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PV Combiner Box Voltage To Inverter

brianjw4

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Apr 4, 2022
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Hi all, I am working on putting together a system for my shop and I had a question about voltage going to the inverter from the PV combiner. If I am connecting 2 strings of 6 panels in parrallel does the PV combiner combine to the total voltage of the 2 strings? So if each PV string going into the combiner is 40v does it input 80v to the inverter?
 
When wiring in parrell the bolts stay the same and the amps increase. Wiring in serial you get the opposite effect, volts increase and amps stay the same.
It is my understanding that you would wire your array into a combiner box, then to a charge controler. The charge controller will keep your battery(s) charged via solar during the day. Your inverter is connected to your battery(s) which in turn the inverter converts DC to AC to run your home appliances.
Don't forget to use fuses, and circuit breakers that are correctly rated. No fires, or fried wires in your array or balance of systems.
 
If I am connecting 2 strings of 6 panels in parrallel does the PV combiner combine to the total voltage of the 2 strings? So if each PV string going into the combiner is 40v does it input 80v to the inverter?

A "string" (meaning series connected) of 6 panels is not going to be 40V.
Even 2 panels in series is unlikely to be as low as 40V.

Better sketch a drawing of how you plan to connect the panels.

Maybe you mean 6 panels in parallel, 40V output. Another 6 panels in parallel. Those two groups in series. Yes, that would be 80V. We would call that 6p2s. There are a bunch of problems with doing that.

Sketch what you mean and we'll make a recommendation.
Good to include all PV panel specs (or picture of label) and specs of inverter (ideally a link.)
There are several "Gotcha!" to address so no damage.
 
Thanks for the quick responses. Was planning to run the 2 sets of 6 panels in parallel, so string was the wrong term :)

Don't have a diagram, but am planning to use the following components:

MPP LV6048 Inverter
Panels are 30.3V / 8.27A for 250 Watts Each - starting with 2 sets of 6 in parallel
PV combiner box
48V 100ah Rack Battery
 
Was planning to run the 2 sets of 6 panels in parallel, so string was the wrong term :)

If you have 6 panels in parallel (or 6 strings), each should have a fuse of the size listed on panel label.

6p2s is a bad thing. If some panels are shaded or disconnected, the current from 6p is forced through the remaining 5p, 4p, 2p, whatever.
Better to do 2s6p. Connect two panels in series for 60.6V. Then connect a fuse. Then combine 6 of these in parallel. Fuse or breaker can be in combiner box. (I do NOT like "polarized" breakers or this purpose.)

30.3V is probably Vmp. What is Voc?

What are PV input specs of LV6048? They have so many models I can't be certain of pulling up right one.

Voc spec of the PV panel is not what is used to see if it meets max Voc spec of inverter. You need to take into account the record coldest temperature of your location. Also temperature coefficient of the PV panel. These may increase voltage about 16%, give or take.

If you have pencil and paper, you can make a diagram of what you're planning to do. Take a photo and upload.
We use certain nomenclature to reduce "1000 words" to a single sentence, but best to show the picture when you're unfamiliar. It can save burning up electronics or wires.
 
Thanks so much for this information. VOC on the panels is 37.6V. The max input is on the LV6048 is 145VDC, ~115VDC is what they recommend. I'll work on a diagram and upload as soon as I can.
 
Also, a low temp in winter where I live is about 30F which occurs once in a while. Average would be in the 40s to low 50s.
 
Also, a low temp in winter where I live is about 30F
30F is -1C so a 26 deg C drop from rated temp
Assuming temp coefficient of .35% per deg C

37.6Voc x 26 x .0035 = 3.42V increase to 41.2Voc temp compensated.

3x 41.2Voc = 123.6Voc perfect for your SCC. The operating (3x Vmp) will be closer to 110V.
 
Great thanks. This is starting to make more sense. Here is the rough diagram.
 

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  • solar diagram.pdf
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Ok great, that will be better. There will be four or potentially more, I would like to be able to run some other shop items as well.
 
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