it is easily managed. It's just not so
easy to do without the battery pack output regulation stage.

Think about it... laptops already do this. They are fed DC and charge their
own battery pack and can run for hours. How hard could it be to duplicate
this for a normal PC and get 5 minutes runtime, so you can get a safe
hibernation?

It's not that it's hard any way you do it, but some
implementations could be costly, costly per capacity,
trouble-prone (if not regulated), or short lived if current
requirement exceeds the design capability.

Laptops run all power through a DC-DC regulation stage.
That's why they can work well doing that. It is also what I
proposed, that the battery pack not be a direct supply, just
an alternate input to a AC/DC conversion board.

 

[Guest]

| On 3 Oct 2007 01:25:54 GMT, (e-mail address removed) wrote:
|
|>
|>| Believe whatever you like, but typically it's just a bridge
|>| rectifier, then a voltage doubler in 110VAC locations, so
|>| it's 2 x diode drop of about 0.7V. You still have to have a
|>| capacitor, though perhaps a smaller capacity would suffice
|>| if the power were already DC. That combined with removal of
|>| the bridge rectifier isn't much cost or space savings. Some
|>| AC filtration circuitry could also be reduced or removed but
|>| not all of it. These parts are only a small % occupancy of
|>| the real-estate in a PSU.
|>
|>Sure, it's not a great deal of advantage to remove them. But
|>it's definitely more than 1% of the wasted power.
|
| Nope, you're only talking about conversion to DC first,
| which as I already mentioned means necessarily elimination
| of the rectifier, a (roughly) 1.4V drop on a 110 or 220V AC
| supply, which is about 1%.

There's more loss than that. The rectifiers do get quite hot.
It's more like 4%.

Maybe you have one that has gotten it down to 1%? What are the
rectifier part numbers?

Still, 1% or 4% it is not a significant portion of the BIG PICTURE
in power systems and savings. It might be in rare cases where DC
is more readily available for other reasons (such as direct solar
powered systems).


|>|>Where there's dissipation, there is efficiency gained if that part can be
|>|>eliminated without incurring that cost elsewhere (but that may be an issue
|>|>in the data center to convert its incoming 3 phase 480VAC to 400VDC and
|>|>managing the paralleling with the battery banks).
|>|
|>| yes but only a minimal amount of efficiency gained. There
|>| are lots of other ways to reduce power consumption so it is
|>| stretching a point too far.
|>
|>There are lots of things that can be done with minimal efficiency
|>improvements. Do them all and you get a lot.
|
| Do them all and you have an obscene expense, a lot of time,
| manufacturing and delivery costs to offset the trivial gain.
| If you are serious about power conservation it is not the
| answer, the answer is more energy efficient PSU and powered
| hardware, which make these tiny power savings quite trivial
| in comparison. The numbers don't lie.

Of course there are a lot of complex tradeoffs for power. These
things do change as costs of parts and costs of power change even
a little. What is efficient in equipment cost today might seem
like a bad idea in a couple years when there is a new power crisis.

But I do agree, a large scale all-DC system is NOT the way to go.
I would not do it. But that would be reasons other than eliminating
the waste of the first stage rectifiers.


|>|>| Further, commodity grade electrical supply line wire is not
|>|>| very expensive relative to most other components, the loss
|>|>| on the (existing AC, or per your idea going to DC) supply
|>|>| wiring is also negligible.
|>|>
|>|>It's not too bad at 120VAC, though a it better at 240VAC (which I would
|>|>prefer to use). But a design around 12VDC would be some very big wires.
|>|
|>| ??? Who suggested using a 12VDC whole-site supply? It's
|>| non-applicable.
|>
|>It has been suggested as a means to make use of car or golf cart
|>batteries. At least 12VDC is interruptible by circuit breaker
|>reasonably easy.
|
| There is no problem designing a circuit breaker for the
| current it would use, the only issue is that the rarity of
| the implemention means fewer units sold = higher cost per
| unit.

The current is not the issue in the circuit breaker at DC. The voltage is.
Circuit breakers have to establish an arc voltage drop sufficient to cut
the arc, regardless of the current level. Current does affect other things
such as contact size. But voltage is crucial at DC, because DC does not
frequently (100 to 120 times a second) drop down to zero volts, as it does
with AC. A circuit breaker suitable for 240 volts AC might be no good at
DC for more than 48 volts. With DC the FULL VOLTAGE has to be reliably
interruptible. A breaker than can interrupt 120VDC would have a much wider
contact break spacing, and include other features to break the arc that
would not be needed at lower voltages like 12 volts, which cannot even
sustain a gap arc across the contacts as they open.


|>If things are kept entirely in a metal box and properly constructed,
|>the hazard is under control. But running high voltage DC through the
|>building poses serious hazard issues that need to be designed very
|>carefully (especially with respect to electrical code compliance).
|>
|
| Wrong. It's not a significant jump from 220AC to 340DC.
| Yes it has to be designed carefully, but so does 220VAC.

That's a MAJOR jump ... because of the jump from AC to DC. Take a look
at any good quality circuit breaker made by reputable companies like
Square-D or Cutler-Hammer. Look at the AC rating. Then look at the DC
rating. DC is always much lower. DC does not have zero crossing where
the arc can be extinguished much easier.


|>| The current isn't THAT much lower, if all these proprietary
|>| supply parts were being installed it would simply be a
|>| matter of also sourcing suitable breakers.
|>
|>The types of breakers needed for equipment supplementary protection are
|>quite different than those needed for structural wiring. If you keep
|>all the DC wiring out of the structure, then you can use cheaper circuit
|>breakers.
|
| It's not a hard thing, every device needs independant cutoff
| anyway, so the same rules apply per site circuit when
| choosing a breaker designed for the purpose.

Supplementary isolation breakers are not intended for short circuit
fault interruption. Structure based breaker are required to be due
to the risk of short circuit faults in the structure causing fires.
Risks inside equipment enclosures are different.


|>Try checking the UL listed voltage ratings of breakers for AC vs. DC.
|
| We dont' have to care, the manufacturer of the breaker is
| the one to use the spec to design it, all you have to do is
| purchase and install it.

And their requirements are different. But if you have wiring in the
building, that wiring has to be protected at the SOURCE, and it has to
meet more requirements than needed for the equipment.


|>|>Even common DC to 120VAC inverters are dangerous for homes because such
|>|>inverters can't properly trip circuit breakers when there is a short on
|>|>the AC side.
|>|
|>| There's no need for them to trip a home circuit breaker
|>| until the current exceeds a safe level to that inverter.
|>| Instead they have internal fuses, it is shutting off the
|>| device with a problem instead of the entire AC circuit,
|>| exactly the solution you'd want.
|>|
|>| Not dangerous, optimal.
|>
|
|
| What you wrote that was snipped doesn't matter.
|
| If the AC supply to the DC-AC invertor is not exceeding the
| capacity of that AC circuit, that AC circuit should NOT
| trip. The trip point is always needing to be where the
| device with the excessive current lies and no further
| problems upstream of that point by cutting breakers which
| effect other devices, before that point.

A DC-AC inverter is not supplied with AC ... it is supplied with DC.

Circuit breaker protection against short circuit faults must always be
placed at the SOURCE of the power system involved. Where there is any
change of derived system or any change of circuit capacity, protection
is required. That's why every branch circuit in your home has a breaker
or fuse protecting it at the level that circuit needs. If you put in a
big central AC to DC converter and feed the DC through the building to
various outlets, hat _wiring_ must be protected at the source of the DC
(which means the output of that converter goes to a circuit breaker box
with a circuit breaker rated for DC at that voltage).

 

[Guest]

| Granted, cost is not always the limit. Even so, describe
| this system that will not run (using a standard ATX 2.x
| revision) from a non-sine ups. Any decent PSU will run from
| a non-sine wave ups. To this extend, those selling
| since-wave ups for switching psu use are selling an ideal
| more than a benefit. Actually, on a sine wave ups, it can
| actually create MORE of a current rush than not, because
| there is shorter duration at the peak voltage above that of
| the charged capacitors. I mean on average, there might
| still be a very momentary higher rush with non-sine UPS, but
| really the important factor is if that surge current exceeds
| the capacity of the PSU or ups, not just an ideal onto
| itself. Since plenty of systems do run fine from non-sine
| ups, we should assume the ideal is less useful than the
| reality of it working without needing to be a sine-wave for
| a computer PSU load.

Sine wave may still be needed for some other equipment often used
in association with a computer. Some wall-wart type "transformers"
may still need it, though most of these are now switching type that
can handle square wave.

Square wave does cause greater current-loss heating. But it is
not a significant thing on a small scale like a computer plugged
into a UPS.


|>Also, I can understand that this device may not be something that will work
|>in every PC, but as new cases are developed a standard could emerge that
|>would allow for an inboard DC UPS.
|
| yes, a standard could emerge, it would be possible.
| My prior comments about it being problematic were in the
| context of it being directly battery powered, not that it
| being internal was a problem per se (for shorter duration
| power since being internal limits the capacity of it). IOW,
| a good universal solution will have a DC-DC switching
| converter after the battery pack, which can regulate output
| regardless of changing input voltage from the battery pack.
| Once there is a regulated output and a defined input current
| and voltage range, it is easily managed. It's just not so
| easy to do without the battery pack output regulation stage.

Maybe someone could make such a device entirely in a power supply form
factor? It depends on how much time we're asking it to handle. If
we want to ride though the 2-4 second power blinks which make up over
half of power outage problems, rather small batteries would do, and
this might even be doable with capacitors alone.

If we want a couple minutes to do a quick clean automatic shutdown,
that could be harder, but considering the running time of batteries
in a laptop, I think even this is doable in a full sized PSU box.

 

[kony]

| On 3 Oct 2007 01:25:54 GMT, (e-mail address removed) wrote:
|
|>
|>| Believe whatever you like, but typically it's just a bridge
|>| rectifier, then a voltage doubler in 110VAC locations, so
|>| it's 2 x diode drop of about 0.7V. You still have to have a
|>| capacitor, though perhaps a smaller capacity would suffice
|>| if the power were already DC. That combined with removal of
|>| the bridge rectifier isn't much cost or space savings. Some
|>| AC filtration circuitry could also be reduced or removed but
|>| not all of it. These parts are only a small % occupancy of
|>| the real-estate in a PSU.
|>
|>Sure, it's not a great deal of advantage to remove them. But
|>it's definitely more than 1% of the wasted power.
|
| Nope, you're only talking about conversion to DC first,
| which as I already mentioned means necessarily elimination
| of the rectifier, a (roughly) 1.4V drop on a 110 or 220V AC
| supply, which is about 1%.

There's more loss than that. The rectifiers do get quite hot.
It's more like 4%.

At the currents used these typical silicon bridge
rectifiers have about 0.6(n)V drop each... so ok, I rounded
up to 0.7V, and it's going through 2 of them so that's
0.6(n)V * 2, I'll round up in your favor to 1.4V drop (out
of about 340VDC total).

1.4/340 = 0.4%

If you have some specs and math to back up your claim,
please share it.

Maybe you have one that has gotten it down to 1%? What are the
rectifier part numbers?

Any of them. They're nothing special, typical silicon
rectifiers, 4 of 'em in an epoxy casing rated for that
voltage and typically about 4-8A current.

Still, 1% or 4% it is not a significant portion of the BIG PICTURE
in power systems and savings. It might be in rare cases where DC
is more readily available for other reasons (such as direct solar
powered systems).

You're beating a dead horse at this point. If we're talking
about solar, it's already a DC battery array so there was no
nead for the rectifier.

The current is not the issue in the circuit breaker at DC. The voltage is.
Circuit breakers have to establish an arc voltage drop sufficient to cut
the arc, regardless of the current level. Current does affect other things
such as contact size. But voltage is crucial at DC, because DC does not
frequently (100 to 120 times a second) drop down to zero volts, as it does
with AC. A circuit breaker suitable for 240 volts AC might be no good at
DC for more than 48 volts. With DC the FULL VOLTAGE has to be reliably
interruptible. A breaker than can interrupt 120VDC would have a much wider
contact break spacing, and include other features to break the arc that
would not be needed at lower voltages like 12 volts, which cannot even
sustain a gap arc across the contacts as they open.

You're overlooking something quite important - you don't
have to build your own circuit breaker from scratch, you can
buy it just as you would the other parts for that power
delivery system.

| Wrong. It's not a significant jump from 220AC to 340DC.
| Yes it has to be designed carefully, but so does 220VAC.

That's a MAJOR jump ... because of the jump from AC to DC. Take a look
at any good quality circuit breaker made by reputable companies like
Square-D or Cutler-Hammer. Look at the AC rating. Then look at the DC
rating. DC is always much lower. DC does not have zero crossing where
the arc can be extinguished much easier.

Yes it's lower because it wasn't designed for this, they
make it cost effective for the intended purpose. As I'd
said already going with this proprietary supply would have
expense. The general idea here is not to think about trying
to use parts unsuited for the purpose but rather the right
parts to meet the goal. Otherwise, there's going to be some
fires and lawsuits.

|>The types of breakers needed for equipment supplementary protection are
|>quite different than those needed for structural wiring. If you keep
|>all the DC wiring out of the structure, then you can use cheaper circuit
|>breakers.
|
| It's not a hard thing, every device needs independant cutoff
| anyway, so the same rules apply per site circuit when
| choosing a breaker designed for the purpose.

Supplementary isolation breakers are not intended for short circuit
fault interruption. Structure based breaker are required to be due
to the risk of short circuit faults in the structure causing fires.
Risks inside equipment enclosures are different.

You're trying to make distinctions where there aren't any.
The same fault protection topology is needed either way,
it's just the means towards that end that differs in
component selection.

| If the AC supply to the DC-AC invertor is not exceeding the
| capacity of that AC circuit, that AC circuit should NOT
| trip. The trip point is always needing to be where the
| device with the excessive current lies and no further
| problems upstream of that point by cutting breakers which
| effect other devices, before that point.

A DC-AC inverter is not supplied with AC ... it is supplied with DC.

I was thinking of a typical UPS, but regardless the same
applies. You don't want to shut down an entire circuit due
to an output fault from one device on that circuit. The
circuit itself is still viable and within safe limits until
that device is ALSO drawing excess current, which was not
the scenario mentioned, and with any properly designed DC-AC
inverter will not happen because it will shutdown through an
active monitoring circuit or passive (fuse or breaker
internal to it).

Circuit breaker protection against short circuit faults must always be
placed at the SOURCE of the power system involved.

You were talking about the output of the supply having a
fault, that is not a "short circuit fault" on the supply you
claim needs shut off. It would be crazy to shut off
everything upstream and in parallel to a fault, only that
fault point onward is shut down. Only when a faulty device
causes a fault condition on it's supply line would that
supply line be shut down, we can totally ignore that there's
a DC-AC inverter, we can totally ignore if it's working
right or shorting itself out into a load/whatever, all we
have to care about is whether that condition is causing the
supply to it, to exceed the cutoff threshold, and this is a
variable not specified. Perhaps you were thinking this
would be the case but without defining this, there was no
cause for the supply shutoff from some "event" unless that
event causes the capacity of the supply to be exceeded, OR
if there is risk of human safety but nothing was detailed on
this front either.

 

[kony]

Maybe someone could make such a device entirely in a power supply form
factor?

I fail to see what purpose that would have, since it's not
as though we'd have a system without the main power supply
and very few cases can accomdate two PS2/ATX supplies. I
suspect we were talking about putting it in one or two 5
1/4" bays because that's the only likely available space in
a typical computer case. Most people don't have more than
one, maybe two optical drives and most midtower cases have
at least 3, 5 1/4 bays unless we also consider many of the
OEM systems which have only two bays, but these typically
come with only one optical drive so there is still one bay
available.

It depends on how much time we're asking it to handle. If
we want to ride though the 2-4 second power blinks which make up over
half of power outage problems, rather small batteries would do, and
this might even be doable with capacitors alone.

Yes it would be possible with capacitors, but to have only a
few seconds of runtime vs several minutes with a typical $30
UPS, the market for it seems quite small, driving up the
price even more. If surviving a power outtage, even
briefly, is important, it's not that much of a problem to
have a modest sized UPS nearby. It's certainly smaller than
the system is and we don't see everyone rushing out to be a
miniMAC just to shave this space. Instead the typical
owner/user appears to prefer versatility, power, and value
over small size.

If we want a couple minutes to do a quick clean automatic shutdown,
that could be harder, but considering the running time of batteries
in a laptop, I think even this is doable in a full sized PSU box.

Given a decent DC-DC regulation circuit on it's output, yes
it would be possible. However, filling the entire volume of
a power supply with Li-Ion batteries as used in a laptop
would be very expensive. That it's a niche product with a
custom DC-DC power supply adds even more to the cost. IMO,
the finished product would have to sell for several hundred
dollars to be profitable enough for the manufacturer to
continue production.

That seems like a pretty large cost, especially considering
that if all one really needed was to survive brief power
outtages, they could just hook a std keyboard, mouse and
monitor up to a laptop and use that instead. Since it is
targeted towards, and bought by the masses, it becomes far
more cost effective.

 

[Guest]

| On 4 Oct 2007 14:05:00 GMT, (e-mail address removed) wrote:
|
|>| On 3 Oct 2007 01:25:54 GMT, (e-mail address removed) wrote:
|>|
|>|>
|>|>| Believe whatever you like, but typically it's just a bridge
|>|>| rectifier, then a voltage doubler in 110VAC locations, so
|>|>| it's 2 x diode drop of about 0.7V. You still have to have a
|>|>| capacitor, though perhaps a smaller capacity would suffice
|>|>| if the power were already DC. That combined with removal of
|>|>| the bridge rectifier isn't much cost or space savings. Some
|>|>| AC filtration circuitry could also be reduced or removed but
|>|>| not all of it. These parts are only a small % occupancy of
|>|>| the real-estate in a PSU.
|>|>
|>|>Sure, it's not a great deal of advantage to remove them. But
|>|>it's definitely more than 1% of the wasted power.
|>|
|>| Nope, you're only talking about conversion to DC first,
|>| which as I already mentioned means necessarily elimination
|>| of the rectifier, a (roughly) 1.4V drop on a 110 or 220V AC
|>| supply, which is about 1%.
|>
|>There's more loss than that. The rectifiers do get quite hot.
|>It's more like 4%.
|
| At the currents used these typical silicon bridge
| rectifiers have about 0.6(n)V drop each... so ok, I rounded
| up to 0.7V, and it's going through 2 of them so that's
| 0.6(n)V * 2, I'll round up in your favor to 1.4V drop (out
| of about 340VDC total).
|
| 1.4/340 = 0.4%

Why do you think this is the correct formula?


| If you have some specs and math to back up your claim,
| please share it.

I don't have specs on the rectifiers. Why would I? But what I do
have is heat sense. They, and the heat sinks attached, do get very
hot. Perhaps your measurements are missing some harmonics? I am
curious why the math doesn't match the reality. I wasn't before as
I never had a reason to do the math, myself.

Maybe if you work out the math for all the other parts in the PSU,
maybe we can see where the other 99% of the power is lost.


|>Maybe you have one that has gotten it down to 1%? What are the
|>rectifier part numbers?
|
| Any of them. They're nothing special, typical silicon
| rectifiers, 4 of 'em in an epoxy casing rated for that
| voltage and typically about 4-8A current.
|
|
|>
|>Still, 1% or 4% it is not a significant portion of the BIG PICTURE
|>in power systems and savings. It might be in rare cases where DC
|>is more readily available for other reasons (such as direct solar
|>powered systems).
|
| You're beating a dead horse at this point. If we're talking
| about solar, it's already a DC battery array so there was no
| nead for the rectifier.

That's _why_ I suggested solar ... because it does not need a rectifier.
It's just a special case that _maybe_ someone might have at some point.
It's certainly not a normal case, at least not to run the solar power
directly into the post-rectifier stage of the PSU. Of course they would
have to be sure they are getting sufficient voltage from the solar array
without an overvoltage.

Lots of PSUs these handle the full 100-240 VAC range, so they do have a
means to work on anything in between without switching to voltage doubling.
I don't know if the DC stage (where you typically see 340 VDC) is where
the wide voltage swing happens (e.g. 140-340 VDC for 100-240 VAC in), but
if it is, then direct solar probably could be configured to that range and
made to work. If they wanted to (I don't care to).



|>The current is not the issue in the circuit breaker at DC. The voltage is.
|>Circuit breakers have to establish an arc voltage drop sufficient to cut
|>the arc, regardless of the current level. Current does affect other things
|>such as contact size. But voltage is crucial at DC, because DC does not
|>frequently (100 to 120 times a second) drop down to zero volts, as it does
|>with AC. A circuit breaker suitable for 240 volts AC might be no good at
|>DC for more than 48 volts. With DC the FULL VOLTAGE has to be reliably
|>interruptible. A breaker than can interrupt 120VDC would have a much wider
|>contact break spacing, and include other features to break the arc that
|>would not be needed at lower voltages like 12 volts, which cannot even
|>sustain a gap arc across the contacts as they open.
|
| You're overlooking something quite important - you don't
| have to build your own circuit breaker from scratch, you can
| buy it just as you would the other parts for that power
| delivery system.

I never said you have to build it from scratch. For building structure
wiring (where you have the AC-DC in a separate room from the DC utilization)
then you have to buy listed and rated breakers. What I did was explain why
breakers for DC have to be designed better than for the same AC voltage.


|>| Wrong. It's not a significant jump from 220AC to 340DC.
|>| Yes it has to be designed carefully, but so does 220VAC.
|>
|>That's a MAJOR jump ... because of the jump from AC to DC. Take a look
|>at any good quality circuit breaker made by reputable companies like
|>Square-D or Cutler-Hammer. Look at the AC rating. Then look at the DC
|>rating. DC is always much lower. DC does not have zero crossing where
|>the arc can be extinguished much easier.
|
| Yes it's lower because it wasn't designed for this, they
| make it cost effective for the intended purpose. As I'd
| said already going with this proprietary supply would have
| expense. The general idea here is not to think about trying
| to use parts unsuited for the purpose but rather the right
| parts to meet the goal. Otherwise, there's going to be some
| fires and lawsuits.

Yes, you must use the parts properly suited for the purpose. And that does
mean breakers that are rated for the ability to interrupt DC fault currents
at the operating voltage. And no matter how you design it, the physics of
DC is that you need a greater ability to quench an arc because you always
have to deal with full peak voltage/current because it is DC, unlike AC
which gives you some times of much lower voltage/current when it can be
quenched more easily.


|>|>The types of breakers needed for equipment supplementary protection are
|>|>quite different than those needed for structural wiring. If you keep
|>|>all the DC wiring out of the structure, then you can use cheaper circuit
|>|>breakers.
|>|
|>| It's not a hard thing, every device needs independant cutoff
|>| anyway, so the same rules apply per site circuit when
|>| choosing a breaker designed for the purpose.
|>
|>Supplementary isolation breakers are not intended for short circuit
|>fault interruption. Structure based breaker are required to be due
|>to the risk of short circuit faults in the structure causing fires.
|>Risks inside equipment enclosures are different.
|
| You're trying to make distinctions where there aren't any.
| The same fault protection topology is needed either way,
| it's just the means towards that end that differs in
| component selection.

The legal requirements for breakers inside equipment is different than
for breakers protecting building wiring (which must be involved if you
feed the power in question through building walls).


|>| If the AC supply to the DC-AC invertor is not exceeding the
|>| capacity of that AC circuit, that AC circuit should NOT
|>| trip. The trip point is always needing to be where the
|>| device with the excessive current lies and no further
|>| problems upstream of that point by cutting breakers which
|>| effect other devices, before that point.
|>
|>A DC-AC inverter is not supplied with AC ... it is supplied with DC.
|
| I was thinking of a typical UPS, but regardless the same
| applies. You don't want to shut down an entire circuit due
| to an output fault from one device on that circuit. The
| circuit itself is still viable and within safe limits until
| that device is ALSO drawing excess current, which was not
| the scenario mentioned, and with any properly designed DC-AC
| inverter will not happen because it will shutdown through an
| active monitoring circuit or passive (fuse or breaker
| internal to it).

Certainly it is better to minimize how much gets cut off by a breaker.
If you have a DC short inside a UPS, then it's breaker is supposed to
handle it, whatever that takes. One advantage a UPS has is that it
can cut off the AC power on the input when it detects the DC power is
at a serious overcurrent situation. Then you only have to deal with
the battery power instead of both the battery and converter power.

Of course you don't want the while AC circuit the UPS is pluged into
to trip off. The converter is generally current limiting and if there
is a DC short, it will typically at most just raise the AC current by
a fair amount or so (maybe double the current which will leave an AC
breaker on for several seconds to a few minutes).


|>Circuit breaker protection against short circuit faults must always be
|>placed at the SOURCE of the power system involved.
|
| You were talking about the output of the supply having a
| fault, that is not a "short circuit fault" on the supply you
| claim needs shut off. It would be crazy to shut off
| everything upstream and in parallel to a fault, only that
| fault point onward is shut down. Only when a faulty device
| causes a fault condition on it's supply line would that
| supply line be shut down, we can totally ignore that there's
| a DC-AC inverter, we can totally ignore if it's working
| right or shorting itself out into a load/whatever, all we
| have to care about is whether that condition is causing the
| supply to it, to exceed the cutoff threshold, and this is a
| variable not specified. Perhaps you were thinking this
| would be the case but without defining this, there was no
| cause for the supply shutoff from some "event" unless that
| event causes the capacity of the supply to be exceeded, OR
| if there is risk of human safety but nothing was detailed on
| this front either.

You would have to put a breaker at each point where you want to limit
the scope of outages caused by breaker tripping. If you have multiple
loads on a UPS, do you want to bother with a separate breaker on each
one, or just one for the whole UPS output. Each situation will differ.
For very large UPSes powering lots of computers, then yes, many breakers
is a good idea.

Nevertheless, if you have a DC source in a different room of the building,
then you _must_ have a breaker at that DC source, in addition to any others
you may have. That is because what is being protected is the wiring that
is in the building. Having individual breakers at each DC utilization is
fine, but you cannot depend on only that. The electrical code requires
the protection on all building wiring. Just because it is DC does not get
you a free pass. The NEC covers DC as well.

 

[Guest]

|>Maybe someone could make such a device entirely in a power supply form
|>factor?
|
| I fail to see what purpose that would have, since it's not
| as though we'd have a system without the main power supply
| and very few cases can accomdate two PS2/ATX supplies. I
| suspect we were talking about putting it in one or two 5
| 1/4" bays because that's the only likely available space in
| a typical computer case. Most people don't have more than
| one, maybe two optical drives and most midtower cases have
| at least 3, 5 1/4 bays unless we also consider many of the
| OEM systems which have only two bays, but these typically
| come with only one optical drive so there is still one bay
| available.

Many computers I have seen with dual/redundant PSUs have half
size PSUs. Use that half size design and make a battery box
in the other half. If the port for redundant PSUs can supply
power from one to the other, it might be plausible to make a
battery box that plugs straight in to where redundant PSUs
plug in.

But sure, for other cases, grabbing some unused space in the
drive bays for the battery box would work.


|> It depends on how much time we're asking it to handle. If
|>we want to ride though the 2-4 second power blinks which make up over
|>half of power outage problems, rather small batteries would do, and
|>this might even be doable with capacitors alone.
|
| Yes it would be possible with capacitors, but to have only a
| few seconds of runtime vs several minutes with a typical $30
| UPS, the market for it seems quite small, driving up the
| price even more. If surviving a power outtage, even
| briefly, is important, it's not that much of a problem to
| have a modest sized UPS nearby. It's certainly smaller than
| the system is and we don't see everyone rushing out to be a
| miniMAC just to shave this space. Instead the typical
| owner/user appears to prefer versatility, power, and value
| over small size.

Someone might consider the capacitors, even if more costly than
a cheap UPS, to be a good choice because it fits inside the case.

Some cases these days are made with PSU at the bottom. Maybe
they can just make a case with a full length space at the bottom
for a complete UPS-like integrated power system much like the OP
seems to want.


|>If we want a couple minutes to do a quick clean automatic shutdown,
|>that could be harder, but considering the running time of batteries
|>in a laptop, I think even this is doable in a full sized PSU box.
|
| Given a decent DC-DC regulation circuit on it's output, yes
| it would be possible. However, filling the entire volume of
| a power supply with Li-Ion batteries as used in a laptop
| would be very expensive. That it's a niche product with a
| custom DC-DC power supply adds even more to the cost. IMO,
| the finished product would have to sell for several hundred
| dollars to be profitable enough for the manufacturer to
| continue production.
|
| That seems like a pretty large cost, especially considering
| that if all one really needed was to survive brief power
| outtages, they could just hook a std keyboard, mouse and
| monitor up to a laptop and use that instead. Since it is
| targeted towards, and bought by the masses, it becomes far
| more cost effective.

I agree. A laptop would be a good choice even for someone like me who
has relatively little need for portable computing, just to have something
that can be usable in a long term power outage.

For my servers, my ISP has a big (3 phase) UPS system backed up by a
generator.

For my other computers, I just want them to shut down clean for a long
outage. A common UPS will do. The only issue I have is it would help
to run everything on 240 volts instead of 120 volts (I've reached the
limit of the one dedicated 120 volt circuit that was originally in that
room. Now I either need to add a 2nd one, or find a 240 volt UPS that
can handle the double-hot power system 240 volts in the USA has. There
are some around.

 

[kony]

| At the currents used these typical silicon bridge
| rectifiers have about 0.6(n)V drop each... so ok, I rounded
| up to 0.7V, and it's going through 2 of them so that's
| 0.6(n)V * 2, I'll round up in your favor to 1.4V drop (out
| of about 340VDC total).
|
| 1.4/340 = 0.4%

Why do you think this is the correct formula?

Why do you think it isn't? 1.4V loss with resultant ~
340VDC immediately following the rectification stage in a
typical passive PFC PSU. In active PFC the voltage would be
a little higher, even less rectification loss. Since the
loss stage directly feeds the following, the current is
constant between the two. voltage loss divided by resultant
voltage.

| If you have some specs and math to back up your claim,
| please share it.

I don't have specs on the rectifiers. Why would I?

Because any sane discussion of loss in a discrete part would
entail referencing the datasheet specs, or at least a
datasheet of same kind of device. In this case we can be
even lazier though and still reach a rough ballpark because
it's a typical moderately high voltage rated silicon diode
bridge as already mentioned.

But what I do
have is heat sense. They, and the heat sinks attached, do get very
hot. Perhaps your measurements are missing some harmonics? I am
curious why the math doesn't match the reality. I wasn't before as
I never had a reason to do the math, myself.

Something can feel warm to hot while still having a fairly
low power loss. A TO220 cased part for example will feel
quite hot with only 1W loss, unless heatsinked fairly well
and no bridge rectifier has a very massive 'sink, actually
the 'sink itself can make it seem even hotter because when
you touch it, the metal conducts heat to your finger at
higher rate than the epoxy casing would, though of course it
is offset by that epoxy casing being a bit cooler due to
having the 'sink on it.

Suppose the PSU is using 1A (@340VDC), that 1A * 1.4V =
1.4W, certainly enough to make it feel hot, and yet still a
very small loss in the context of powering a computer.

Maybe if you work out the math for all the other parts in the PSU,
maybe we can see where the other 99% of the power is lost.

There isn't 100% power lost, if there were there wouldn't be
any output to the system.

| You're beating a dead horse at this point. If we're talking
| about solar, it's already a DC battery array so there was no
| nead for the rectifier.

That's _why_ I suggested solar ... because it does not need a rectifier.

But it needs the cells, battery, wiring for it, when there
is an existing AC grid ready for the purpose. These parts
also have loss in manufacturing, minor loss in use. If it
were a better general way to power a computer, that's what
we'd be using.

It's just a special case that _maybe_ someone might have at some point.

Well yes some have used solor power, I believe
http://www.tomshardware.com has such a project ongoing and
has written an article or two about it. However I don't
recall the details of their plan, didn't think it involved
generating 340-odd VDC, probably lower voltage then a DC-DC
supply or inverter.

It's certainly not a normal case, at least not to run the solar power
directly into the post-rectifier stage of the PSU. Of course they would
have to be sure they are getting sufficient voltage from the solar array
without an overvoltage.

There is something else being overlooked though, that often
solar systems also have a rectifier between panels and
battery array.

Lots of PSUs these handle the full 100-240 VAC range, so they do have a
means to work on anything in between without switching to voltage doubling.
I don't know if the DC stage (where you typically see 340 VDC) is where
the wide voltage swing happens (e.g. 140-340 VDC for 100-240 VAC in), but
if it is, then direct solar probably could be configured to that range and
made to work. If they wanted to (I don't care to).

Wide input range units (without a switch to select voltage)
tend to be active PFC type, using a voltage boost circuit
(something like a fet switched inductor) to reach a point
at least a few dozen volts above 340V. If you really really
wanted to go all out and save every last fraction of a
percent in efficiency, these active PFC PSU would not be
used as there is no need for active PFC if there were a high
voltage DC supply, it is then just another point of loss in
the PSU.

I never said you have to build it from scratch. For building structure
wiring (where you have the AC-DC in a separate room from the DC utilization)
then you have to buy listed and rated breakers. What I did was explain why
breakers for DC have to be designed better than for the same AC voltage.

Ok, but fortunately we don't have to design, just by all
these special parts... I mean if I thought it was a useful
goal.

| You're trying to make distinctions where there aren't any.
| The same fault protection topology is needed either way,
| it's just the means towards that end that differs in
| component selection.

The legal requirements for breakers inside equipment is different than
for breakers protecting building wiring (which must be involved if you
feed the power in question through building walls).

Didn't "differs in component selection" already cover that?

You would have to put a breaker at each point where you want to limit
the scope of outages caused by breaker tripping. If you have multiple
loads on a UPS, do you want to bother with a separate breaker on each
one, or just one for the whole UPS output. Each situation will differ.
For very large UPSes powering lots of computers, then yes, many breakers
is a good idea.

Nevertheless, if you have a DC source in a different room of the building,
then you _must_ have a breaker at that DC source, in addition to any others
you may have. That is because what is being protected is the wiring that
is in the building. Having individual breakers at each DC utilization is
fine, but you cannot depend on only that. The electrical code requires
the protection on all building wiring. Just because it is DC does not get
you a free pass. The NEC covers DC as well.

I didn't say it didn't need a breaker, you were suggesting
that breaker should trip upstream of an invertor that was
not causing a fault condition on that supply line to the
invertor, rather a fault on the invertor output... which
should only break the circuit at the point of the fault
which is at the inverter, not upstream of it until the
inverter itself causing this secondary problem which it may
not, actually should not ever because it has it's own
inbuilt breaker, fuse, and probably overcurrent shutdown
circuit.

 

[kony]

|>Maybe someone could make such a device entirely in a power supply form
|>factor?
|
| I fail to see what purpose that would have, since it's not
| as though we'd have a system without the main power supply
| and very few cases can accomdate two PS2/ATX supplies. I
| suspect we were talking about putting it in one or two 5
| 1/4" bays because that's the only likely available space in
| a typical computer case. Most people don't have more than
| one, maybe two optical drives and most midtower cases have
| at least 3, 5 1/4 bays unless we also consider many of the
| OEM systems which have only two bays, but these typically
| come with only one optical drive so there is still one bay
| available.

Many computers I have seen with dual/redundant PSUs have half
size PSUs. Use that half size design and make a battery box
in the other half. If the port for redundant PSUs can supply
power from one to the other, it might be plausible to make a
battery box that plugs straight in to where redundant PSUs
plug in.

yes that might work, but it's also going to drive up the
cost further and I still feel the short runtime couldn't
justify the cost of doing it in even the cheapest way
possible.

Someone might consider the capacitors, even if more costly than
a cheap UPS, to be a good choice because it fits inside the case.

I doubt it, there's just not many scenarios where you can't
fit a small external UPS as it's not that large relative to
the computer itself, or the user, or anything else in a
typical office. Outside a typical office, maybe there would
be some special application for it, but it would seem a bit
backwards to design a thing without a clear application and
then go looking for one. Capacitors definitely won't
provide more than a few seconds of runtime, within normal
volumes being discussed) that's a very high cost for
coverage of only very short power interruptions.

Some cases these days are made with PSU at the bottom. Maybe
they can just make a case with a full length space at the bottom
for a complete UPS-like integrated power system much like the OP
seems to want.

Why not just use the external UPS and put the case on top of
it? I seem to be stuck on this idea of external being
better for most practical uses, so I doubt I'll be adding
much more to this thread.

 

[meow2222]

With Sub-C yes, but I am not convinced you could get enough
D cells plus supportive circuitry including the connectors,
wiring harness, etc, in that space (not just volume but also
the form factor dimensions.

Maybe it simply uses two drive bays instead, if the case has
the bays that isn't a problem. If it were important to have
this internal I would just as soon select a case with two
bays available so as to be able to reach higher capacity.




It'll drive the price up even more when it seems cost
prohibitive already vs a standard external UPS.


Each alone, yes, but they'll all have to be on a circuit
board isolated and/or mounted to the casing in the rear, and
all these low volume parts add up, as well as requiring
fairly beefy wiring or traces to keep voltage drop to a
minimum since it is already a large concern by extending the
primary PSU harness to this circuit, through it and away
from it. Maybe it's not impossible but to know for sure
with a given battery cell size you will have to make a
prototype or at least a detailed model.




Yes, as well as degradation of the wiring and connectors.
You can't just push multiple times as much current through
these connectors and wiring for more than a few seconds
without it causing a problem and even for a few seconds
there is definitely going to be a voltage drop. Given brief
enough runtime that these parts stay within thermal
thresholds, you could just factor for the lower delivered
voltage and start out with a higher supply voltage, but this
current supplied will vary per system so it becomes more
complex to calculate or not a universal solution because you
have multiple variable factors effecting whether your
battery supply remains within the upper and lower limits the
system needs, particularly for 3.3 and 5V. You could make
it all easier by just using a regulated (switching) supply
after the battery, but this also raises the cost and size.



As I'd stated previously, there is no new technology
suddenly making this possible where it wasn't before. I
have not heard of any demand for such a product except this
one thread on usenet.


... but it's not, I guarantee this won't sell for less than
a $30 UPS. I'm thinking due to low volume the retail price
would be closer to $200. Remember, it's not just bare parts
costs, there's construction, development, advertising,
distribution, etc, and then there's the profit that has to
be made off the product.



Maybe I'm wrong and your idea puts you one step away from
millions in profit... but I doubt it. Build a prototype and
try it with multiple varying platforms. Keep a BOM and then
take a poll of who will pay $X for Y performing internal
UPS.



It has to have the main psu running through it.

Remember, the computer has to get power from both supplies.
They both have to be wired to the (motherboard for example)
part powered to deliver the power to it, BUT you can't just
use a splitter, because the output from the battery pack
being commonly connected to the main PSU would result in
high current into the battery pack or vice versa, depending
on which had a higher actual voltage level. With more
sophisticated electronics this could be overcome but not as
you'd described it. The cheapest solution would be to just
use isolation diodes, but once again the volume of the parts
goes up, towards being too big to fit in the bay space.





As I mentioned above, you can't just connect it to the PSU
wiring harness, because you have two supplies with
inevitably, slightly different voltage levels. With an
isolation method you could use the PSU wiring harness but
you still have to break that wiring harness by splicing into
it before it gets to the components from the PSU, or have an
inbuilt circuit on the internal UPS to do this.




You mean disconnected, right? If so, ok BUT this is yet
another part taking up space that had not been mentioned
yet, and multi-pole or multiple relays capable of this much
DC current aren't particularly small, and further PCB space
and traces continue to add to the volume required.




15 seconds is not long enough to make this product worth
buying/owning/etc, IMO.

It may also need to distinguish mains failure from normal
power down.




?? What do you mean connect the half way point?

Yes you could get a usable result with resistors and diodes,
providing all parts are suitably spec'd. It still may not
be a univeral solution since different systems have
different current requirements and the voltage will vary
based on current. IMO, it really needs to stay within ATX
specs which is 5%. I suspect a difference in current from
one system to the next, alone will exceed this 5% meaning it
would have to be custom designed for each system...
something an OEM could do but would eliminate it from being
an aftermarket product unless the system integrator knows
exactly how to spec the current requirement and there were
multiple models of this internal UPS to meet each different
system requirement.

It would be much easier to just use a DC-DC switching
regulator supply after the battery pack. That makes it
nearly universal (within the current capability it can
handle as a max. amount).





If the system has enough power interruptions to make this
UPS viable, we're talking about a continual overcurrent
which will degrade the connectors (first, and then wiring).
The ATX spec allows 5% but with battery voltage dropping
while discharging, battery voltage dropping with changes
(increases) in current, and the wiring plus connectors
causing further drop with increases in current, very quickly
the UPS needs matched to a system within a certain current
usage, and this also greatly depends on what that system is
doing at the moment the power goes out since it is very easy
for modern processors/GPU/etc to have changes in current
over 30% if not a lot more.




Well... for the purposes of what I wrote, a relay is a
switch.



The sense wire would need to be from the load to the
feedback in the main PSU, meaning the system as it started
can't remain intact, it has to have the PSU wiring modified
regardless of whether that went to the UPS before the
components.

As for a sense wire from the UPS to the load, that too would
be a good approach to take to keep the voltage right, as a
feedback to the UPS which has a regulation stage on the
output. This is really the only universal solution to
ensure compatibility, the way it needs to be done to work
well. As for high current regulator, you want a switching
regulator circuit anyway not a linear because linear is too
lossy. A typical voltage drop across one might be roughly
1.5 to 2.5V, which times at least a dozen amps total as a
sum of all power rails to power the system, is 18W+ loss,
reducing the battery pack's runtime. An LDO linear could be
used instead with lower loss but still it's a significant
loss when running from battery power and with the battery
capacity constrained by available space in a drive bay.

The current isn't necessarily much of a problem for the
regulator though, as I'd mentioned in a past rely all one
would have to do is put a pass transistor into the regulator
subcircuit. Examples of this can be found in some linear
regulator datasheets, for example I think National's LM317
datasheet has one.

http://www.national.com/ds.cgi/LM/LM117.pdf
pg 16, but using pass transistor(s) capable of the current
instead of the default 3 * LM195 shown.

I went off on a tangent there, a switching supply output
from the pack is really the best alternative.


Proprietary vs univeral means the OEM can determine the
current consumption per rail of the target system, and match
the DC ups to it. Without having the target system's
current requirement there is another variable in whether the
UPS' DC output stays in spec, unless it has the regulation
stage following it before the load and ideally the feedback
remote sense lead.




yes, and that is exactly why it needs the regulation stage
to make it universal instead of just running straight from
the pack to the load, which is basically the same reason why
a switching main PSU also needs (already has) a feedback
loop so it can adjust for differing loads.

hope you got the reply, it hasnt showed up on this server yet.


NT

 

[Guest]

|>Maybe if you work out the math for all the other parts in the PSU,
|>maybe we can see where the other 99% of the power is lost.
|
| There isn't 100% power lost, if there were there wouldn't be
| any output to the system.

I think I figured out where the difference is. We were not talking
about the same thing. You were giving the percentage of the overall
power UTILIZATION that the rectifier represented as a loss, whereas
I was giving the percentage OF THE LOSS that the rectifier contributed.


|>That's _why_ I suggested solar ... because it does not need a rectifier.
|
| But it needs the cells, battery, wiring for it, when there
| is an existing AC grid ready for the purpose. These parts
| also have loss in manufacturing, minor loss in use. If it
| were a better general way to power a computer, that's what
| we'd be using.

I'm not saying solar is a better way to power a computer. But it might
get uused in some cercumstance "because it is there". If I were doing
it, I'd rather have the solar charge a bank of batteries that drive a
set of paralleled inverters to produce AC and run the AC through the
whole house. Other power source (utility, generator, windmill, etc)
would also be driving the battery charging, if I had a system like that
(I'd like to, but I don't right now).

 

[Guest]

| I doubt it, there's just not many scenarios where you can't
| fit a small external UPS as it's not that large relative to
| the computer itself, or the user, or anything else in a
| typical office. Outside a typical office, maybe there would
| be some special application for it, but it would seem a bit
| backwards to design a thing without a clear application and
| then go looking for one. Capacitors definitely won't
| provide more than a few seconds of runtime, within normal
| volumes being discussed) that's a very high cost for
| coverage of only very short power interruptions.

In my office (a downtown location on "network power") I have never seen
any outage longer than a blink. Those a possibly caused by some end of
the secndary network experiencing a fault and tripping out. But they
typically take out well more than half the computers that are not on a
UPS. We use rather small UPSes because such blinks is all we really
ever see.

Suburban and rural locations would be worse off. I live in a rural
location and when power goes out here, I typically see 3 recloser
actions with increasing outage times. Causes are typically trees
falling onto utility distribution (12.47kV) lines (yes, the trees
are well above them out here).


|>Some cases these days are made with PSU at the bottom. Maybe
|>they can just make a case with a full length space at the bottom
|>for a complete UPS-like integrated power system much like the OP
|>seems to want.
|
| Why not just use the external UPS and put the case on top of
| it? I seem to be stuck on this idea of external being
| better for most practical uses, so I doubt I'll be adding
| much more to this thread.

Personally, I'm all for the external, too. I'm just holding off to find
the right set of parts to put together a 240 volt system (with a small
transformer to make some 120 volts for a small few things that might not
handle 240). Then I can handle those phase loss brownouts (we've had 2
of those in as many years, lasting a couple hours each).

 

[kony]

|>Maybe if you work out the math for all the other parts in the PSU,
|>maybe we can see where the other 99% of the power is lost.
|
| There isn't 100% power lost, if there were there wouldn't be
| any output to the system.

I think I figured out where the difference is. We were not talking
about the same thing. You were giving the percentage of the overall
power UTILIZATION that the rectifier represented as a loss, whereas
I was giving the percentage OF THE LOSS that the rectifier contributed.

I see what you mean. As percent loss, it'd be closer to
that 1%/25% total efficiency losses = 4%