Blowing fuses occasionally

Amishdude

Running a Morningstar Sunsaver 12/20 charge controller with 2 Kyocera 12v/135w panels. I have a 15A cartridge fuse on each side of the line feeding the controller. Any ideas as to why one of the fuses blows every couple of months?

Cariboocoot

Re: Blowing fuses occasionally

What do you mean by "fuse on each side of the line feeding the controller"? You mean a fuse on each panel's positive wire? Or do you mean the panels are in parallel and you've put a fuse on the positive wire and another on the negative wire?

Technically with just two panels in parallel you don't need any fuses on the panels; they can't produce more than their short-circuit current rating. In any case check all the wiring for proper sizing and connections. It never hurts to check. There could be an intermittent short when the wire moves a little.

You should have a 20 Amp fuse on the charge controller's positive output to the battery.

Amishdude

Re: Blowing fuses occasionally

Yes, there is actually a fused disconnect between the panels and the controller. It was designed for additional panels, but they just haven't been added yet. And yes, I do have a 15 Amp fuse on the charge controller's positive output to the battery.

2manytoyz

Re: Blowing fuses occasionally

Just read the OPs response, which was posted while I typed this, hence the edit...

These panels are rated at 7.63 Amps at peak power. The short circuit rating is 8.37 Amps, but I have measured slighly higher than that just prior to installing mine. So on a clear day, and a battery bank state of charge low enough to demand max charging from the solar panels, it obviously can exceed the 15A capacity of your fuse. 7.63 x 2 = > 15A.

I tend to fuse everything as well, and have a fuse on the + wire from each bank of solar panels, and another fuse from each charge controller to the bus bars tied to the battery bank. May be overkill, but I try to protect wires with fuses, just in case something goes "very wrong".

Amishdude

Re: Blowing fuses occasionally

2manytoyz wrote: »

Just read the OPs response, which was posted while I typed this, hence the edit...

These panels are rated at 7.63 Amps at peak power. The short circuit rating is 8.37 Amps, but I have measured slighly higher than that just prior to installing mine. So on a clear day, and a battery bank state of charge low enough to demand max charging from the solar panels, it obviously can exceed the 15A capacity of your fuse. 7.63 x 2 = > 15A.

I tend to fuse everything as well, and have a fuse on the + wire from each bank of solar panels, and another fuse from each charge controller to the bus bars tied to the battery bank. May be overkill, but I try to protect wires with fuses, just in case something goes "very wrong".

So I'd be OK upping the fuses to 20A then, right?

Cariboocoot

Re: Blowing fuses occasionally

Amishdude wrote: »

So I'd be OK upping the fuses to 20A then, right?

Yes.

That's the part that wasn't clear to me: one 15 Amp fuse per panel should not blow. Both panels on a single 15 Amp fuse ... POP!

Amishdude

Re: Blowing fuses occasionally

Cariboocoot wrote: »

Yes.

That's the part that wasn't clear to me: one 15 Amp fuse per panel should not blow. Both panels on a single 15 Amp fuse ... POP!

Got it! Thanks again to the experts!

2manytoyz

Re: Blowing fuses occasionally

Agreed, 20A fuse - good to go. We're all on the same page now!

As mentioned, my short circuit test on my first Kyocera 135W panel was higher than rated:



The conditions weren't as ideal when I tested the next one (weeks later):



Typical for good solar panels to produce higher than the rating when new.

samuel

Re: Blowing fuses occasionally

I have Kyocera 135W 12V panels as well. During "edge of cloud effect" they can really overproduce, sometimes making upwards of 61Amps from 6 panels - over 10Amps per panel!

There is really only one time of the year when this happens. Right now is about that time. Fall at the 46th parallel provides some excellent solar production. Cheers.