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power draw dilema

Forum CPU & Components : Power Supplies, PC Cases & Case Mods - power draw dilema

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dragonmage   10-04-2006 at 03:36:53 PM

Hi, I am building a new PC with:
Asus SLI mobo
dual AMD2 4800+
only one Nvidia 7950 gx2 (for now)
4 sata HD (2 7200, 2 1000rpm)
DVD rom

The PSU should be no trouble - I'm getting a 750W Tt

Problem is ... no matter what I calculate, I am sure that the power draw will be more than the 15A that the mains AC socket can supply.
I may be able to get a 20A circuit put in but regulations seem to prohibit higher than that in the home.

I can't see how other ppl use such systems (and bigger ones) on home AC power!

So, will I have trouble when I finish building the system from the point I plug into a 15A (or 20A) AC socket and turn it on?

Yes I have read the FAQs and calculators but seen nothing that tells me how ppl normally deal with this type of issue.

thx in advance

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doolittle   10-04-2006 at 03:44:13 PM
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Take the psu calc value, divide by the approx. efficiency of the unit, then calc the AC current by dividing by 120v:

e.g.:

psu calc: 350w draw from psu
wall socket draw: 350w / 75% efficiency = 466.7w
AC current: 466.7w / 120 = 3.9A from your circuit breaker

I guess that would be "basic circuit theory 101", a lot of times people confuse PFC (AC reactance) and efficiency (power wasted in heat) values.

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RichPLS   10-04-2006 at 10:50:30 PM
- 0 +

No need to worry about your PC overloading your 20A breakers for your home...

Reply to RichPLS
dragonmage   10-05-2006 at 01:46:14 AM
- 0 +

Yeah thanks everyone, I was not multiplying the rated amperage by the ratio of 12V/wall socket voltage.
e.g. the rating is 48A and at 85% efficiency that is 56A. So if I assume most of the power is taken on the 12V rails then draw on the wall socket is
56 * 12/120 = 5.6A

so no problem, like you say!

Reply to dragonmage
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