How Much Can My Power Supply Take ?

  • Thread starter Thread starter Rev. Bleech_
  • Start date Start date
R

Rev. Bleech_

I recently ordered a new cooling fan that fits into an open 5 1/4" bay
on the front of my case. Now what I want to know is, does anyone have
idea just how much my PSU can take before bad things happen ? I have
2 HDs, 2 DVD-ROM/Rs, 2 80mm case fans, one PCI slot fan, the chipset
fan and CPU heatsink/fan already attached. Will I be overtaxing my
400W PSU by adding the new one ? How much can I reasonably expect to
connect to it before it catches fire or something ?
--
=-=-=-==-=-=-==-=-=-==-=-=-==-=-=-==-=-=-==-=-=-==-=-==-=-=
Pink Floyd on Video - http://www.frostwarning.com/~pfov
To e-mail me, nevermind the BOLLOCKS | Yar. FOAD.
=-=-=-==-=-=-==-=-=-==-=-=-==-=-=-==-=-=-==-=-=-==-=-==-=-=

"Hey you! How about lending me your clothes? No dice? What a drag!"

Floyd Code : v1.2a r FU 0/0/r FD 0- 0 Animals/WYWH 46 374 28.3% <02jun03>
 
I recently ordered a new cooling fan that fits into an open 5 1/4" bay
on the front of my case. Now what I want to know is, does anyone have
idea just how much my PSU can take before bad things happen ? I have
2 HDs, 2 DVD-ROM/Rs, 2 80mm case fans, one PCI slot fan, the chipset
fan and CPU heatsink/fan already attached. Will I be overtaxing my
400W PSU by adding the new one ? How much can I reasonably expect to
connect to it before it catches fire or something ?
Click to expand...

You did not mention your CPU... A P4 CPU will use more power than all
those parts combined, so without additional system detail a total
power consumption is impossible. Since fan speeds and efficiencies
can vary even a good guess might be quite off, but for the sake of
"throwing a number out there", lets say the above load is 4A, perhaps
peaking at 5-6A when the HDDs spin-up on power-on. Your new bay cooler
is probably drawing less than 0.4A, so it's not really all that
significant, you could add 4 of them and have roughly the same load as
another hard drive.

The other issue is the exact make/model of power supply. "400W"could
be the peak load rating, continuous, or just wishful thinking. Better
name-brand power supplies are usually less agressive in their ratings,
able to output near or exceed the rating, while generics typically
can't. Actually many generics are made by name-brand companies who
won't put their own name on the label.

Regardless, if you overtax your 12V rail you may notice a couple of
things, a drop in 12V reading from the BIOS or windows hardware
monitor, or the system might not detect the drives at post (or with a
P4 cpu, the system might not post at all). Keep in mind though that
excessive 12V consumption by devices on the motherboard may drop the
motherboard 12V reading due to trace resistance while the power supply
is still outputting a higher value, so for diagnostic purposes it's
essential to test the power supply leads with a voltage meter, not
relying only on a motherboard hardware monitor reading.

If you have a name-brand power supply and anything but a highly
overclocked P4 > 3GHz, there's still plenty of capacity left for more
12V devices on a "true" 400W power supply, though if it's a generic
all bets are off, it could be dropping voltage due to inadequacy even
before you added the bay cooler.

A power supply complying with safety regulations should turn-off to
prevent fire, though again it's harder to know the accuracy of a label
if it's an unknown generic brand. Any decent power supply will
gracefully shut itself down if you overload it with too many devices,
it will gradually drop the voltage with each incremental load
increase, until it reaches a cutoff point, when it will shut off.
Often the system will have "issues" of instability, can't detect
drives at POST, or won't POST at all before the voltage drops low
enough to reach that cuttoff point.


Dave
 
You did not mention your CPU...
Click to expand...

Athlon XP 1700+ on an Epox 8KHA+ mobo...only things plugged into the
PCI/AGP bus are a GeForce3, firewire adapter, NIC, and the 2 extra USB
ports on the mobo.
The other issue is the exact make/model of power supply.
Click to expand...

Antec...couldn't see a specific model number, but it has an intake fan
on the bottom and the standard exhaust fan on the back

That sound like it would be overtaxing ?
--
=-=-=-==-=-=-==-=-=-==-=-=-==-=-=-==-=-=-==-=-=-==-=-==-=-=
Pink Floyd on Video - http://pfov.frostwarning.com/
To e-mail me, nevermind the BOLLOCKS | Yar. FOAD.
=-=-=-==-=-=-==-=-=-==-=-=-==-=-=-==-=-=-==-=-=-==-=-==-=-=

"Come, Wendy. Let us jump the hilly brush"

Floyd Code : v1.2a r FU 0/0/r FD 0- 0 Animals/WYWH 46 374 28.3% <02jun03>
 
Athlon XP 1700+ on an Epox 8KHA+ mobo...only things plugged into the
PCI/AGP bus are a GeForce3, firewire adapter, NIC, and the 2 extra USB
ports on the mobo.


Antec...couldn't see a specific model number, but it has an intake fan
on the bottom and the standard exhaust fan on the back

That sound like it would be overtaxing ?
Click to expand...

What I was getting at with the prior guesstimation of power usage was
the consumptiono on the 12V rail, since that's where the bay cooler
and other mentioned devices would draw the most power. Since your CPU
(on that particular motherboard) derives it's power from the 5V rail,
you have quite a few amps of 12V power to spare, probably (roughly)
around 10A at post but even more after the HDDs have spun-up.

Your power supply has lesser reserves on the 3V & 5V rail since you
have both the Geforce3 and the Athlon XP, though it still shouldn't be
anywhere near max capacity yet, you could probably o'c the XP1700 and
throw a second video card in and it'd still be fine.

Dave
 
Back
Top