GFCI Intermittently Tripping

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GFCI Intermittently Tripping

Postby freedompower on Sun Mar 06, 2011 6:55 pm

I installed a FlexWare 500 about two months ago. The FlexWare system has two GVFX3648 inverters, and two FM80 charge controllers. The system is powered by 39 Sharp 180 Watt NU-U180FC modules in 13 strings of 3 modules each. One FM80 operates 6 strings and the other has 7 strings.

The system's GFCI breaker is tripping intermittently. I have megged all circuits at 500 VDC to 550 Meg ohms. The system has operated over a week with all types of weather (full sun, rain, high winds) before tripping on a benign day. The only condition that seems to be the same is it seems to trip when the weather is partly cloudy.

Any ideas as to what is going on or how I might find the issue?
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Re: GFCI Intermittently Tripping

Postby tallgirl on Sun Mar 06, 2011 7:01 pm

If the weather there is cool and you're having sharp cloud edges at mid day, it's not the ground fault part that is tripping out, it's the current side of the breaker.

I've seen this problem more and more on high power arrays where Vmpp is close to Vre (sell voltage). When a cloud edge hits a cold array, Iarray can easily exceed the ampacity of the breaker. I've seen 100+ amps out of arrays similar to what you've got.
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Re: GFCI Intermittently Tripping

Postby freedompower on Mon Mar 07, 2011 6:03 am

That is exactly the kind of conditions where it is tripping. What would be your recommendation of how to remedy this problem?
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Re: GFCI Intermittently Tripping

Postby tallgirl on Tue Mar 08, 2011 11:06 am

(We've already spoken by phone, but I thought I'd share)

There are two viable solutions --

1). Find a vendor who makes a 100A / 0.5A GFDI breaker.
2). Add an additional charge controller.

The cause of the tripping is transient outputs well in excess of the nominal output during cloud edge events on cold days. Add "during the Spring" into the mix and it's worse. It's not at all unusual to see more than 120 percent of STC current under very cold weather where there are distinct clouds. The problem is particularly annoying on grid-tied systems where the inverters fight to hold the battery voltage down, further increasing DC current through that breaker.

In many cases, the 80 amp output is somewhat misleading, when it comes to array sizing. There is a big difference between 80 amps at 48 volts and 80 amps at 57.6 volts. With AGM banks being kept closer to 52 volts than 57.6 volts, the maximum output is on the order of 4160 watts -- and the 3,780 array is close enough that some nice healthy cloud edges during a chilling lunch hour in March is very likely to pop an 80 amp breaker.
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Re: GFCI Intermittently Tripping

Postby tigerwillow1 on Mon Mar 14, 2011 8:39 pm

I'm having the same problem with a Flexpower One system, a single inverter with a FlexMax 80 charge controller. The 80 amp breaker is on the output of the FlexMax 80. It's supposed to handle a continuous 80 amps, and the charge controller output is supposed to be limited to 80 amps, so in theory the breaker should never trip. If the peak amps in the FlexMax log are correct, the breaker has tripped as low as 70 amps, and the charge controller has frequently pushed more than 80 amps, going over 90 on one occasion. This suggests that both the breaker and charge controller are not working correctly. Is there any other explanation?
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Re: GFCI Intermittently Tripping

Postby Kent Osterberg on Mon Mar 14, 2011 9:00 pm

Replace the 80-amp breaker. The manufacturing tolerance on these breakers makes operation at 100% a marginal design. Most units will do it, some won't.
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Re: GFCI Intermittently Tripping

Postby tallgirl on Tue Mar 15, 2011 8:03 am

Also, it's not uncommon to see a FM-80, or even FM-60, with a large enough array produce well over the nameplate rating of the array and the output limit of the charge controller. For an FM-80 with a 4KW array, I'd go with a 100A breaker, assuming the conductors had the correct ampacity.
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Re: GFCI Intermittently Tripping

Postby Kent Osterberg on Tue Mar 15, 2011 9:55 am

Outback sells a 100-amp panel mount breaker, but it is a different size than the 80-amp breaker and won't even fit in many Outback Fleware panels (it depends on what else is installed). A 100-amp GFP isn't in the Outback product listing and probably isn't available from anyone else either. Also, installing a 100-amp breaker will probably necessitate upgrading the charge controller output wiring from 4 AWG copper to 3 AWG copper.

If 100-amp breakers were installed originally, no one would have trouble with intermittent tripping. Under the existing circumstances, replacing the troublesome 80-amp breaker or 80-amp GFP with another 80-amp unit will probably solve the problem - cheaply and easily.

Call Outback tech support, if your system is still under warranty they should send a replacement breaker for free.
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Re: GFCI Intermittently Tripping

Postby tigerwillow1 on Tue Mar 15, 2011 6:30 pm

Thanks for all the responses. I forwarded them to my installer, and he's going to check with some of his inside contacts. I cranked the FM80's max output down to 75 amps and haven't tripped since then, but it's not a good test because the weather has been horrible. The max amps still go over the 75 setting, but haven't gone over 80 yet.
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Re: GFCI Intermittently Tripping

Postby tigerwillow1 on Wed Apr 13, 2011 12:40 pm

I've been able to gather enough data to have a pretty good idea of what's going on with the 80 amp breaker now. The lousy Central Oregon weather this spring has made data gathering a lengthy process (e.g. it just started snowing - and it's mid-April!). I view the problem as a combination of the FM80 not being able to quickly control its output, and the breaker not being tolerant of short overloads.

The FM80 appears to have pretty good output current control if the PV input is steady or doesn't change very fast. When a cloud edge hits, it passes current spikes for one to two seconds. When set to the 80 amp limit, I've seen spikes over 90 amps. When set to a 70 amp limit, the spikes go into the low 80s.

The breaker appears to me to be a strictly thermal device (I don't know that it actually is, but it behaves like it is). It will pass a steady 80 to 81 amps without tripping, but if the steady-state current is about 75 amps or more, any short spike above 80 trips it. My experience so far is I have to keep the FM80 output set to 70 amps to not have breaker trips on the cloud edges. The spikes go above 80, but haven't caused a trip so far. The 70 setting is what Outback tech support recommended to my installer. We might try the 100 amp breaker, but for now I'm running a limit of 70 amps.
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