Single-rail vs. multi-rail power supplies?

[Yousuf Khan]

I currently have a desktop with a Zalman 600W PS, it was a pretty nice
PS a few years ago when I got it, but now it looks like the system has
been upgraded and grown again, and I'm starting to see signs that it's
not producing enough power for the components anymore. So I'm looking at
the market for bigger PS's, likely 750W+.

When I got the Zalman, multi-rail +12V were the de riguer feature of the
day. Now that I'm shopping for them again, I see that the manufacturers
have done an about-face, and they are advertising the advantages of
single-rail +12V. The old 600W had 4 rails at 16 Amps each. The new
single rails I'm seeing seem to have a rail at anywhere from 45A to 65A!
Why have the manufacturers done the about-face on single-rail vs.
multi-rail?

Yousuf Khan

 

[Paul]

I currently have a desktop with a Zalman 600W PS, it was a pretty nice
PS a few years ago when I got it, but now it looks like the system has
been upgraded and grown again, and I'm starting to see signs that it's
not producing enough power for the components anymore. So I'm looking at
the market for bigger PS's, likely 750W+.

When I got the Zalman, multi-rail +12V were the de riguer feature of the
day. Now that I'm shopping for them again, I see that the manufacturers
have done an about-face, and they are advertising the advantages of
single-rail +12V. The old 600W had 4 rails at 16 Amps each. The new
single rails I'm seeing seem to have a rail at anywhere from 45A to 65A!
Why have the manufacturers done the about-face on single-rail vs.
multi-rail?

Yousuf Khan

That's a good question.

The terminology is adjusted, to whatever sells power supplies.
That's a rule of thumb about marketing. You don't actually
have to be honest about what you're selling. You describe it
in any way, that will make you successful. if a competitor
touted single rail output, and he's selling supplies,
then you chime in with a matching story.

These are some examples of power supply designs.

AC ---- switcher --- 65A ---- 75A_limiter ----+---- 12V1
|
+---- 12V2
|
+---- 12V3

OK, let's take a Molex, and short +12V to ground on that one.
The whole yellow and black wires on the Molex, start to glow,
the plastic melts off the wire, and so on. While this is a
"true single rail" design, notice it's a safety hazard. The
design could provide around 12*75 = 900W of thermal energy,
if you adjusted the loading just right. If the short had a
resistance of 0.2 ohms, the supply likely wouldn't shut off.
A dead short, might trip it OK. Hard to guess...

Now, let's make a design closer to the intentions of the
IEC60950 spec, and limit individual outputs to a safer level.
This still isn't compliant, but its closer to the spirit
of the limitations you're supposed to apply to secondary outputs.

AC ---- switcher ----- 65A ---+-- 25A_limiter --------- 12V1
|
+-- 25A_limiter --------- 12V2
|
+-- 25A_limiter --------- 12V3

Now, the wires may still get hot, the connectors burn, but
the amount of power in any individual circuit, cannot exceed
12*25 = 300W. The limiter works, by switching off the supply,
if the current flow level is exceeded. An overload in any
branch, can switch it off.

Power supplies built as follows, are "true independent output"
circuits. A hint you're getting the real McCoy, is the chassis
is 1" to 1.5" longer than the competing power supply of the
same capacity. The density cannot be as great, because of
the replicated circuits. I don't think that many, were
actually built this way. If you open your Zalman, it probably
doesn't match this topology. Your Zalman, might be the
previous figure.

AC -- DC ---+-- switcher ----- 22A ------ 25A_limiter --- 12V1
300V |
+-- switcher ----- 22A ------ 25A_limiter --- 12V2
|
+-- switcher ----- 22A ------ 25A_limiter --- 12V2

I'd say that middle design, looks pretty good. No matter
whether my marketing department describes it as "one rail"
or "multi rail". The size of the supply, or the lack of
replicated circuits inside, can help you judge the
true topology.

I don't own a copy of IEC60950, so I can't copy/paste
the appropriate part. And the last time I looked, I couldn't
find a copy "floating" on the web. The keyword "SELV" comes
to mind, but that's about all I remember now.

HTH,
Paul

 

[Rod Speed]

Yousuf Khan wrote

I currently have a desktop with a Zalman 600W PS, it was a pretty nice PS a few years ago when I got it, but now it
looks like the system has been upgraded and grown again, and I'm starting to see signs that it's not producing enough
power for the components anymore.

What signs are those exactly ?

That wouldnt normally be the case unless you have one hell of a video card in it.

So I'm looking at the market for bigger PS's, likely 750W+.

When I got the Zalman, multi-rail +12V were the de riguer feature of the day. Now that I'm shopping for them again, I
see that the
manufacturers have done an about-face, and they are advertising the
advantages of single-rail +12V. The old 600W had 4 rails at 16 Amps each.

And I would be amazed if you are exceeding that.

The new single rails I'm seeing seem to have a rail at anywhere from 45A to 65A!

And even the biggest is only 1A more than you currently have.

Why have the manufacturers done the about-face on single-rail vs. multi-rail?

So they dont have to have 4 separate 12V regulators.

 

[Rob]

I currently have a desktop with a Zalman 600W PS, it was a pretty nice
PS a few years ago when I got it, but now it looks like the system has
been upgraded and grown again, and I'm starting to see signs that it's
not producing enough power for the components anymore. So I'm looking at
the market for bigger PS's, likely 750W+.

When I got the Zalman, multi-rail +12V were the de riguer feature of the
day. Now that I'm shopping for them again, I see that the manufacturers
have done an about-face, and they are advertising the advantages of
single-rail +12V. The old 600W had 4 rails at 16 Amps each. The new
single rails I'm seeing seem to have a rail at anywhere from 45A to 65A!
Why have the manufacturers done the about-face on single-rail vs.
multi-rail?

Yousuf Khan

Well get yourself one that has good weight and a three year warranty.

Bigger is not necessarily any better and depends on your PC configuration.

 

[Yousuf Khan]

Yousuf Khan wrote


What signs are those exactly ?

Well, we've discussed those on csiphs already, mainly the optical drives
sending controller error messages even when they are not being used, and
I'm also noticing some occasional spin retry errors on a few of my
internal HDD's.

That wouldnt normally be the case unless you have one hell of a video card in it.

Well, the video card is not a monster of any kind, it's more upper
mainstream, an AMD Radeon 6870.

And I would be amazed if you are exceeding that.

Well, I ran my system components through a few power supply calculators:

http://extreme.outervision.com/PSUEngine said I needed 580W.
http://www.thermaltake.outervision.com/Power said I needed 574W.
http://support.asus.com/powersupply.aspx said I needed 900W!!!

Obviously, the Asus rating is an outlier so I'm ignoring that one, but
the other two seem to agree pretty close to each other, and that level
is pretty close to the maximum power rating (within 96-97%) of my old
PS. And with the age of the PS advancing in years, its maximum capacity
might actually be decreasing over time.

When I first obtained this 600W PS, the PS calculator showed that my
system requirement was only in the upper 400W range. So I thought I had
more than enough leeway, but it looks like the various upgrades have
quickly taken up most of that leeway since then.

And even the biggest is only 1A more than you currently have.

When you add it up, yes the 4 separate rails come out to about 64A, but
the point is is it possible that some of the rails are overloaded by
themselves? Would it be easier to distribute the power if there was a
single larger rail rather than 4 smaller rails?

So they dont have to have 4 separate 12V regulators.

I found one possible explanation here:

http://www.overclock.net/t/88626/info-do-you-need-multiple-12v-rails

According to the above, the EU had mandated that no single +12V rail
could exceed 20A, and that later Intel also embraced that EU rule, and
further reduced that down to 18A. But now it looks like Intel no longer
requires the 18A rule. I'm not sure if the EU has also dropped its 20A
requirement, but here in North America there is no longer a need to have
separate rails anymore, so we can go to single super-rails.

Yousuf Khan

 

[Paul]

Well, I ran my system components through a few power supply calculators:

http://extreme.outervision.com/PSUEngine said I needed 580W.
http://www.thermaltake.outervision.com/Power said I needed 574W.
http://support.asus.com/powersupply.aspx said I needed 900W!!!

Obviously, the Asus rating is an outlier so I'm ignoring that one, but
the other two seem to agree pretty close to each other, and that level
is pretty close to the maximum power rating (within 96-97%) of my old
PS. And with the age of the PS advancing in years, its maximum capacity
might actually be decreasing over time.

When I first obtained this 600W PS, the PS calculator showed that my
system requirement was only in the upper 400W range. So I thought I had
more than enough leeway, but it looks like the various upgrades have
quickly taken up most of that leeway since then.

The HD6870 is 124 to 147 watts. One of the cards quoted here could be
an overclock. Try doing your power calculation manually.

http://www.xbitlabs.com/articles/graphics/display/asus-eah6870-directcu_4.html#sect0

Paul

 

[KR]

I currently have a desktop with a Zalman 600W PS, it was a pretty nice
PS a few years ago when I got it, but now it looks like the system has
been upgraded and grown again, and I'm starting to see signs that it's
not producing enough power for the components anymore. So I'm looking at
the market for bigger PS's, likely 750W+.

When I got the Zalman, multi-rail +12V were the de riguer feature of the
day. Now that I'm shopping for them again, I see that the manufacturers
have done an about-face, and they are advertising the advantages of
single-rail +12V. The old 600W had 4 rails at 16 Amps each. The new
single rails I'm seeing seem to have a rail at anywhere from 45A to 65A!
Why have the manufacturers done the about-face on single-rail vs.
multi-rail?

        Yousuf Khan

Traditionally it was always considered good practice to separate the
power for
digital and analog circuits as much as possible to prevent
interference.
This would especially be the case in audio systems.

In the case of a PC, this would mean keeping the supply for motors
(such as
Hard Drives, CD ROMS etc on a separate circuit, so as to minimise any
electrical
noise from these from interfering with digital circuits - assuming
this really is a problem in a modern PC.

Usually having separate supply cables from a common power source is
sufficient.



I would suggest it is more likely done to keep the currents manageable
on particular circuits however.
You might have 60A available, but in cases like this where one circuit
is never going to need more than (say) 15a,
it is safer to split it into 4 separate circuits.

Exactly the same is done in your home fusebox in having separate fuses
and circuits for your lights, power points,
air con, water heater, stove etc, rather than just having a single
200A fuse for the entire lot.

 

[Rod Speed]

Yousuf Khan wrote

Rod Speed wrote

Well, we've discussed those on csiphs already, mainly the optical drives sending controller error messages even when
they are not being used,

OK, I dont believe that those would be because you
are exceeding the 600W rating of the power supply.

I meant that the power supply may be failing, putting more noise
on the rails than is allowed. If thats the case, just replacing it with
another copy of the 600W supply should see that problem go away.

and I'm also noticing some occasional spin retry errors on a few of my internal HDD's.

Thats unlikely to be because doesnt have enough current on the
12V rail even tho you do have quite a few hard drives from memory.

If that is the problem, it makes more sense ot replace some
of the smaller drives with new much larger ones than it does
to change the power supply, tho you should change the power
supply because of the optical drive symptoms you are getting
to see if thats due to the power supply.

You dont necessarily need such a big supply for that test tho.

Well, the video card is not a monster of any kind, it's more upper mainstream, an AMD Radeon 6870.

Yeah, it only need 2 75W power connectors.

The 12V rails on that power supply are way above what it needs.

Well, I ran my system components through a few power supply calculators:

I dont buy those. What matters is AMD's statement of what the video card needs,
http://www.amd.com/us/products/desk...6870/pages/amd-radeon-hd-6870-overview.aspx#3
and thats where that 2 75W power connectors comes from,
and that detail you have already provided on 4 12V 16A rails.

Those are 192W rails, each one of them.

http://extreme.outervision.com/PSUEngine said I needed 580W.
http://www.thermaltake.outervision.com/Power said I needed 574W.
http://support.asus.com/powersupply.aspx said I needed 900W!!!

Yeah, thats obviously silly.

Obviously, the Asus rating is an outlier so I'm ignoring that one, but the other two seem to agree pretty close to
each other,

But nothing like what you get when you calculate the 12V rails explicitly.

That power supply handles the video card fine with 2 of the rails
and you have two more for your hard drives which wont take
anything like 384W even if they are all trying to spin up at once.

and that level is pretty close to the maximum power rating (within 96-97%) of my old PS.

Thats the problem with those power supply 'calculators', they
dont actually calculate what matters, the 12V rail currents.

And the 900W supply you are considering only has 1A more
12V current available anyway.

And with the age of the PS advancing in years, its maximum
capacity might actually be decreasing over time.

Nope, that doesnt happen.

What you can get is a deterioration of the low ESR caps and that
sees a lot more noise on the rails than there should be, but you dont
see a reduction in the rail current capacity and even if you did you
are nowhere near the maximum currents on any of those 12V rails.

When I first obtained this 600W PS, the PS calculator showed that my system requirement was only in the upper 400W
range.

Do you mean that the calculator has changed, or that
what you have in that system has changed that much ?

So I thought I had more than enough leeway, but it looks like the various upgrades have quickly taken up most of that
leeway since then.

Or the calculator has changed since then. What have you changed upgrade wise ?

When you add it up, yes the 4 separate rails come out to about 64A, but the point is is it possible that some of the
rails are overloaded by themselves?

Nope, not with that particular video card.

Would it be easier to distribute the power if there
was a single larger rail rather than 4 smaller rails?

No, in fact its harder because you cant do a remote sense
so that the highest current rail is seeing 12V at the pins
without increasing what the other connects get at the pins.

Not that that matter much, the specs on the variation in the 12V rails is pretty wide.

And you have the other problem with a single rail too, limiting the
current to say 75A can still see a decent fire with some shorts.

You dont get that with 4 seperate 16A max current rails. 200W
isnt that bad as long as there is someone around to turn it off.

800W can be pretty spectacular in the very small space of a
single molex nylon connector.

I found one possible explanation here:

According to the above, the EU had mandated that no single +12V rail could exceed 20A, and that later Intel also
embraced that EU rule, and further reduced that down to 18A. But now it looks like Intel no longer requires the 18A
rule.

Yeah, if thats accurate, it likely is the reason for the change.

I'm not sure if the EU has also dropped its 20A requirement, but here in North America there is no longer a need to
have separate rails anymore, so we can go to single super-rails.

I dont like the idea of a single rail that can in theory deliver 800W
being able to do short circuit protection adequately myself.

Corse most of the time a short would just blow off quite literally but that doesnt always happen.

 

[Yousuf Khan]

The HD6870 is 124 to 147 watts. One of the cards quoted here could be
an overclock. Try doing your power calculation manually.

http://www.xbitlabs.com/articles/graphics/display/asus-eah6870-directcu_4.html#sect0

No, mine is a Sapphire 6870, which might be pretty close to a reference
design.

Yousuf Khan

 

[Yousuf Khan]

Yousuf Khan wrote

OK, I dont believe that those would be because you
are exceeding the 600W rating of the power supply.

Maybe not the overall power supply rating, but maybe some of the
individual rails might be undercharged.

I meant that the power supply may be failing, putting more noise
on the rails than is allowed. If thats the case, just replacing it with
another copy of the 600W supply should see that problem go away.


Thats unlikely to be because doesnt have enough current on the
12V rail even tho you do have quite a few hard drives from memory.

Well, I do have six internal hard drives right now, and one optical
drive (Blu-Ray burner). It's the number of error messages that I'm
seeing on the BR burner that's got me most worried, but also recently I
saw a worrying pop-up message from Hard Disk Sentinel that it is
predicting an imminent failure of my boot drive too. I don't know which
of the rails all of these drives are connected to, but if they are all
connected to the same rail (very likely) then they might be all sharing
current from a diminished resource. I wonder how much current each of
the optical and hard drives use?

Yeah, it only need 2 75W power connectors.

The 12V rails on that power supply are way above what it needs.

One or two rails would go to the motherboard, another one would go to
the video card, and the last rail would be left for all of the rest of
the peripherals. I've mostly had no problems with motherboard components
(CPU, RAM, PCI cards), no problems with the video card, but the rest of
the system is all supplied by one rail, such as drives and fans and
lights. I won't really notice any power problems with the fans or
lights, but the drives might be pretty sensitive.

That power supply handles the video card fine with 2 of the rails
and you have two more for your hard drives which wont take
anything like 384W even if they are all trying to spin up at once.

I don't think the video card gets two whole rails to itself. The
motherboard 24-pin connector is one rail which would power the PCI/PCI-e
slots, chipset and RAM; and maybe it'll feed a few Watts to the CPU too.
Then another 6-pin plug would be a rail for the CPU alone, which also
plugs into the motherboard. Then a couple of video power connectors
would go into the video card, which would likely come from one rail by
itself. The video card would also receive some power from the
motherboard through the PCI-e slot. So the video card might have at most
maybe 1.5 rails for its use (partial motherboard rail & full video
rail). And the last rail for everything else in the system.

Thats the problem with those power supply 'calculators', they
dont actually calculate what matters, the 12V rail currents.

And the 900W supply you are considering only has 1A more
12V current available anyway.

Well, I'm not really considering a 900W PS, more likely a 750W one.

Do you mean that the calculator has changed, or that
what you have in that system has changed that much ?

Yup, the stuff in the system has changed that much. This system is in a
constant state of evolution, including the case itself. I upgraded from
a mid-tower with a capacity for only four 3.5" drives to one with six
3.5" drives, and then it quickly evolved to to fill up those additional
drive slots. Also there was a video card upgrade, and a CPU upgrade
along the way too.

Nope, not with that particular video card.

I don't think the video card is the issue here at all! Just those drives
in combination with all of the other powered peripherals inside that
system. I played around with the figures in one of the PS calculators,
and I found out that it's assuming 13W per 7200-rpm SATA hard drive, 24W
per 7200-rpm IDE HDD, 29W per Blu-Ray burner, 34W per DVD burner.

Based on that I currently have 129W in internal drives alone (4 SATA
HDD, 2 IDE HDD, 1 BR). When I previously had the dual DVD burners rather
than the single Blu-Ray, I had 168W worth of drives! This is now
starting to explain why my two DVD burners failed simultaneously.

I also have 4x 250mm case fans on the system (they came with the new
case). Each is regular fan is rated at 12W, and each LED fan is 13W.
Based on that I have 49W worth of fans (3 regular, 1 LED). Adding to the
previous figures of 129W and 168W brings them to overall totals of 178W
and 217W, respectively! If I only have 192W to play with per rail, then
I was well over when I had two DVD burners, and I'm sitting on the edge
still now.

No, in fact its harder because you cant do a remote sense
so that the highest current rail is seeing 12V at the pins
without increasing what the other connects get at the pins.

Not that that matter much, the specs on the variation in the 12V rails is pretty wide.

And you have the other problem with a single rail too, limiting the
current to say 75A can still see a decent fire with some shorts.

That is obviously a worry, and that's why they didn't do this in the
past. I'm hoping that now that they are doing it, that they may have
found a way to keep it under control these days?

Yousuf Khan

 

[Rod Speed]

Yousuf Khan wrote

Paul wrote

No, mine is a Sapphire 6870, which might be pretty close to a reference design.

Most Sapphires arent, actually.

Its all completely academic, you know that video card works fine on that particular power supply.

Even if it is loading down one of the 12V rails too much,
that wont be the rail that used for the optical drives.

 

[Rod Speed]

Yousuf Khan wrote

Rod Speed wrote

Maybe not the overall power supply rating, but maybe some of the individual rails might be undercharged.

You mean overloaded.

No, that isnt possible. The video card needs 2 75W supplys.

Even if they are both supplied from a single 12V rail in that supply,
thats only 150W from a rail that can deliver 192W, so there is bags
of margin in hand and you know the video card works fine anyway.

You cant possibly be exceeding what the other rails can deliver,
even 10 hard drives wouldnt do that if they are all starting at once,
and the symptoms you see arent when the drives are starting up
anyway with the optical drive symptoms.

Well, I do have six internal hard drives right now, and one optical drive (Blu-Ray burner).

Thats fine even if they are all on a single 192W 16A rail.

And you dont see the optical drive symptom at hard drive spinup time anyway.

It's the number of error messages that I'm seeing on the BR burner that's got me most worried,

Yes, and they wont be happening when all those drives are spinning
up. Thats the only time that those drives will be taking a lot of current.

but also recently I saw a worrying pop-up message from Hard Disk Sentinel that it is predicting an imminent failure of
my boot drive too.

Its notorious for crying wolf.

I don't know which of the rails all of these drives are connected to, but if they are all connected to the same rail
(very likely) then they might be all sharing current from a diminished resource.

I doubt it. I bet that if you do total the startup currents for all those
drives which you havent specified, they wont exceed the surge rating
of one of the rails. And even if they do, the most that you might see
is a few slow starts with the worst of the drives which might be what
HDS is mindlessly screaming about.

I wonder how much current each of the optical and hard drives use?

Its in the datasheets for all of them. You want the startup current.

You dont need to worry with the optical drive, it will be
be peanuts compared with the total of the hard drives.

One or two rails would go to the motherboard, another one would go to the video card,

Those rails can supply all the video card needs fine.

The video card needs 150W and each rail can deliver 192W

and the last rail would be left for all of the rest of the peripherals.

Likely. But thats still plenty.

I've mostly had no problems with motherboard components (CPU, RAM, PCI cards), no problems with the video card,

So it must be getting the power it needs.

but the rest of the system is all supplied by one rail, such as drives and fans and lights.

Yes, but even if that rail is a bit overloaded when the hard
drives are all spinning up at once, the worst that can do is
see the spinup time a bit longer than it would otherwise be
with just one drive connected.

They clearly do spin up.

I won't really notice any power problems with the fans or lights, but the drives might be pretty sensitive.

Nope, they arent at spinnup time and thats the only
time they are likely to be overloading even one rail.

I don't think the video card gets two whole rails to itself.

The video card datasheet does say it has two power connectors.

The motherboard 24-pin connector is one rail which would power the PCI/PCI-e slots, chipset and RAM; and maybe it'll
feed a few Watts to the CPU too. Then another 6-pin plug would be a rail for the CPU alone, which also plugs into the
motherboard.

And clearly that works fine.

Then a couple of video power connectors would go into the video card, which would likely come from one rail by itself.
The video card would also receive some power from the motherboard through the PCI-e slot. So the video card might have
at most maybe 1.5 rails for its use (partial motherboard rail & full video rail).

And it works fine so it must be getting what it needs 12V wise.

And the last rail for everything else in the system.

You dont kinow that with the fans etc particularly.

Yes, the hard drives may well be on one rail, but that should
be fine too and the worst you might see is some of the drives
being a bit slow to spin up, a complete yawn basically.

It wont be whats producing the symptoms with the optical drive
because the hard drives will have spun up long before you ever
write anything with the optical drive and so the current draw of
the hard drives will be well down on the startup currents.

Well, I'm not really considering a 900W PS, more likely a 750W one.

So you may not end up with any more 12V current at all.

Yup, the stuff in the system has changed that much. This system is in a constant state of evolution, including the
case itself. I upgraded
from a mid-tower with a capacity for only four 3.5" drives to one with six 3.5" drives, and then it quickly evolved to
to fill up those additional drive slots. Also there was a video card upgrade, and a
CPU upgrade along the way too.

I've never believed those calculators, I calculate the actual rail currents.

I don't think the video card is the issue here at all! Just those
drives in combination with all of the other powered peripherals
inside that system.

They arent all necessarily on just one rail and their currents arent
significant anyway compared with the hard drive startup currents.

I played around with the figures in one of the PS calculators, and I found out that it's assuming 13W per 7200-rpm
SATA
hard drive, 24W per 7200-rpm IDE HDD,

Thats pretty bogus when what matters is the startup currents.

29W per Blu-Ray burner, 34W per DVD burner.

Its silly to assume that all blue ray and dvd burners will consume
the same amount within 1W

Based on that I currently have 129W in internal drives alone (4 SATA HDD, 2 IDE HDD, 1 BR).

And one rail can deliver 192W, bags of margin.

When I previously had the dual DVD burners rather than the single Blu-Ray, I had 168W worth of drives!

Still fine for a 192W rail.

This is now starting to explain why my two DVD burners failed simultaneously.

Nope. Even if the rail was overloaded, and it isnt,
that wont kill two DVD burners simultaneously.

I also have 4x 250mm case fans on the system (they came with the new case). Each is regular fan is rated at 12W, and
each LED fan is 13W. Based on that I have 49W worth of fans (3 regular, 1 LED). Adding to the previous figures of 129W
and 168W brings them to overall totals of 178W and 217W, respectively!

Yebbut the hard drives numbers are bogus.

If I only have 192W to play with per rail, then I was well over when I had two DVD burners, and I'm sitting on the
edge still now.

Nope, because the worst that might happen is that a couple of the
hard drives might spin up a little more slowly than they would if they
were the only drive in the system and thats a complete yawn in practice.

That is obviously a worry, and that's why they didn't do this in the past. I'm hoping that now that they are doing it,
that they may have found a way to keep it under control these days?

Nope, it isnt even possible. 75A is one hell of a current at DC.

 

[Rod Speed]

KR wrote

Traditionally it was always considered good practice to separate the power
for digital and analog circuits as much as possible to prevent interference.
This would especially be the case in audio systems.

In the case of a PC, this would mean keeping the supply for motors
(such as Hard Drives, CD ROMS etc on a separate circuit, so as to
minimise any electrical noise from these from interfering with digital
circuits - assuming this really is a problem in a modern PC.

Thats why there are separate 5V, 3.3V and 12V rails.

Usually having separate supply cables from a common power source is sufficient.

I would suggest it is more likely done to keep the
currents manageable on particular circuits however.

Particularly when there are separate rails at the same voltage.

You might have 60A available, but in cases like this
where one circuit is never going to need more than
(say) 15a, it is safer to split it into 4 separate circuits.

Doesnt explain why they have now reverted to a single 12V rail.

Exactly the same is done in your home fusebox in having
separate fuses and circuits for your lights, power points,
air con, water heater, stove etc, rather than just having
a single 200A fuse for the entire lot.

The british do in fact have a single ring main for most of the GPOs.

That for other reasons tho, particularly minimising the wire guage used
and making the system more tolerant of poor connections at the GPOs etc.

 

[PeterC]

On Wed, 21 Mar 2012 18:30:38 -0400, Paul wrote:

The keyword "SELV" comes
to mind, but that's about all I remember now.

"SELV" means, IIRC, "Safe Extra-Low Voltage", often used for light fittings
in bathrooms etc.
Bear in mind that "LV", to a mains engineer, means <1000V!

 

[Yousuf Khan]

Yousuf Khan wrote


So you may not end up with any more 12V current at all.

Unless it's a single-rail, then it'll have a *lot* more 12V current.
I've been window-shopping, most of the latest high-end PS'es are now all
single-rail, very few multi-rail left anymore.

Thats pretty bogus when what matters is the startup currents.

Well, that's likely what they are assuming, the worst-case scenarios,
which is usually startup currents.

Its silly to assume that all blue ray and dvd burners will consume
the same amount within 1W

It's probably just an average they are taking, or maybe a worst-case.

And one rail can deliver 192W, bags of margin.


Still fine for a 192W rail.


Nope. Even if the rail was overloaded, and it isnt,
that wont kill two DVD burners simultaneously.

But the fact remains that they *did* die simultaneously, so if this is
not the most likely reason for it, then I invite you to come up with
another reason.

Yebbut the hard drives numbers are bogus.

Again, I'm just working with the online PS calculator figures here, I
have no reason to doubt them. So again, if you got better numbers, I
invite you to present them, and why.

Nope, because the worst that might happen is that a couple of the
hard drives might spin up a little more slowly than they would if they
were the only drive in the system and thats a complete yawn in practice.

Which is basically the problem that's happening with most of the hard
drives, but it still counts against the drive as a SMART error in the
logs regardless. There's no way to tell if a spin retry error is due to
power supply problems or due to actual mechanical stiction. But
PS-generated spin retry is easy to fix, and I'd rather leave the spin
retry errors to detect actual mechanical stiction rather than these
bogus power problems. Mechanical stiction will tell me that it's really
time to replace the drives.

As for the optical drive(s), the errors don't crop up during startup,
they show up in the Windows Event logs randomly. That means that they
occur when the system is already up and running and in a steady state or
even idle. As mentioned, the optical drives are empty most of the time,
so why they are sending out error messages when there is nothing in them
is beyond me. I can only assume Windows periodically polls the status of
these optical drives, and that's when we see these error messages.

Yousuf Khan

 

[Loren Pechtel]

Well, I ran my system components through a few power supply calculators:

http://extreme.outervision.com/PSUEngine said I needed 580W.
http://www.thermaltake.outervision.com/Power said I needed 574W.
http://support.asus.com/powersupply.aspx said I needed 900W!!!

Obviously, the Asus rating is an outlier so I'm ignoring that one, but
the other two seem to agree pretty close to each other, and that level
is pretty close to the maximum power rating (within 96-97%) of my old
PS. And with the age of the PS advancing in years, its maximum capacity
might actually be decreasing over time.

I would get a Kill-A-Watt and see what it's really using.

I haven't checked mine when the needles are pegged but at normal
desktop usage I was surprised at how little my UPS says it's
delivering.

 

[Rod Speed]

Yousuf Khan wrote

Rod Speed wrote

Well, that's likely what they are assuming, the worst-case scenarios,

Nope. There is no 2:1 ratio between the startup currents with SATA
and IDE HDDs, most obviously with the drives available in both formats.

which is usually startup currents.

It's probably just an average they are taking, or maybe a worst-case.

It isnt even an average with that silly 1W precision,
its straight from someone's arse.

But the fact remains that they *did* die simultaneously,

Yes, but it cant have been due to that rail being overloaded
with all the hard drives spiinning up at once, because the most
that will do is see the 12V rail sag a bit for the short time that the
hard drives are taking the maximum startup current, and a small
sag in the 12V wont be what killed both drives simultaneously.

so if this is not the most likely reason for it,

It isnt.

then I invite you to come up with another reason.

Dont have to, it cant be that.

Bet if you actually put a decent max min multimeter on the rail,
you wont find it sags much at all.

Again, I'm just working with the online PS calculator figures here,

And that is where you are going wrong. You have to use the real
startup current numbers from the hard drive datasheets instead.

I have no reason to doubt them.

You have every reason to doubt them on that terminal
stupidity of a 2:1 ratio between sata and ide drives
when the same drive is available in both formats alone.

And you cant just add the DVD and blue ray numbers
to the hard drive numbers either, because the hard drive
spinup currents dont happen at the same time that the
burners are presenting their maximum load to the 12V rails.

So again, if you got better numbers,

I already told you where to get them, from the
hard drive datasheets, the spinup currents.

I invite you to present them,

Cant do that, you never specified the hard drive model numbers.

Everest will give them to you without even opening the case.

and why.

I already told you why, repeatedly.

Which is basically the problem that's happening with most of the hard drives,

I dont believe that with that most claim.

but it still counts against the drive as a SMART error in the logs regardless.

Nope. Its just REPORTING the longer spin up time, it isnt counting against anything.

There's no way to tell if a spin retry error is due to power supply problems or due to actual mechanical stiction.

Corse there is, you run it with just a couple of drives for a test.

But PS-generated spin retry is easy to fix, and I'd rather leave the spin retry errors to detect actual mechanical
stiction

You dont get enough mechanical stiction now to matter because
modern drives unload the heads from the media at shutdown now.

rather than these bogus power problems. Mechanical stiction will tell me that it's really time to replace the drives.

If you see mechanical stiction, the drive wont spin up at all.

As for the optical drive(s), the errors don't crop up during startup, they show up in the Windows Event logs randomly.

So they cant be due to the rail not being adequate.

That means that they occur when the system is already up and running and in a steady state or even idle.

So they cant be due to the rail not being adequate.

As mentioned, the optical drives are empty most of the time, so why they are sending out error messages when there is
nothing in them is beyond me.

One obvious possibility, is, as I said, that the
power supply has too much noise on the 5V rail.

The only real way to check that possibility if you dont have
a CRO etc and dont know how to use one is to replace the
power supply and see if the problem goes away.

And you dont need anything special power supply wise for that
test, you can see if the problem goes away with a normal power
supply by leaving most of the hard drives unplugged for the test.

I can only assume Windows periodically polls the status of these optical drives, and that's when we see these error
messages.

Even if it does, it cant be because the rail is overloaded,
because the hard drives arent spinning up at that time.

 

[Rod Speed]

Loren Pechtel wrote

I would get a Kill-A-Watt and see what it's really using.

That doesnt tell you if a particular rail is getting overloaded.

You need a multimeter on the individual rails to check that.

I haven't checked mine when the needles are pegged but at normal
desktop usage I was surprised at how little my UPS says it's delivering.

Thats normal.

 

[Yousuf Khan]

I would get a Kill-A-Watt and see what it's really using.

I actually did get one at one time, but it turned out to be bad, so I
returned it, and I never bothered again.

Yousuf Khan

 

[Charlie]

As for the optical drive(s), the errors don't crop up during startup,
they show up in the Windows Event logs randomly.

I had the same thing and cured it by raising the CPU voltage slightly.

Charlie