Combiner breaker tripped mid day

[Greendream]

I'm going to shut down absolutely everything once the sun is down. With my headlamp I'm going to remove the old breaker and install the new one in the correct orientation. I took some videos today of my system running right about solar noon. Saw 63.1 amps on the PT100 once. About a 9A load on the AC side and 54-55A going to the batteries. I did see higher amperage going to the batteries at one point up to 58A but I think the AC load dropped at that point. I checked the combiner box and wow it was warm after I opened it up. You could smell hot electronics. I checked the temps with my fluke HVAC IR thermometer and read 150F on the anti-backfeed diodes. The wires at the top of the box were all fairly warm as well, maybe 120F I took video while holding the IR gun kneeling over so I need to go back and review the videos. The big 63A breaker wasn't as hot as the anti-backfeed diodes. Those were the hottest.

Never saw 3.4 Kw today so that part of the equation wasn't able to be replicated.

The fuses inside of the holders are 12A, pics below -



I dont find any specifications on the fuse size from the manufacturer. I will add this, the kit that this equipment came from I believe was setup to run 5 strings of 4 panels into a PWM controller then charging AGM batteries. Because I wanted to get a magnum inverter and charge controller for a more robust off-grid setup, I discovered that I needed to run 5 panels in series to get the voltage required to power the PT100. The combiner box is more than likely built around that configuration and not mine. It looks like I can upgrade the fuses up to 20A based on the fuse holder's rating? Would that reduce the heat?

I am having some concerns with the Llama's but I will save that for after I get this trouble at the combiner box resolved. The SOC was pretty low, it was 30% (345 total AH @ 48V) when I woke this morning and was basically in bulk mode until around 2:30PM. We constantly have a 3-9A draw on the system for the AC loads. This is our setup to power our campers while we build the house, then everything will move inside. Hoping by that point we have most of the kinks ironed out and we'll be able to decide if we need an additional battery or more panels.

Thanks again and I'll post an update tonight or tomorrow.

 

[Bud Martin]

Those blocking diodes do get very hot, they dissipate about 3W (if it is Schottky diode) power each based on 10A of current flow. I look up the spec of the diode but it does not say if it is Schottky diode or not, you can check the Vf (Forward Bias Voltage of the Diode to find out).
It will be interesting to see what PV panels current are once you have clamp on DC Amp meter.
I doubt that 20A fuse in place of 12A fuse will reduce the heat much.
Fuse dimension looks to be 10mm x 38mm.

 

[Greendream]

Those blocking diodes do get very hot, they dissipate about 3W (if it is Schottky diode) power each based on 10A of current flow. I look up the spec of the diode but it does not say if it is Schottky diode or not, you can check the Vf (Forward Bias Voltage of the Diode to find out).
It will be interesting to see what PV panels current are once you have clamp on DC Amp meter.
I doubt that 20A fuse in place of 12A fuse will reduce the heat much.
Fuse dimension looks to be 10mm x 38mm.

I tried to research how to check the Vf and got overloaded. I'll read up on it and see if my multi meter will work.

Breaker was successfully swapped out at about 7:30PM. Panels were only drawing 10 watts in total and 0.2A. Figured it was safe to turn everything off and take care of it. Flipped the breaker on and the PT100 is harvesting 20 watts and 0.5A at 7:45PM. Not sure if that signifies anything at this point. Will see how everything performs tomorrow morning.



I discovered the wire inside the combiner box is aluminum. Looks like 6 gauge is the larger wires and maybe 10-12 gauge for some of the others. Not sure if I should think about rewiring it with copper?

 

[HRTKD]

I discovered the wire inside the combiner box is aluminum. Looks like 6 gauge is the larger wires and maybe 10-12 gauge for some of the others. Not sure if I should think about rewiring it with copper?

Check the writing on the sheathing. What looks like aluminum could be plated copper wire.

 

[Hedges]

Even at 10 watts, there can be high enough voltage to shock you. Check it with the meter.
After turning off breaker, you can open all the touch-safe fuse holders and then positive side of panels are disconnected. Better for working on wiring in the box that way.

Vf - just voltage across diode with current flowing.

12A fuses are a bit small for PV panel rating. It could open under some operating conditions. I would use 20A.
That would never blow with proper operation, but a shorted PV string (and failed diode) would let the other three backfeed 30A and that's when the fuse opens.

If aluminum, 12 awg is still OK for 20A.
6 awg is rated 60A (at 90 degrees C) in a cable. Single conductor in free air, 80A. (but that box probably doesn't allow so much cooling.)
One would hope it is tinned copper.

 

[Kevox]

Your solar panels could exceed the nameplate power depending on your elevation. What is your elevation?

 

[Greendream]

Even at 10 watts, there can be high enough voltage to shock you. Check it with the meter.
After turning off breaker, you can open all the touch-safe fuse holders and then positive side of panels are disconnected. Better for working on wiring in the box that way.

Vf - just voltage across diode with current flowing.

12A fuses are a bit small for PV panel rating. It could open under some operating conditions. I would use 20A.
That would never blow with proper operation, but a shorted PV string (and failed diode) would let the other three backfeed 30A and that's when the fuse opens.

If aluminum, 12 awg is still OK for 20A.
6 awg is rated 60A (at 90 degrees C) in a cable. Single conductor in free air, 80A. (but that box probably doesn't allow so much cooling.)
One would hope it is tinned copper.

Thanks, that is a good call on the fuses. Going forward I'll be sure to do that. My multi meter has a setting for 200V and it registers 0.00 across the diode. I will have a better meter tomorrow and will check it out. Would a 15A fuse work or do you think the 20A would be necessary in my case?

I am looking at making some sort of vent with flashing (something to prevent moisture from getting inside), that should help with the heat.

Check the writing on the sheathing. What looks like aluminum could be plated copper wire.

I'll research what kind of wires they are to be sure.

Your solar panels could exceed the nameplate power depending on your elevation. What is your elevation?

Thanks, I didn't know that. I am at 6700ft

 

[Hedges]

Actually, with MC connectors, after turning off breaker you can disconnect both + and - of all strings. Check voltage on capacitors of SCC; once that drops to zero should be safe.

Going by Isc x 1.56 I came up with 18.5A, so I would use 20A fuse. PV panel label or data sheet should list a maximum fuse size.

Across a diode (assuming forward biased, not blocking reverse flow into a shorted PV string), reading will be in the 0.3V to 1.5V range. If zero reading on 200VDC scale, try lower scales.

10W into 50V = 0.2A, so PV array are still putting out 60V or so.

 

[Greendream]

Should have the new clamp meter today to do measuring. The replacement breaker didn't change the amps coming into the SCC. Saw a max of 66.1A running near solar noon. This makes me a little nervous about the 63A breaker there and if it may trip again.

Yesterday was partly cloudy and they seemed to be hanging over the property so max PV power was 3.2Kw.

The combiner box wasn't as hot as the other day but neither were the temps so I'll continue to monitor that.

Thanks for everyone's input and time.

 

[Greendream]

Would an 80A breaker like this work to replace the 63A breaker I have? I see the wire size compatible up to 2 AWG.

Midnite Solar MNEPV80 -

Product - MidNite Solar

MidNite Solar Product Page.

www.midnitesolar.com

 

[Hedges]

Should have the new clamp meter today to do measuring. The replacement breaker didn't change the amps coming into the SCC. Saw a max of 66.1A running near solar noon. This makes me a little nervous about the 63A breaker there and if it may trip again.

Yesterday was partly cloudy and they seemed to be hanging over the property so max PV power was 3.2Kw.

The combiner box wasn't as hot as the other day but neither were the temps so I'll continue to monitor that.

Thanks for everyone's input and time.

66.1A x 47V = 3107W (using previous battery voltage display)
195W x 4 x 6 = 3900W (STC) of panels.
That's believable.

3107W / (5 x 18Vmp) = 34.5A from array
That isn't going to trip a (properly functioning) 63A breaker.

3900W/ (5 x 18Vmp) = 43.3A if delivering STC watts on a cold bright day.
The 63A breaker is an appropriate size.

See if clamp meter confirms about 35A from array.

Shouldn't be any need for an 80A breaker. Between two brands of 63A and getting the orientation as original, something ought to work. Off-brands (especially little lever types) have been seen to trip below rating, but I would expect a combiner assembly to have no problems especially this far below its rating - otherwise it would malfunction for most of their customers.

I'm thinking it was the polarized breaker used backwards. These have magnetic trip (and a hydraulic dashpot to cause time delay). They use a magnet to pull the arc into arc chutes so they extinguish arc in one polarity, to be effective for DC. I can imagine a permanent magnet plus electromagnet causing an offset in trip current between polarities.

 

[Greendream]

New clamp meter reads 60A at 0.01A resolution. Panel strings are giving off between 4.8-5.1A (they are not all fully in the correct position, some are magnetic south, the others are true south. I will see this tool being handy to get them positioned right). The 4 awg PV wire coming into the PT100 is showing between 20-21A with 1.9Kw (batteries fully charged and in absorb, just powering AC loads now). The PT100 controller however is showing about 39A, which I expect is some combination of AC amperage being processed by the panels. The batteries are all getting between 0.4-0.5A

So now it seems I understand why the new 63A breaker didn't trip. They were likely as you mentioned @Hedges around 35A. We suspected the other breaker was defective as it wouldn't function properly in ON position, thus flipping it during troubleshooting.

I feel a lot better knowing the combiner box isin't overpowered though I do have some 20A 10x38mm fuses coming to replace the 12A ones in there.

Good solar day here, enjoying it.

Thanks again!