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PV Combiner temperature > 150F (65C)

JWLV

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May 27, 2020
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I just got a thermal imaging camera, so the first thing I did was to see the temperatures of my entire solar system.

Today's weather is nice, about 75F and sunny.

All the PV wires and battery cables are not notable. They are all near the ambient tempature. My Growatt inverter is running around 105F which I think is normal since it is currently charging my EV at around 1600 watts.

The only notable thing I can see is the PV combiner box. See pic 1. It is measuring 146F on the fuse as seen in the picture. As I was moving the thermal imaging camera around, it was as high as 151F. This is the PV combiner I have: https://www.amazon.com/gp/product/B0BB9R25CF
Each string of my solar panels to the combiner box is delivering about 11A @ 78.2V. There are 3 strings. These measurements are taken by a clamp meter and volt meter. According to the PV combiner box, it can handle up to 15A for each string. Each of my strings is 11A. And I am also well below the 60A circuit breaker. The PV wires going in and out of the combiner box are all near ambient temperature. The only HOT zone is directly on each of the fuses and a small section of the PV wire that attached to the fuses. The fuses are these rather large ceramic ones like pic 2. I've never used these types of fuses before, but that's what the combiner box came with.

Any ideas why the fuses are running so hot? Is this normal for ceramic fuses?

BTW I love this thermal imaging camera. I bought it used on Ebay for $100. It's a very low-end thermal camera made by Kobalt (Lowes).
 

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presumably These are the only connections you did not make personally, when the Sun goes down I would loosen each of the fuse wire connections and ensure that whoever assembled that box did not accidentally push the wire too deep thereby catching some insulation in the contact area of the fuse holder
 
Heat is a part of fuse and breaker operation. Measure DC voltage across each fuse.
And voltage drop across the entire system. Breakers and fuses tend to be biggest source of Vd in my experience. FWIW, Vd x Amps = heat.

When things get above ambient plus ~20f I start to pay attention and look for issues.
 
presumably These are the only connections you did not make personally, when the Sun goes down I would loosen each of the fuse wire connections and ensure that whoever assembled that box did not accidentally push the wire too deep thereby catching some insulation in the contact area of the fuse holder

That's a good suggestion. The fuse wires were pre-assembled. I've just loosened each one, pulled and re-inserted the wire, and tightened it. I'll check temperature w/ the thermal imager during the day tomorrow.
 
Today I took a new meaurement with the thermal imager. The temperature is much lower than the first day. The max temperature is 107F. Ambient temperature is 80F. So the max wasn't excessive like yesterday at 150F. Attached is a picture taken by the thermal imager. As you can see, the heat is still focused directly on the fuses and the bus bar.
 

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Is it possible the wiring is not big enough for your combiner box, or even not copper?

Is this box indoors or outdoors?

The box seems to be a pre-manufactured 4P combiner box, perhaps the Eco-Worthy model.

A couple of comments that may or may not apply.

1) Small wires can heat up with amps. Normally those boxes are built for a 6 amp 100 watt panel, so if bigger panels are used, voltage could go up so that amperage tops out around 11 amps for any number of panels in series. Could be the pre-made wiring is 16 AWG for lower amperage panels, but larger panels running all out, all day long could have an effect. I also notice your wires coming out of the fuse thatis combined are hot. I would want 8 AWG wire or thicker for a 4P system. 8 AWG if its 4 100 watt panels; 6 AWG if its 4 175 watt panels.

2) few strand wire loosening up . In a user manual for their larger SCCs, Victron recommends a finely stranded wire, and not the 7 or 12 strand wire I normally purchase. IMO, I have found. My thicker stranded wire needs a periodic tightening on the circuit breakers every few months when first installed.

3) Excessive contact points. These boxes come with the MC4 connectors installed in the bottom for easy connection. I prefer replacing those with a cable gland that a wire can slide through easily, and then be secured to hold the wire in place so it can be connected directly to the fuse holder. This gets rid of the extra contact/fail point.

4) Fuses will heat up to melt, and the closer they are to the fuse rating, teh hotter they will get. If the box was built for a 6 amp panel, it likely comes with a 10 amp fuse, but running it at 10 amps will likely not blow it for quite a while. I would not think a hot fuse would give a picture like that. That seems to be on the entire wire.
 

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