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Pv combiner box keeps throwing 80amp breaker

Jazzmonger

Jazzmonger

Hacker at heart
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Apr 29, 2022
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Location
Wilder, Idaho
One of my combiner boxes keeps throwing the breaker. It's happened multiple times now.

83EB295A-4DBD-4E65-A67D-75CA6310A6B2.jpeg

Brand new install - I have 3S4P config on Canadian Solar 420 watt panels. I see the current touching 80amps from time to time. The breaker says
In-80A, I'm assuming that's the trip value. Solar Assistant shows 80A peaks, but not at the time it tripped. Im sure there's a delay in the reporting of values. It's too bad there not a table of max/min values for each stat.

E9450ED2-3729-4741-9E57-C909E0D13FF0.png
Options:
I could move one of the parallel strings to my second combiner box to reduce the input current. The other box has the same number of panels but only shows 2/3 the current as the overloaded box for some reason - that's a topic for another thread.

Any other ideas?

Jeff
 
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It looks like inverter 2 has the high amps, but you show inverter 3's voltage input.
What is the voltage input at inverter 2?
 
420W panels should output around 6A max, if 4P is giving 80A, something is wired wrong...
 
I meant 4p PV strings x 6A each, 24A into an SCC and 80A out is more plausible than the strings tripping 80A breaker themselves.

But I can't follow the wiring well enough to be sure if the breaker is array disconnect, or is separate circuit for SCC to battery.
 
Looking closer, it appears each breaker is 2, 500V poles in series for 1000V, and is fed by a pair of wires from the two electronic boards. Output is a single wire.

80A is high but not impossible for breaker poles that size. Some brands combine two in parallel; if this was meant to be used that way and isn't, it would trip at 40A. But I think it is meant to disconnect both positive & negative.

Display shows 80A, which I think is SCC output.

Other devices in box say surge arrestor, not GFCI (which is something else that can trip.)
 
Those graphs are both inverter 2. Each line into the box shows 15-20 amps at full sun so it is hovering at 80amps total.
 
We see 4 wires into the box.
Does each wire have one PV string? Or multiple strings joined with "Y" cables?
You said each line into box 15 to 20A, which is awfully high for one string.
 
Supervstech said:
And it is tripping... which means there is a problem with the wiring.
Click to expand...
"with the wiring".... actually i would rephrase. The wire is fine... "How it's wired" is the issue. I think I need to move one parallel string to a different combiner box to balance the loads. The "way" it's wired is causing too much current to flow through the breaker, thus tripping it.
 
Does the body of the breaker get very hot at full load?
BTW, What is the spec of the panel?
You have 80A breaker and you are pulling less than half of the breaker spec, may be defective breaker, I see that has a link that joint the breaker handles together, I wonder if you can remove the clear plastic linker that join the breaker for the positive and the negative breaker together and see which one will trip.
If you have clamp-on DC Amp meter with peak hold reading then you use it to monitor the current to see what you get.
 
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I'll check tomorrow at peak production... it's on the down swing of production right now - 6:30pm. I'll also measure the actual DC current on each leg of the combiner box inputs at peak product (1pm or so) as well as the output.

canadian solar 420watt panels.
1658104285066.png
 
Jazzmonger said:
On standard PV wire?? I don't think that's a good idea... However, I'm thinking of running 6 awg to the inverters or 2 pv wires each on +/- to the inverter.
Click to expand...

After combining (inside box and outside), wire needs to be heavy enough for whatever you're putting through it.
If 80A delivered, need 100A breaker and wire thick enough for 100A ampacity.

We run higher voltage, lower current, where possible (when SCC tolerates
it.)

Jazzmonger said:
Each wire has one string. No Y cables.
Click to expand...

But the panels are rated 9A. How do you get 15A to 20A on a wire fed by one series string?

We still can't figure out how four, 9A strings in parallel deliver enough current to trip 80A breaker.
 
Hedges said:
westill can't figure out how four, 9A strings in parallel deliver enough current to trip 80A breaker.
Click to expand...
I agree. It's a head scratcher. Let me get some real world, hands on data measurements tomorrow and report back with more info.

jeff
 
Searching part number of breaker, haven't found same one, but other brand a bit different ratings:


Appears to be up to 220VDC per pole and up to 125A per pole. 80A is one available. Two poles for 440VDC.

I thought your breaker was supposed to be 500V per pole (so two in series is 1000V), and 80A/pole.
Or maybe that is that 1000V with all 4 poles in series? That's how it is used. Two in series on positive, two in series for negative.
OK, in line with the other I found.

But supposed to handle 80A, apparently tripping near 40A from four strings in parallel.
Can you explain 80 to 100A reported by upper chart? Is that output to battery?
Lower chart MPPT 1 has pulses going as high as 80A. Why does it jump around so much?
I wonder if it has capacitor charged to PV voltage, which it dumps as brief high bursts into battery, possibly exceeding breaker limit. Ought to be smooth.
Can you measure PV string and combiner current, e.g. with DC clamp ammeter?
 
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