[RE-wrenches] Outback Chargers

[Exeltech]

Bruce,

The capacitors may or may not help, and could make things worse.  If you've already encountered and solved this exact issue on other identical systems .. carry on.

If not ... 

Switching power supplies have a double-whammy of being non-linear AND reactive.  The reactive component is almost always a capacitive "front end" in the power supply.  If the predominent issue happens to be harmonics .. then power-factor correction capacitors MAY help by filtering out some of the higher frequency aspects.  If the predominent issue is the reactive front end of the power supply .. caps could make the situation worse.

As a side-note, PF correction caps connected across the output of an inverter can cause the inverter's voltage control loop to go unstable, and blow the inverter.  Not a guaranteed failure .. but an enhanced possibility.


Dan

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On Mon, 2/10/14, bruce at willpowerelect.com <bruce at willpowerelect.com> wrote:

 Subject: Re: [RE-wrenches] Outback Chargers
 To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
 Date: Monday, February 10, 2014, 10:43 PM
 
Matt,

I don't have a lot of experience with undersized generators for the application, but I will share some thoughts about my recent experience.
Having 3 VFX 3648 on a 12 kw Kohler, the math said I shouldn't have difficulty getting 7 kw total charge current which would put 135 amps into the battery.

My experience said the imbalanced load of 2 VFX on one leg and 1 on the other may cause problems. To address that issue I installed an autoformer.

The best compromise/solution so far is one VFX on each leg dialed back to 15 amps maximum charge current. This gives 3.6kw total charge current or about 70 amps ~52 volts. The third VFX (master) is programmed at 0 charge but maximum ac. It's only job is to invert or pass through. The two slaves don't have to worry about adjusting for loads, just charging.

Why can't we get more power? Switching power supplies in the chargers that create harmonics not readable by your standard amp meter, and that inherently, chargers seem to use only a portion of the sine wave presented to them. Harmonics of several orders induce current into the line and the windings of a generator. Some breakers are also susceptible.

In my case, a 70 amp breaker is tripping after a period of time with less than 8kw of charger. I have not yet scoped the line but I suspect the other 50-60% of load is harmonics.

Possible solution: I have found some power correction capacitors (600 Kvar @ 480, should give me 300 Kvar @ 240) that I'm going to put in a box and hang on the wall next to the VFX's. The VFX's will get scared and stop doing that! No, seriously, I'll wire the capacitor bank to the ac input busses of the FW 500 and they'll soak up a lot of the ripples that are trying to get back to the generator.
It may take a week or so to get back up there, but I'll let you know how it works.