SMA 10kW inverter DI converter fault mystery

[nwdiver]

I helped a friend install a 13kW system with a 10kW SMA inverter about 5 years ago. The system is doing great but some mornings (~20%) it will get a string of 1 - 10 'DI Converter' Faults These are most common between 9am and 10am but I've seen them earlier and as late as noon. I've never seen this fault in the afternoon.

Any ideas?

Screen Shot 2019-08-25 at 9.04.24 AM.png

[J.P.M.]

What did SMA say when you called them and asked the same question ?

[khanh dam]

https://www.sma-service.com/en/faq-support/wok/Diagnosis/show.html?no_cache=1&tx_lwsmawok_pi1%5BsymptomId%5D=%3Csg%3Asymptom%3A755%3E&tx_lwsmawok_pi1%5Bsearchword%5D=&tx_lwsmawok_pi1%5Bproduct%5D=&cHash=5d7bea750bdd59d6cdbe0f2a75e3dffa

[nwdiver]

What did SMA say when you called them and asked the same question ?

The low level tech I talked to didn't know what it could be other than maybe something with the grid...

https://www.sma-service.com/en/faq-s...be0f2a75e3dffa

Yeah... I've dug through the FAQs and spent several hours on hold and a few minutes talking to techs without getting a clear resolution. Just wondering if anyone has seen/solved anything like this before...

[Markyrocks69]

My uneducated guess would be that something is getting wet due to morning dew and its causing current to go to ground....so there might be wire with broken or rubbed off insulation that's being grounded or maybe a junction that's getting moisture in it. Could even be a bad seal or the cover of the inverter not on tight (if its outside).

[nwdiver]

My uneducated guess would be that something is getting wet due to morning dew and its causing current to go to ground....so there might be wire with broken or rubbed off insulation that's being grounded or maybe a junction that's getting moisture in it. Could even be a bad seal or the cover of the inverter not on tight (if its outside).

That was my thought too and I did find a broken ground WAAAY out at the utility pole but I fixed that and the problem still persists. The inverter is also located indoors. One odd feature that I've never seen before is that there are 3 more transformers on his street and as near as I can tell they're all wired in parallel. That's weird... right? Usually each transformer is separate... right? I wonder if there's some weird resonance that builds in the mornings? No trips today at all... just odd.

[Markyrocks69]

That was my thought too and I did find a broken ground WAAAY out at the utility pole but I fixed that and the problem still persists. The inverter is also located indoors. One odd feature that I've never seen before is that there are 3 more transformers on his street and as near as I can tell they're all wired in parallel. That's weird... right? Usually each transformer is separate... right? I wonder if there's some weird resonance that builds in the mornings? No trips today at all... just odd.

I was thinking more along the lines of a DC wire in the array. Water equals more conductivity. Even if a connector was failing and it was getting wet and that DC started arching. I even saw a video where a cracked panel that gets wet can energize the frames of the array so it doesn't take much.

[nwdiver]

I was thinking more along the lines of a DC wire in the array. Water equals more conductivity. Even if a connector was failing and it was getting wet and that DC started arching. I even saw a video where a cracked panel that gets wet can energize the frames of the array so it doesn't take much.

I don't think that would cause a 'DI converter fault'; My understanding talking to SMA and reading some of the FAQs is that it's usually a voltage on the ground. The panels are some distance (~100') away and I doubt voltage from the panels could make it back to the AC ground.

[Markyrocks69]

I don't think that would cause a 'DI converter fault'; My understanding talking to SMA and reading some of the FAQs is that it's usually a voltage on the ground. The panels are some distance (~100') away and I doubt voltage from the panels could make it back to the AC ground.

I obviously don't know how its wired but my best understanding of that particular type of inverter is that the panels are grounded (most usually are by code). That ground will either go to the inverter or to a ground electrode (rod), that inverter I believe calls for it's own ground rod, from the ground rod to the inverter, then the ac ground and the new ground are bonded in the inverter. In other words everything is connected. Usually all grounds on a property are connected unless you're using auxiliary ground rods.

[nwdiver]

I obviously don't know how its wired but my best understanding of that particular type of inverter is that the panels are grounded (most usually are by code). That ground will either go to the inverter or to a ground electrode (rod), that inverter I believe calls for it's own ground rod, from the ground rod to the inverter, then the ac ground and the new ground are bonded in the inverter. In other words everything is connected. Usually all grounds on a property are connected unless you're using auxiliary ground rods.

We used Aux ground rods. The panels are also mounted to a metal shop so there would be lots of opportunities for the voltage to dissipate before reaching the inverter. Good thinking though. I can certainly see how this could be the culprit in some circumstances.

[Markyrocks69]

We used Aux ground rods. The panels are also mounted to a metal shop so there would be lots of opportunities for the voltage to dissipate before reaching the inverter. Good thinking though. I can certainly see how this could be the culprit in some circumstances.

The only other things I can think of is some other failing appliance in the house could be putting small amounts of current on the ground. I saw a poorly installed hotwater tank where the pressure relief valve wasn't directed away from the top of the tank and it would drip a few drops of water into the box where the electrical connection was made , something like that. Even condensation dripping off of hvac ductwork getting into a light switch ect. Or the DC circuit coming into the house usually is in metal conduit that is in turn grounded, there could be wire damage inside the conduit and moisture inside of the conduit. Theres alot of potentially stupid situations how this could happen. Part of the reason this stuff is so dangerous.

[sdold]

I'm wondering if there is a potential difference between the service ground and the aux ground rods. I know they're not required to be bonded to service ground in some codes (2014?) but based on some voltages I've seen between stakes in soil resistance tests I wouldn't be surprised if there was several volts between the two. I've seen small sparks from the stake cables and never really knew where it came from. Something from the utilities I assume.

[Markyrocks69]

I'm wondering if there is a potential difference between the service ground and the aux ground rods. I know they're not required to be bonded to service ground in some codes (2014?) but based on some voltages I've seen between stakes in soil resistance tests I wouldn't be surprised if there was several volts between the two. I've seen small sparks from the stake cables and never really knew where it came from. Something from the utilities I assume.

That's actually a very good point. I have heard (from the utility company) that the pole if it absorbs water can become energized and send voltage into the ground. If the ground for the ac side goes to a pole its possible that the ground is getting some current on it that way. The trick is to isolate the problem and move towards a solution.

As a side note you said you found a broken ground wire at the pole. How did you fix that and what does the rest of the grounding situation look like on the ac side? are the rods holding up? Is the waterlinew bonded? How many rods are there? I'm wondering if theres other deficiencies in the system.

Also how far away from the house is the meter? Is there a ac shutoff for the main service outside? Where is the ground and neutral bonded?

[nwdiver]

That's actually a very good point. I have heard (from the utility company) that the pole if it absorbs water can become energized and send voltage into the ground. If the ground for the ac side goes to a pole its possible that the ground is getting some current on it that way. The trick is to isolate the problem and move towards a solution.

As a side note you said you found a broken ground wire at the pole. How did you fix that and what does the rest of the grounding situation look like on the ac side? are the rods holding up? Is the waterlinew bonded? How many rods are there? I'm wondering if theres other deficiencies in the system.

Also how far away from the house is the meter? Is there a ac shutoff for the main service outside? Where is the ground and neutral bonded?

- I found a broken ground at the pole where the transformer is mounted ~200' away from the house but it's wired in parallel to 3 more transformers so there were other grounds further away. It looked like it had been cut by something hitting it. I took a piece of #6 bare copper wire and reconnected it to the ground rod.

- There are ~3 ground rods on the service side. One at the meter, one outside the home and one aux ground rod at the shop. I think the water line is pex now so no grounding there.

- I think the ground and neutral are bonded at the main panel.


Screen Shot 2019-08-27 at 10.08.44 AM.jpg

[Markyrocks69]

Are you absolutely positive there is no service disconnect at the meter? I only ask bc by code there should be a shutoff within 5 feet of the meter. That's kinda the point I'm getting at is in theory theres should be a shutoff (molded case breaker) and the ground and neutral should be bonded there and nowhere else. I realize this kinda seems off the subject but if the neutral is bonded in multiple places that could be part of the issue.

Another question is if the ground and neutral aren't bonded at the meter pole why is there even a ground out there? To ground the meter box? The meter box (I believe) should just be bonded to the neutral. I'm not 100% positive on that fact but fairly certain.