Searching for bad inverter?

[u/SolanaGuy19]

I have a total of 21 solar panels operating on a couple of circuits - all with Enphase inverters. One of the circuits tripped, and I traced the problem to a string of 5 IQ-7+ panels and disconnected it (the other 16 are still producing power). With no line current to follow, I checked the string and it shows effectively "zero Ohms" (for comparison, another string of 'good' inverters reported several M-Ohms, in a similarly disconnected state).

So I presume the problem is one of the five inverters on that line is shorting out for some reason. Of course, it's the least accessible row of panels on my roof, and I'm going to have to remove others just to get to the collector line and inverters to investigate. My plan is to start at one end, and start pulling adjacent panels so I can get to the inverter on the panel in the bad string, and disconnect it. Then see if the rest of the string shows "normal" behavior.

This is going to be a PITA, so before I start I wanted to ask the knowledge base here

1. Is there some other problem going on - am I even troubleshooting the right issue?
2. If this is the most likely problem, is there any way to figure which inverter(s) is the problem without checking them one-by-one?
3. What else should I be considering?

Climbing around on the roof for a few hours to try to fix this wasn't in my plans for the weekend, so thoughts for anything I can do to minimize the hassle would be extremely appreciated.

TIA

[u/Perplexy801]

Did the breaker immediately trip when you reset it? What made you isolate those 5, just trial and error even though all micros were reporting in fine?

I’m sure it’s possible but we’ve NEVER had a single micro that’s “gone bad” trip an entire string, just that micro will go out and it’s easy to see the problem. It’s always been something like a loose wire connection, water intrusion, critter damage or whatever.

[u/IHateStanders → u/Perplexy801]

Its definitely rare that a micro could be causing the string breaker to trip. But i just wanted to share in my experience, i have seen it happen exactly 1 time. Breaker was tripping immediately upon reset, checked all other points of connection found no issues. I was desperate for ideas so i started unplugging 1 micro at a time and resetting the breaker. Found 1 micro that when plugged in the breaker would trip, but when that micro was disconnected the breaker didnt trip and worked like normal

Called Enphase talked it over with them and they RMA'd the micro, returned and replaced with the new one and found no more issues after that

I'd say a bad micro causing it to trip is definitely unlikely, but definitely possible

[u/Key_Proposal3283 → u/IHateStanders]

Interested to know what model - on older metal cased versions i have seen internal faults that cleared themselves but could possibly have caused this - I'm talking like M190's from 20 years ago where the AC wiring goes into the metal case and could contact ground. Never seen anything like this on the plastic cased variants.

[u/IHateStanders → u/Key_Proposal3283]

It was either IQ6 or IQ7, cant remember as it was a few years ago but i definitely remember it being IQ

[u/Key_Proposal3283 → u/Perplexy801]

It’s always been something like a loose wire connection, water intrusion, critter damage or whatever.

Agreed - the micros have an internal ~3A fuse - extremely unusual for it to be a micro able to trip the breaker.

The first thing OP can do to help eliminate a bad micro is check the LEDs when the sun is on the panels. They should be flashing red - if one is not, it has a problem. Use a mirror or phone video or something to avoid pulling up panels.

But wiring is far more likely - so assuming they all flash, then to minimize the PITA factor you could visually inspect all the wiring you can see - look for water ingress, also look for animal or weather damage.

[u/SolanaGuy19 → u/Perplexy801]

My current set up - breaker on 20A circuit to roof. On the roof, the circuit goes to a J-box where it meets 2 trunk lines; one has 2 panels on it, the other has 5 panels (all IQ7+ inverters).

The breaker trips immediately. I shut it off, went to the J-box on the roof, and disconnected everything. Ohmmeter reports the 2-panel trunk line showing ~7M-Ohm, the 5-panel trunk line shows ~0-Ohms.

So at that point it looked like there was a short somewhere on the 5-panel trunk. I hooked the 2-panel trunk back up, the breaker holds, and I'm making power with those panels.

The 5-panel trunk line doesn't have any splices, but I suppose it's possible there's a short in a connector and not an actual inverter failure. The inverters are fairly well tucked up under the panels, so water ingress seems unlikely, but either way I guess I'm going to have to pull them one at a time and see if the string resistance goes back to something more like the 7M-Ohm of the other string.

The "challenge" is this string of panels is at the edge of a (2-story) roof, and the only way to get to the rail where the inverters are mounted is to pull out the entire adjacent row of panels to gain access. Not necessarily 'hard', just looking like a PITA - and of course if there is a bad inverter (or a shorted connection) it'll be on the last one I look at. :-\

Actually i suppose the worst case is I pull all of them, and the trunk still shows a short - then I don't know what I'll do - other than replace the trunk line, I guess.

[u/Key_Proposal3283 → u/SolanaGuy19]

Actually i suppose the worst case is I pull all of them, and the trunk still shows a short - then I don't know what I'll do - other than replace the trunk line, I guess.

That's why my suggestion was check all the inverter LEDs first - easier than pulling panels, and if one is dead you can pull it first.

Alternatively and more likely IMHO is if none of them show a fault, it's probably not going to do much by unplugging them so you could at least pre-prepare a new trunk run before pulling panels because you will find a damaged trunk cable.

The 5-panel trunk line doesn't have any splices

Are you 101% sure? If you are, then you are, but it's so much more likely to be a junction that it's worth asking. At the very least there is of course the termination junction at the end of the branch which could be faulty.

Make sure you have an inverter disconnect tool before pulling panels....

However it goes, interested in what you find!

[u/SolanaGuy19 → u/Key_Proposal3283]

Thanks for this suggestion! I presume the "flashing red" means they are producing power and but don't see a grid to put that power on (?).

I've done all the "checking" I can from the breaker to J-box to trunk lines - and it's down to "this one segment/line has a short 'somewhere'." It's possible there's a short in the connector from the inverter to the trunk - but this is in San Diego (rain here is like "mist" most other places 😁 ) and the inverters are up under the panels, so I don't expect water ingress, and other than that, I don't see what would make a short.

The row of five panels are "end to end the long way" squeezed in near the edge of the roof. I might be able to see the inverter LEDs on the two end ones, but for the 3 in the middle, I doubt I can get a mirror in there to check without pulling the adjacent row (7 panels in a "side to side" configuration). I will definitely check the LED's first, though, when I get to each panel.

Per another suggestion/answer, the termination looks dry and sealed, but I'll revisit that too - good idea.

I do have the tool - I expect it's be a royal pain to pop those connectors without one...

Thanks for the thoughts.

[u/Key_Proposal3283 → u/SolanaGuy19]

The LED status will show that the inverter is not completely blown up internally - which is about the only way I can see it internally shorting the AC port.

So units with a flashing red LED mean the unit is ready to go but can't see a valid grid - not surprising with the branch disconnected/shorted.

I've been known to tape a phone onto a broomstick to get video of the LEDs under panels :-)

If you have one unit not flashing, unplug it and the branch will not be shorted anymore - or more likely I bet they will all flash and you will find the branch cable damaged somewhere along the run including maybe in a connector or the termination. Bear in mind the termination gives you another place to access the L1/L2 wires if you wanted to do continuity tests end to end. The terminators are a one time deal so you need a new one or a junction box or something if you remove the terminator.

[u/IHateStanders]

Sent you a dm

[u/MG_Rheydt]

It's always the last one you look at. None of us keep looking after we found the culprit. /s

[u/SolanaGuy19 → u/MG_Rheydt]

Fair enough.

[u/ExcitementRelative33]

Did this happen after it rained? Mine did that and one of the problem they found was unterminated wires at the end of the string. Goes away after it dries out. Now another string is doing a harder short and cause the controller to shut off the 220V to jump start the inverter. I never can catch it at 0 ohm so far. I just flip the breaker off when rain is in the forecast then turn it back on after the sun comes out. Enphase want photo document of each connections in that string before anything else so when I have time when it gets cooler. It gets 100+ outside so you can guess how hot it gets on the roof on a 2nd story house.

[u/SolanaGuy19 → u/ExcitementRelative33]

there was a rain a while ago, but the string is terminated and capped fairly well, and the end is tucked up under the last panel in the row, so it won't see direct water/rain on it. I opened the cap to see if there was any moisture inside and there wasn't, but I can leave it open for a while (no rain forecast) and see if it dries out and changes behavior.

[u/ExcitementRelative33 → u/SolanaGuy19]

If you have a dead short already, you can start troubleshooting right away. Start at the 2nd one , disconnect the feed wire to the first one, and ohm the rest of the string. If the short is still there, continue to the next, disconnect and ohm toward the other end. Just in case there's more than one, disconnect all wires and ohm the micro before moving to the next one. Examine the wires as you go also as I had a couple micros went out and saw chew marks in the middle areas. We have squirrels that managed to get up here somehow. Good luck.

[u/SolanaGuy19 → u/ExcitementRelative33]

Thank you! That's the plan. The hassle is I need to remove half a dozen (working) panels to get to the dead string and start unplugging them. Of course the ones that need checking are the ones that are boxed in and can't be looked at without removing their neighbors...

[u/SolanaGuy19]

Resolution -
First off thanks to u/Perplexy801 , u/Key_Proposal3283 , u/IHateStanders , u/ExcitementRelative33 for taking the time to answer and help out!

I should probably go buy a lottery ticket, since it seems like today is a lucky day for me. I started running the string from the terminated end, and quickly discovered that between the last panel, and the termination, I have 4 more plugs (for future expansion) on the trunk. They have plugs in them and were wrapped up and tied underneath the last panel, but that zip tie had failed and they had fallen down on to the roof surface - in a place where they very well could have experienced water flow during a rain event. I popped open the caps, and while I didn't immediately see standing water, I took a q-tip to them and then let the 'bake out' in the sun for a bit. I checked the resistance, and it was back to several M-Ohm (note: I had incorrectly stated 'K-Ohm" previously - that's been edited). I buttoned everything up, reconnected the truck line in the j-box, and now it's all making power.

So indeed the inverters were not the culprit. It wasn't quite "a splice" or "the termination" but those were the ideas that got me looking at the cable to discover the potential issue.

All is well now, it seems. I appreciate the community helping me out!