Power Factor Correction for Rectified Battery Chargers

[Paul Z.]

Hi everyone, I have a question about PFC.

For a while now, I've been using some very large battery chargers to charge from the grid.  These chargers use a rectifier bridge and filter, which inherently has very low power factor.  I haven't measured it, but it's probably 0.7 or something horrible like that.

Up until this point, I really didn't care, because residential utilities only charge for actual power used, so it did not cost me any extra if energy was wasted via poor PF.  However, now that I'm charging off-grid via AC-coupled solar, I want to be a little more careful.

I have a 240 VAC solar system is AC-coupled to the Powerjack, so my 240V battery chargers are charging primarily off the 240VAC coming from the solar string inverters.  Now, my question is, will the poor power factor make a difference since I am running a closed system? 

My guess is that, with a closed system, the resonance from the poor power factor will not cause any major losses, unlike on the grid.  But, since my guesses are typically wrong at least half the time, I would rather get some input from someone who knows about this stuff.

Because all the current losses will be contained with in the walls of the house, I am assuming that the minimal wiring will cause very little energy loss.  But, please correct me if I'm wrong.

- Paul

[InPhase]

I don't think you have much to worry about. Moving reactive current around in your own system costs just about as much as not moving it around. But if you're worried about it, start up a big induction motor to balance it out.

[Sid Genetry Solar]

Second that.  Power Factor doesn't usually affect off-grid systems too much...it's more surge loads that wreck havoc with things.

[kuhrd]

All power factor will likely do is make it appear as though it is a larger load than it is to the inverter but 0.7 isn't all that bad for a LF inverter considering some of the loads your inverter may see like non-PFC power supplies, and capacitive dropper circuits used in all kinds of things like LED lamps and logic boards in a lot of appliances.  The large transformer in the inverter is going to handle power factor far better than say a high frequency inverter would.  If the load is mostly inductive, you can use a motor start capacitor to bring it back in balance, and if the load is mostly capacitive you can use an inductive load like a motor, transformer or even just an inductor rated for the current to even out the PF.  If the transformer in the inverter isn't complaining I would guess it will be alright either way.