Panel fuse size parallel

SolarT

Two parallel panels at 30.3 Vmp and Imp are 7.52A and 5A. What fuse size do I need at the input side of the charge controller?

The existing setup has 15A fuse single panel 30.3V and 7.52A. 10 awg wires for now, will upgrade to 2 awg in two weeks.

Cariboocoot

Re: Panel fuse size parallel

SolarT wrote: »

Two parallel panels at 30.3 Vmp and Imp are 7.52A and 5A. What fuse size do I need at the input side of the charge controller?

None, really. You might want to fuse the 5 Amp panel according to its Isc just in case it shorts and is fed the full output of the larger panel. Usually there's no worries unless there are three or more panels in parallel (ordinarily same size) in which case one shorted panel could potentially be fed twice its current rating. Not enough difference here to make an issue in my opinion. No doubt someone will tell me why I'm wrong. :roll:

The existing setup has 15A fuse single panel 30.3V and 7.52A. 10 awg wires for now, will upgrade to 2 awg in two weeks.

Why would you need 2 AWG wire for 12.5 Amps @ 30 Volts? How long is this wire run?

SolarT

Re: Panel fuse size parallel

Close to 50' each way. I got a good deal on 2 gauge stranded wire - new old stock. Priced about 6 awg wire.

Cariboocoot

Re: Panel fuse size parallel

Ah; a good deal that allows for a good deal of expansion.

In case you want to do an actual Voltage drop calculation: www.solar-guppy.com/forum/download/voltage_drop_calculator.zip

SolarT

Re: Panel fuse size parallel

OK, how about this mix and match panels: 47.8Vmp 7.52Imp 8.1Isc parallel to 37.5Vmp 5Imp 5.27Isc. Do I need 5A fuse on the second panel?

What are the guide for fusing panel to MPPT controller? The only guide is 10% or better Vmp match for parallel. And the above combo is 21% diff in Vmp.

BB.

Re: Panel fuse size parallel

The fuse size should be around 2x Isc if the panel spec. does not have a value.

In this case, because the other panel is 8.1 Isc--It probably would never blow a 10 amp fuse on the smaller current string. If you had more panels in parallel, each string should have its own fuse--at rated value or ~2x Isc.

Regarding paralleling panels with a greater than 10% mismatch, you run the possibility of losing substantial output.

In this case, you have two strings of panels. On a clear day with a discharged battery (or substantial load), try each string by itself and then both strings in parallel--See which configuration produces the most current--If both strings in parallel produce the most--then just use that setup.

-Bill

niel

Re: Panel fuse size parallel

actually it's 1.5 x isc and round up to the nearest commercial value fuse available.