# mppt and wiring panels



## mike3367 (Dec 15, 2004)

i just ordered my fourth 100 watt solar panel. i am wondering which way is best to get the most amps out of them. right now the 3 panels are in Series making around 55 volts, ive seen as high as 20 amps on the amp meter. to see more amps. do i just add the panel to make 4 in series or make 2 sets of 24 volts panels. for now this is going to a 12 volt battery bank.


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## TnAndy (Sep 15, 2005)

100w panel, nominal 12v, should put out around 18v, with an amp rating of around 5-6a. 

Three of them in series results in that 55v reading you see....on the input side.

The amps should be the same as a single panel when you connect in series....around 5-6amps on the input side of an MPPT controller....so either your meter is wrong, or you are looking at voltage in, and amperage out. 

The output reading might hit close to 20amp, but your voltage out would be in the 14-16v range. That is what an MPPT controller does....takes the excess voltage, lowers it to your battery voltage (little over so the batteries will charge), and gives you the excess as amperage.


OK....now as to connecting that 4th panel. You can connect it in series, assuming your controller is rated for 4x18v, plus a de-rating for the most cold you ever see.....I allow about 20% here. Cold temps increase voltage. So that means (here), the controller would have to be rated for 72v + 20%= ~87 v.

You will get the same power whether you connect 4 in series, or 2 strings of 2 in parallel.

There ARE other considerations: 

If *one panel *gets any shading, the entire string goes to pot, powerwise. Sometimes multiple strings are better for this reason.

If the run from the panels to the controller is long, higher voltage from a single string of 4 (72v) can result in less voltage drop (loss) than two strings of 2 (36v).....you can overcome that by increasing wire size.

That help ?


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## mike3367 (Dec 15, 2004)

im lucky, only the house gets in the way of shade around 6pm here for me. so no matter how i set the 4 panels up i will only get about 20 amps out put from the mppt controller? my controller is BlueSolar MPPT 100/30


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## Gary in ohio (May 11, 2002)

What voltage is your controller rated for? That may drive the series or parallel question. 
4 100watt panels is about 80v.


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## mike3367 (Dec 15, 2004)

it can take up too 100 volts and the run from the panels to controller is less than 20 feet if that make any difference


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## TnAndy (Sep 15, 2005)

mike3367 said:


> so no matter how i set the 4 panels up i will only get about 20 amps out put from the mppt controller? my controller is BlueSolar MPPT 100/30


4 Panels in series: 

On the INPUT side, you will get about 72-80v and about 5-6amps, peak.

On the OUTPUT side, you will get 14-17v, and about 20-24amps, peak.



TnAndy said:


> *That is what an MPPT controller does*....takes the excess voltage, lowers it to your battery voltage (little over so the batteries will charge), *and gives you the excess as amperage.*


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