Power Factor correction with CFL bulb question?

[BB.]

Unfortunately, PF issues can be a relatively big issue for off-grid applications...

For example, the MorningStar SureSine TSW inverter is rated at 300 watts continuous at 25C... In reality, it is probably rated at 300 VA (Volt*Amp) or:

VA = Watts/PF ; or Watts = PF * V * A

Say you have 10x 13 watts CFLs with a PF of 0.5 (bad, but I have seen worse).

Somebody looking at the specifications--they see a 300 watt inverter - 130 watts = 170 watts for other loads... A laptop PC at 60 watts and a 25 watt Halogen desk lamp looks doable... But--the PC is an old one with PF = 0.6 -- we add everything up in watts and VA:

Watts = 10 x 13 Watts + 60 Watts + 25 watts = 215 Watts
VA = (10 x 13 Watts / 0.5) + (60 Watts / 0.6) + 25 watts = 385 VA

So--if you add everything up in watts--you are running at 72% of the inverter's rating.

In VA, you are running at 128% of the inverter's rating...

Battery/solar panel wise--you are still running 215 watts (+ losses). But your inverter is actually overloaded at this point (may shutdown in hot weather -- or may not last as long because of elevated operating temperatures). Also--your wire is carrying more current than you planned on -- so you may have more voltage drop and/or more wasted energy than you allowed for.

PF issues have hit large companies before (decades ago, a local credit card processor using a whole building full of, then new, PC's kept burning out wiring and popping fuses--even though the the circuits were well under the power ratings--bad PF was the cause).

-Bill

[john p]

Unfortunately, PF issues can be a relatively big issue for off-grid applications... BUTwe only talking about running a few CFL in a house.. not using enough of them to light up a football stadium...
My house has 12 on almost all the time as I said running of small inverter it never gets hot enough for its internal fan to come on and I live where average day temp is 90 to 100 deg f.

[Cariboocoot]

Bill has quite accurately pointed out that this is a cumulative problem. The more devices you have with a bad PF, the worse it gets. If your system has nothing with a low PF on it, you'll never have any trouble. But when you're trying to squeak maximum efficiency out of an off-grid system, it's important.

It's also important to utilities, as they notice more power being used than they get to bill for. Oh, did I imply it had something to do with profits? Sorry! Didn't mean to!

[icarus]

Bill has my situation down perfectly.

(We don't routinely run 10 bulbs at any one time,, but we could)

TS 300 inverter,, 4-6 cfls with Pf ~.5,, add in 2 lap tops @ 58 watts PF .51,, the modem @ ~20 watts PF .5, router 15 watts PF .5 etc and all of a sudden my inverter is working much harder than I think it is. (as you all well know,, I'm not going to do the math since we will end up with gibberish!

So in reality,, it isn't a huge deal, but it certainly is something to consider in the design phase of any project. Nothing is free.

Tony

[RCinFLA]

I would have to agree with John P, don't get too upset if you are only talking about three or four 20 watt CFL running at any given time. You will likely burn more oil in PC electric searching web for them, or worse, driving further to a store that carries them.

Couple of points from an earlier thread.

1) Most PC's still sold today still do not have PFC power supplies in them. The Energy Star 2.0 of last year does not have much teeth. Within the next year or two should see much more switching power supplies with PFC. Texas Instruments and ST Microelectronics, to mention two manufacturers, have marketed integrated switcher controller I.C.'s that contain PFC systems. Regulation does not address PF for devices less then 75 watts which is where most CFL fall.

I bought a Lenovo six months ago with Q6600 quad core CPU (90 nanometer process). It draws 200VA / 120 watts during boot for PF of 0.6. I just build a computer using Intel motherboard with E7400 dual-core CPU (65 nanometer process) where I specifically bought a PF corrected power supply that draws 60VA / 58 watts during same boot process for PF of 0.98 . Just examining Newegg's large selection PC power supplies I would be surprised if PF corrected units accounted for 20% of the offerings.

2) The main concern from electric utilities about power factor is increased transmission line losses due to higher IR loss. A PF of 0.5 does not mean twice the generator power. Yes, there is reduction in generator capacity due to winding current and core saturation limitations but other then primarily making up IR loss it does not burn that much more fuel. Typical rough average for electric utility grid distribution is about 10% loss in the step-up transformers, transmission line wires, and step-down transformers getting to end user of the electric. Your meter spins to true power (watts), not appearent power (VA). You can see square boxes with two insulators coming out the top, sometimes stacks several in parallel, on mid-level (100-250 kV) lines power poles that are oil filled capacitors used to correct PF by electric companies. Electric motors are primary culprit which create inductive PF.

[BB.]

Capacitors can do a good job of PF correction for induction motors (can be brought back to near 1.0 with motor+capacitor)...

With digital power supplies (non-PFC)--a capacitor cannot offset bad PF because of the non-linear current profile of those supplies (basically a sharp peak of current, vs the the offset of current vs voltage of an inductive motor).

-Bill