Stacking charge controllers?

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bossrox asked Apr 19, '20

Stacking charge controllers?

I have a 150/100 mppt controller hooked up to 12 320 watt 40 volt panels in a 3 in series with 4 sets of 3 in parallel on a 24 volt system with a 550 amp/hr battery bank. Intrestingly I found that when the Victron was putting out the full 100 amps charging, my input from the solar panels was just 25 amps.

Well my total solar output from those 12 panels can do up to 100 amps so it appears I have up to 4 times more charging capacity than a single controller can make use of, so my question is this, I understand controllers can be stacked but I can't find any info on how to do that. Like can I just add another controller & just link the battery outputs or is there a special hookup method to sync more controllers?

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Answer 1 · 2020-04-23T04:32:31Z

JohnC answered · Apr 23, 2020 at 04:32 AM

Hi @Bossrox

Yes, you can just parallel them in to your battery terminals/bus. They'll work well independently, and some models can be fully synced, but that's another story.

But be aware that '25A' you quote is at panel V, which may be (say) 110V, meaning 2750W. The 100A rating is at Vbatt, let's say 28V, so 2800W also (ballpark figures).

Your panels rated 3840W, so perhaps at the peak of the solar day there may be some untapped energy available. If you wanted, you could separate off one of your 4 panel strings into a 150/35 mppt, giving you 135A at Vbat, ~3780W - pretty close.

If your batts are Pb's then they won't accept that much for long. Li's and loads could, so up to you to determine your needs..

(Moved this Question to here from Modifications Space).

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bossrox commented · Apr 23, 2020 at 05:14 PM

Thx John, that helped & my electrical math is rusty as I'm finding out. My 12 panels can do 320 watts or about 8.5 amps @ 40v. I mistakenly presumed that you multiply the amps times the panels to tally the total but the amps stay the same stringing them in series, just the voltage increases so the 25 amp input I'm reading going into the Victron while getting 100 amps out to the 24v battery bank is about the max I can expect from the panels & intrestingly without me planning it, is a perfect utilization match for the Victon.

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