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PSU's Power Factor?

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May 23, 2002
Do PSU's have a unity PF? If not anyone know what they are? (I'll assume if they all arn't unity they'll be some difference, but in general...)

Here I go off on something that I'm not completely sure about...If I'm completely wrong, for the love of all that's sacred, please correct me.

From what i get here


and my other thread here


it seems to me that you would be incredibly lucky to have a power factor of unity. I believe that the efficiency rating found on newegg for many of their power supplies would be ok to use. With a semi-randomly chosen 350W Fortron power supply, we see


that the efficiency is a minimum of 65%, typically 70% under full load (which is probably what most people here are at. If you're not... fold for team 32! :D) I want to just convert this to a power factor of 0.65-0.7, but that's probably not right.

The primary reason for my stating that the power supplies are not a power factor of unity is the fact that there are power factor correction power supplies. If there was nothing to correct, such things would probably not exist.

I would be interested to see some readings off of some of the forum member's rigs using a wattmeter, ammeter/voltmeter and the math in the first link. I'll try to take some measurements this weekend.

Another link on comparison of power supply efficiency:


What bothers me is the fact that the 450W Fortron with active PFC has the same efficiency as the non-PFC 350W psu. Is this just because power supplies lose efficiency as they become larger?

yes, i like giving links :D