What is PFC as a power supply feature?

[donny_paycheck]

PFC = power factor correction
I know it has something to do with the reactance of the input of a switching power supply and how it adjusts to line voltage changes, but what is it REALLY good for? Why do PFC power supplies cost so much?

[donny_paycheck]

ARGH! BUMP!

I've been charged with building a small exchange server for a friend's company so I'm looking at good power supplies and want to know what this PFC stuff is all about...is it hype or not? I know one of you guys knows so c'mon, hook a brother up!!

[3DMike]

If PFC indeed does refer to power factor correction then this is what its all about. I'm assuming you understand electronics?

Power factor is a measure of how inductive a load the power supply will drive. For example in a purely Capacitive load Curent will lead voltage by 90 degrees, in purely capacitive load Voltage leads current by 90 degrees.

Normally this is fine and groovy because a load will have inductive and capacitive reactances which will more or less cancel each other out, even if they dont its no big deal.

However when you start pulling serious amps from the grid a leading or lagging current can really **** off your electricity suplier because a mormal electric meter wont register that the full amount of Kwh's have been used.

Power factor correction uses active circuitry to measure the reactance of a load and apply a corrective capacitive or inductive load to compensate.

These PSUs you mention must be pretty powerful beasts! I've only ever heard of power factor being an issue in an industrial situation when Megawatts are being used.

On the other hand the power factor may be a problem in a computer PSU which is used to generate an accurate 3 phase supply as used by some high quality (&cost) server boards.

If they are that much more expensive then make sure you explain the benefits to your customer so he understands why hes gotta pay a bit more.

Hope this has helped more than confused.

Mike

[donny_paycheck]

Amateur electronics experience only, via radio, this stuff and dorky-@$$ hobbies similar.

This clears up a bit and I see what you mean about "why would this matter with small switching PSUs?" I agree after reading your explanation.

I'm writing an email to a rep at pc power and cooling right now. They make PFC supplies....Enermax does too but I've only seen pics of the box:eh?: and no merchant sells them yet. Looks like it's a good old Antec server case with good old Antec 400w PSU this time around! They'll be using an UPS so the input will be clean as can be.

Thanks for the help.:)

[3DMike]

Hope you find what your after.

Just out of curiosity; whats the server going to consist of? Presumably a large disk array? This is the sort of thing that requires a smooth and well regualetd suplly. And of course a UPS if its critical data.

I recall a few months back buliding a server for a guy who refused to pay for UPS. "But we never get power cuts!" he says,
and of course fate being what it is sure enough there was a surge the next day that knocked out the server and screwed up his drives after I'd spent all night moving his company database and defragging the drives!

At least I got payed for more work though!

[donny_paycheck]

Abit BH6, PII-450, 384mb ECC, Adaptec AH2400S ATA RAID5 w/4x40gb IBM 7200 drives

Generic sound, graphics, CDROM and 10/100 NIC. It'll be running NT40 and microsoft exchange server but they're installing that, I'm only slapping it in a case for 'em. Clean power is important but I doubt this PFC business matters; I was primarily just curious.