question

skamp_x@hotmail.com avatar image
skamp_x@hotmail.com asked

Parallel and series combo

Hi there,

So far I had 4x65watt and 2x20watt , all in parallel on a mppt 100/20 , charging a 2 AGM 80ah battery bank in parallel.

Now coming up short most days I wanted to upgrade so looked around for info.

I can't go any more in parallel or it would fry the regulator ,

so came up with the solution but have yet to install or test it

got 4 more 65watt panels, same brand so same stats, and ditched the 2 20watt panels

Idea is to hook up 2 banks of 4 panels in parallel , in series.

I should be fine on the single controller , switching to series would make it a 24v system, but the amps don't increase beyond what 1 bank of 4 can produce so it wont blow the fuse on the regulator.

And my hopes are also that , because these is part parallel, the voltage won't drop much either cause I do get some shading along the day.

so yea id say it all sounds good in theory , but reason asking here is to ask if I missed something, or worse , I got it all wrong..

one note, going all series isn't really a option, because of shading it would reduce the setup more then it is producing with 4 panels alone im sure.

So question , am I right or did I miss something vital?

MPPT Controllers
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2 Answers
JohnC avatar image
JohnC answered ·

Hi Skamp. You seem pretty much onto it. Two things to watch for:

1. Total panel Voc in a string, for you 100V max. '12V' panels may be say ~23Voc, so could be strung to a max of 4x. That Voc will get higher in cold weather, so take care with that.

2. Panel Isc is likely ~4A, and added by the number of strings, to a max of 20A for your 20A (that's not the 20A output rating of your mppt, but a separate figure on the specsheet).

So, put an 8x long string out of your mind, shading or no.

2x panels in each string. and 4x strings of those (2S4P) should be safest and perform well into 12V batts. You'll never see the full W potential of the panels into those batts and with that mppt, but should give great poor-weather performance and consistency. But check my figures against your actual panels.

I wish you well with it.

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adev avatar image
adev answered ·
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