'Alfie' wrote, in part:
| Most of that info came from my own experiences when I first put a nVidia
| Geforce 6800 GPU (requiring 1 additional PSU connection) in my PC, it
| would often power down for no reason whatsoever, and then trying to find
| out why
_____
Well, a few anecdotes don't a summer make.
1. ATX specification power supplies (ATX12V and later) don't operate in the
manner you seem to have understood. They have 'load sharing' - wattage is
shared among the important rails, +12V, +5V, and +3.3V.
2. A display adapter using the nVidia 6800 uses far less power (perhaps
half) compared to one using the nVidia 6800 Ultra.
3. New GPUs aren't 'requiring their own power'; some display adapter have
several connecting pins for +12V DC; this connects to the same +12V DC rail
that drives use. This replaces power that was previously drawn from the +5V
DC and/or +3.3V DC rails. The display adapters have on-board DC-to-DC
down-convertor/regulators that work more efficiently with +12V DC input than
with +5V DC or +3.3V DC input. The connecting wires and traces can be
smaller. The higher input voltage provides more stable operation. There is
power wasted and less heat produced using +12V DC than with the lower
voltages. Just because a display adapter requires a +12V DC connector
doesn't mean it draws more power than one which does not - it may even draw
less for the reasons just given. Using multiple +12V DC connectors SAVES
power because less in wasted in contact and conductor resistance.
4. Multiple USB devices ~= multiple fans ~= negligible. Multiple drives ~=
not very much except during spin-up.
ATX power supplies DO NOT SHUT THEMSELVES DOWN IF TOO MUCH POWER IS DRAWN!
ATX power supplies DO shut down if a dead short develops. ATX power
supplies will begin to overheat if to much power is drawn, but this takes a
relatively long period of time, much longer than the period of time for
drives to spin up. The overload protection fuse is to protect the AC wiring
with in the case and the AC wiring between the case and the building breaker
box. This fuse is a safety feature, not an overload protector. An overload
of several times the rated power is necessary to blow the fuse within a few
minutes.
5. | I replaced my system with a
| 500w power system but it would also suffer power downs for no apparent
| reason. I was advised that my system did not draw enough power and the
| PSU was invoking power-over management and reducing power output to
| avoid a 'burn'.
You were advised wrongly.
6. | Hmm, yes, questionable. The calc suggested 310w used, so I put in a
350w
| cheapo and when it got hot it would power down. Using the mobo power
| check, when it was hot the PSU delivered less power, to the point it
| would trip. I bought a more expensive 350w dual rail PSU and it was much
| more stable.
In all probability your system was inadequately ventilated, though it may
also be that your power supply was falsly rated. What was the room ambient
temperature and the temperature of the air leaving the power supply? Did
you check, or did you just rely on what you were told? Power supplies are
rated at a specific temperatures. At higher temperatures they must be
derated. A power supply that is more than adequate at 60 C can be
inadequate at 75 C.
7. | I was advised by others not to put in a 500w PSU as I first wanted to
| do. Yes PSUs have under-draw protection, but prolonged use at low power
| levels supposedly reduces the lifetime of the PSU.
You were advised wrongly.
Really, try studying the two documents from formfactor.org. The next time
you get advice on ATX power supplies, try asking follow-up questions. It
really does sound as if your previous advice came from someone unclear on
the difference between switching powersupplies and linear power supplies.
| On Fri, 07 Oct 2005 18:51:03 GMT, "Phil Weldon"
| >'Alfie [UK]' wrote, in part:
| >| The OP was advised it may be a problem with power supply because of the
| >| shutdowns. Most new graphics card need 1 or 2 direct power connections
| >| and this means a 300w PSU just won't cut it anymore.
| >_____
|
| Most of that info came from my own experiences when I first put a nVidia
| Geforce 6800 GPU (requiring 1 additional PSU connection) in my PC, it
| would often power down for no reason whatsoever, and then trying to find
| out why.
| >
| >Your statement 'Most new graphics card need 1 or 2 direct power
connections
| >and this means a 300w PSU just won't cut it anymore.' isn't necessarily
| >true; a 300 watt PSU may very will be completely adequate.
|
| OK, I should have said MAY not cut it anymore. With the new GPUs
| requiring their own power if you have multiple drives and USB devices
| you MAY run out of power. The PSU will shut itself down in these
| situations, pretty much any PSU has a built in fuse for too much power.
| >
| >Your statement 'if you have a too high rated PSU and are not drawing a
| >significant power level the PSU can shutdown, act erratically, or blow
it's
| >12v rails through 'overheating' is not at all true.
|
| I stand by this statement, to some degree. I replaced my system with a
| 500w power system but it would also suffer power downs for no apparent
| reason. I was advised that my system did not draw enough power and the
| PSU was invoking power-over management and reducing power output to
| avoid a 'burn'.
| >
| >Your statement| 'You want at least 20% more power coming out of your PSU
| >than the calculator says you need to be safe from the typical
fluctuations
| >you can get in a PSU, especially cheaper PSUs that might not have a
stable
| >power profile.' makes no sense at all.
|
| Hmm, yes, questionable. The calc suggested 310w used, so I put in a 350w
| cheapo and when it got hot it would power down. Using the mobo power
| check, when it was hot the PSU delivered less power, to the point it
| would trip. I bought a more expensive 350w dual rail PSU and it was much
| more stable.
| >
| >Your statement 'Over 65% more power means you are at risk of damaging
your
| >PSU through 'overheating' as it's generating a lot more power than you
| >need.' is ludicrous.
|
| I was advised by others not to put in a 500w PSU as I first wanted to
| do. Yes PSUs have under-draw protection, but prolonged use at low power
| levels supposedly reduces the lifetime of the PSU.
|
| As the 2nd link you provided states; PSUs MAY not have over-temperature
| protection, where over-temperature is the result of current overload or
| fan failure.
| >
| >Try a read of
|
| >and
| >
http://www.formfactors.org/developer/specs/ATX12V_PSDG_2_2_public_br2.pdf
| >.
| >Pay particular attention to:
| >"System power supply needs vary widely depending on factors such as the
| >application (that is, for desktop, workstation, or server), intended
ambient
| >environment (temperature, line voltage), or motherboard power
requirements."
| >
| --
| Alfie
| <
http://www.delphia.co.uk/>
| It's called Irony. You know. Like goldy or silvery, only it's made out of
iron.
|
