• Some users have recently had their accounts hijacked. It seems that the now defunct EVGA forums might have compromised your password there and seems many are using the same PW here. We would suggest you UPDATE YOUR PASSWORD and TURN ON 2FA for your account here to further secure it. None of the compromised accounts had 2FA turned on.
    Once you have enabled 2FA, your account will be updated soon to show a badge, letting other members know that you use 2FA to protect your account. This should be beneficial for everyone that uses FSFT.

PSU sizing question

E

ericsan

Weaksauce
Joined
Feb 11, 2002
Messages
103
I've taken some measurements from the plug side of my PSU - trying to gauge the correct size. With Furmark running - I measure 380watts total loaded/hot - then 160watts idle.

P6T Deluxe - i7920 clocked - 6GB - GTX275 OC - stock cooler - no fans - on a test bed

I tried a good Antec 430 - and although the system would run Windows fine - Furmark made the system power off.

But I'm curious as to why the 430 could not handle the load. If I take 380W at the plug, then divide by 80% efficiency factor for DC conversion - I get 304W DC power for the system. A 430 Antec should certainly be able to push out 304W right??

Other measurements are:
OCCT CPU stress - 290W
OCCT PSU stress - 460W
Crysis benchmark - 330W
Vantage benchmark - 301W

But all of these are at the 120AC plug side - the DC side should be 20% lower right? And a PSU is rated at the DC side.

I'm a little confused after all of my playing.

Aloha
 
What is the 12A rail? That, if it is less then about 29A (total), then it would be (rought estimate on the ampres) cause of the crashes.
 
No idea how to measure the 12V rail. I assume you mean Amps - the voltage is fine.
 
Although the PSU might be fine with up to 430watts total, how the individual rails are loaded is more important. If the 12v rail(s) can only handle 25a, you're only going to get 300watts. The 5v and 3.3v rails don't power much in today's computers (drive logic, some simple PCI cards, and memory), so the 12v rail(s) handle the bulk of the load.
 
Ah - there we go. I figured the 12V rail did most of the talking. So its 17A+16A = 33A @ 12V = 396W rated DC power of a Antec 430 on the 12V rails.

If I measured 380W AC - that would be 304W DC (80% eff) - or 25A. Now maybe the amps spiked up a bit more than I was measuring with my $15 wattmeter - but wow. Didn't expect it to cut off with that load. Maybe some CPU load spiked up too - pushed it to 30A.

Anyway - I am going for a Corsair HX650. That would handle the load - probably even a 620. Waiting for a good special.

Thanks for your replies.

Aloha
 
ericsan said:
Ah - there we go. I figured the 12V rail did most of the talking. So its 17A+16A = 33A @ 12V = 396W rated DC power of a Antec 430 on the 12V rails.

If I measured 380W AC - that would be 304W DC (80% eff) - or 25A. Now maybe the amps spiked up a bit more than I was measuring with my $15 wattmeter - but wow. Didn't expect it to cut off with that load. Maybe some CPU load spiked up too - pushed it to 30A.

Anyway - I am going for a Corsair HX650. That would handle the load - probably even a 620. Waiting for a good special.

Thanks for your replies.

Aloha
Click to expand...

You can't just add the 12v rails together. Alot of PSU's (I don't know if yours does) split a single 12v rail into two. So if there's 17a on one 12v rail, the other might only be able handle 8a or something.
 
ryan_975 said:
You can't just add the 12v rails together. Alot of PSU's (I don't know if yours does) split a single 12v rail into two. So if there's 17a on one 12v rail, the other might only be able handle 8a or something.
Click to expand...

Yes - I understand. The sticker on the PSU says +12V1 (17A), +12V2 (16A), Max load 12V1+12V2. I assume that means the max 12V load is the sum of the two.
 
ericsan said:
Yes - I understand. The sticker on the PSU says +12V1 (17A), +12V2 (16A), Max load 12V1+12V2. I assume that means the max 12V load is the sum of the two.
Click to expand...

In that case, I suppose it's alright. But, you might still be overloading a single rail.
 
Keep in mind that for various reasons, the power meter you're using can be quite inaccurate, so you may in fact be consuming more power than the meter is showing.
 
ericsan said:
I assume that means the max 12V load is the sum of the two.
Click to expand...
You determine the amperage on the +12V rails by first finding out what's the total combined or max wattage set aside for the +12V rails/section alone. So for example, the Corsair 450VX has 396W total on the +12V rail. Divide that total wattage for the +12V by 12 and you get how much amps the PSU has on the +12V rail. In this case, 396W divided by 12 is 33A. So the Corsair 450VX PSU has 33A on the +12V Rail.

Yeah, definitely not the case sadly and thats what get many people confused.
Zero82z said:
Keep in mind that for various reasons, the power meter you're using can be quite inaccurate, so you may in fact be consuming more power than the meter is showing.
Click to expand...

That's a good possibility there. Consumer grade power meters do tend to be inaccurate. What power meter are you using OP?

Also, which Antec 430W PSU are you talking about?
 
The PSU in for this test is a Antec Earthwatts 430 EA-430D.

The power meter is a Killawatt. I now know that the PSU can cause the meter to give a false reading - maybe off by 10% or so.

I also tried a BFT 450W unit for the same tests. It held up to the Furmark - but could not handle the OCCT PSU test at 460W.

I will run the test again with a good Fluke power meter and see what the readings are. I sold my Fluke 43B recently - wish I had it now. Will try the basic meter and see what I get in watts.
 
You must log in or register to reply here.
Back
Top