Mc4 fuse blown

[gersus]

Checked my inverter display this morning and it showed 0 on one of my strings so I got to looking and found a melted mc4 inline fuse holder. I have 2 strings of 6 panels in series. Do these fuses show visible evidence of being blown? The fuse itself appeared ok.
Isc for these panels is 10.31 and I am using 20 amp fuses. Everything else appears good.
I have to order more fuses. The inline fuse and holder came from windy nation. Should I be concerned of a bigger problem?

 

[Mattb4]

If your inline fuse holders are like the ones I tried to use they have a problem with making a good electrical connection which leads to heat buildup. The fuses will not blow because excessive amps are not being drawn. At first I had thought the issue was simply not tightening the fuse holder enough but one day I was out checking my panels and noticed the fuse holders were quite warm versus the regular MC4 connections.

 

[gersus]

Oh! That makes sense for what has happened here.

 

[Hedges]

Melted, bad contact?

One would hope a fuse holder could hold a fuse.
Mismatched "MC4" are notorious for failing, starting fires.

 

[Hedges]

I have 2 strings of 6 panels in series.
Isc for these panels is 10.31 and I am using 20 amp fuses. Everything else appears good.

If just two strings paralleled, No fuses required, serves no purpose.

But you were able to distinguish one string from the other on inverter? Must be two separate inputs, each a single 6s string. Really no need for fuse now.

(If you wired 6s2p then had a single fuse, the fuse would be too small but likely wouldn't blow. Would get hot.)

Should I be concerned of a bigger problem?

Check for heat at all connections.

PV panels have MC4 (or rather knock-off) connectors, fuse holders a different one, extension cables yet another.
Only identical model or UL listed mated pairs (after testing together) can be trusted.
Maybe cable + panels will work together, maybe not. To do it right, replace connectors on cables with same brand as on panels. At least check for heat after operating near max current for a while.

 

[gersus]

The connectors are from the ole amazon. I can easily order connectors from windy nation so they should be the same that way.

 

[Mattb4]

I am posting an image of the MC4 inline fuse holder disassembled that I removed from my setup and hopefully people can see the design problem. The fuse in this one shows discolored on one end from heat. The barrel of the inline section does not pinch down on the side flanges that hold the fuse. The only connection is only at the bottom of the fuse holder against the fuse base.

 

[Hedges]

The connectors are from the ole amazon. I can easily order connectors from windy nation so they should be the same that way.

Same retailer doesn't mean same manufacturer and model. But might be higher quality.
PV panel data sheet may specify MC4 connector model, which you could then buy. Or buy matched pair and cut end off one lead on one panel, each end of string, but I hate the idea.

There is no MC4 except Stabuli; all others are knock-offs. There may be a few UL listed to mate with it.

 

[Mattb4]

...

There is no MC4 except Stabuli; all others are knock-offs. There may be a few UL listed to mate with it.

Just out of curiosity I checked to see if Stabuli has an inline MC 4 fuse holder. They do and it looks well designed though it is not inexpensive retailing at ~$30 or more depending on shipping from a couple of retailers I checked (AltE and SS).

 

[gersus]

I think I’m going to just do away with the fuse. That line goes from a panel to the fuse to inside my solar shed to a dc breaker.

 

[Hedges]

not inexpensive retailing at ~$30 or more

Yet not expensive compared to DIN rail fuse holder and a combiner box.

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