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Combiner box issues

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clint0n

New Member
Joined
May 7, 2024
Messages
15
Location
Thomson Station, Nova Scotia, Canada.
My system was working great since installation, until today at peak time when my inverter stopped charging, I came into the electrical room, and smelled a burnt smell. All the strings are producing the correct voltage, but once I flip my circuit breaker on in the combiner box, the lines drop from 160vdc to 2.5v and the output to the inverter reads 1vdc. I'm thinking it's the mds module or the circuit breaker itself. Any help would be appreciated.
 
clint0n said:
My system was working great since installation, until today at peak time when my inverter stopped charging, I came into the electrical room, and smelled a burnt smell. All the strings are producing the correct voltage, but once I flip my circuit breaker on in the combiner box, the lines drop from 160vdc to 2.5v and the output to the inverter reads 1vdc. I'm thinking it's the mds module or the circuit breaker itself. Any help would be appreciated.
Click to expand...
Picture of combiner box?
 
Turn all the strings off, turn main breaker on.
Then turn 1 string at a time on and off, see if you can isolate it to 1 string/breaker.

Otherwise id suspect that ground/arc fault breaker shorted. You could disconnect that and see if everything comes back to life.
 
I would suspect the SPD. It's the only part that is designed to short the circuit.
Although, it doesn't appear to be the correct device or wired properly.
 
Smell from inside the combiner box, or from something else (like inverter?)

I'm not sure whether SPD can clamp output of PV array. 4 strings? Probably 20 ~ 40A Isc and 1.5 to 2.5V across SPD would be 30 to 100W. That should melt things down.

SPD looks to me like it is wired funny. Labels say L, N, PE. But both L and N are wired to PV+. That could protect one end, clamp to ground. But doesn't clamp the other, can go to Voc + clamping voltage relative to ground. Also doesn't protect against differential voltage between PV+ and PV-.

It also doesn't look like turning on the breaker switches in the SPD, rather it is connected to PV+ all the time.

I'm leaning toward a short in the inverter.
To diagnose, (turn breaker off first), disconnect red wire that comes out of 2-pole breaker by SPD from the black coupling block. Cap with a wire nut.
Turn breaker on and check voltage again.
 
Oh by the way, looks like ground wire from inverter goes to SPD, but no ground wires are seen going on to PV panels. Is that outside the combiner box? PV frames should be wired back to inverter chassis. Ungrounded, they can be a DC shock hazard if panels go bad, and with some inverters they are an AC shock hazard under normal operation.
 
Other fun facts - the breaker appears to be polarized, with (+) and (-) designations on the terminals.
You're using it with both poles in parallel. Did you need twice the current that each pole is rated for?

One pole is connected with PV+ going to (+) terminal, which I think is how it is intended to be used. But the other pole has PV+ going to its (-) terminal.

When PV feeds a short (like now), and you open the breaker, the pole used with correct polarity can interrupt arc but the backwards pole might not. If it didn't burn up already I suppose it has margin. 160V, you said.

I can read "63A" on the breaker (probably per pole), but what is its voltage rating?

I would have used the breaker to interrupt both PV+ and PV-; I like to have array completely isolated when working on wiring.
 
clint0n said:
My system was working great since installation, until today at peak time when my inverter stopped charging, I came into the electrical room, and smelled a burnt smell. All the strings are producing the correct voltage, but once I flip my circuit breaker on in the combiner box, the lines drop from 160vdc to 2.5v and the output to the inverter reads 1vdc. I'm thinking it's the mds module or the circuit breaker itself. Any help would be appreciated.
Click to expand...
You don’t have RSD there, do you?
 
I see a number of issues with that box. Two strings doubled on one diode. That’s probably where your problem is.

The breaker and SPD are wired totally wrong.
 
I don't know what "MDS Module" is.

Diodes, if that's what the black module with 5 screws is, don't serve any real purpose in the system, and their failure isn't likely to contribute to this problem (unless they all failed high impedance).

Failure occurred during peak time. When charge controller was working the hardest, PV producing the most? That part failed, is my guess.
If voltage PV+ to PV- goes from Voc to near zero when breaker is closed, there is a short downstream.

How about a link to OP's inverter? "10kw g.s inverter" is all I see in OP's profile under "About", and searching that isn't useful.
 
What is "mds"?

There are busbars from Midnight Solar which can be used to gang several fuse holders together. Or it can be done with wires in various ways.

If you get anything from Google, post it here for review.

Your bigger problem is what failed. I think there is a short somewhere, probably PV input to inverter.
 
Hedges said:
I don't know what "MDS Module" is.

Diodes, if that's what the black module with 5 screws is, don't serve any real purpose in the system, and their failure isn't likely to contribute to this problem (unless they all failed high impedance).

Failure occurred during peak time. When charge controller was working the hardest, PV producing the most? That part failed, is my guess.
If voltage PV+ to PV- goes from Voc to near zero when breaker is closed, there is a short downstream.

How about a link to OP's inverter? "10kw g.s inverter" is all I see in OP's profile under "About", and searching that isn't useful.
Click to expand...

10kw inverter
 
Hedges said:
What is "mds"?

There are busbars from Midnight Solar which can be used to gang several fuse holders together. Or it can be done with wires in various ways.

If you get anything from Google, post it here for review.

Your bigger problem is what failed. I think there is a short somewhere, probably PV input to inverter.
Click to expand...
All my strings are still producing the 160vdc before the combiner but I get next to nothing coming out of it, to the inverter, inverter is working fine on battery mode.
 
"Max DC voltage 270 V"

Plenty of headroom there.

Bridge rectifier, 100A. Maybe heatsinked to box. Probably not a problem for the current. But I don't see the point to using it.

seneysolar said:
Max pv voltage is 145v for that
Click to expand...

That would certainly explain things. But the chart says MPPT range up to 145V. Max 270V.

clint0n said:
All my strings are still producing the 160vdc before the combiner but I get next to nothing coming out of it, to the inverter, inverter is working fine on battery mode.
Click to expand...

Are the strings still putting out 160V WHILE you get next to nothing at the inverter?

If so, there is an open circuit. use volt meter to find out where 158V is being dropped.

But if the strings drop from 160V to 2V when breaker closed, then there is a short (likely at the inverter.
 
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