Arc fault with Sunny Boy 5000TL

PaulRekow

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Jan 21, 2021
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I recently installed a new shed to house the electronics for my solar panels and wind turbine. I have had 18 Evergreen 110w panels and 9 Astronergy 310w panels connected to a Sunny Boy 5000TL inverter since Nov. 2014. The 310w panels were on the roof of a shed that was falling down, so I mounted them on the ground for the summer while I had a new shed built. Everything worked fine before moving them to the ground and while ground mounted. When I moved them back on the roof of the new shed, I cannot get the arc-fault to go away. Sunny Boy's recommendation in the past has always been to disconnect and reconnect all the connectors which I have done several times and I still get an arc-fault on startup when I try to connect the 310w panels. If I leave them out the 110w panels connected to the inverter works fine.

Any thoughts on what else I can try.

Thanks,
 

Hedges

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Trip instantly? Or after some time?

Routing of wires can serve as an antenna to pick up RF. Maybe your wires are routed differently. That could be how big a loop is formed by the wires through the panels and back. Is there a long return wire that could route differently, more under the wires between panels?
Photo of layout would help show.

What happens if you connect just the 310W, not the 110W?

Another possibility, you have a poor connection or damaged wire in the string, and it does arc. But you're already tried unmating/remating the connectors.
 

PaulRekow

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Jan 21, 2021
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Trip instantly? Or after some time?

Routing of wires can serve as an antenna to pick up RF. Maybe your wires are routed differently. That could be how big a loop is formed by the wires through the panels and back. Is there a long return wire that could route differently, more under the wires between panels?
Photo of layout would help show.

What happens if you connect just the 310W, not the 110W?

Another possibility, you have a poor connection or damaged wire in the string, and it does arc. But you're already tried unmating/remating the connectors.
The fault is immediately on start-up

The wires are routed differently, I plugged them in in reverse order, but still have the polarity correct, I've double checked that. The return wire is actually shorter than when it was on the roof previously.

Same thing happens if the 110w is removed.

I was a little concerned that that might be the case

I will send a picture tomorrow
 

Hedges

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The fault is immediately on start-up

The wires are routed differently, I plugged them in in reverse order, but still have the polarity correct, I've double checked that. The return wire is actually shorter than when it was on the roof previously.

Same thing happens if the 110w is removed.

I was a little concerned that that might be the case

I will send a picture tomorrow

So either one string of panels hooked up is fine. Both hooked up causes the problem.

Return wire longer or shorter isn't what I was thinking of, but how big a loop it makes. 20' of wire forming a circle is a big antenna, large "loop" area. Same wire out 10' and back, maybe even twisted, makes a poor antenna, no "loop" area.

I'm not sure how two loops makes a good antenna when neither did by itself. This isn't a "rabbit ear" where each goes to one terminal. each loop connects to both terminals.

There was a time when SMA Sunny Boy had a lot of problems with AFCI, from comments I read on their forum. Yours worked fine before, presumably antenna formed by panels and wires is different. Maybe some kind of damage; a short to frame as Picasso suggests would show up as a fault during startup (if frame grounded). But each works alone. Each having a fault at a different voltage tap of the string, then current would flow between them and arc. Are your mounting frames grounded?

Confirm that arc fault is the error, not some other message given.
Transformerless inverters have no galvanic isolation between grid and panels. They do a test on start up. If used in a 3-phase (208V) system, the panels will carry an AC voltage, and capacitance affects them. Bad grounding of frame might even cause arc noise in that case.

"Sunny Boy's recommendation in the past has always been to disconnect and reconnect all the connectors which I have done several times"
So, not the first time, Huh? But I guess it has been behaving itself for a while?
Maybe it's that d*mn 5G? New transmitters in the area?
 

PaulRekow

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Jan 21, 2021
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Here is a picture of both the 310w panels on the roof and the 110w panels on the ground. The 110's hooked to the SunnyBoy works fine. If I try and hook up the 310w panels either by themselves or with the 110w panels, I get the fault both ways. The issues I've had in the past was with the 110w panels and was if there was a lot of moisture, usually after a heavy thunderstorm, the next morning on start-up, I would get a arc fault, but that hasn't happened in a couple of years.
The wiring starts with a homerun to the bottom right panel on the roof, and goes up to the top, over to the top middle, down that row, over to the bottom left, up that row and then a homerun to the inverter.
How would I test if there is a short to the frame?
 

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Hedges

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OK, so the 310W have a problem whether or not 110W are connected.
Are you sure the error message is "Arc Fault" not "Ground Fault" or anything else?

Moisture causing problems sounds more like short to ground than arc fault.
And that was previously seen with 110W, not 310W.
With both 110W and 310W connected, what if you open circuit the positive end of 310W, leaving negative connected? open circuit only the negative?
I suggest that test so no series current flows (which can arc if poor contact), but it has opportunity to leak to ground.

Some panels develop leakage to frame over time. Probably moisture getting past backsheet.

With both positive and negative disconnected, check voltage from PV positive wire to ground. It may read something like 200V at first, trickle down to zero as capacitance discharges. Test negative wire to ground. If either of those holds a steady voltage and doesn't reach zero, that would indicate a short or leakage. Make sure you don't touch exposed contacts of DMM test leads!

Sunny Boy TL conducts a test where it momentarily grounds one end of the PV string, checks for leakage. Spec has a limit of capacitance it can tolerate. It may only do this to one end of the string, so where a leaky panel is located in the string would affect results.

"HiPot" is how we test such things - a variable transformer able to deliver up to 5000Vrms, trip if > 1 mA flows. Or a Megger, high voltage DC, measure current. Your panels give several hundred volts, which does a decent job. I could use my meter to measure current, but starting with the meter shorted out so capacitance doesn't cause a surge of current. You're better off just measuring voltage, not trying to quantify how much leakage (to avoid meter damage or shock hazard).

Does DC connection to inverter have fuses for both positive and negative? I think that is required to protect inverter from damage in case there is a short in the array, because grid voltage has a path through to the short ("transformerless", non-isolated).
Ground mount isn't required to have arc-fault, which is for fire safety. The building isn't a house, not sure if arc-fault is required by code or not, and appears to have metal roof.
 

PaulRekow

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Jan 21, 2021
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So I trying hooking up the 310w panels today just to check and the AFCI test was successful, unlike the other 10 or 15 times I tried it and got AFCI failure. I didn't do anything different than the other times I had tried. Go Figure!!!
 
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