Understanding Charge Controller Volts and Amps

[Dennis 1]

What voltage battery do you plan to charge? The CC will be most efficient with less voltage drop to the battery, but the solar panel voltage still needs to be somewhat above the battery voltage. 12V or 24V batt : do 4 strings in parallel of 2 panels each in series, VOC will be about 45v. 48V battery: do 4 panels series, 2 parallel strings, VOC will be about 90v. Either will still work for either battery voltage though. Dont' put all the 8 panels in series on one string, that will exceed the CC input voltage.

Thank you I have a 12V battery bank of 3 - 100AH lithium batteries

 

[CoolWill]

Just added the numbers together

Well there you go. Voltages don't add in parallel.

 

[Doggydogworld]

It can help to think of the panels as kinda like water pumps. Put two 10 psi pumps in series and your pressure (i.e. voltage) will be 20 psi, but your flow rate (current) will be limited by the slower pump. Put two 10 psi pumps in parallel and you'll only get 10 psi, but the flow rates will add together. It's not a perfect analogy, but it can be easier to visualize water flow than to remember circuitry rules.

 

[Dennis 1]

88V vs. 90V doesn't matter. They will actually always be at the same voltage - the lower of the two - because they are in parallel, and that will vary with cell temperature (lower temp = higher voltage). An array with 4S Rich in series in parallel with 4S HQST in series will be a 88-90V-ish array with about 11.6AIsc.

So if I had another CC I could have one string on one and the other string go to the second one. I had a real issue here in Michigan over the winter last year with 4 sets of 2 panels in series keeping my 3 - 100AH lithium batteries charged.

 

[sunshine_eggo]

So if I had another CC I could have one string on one and the other string go to the second one. I had a real issue here in Michigan over the winter last year with 4 sets of 2 panels in series keeping my 3 - 100AH lithium batteries charged.

I'll be honest. I'm pretty much lost at the moment. It doesn't matter. One CC or two. You can run 2S4P or 4S2P on your single existing controller with no issues.

Please confirm:

1. You have 8 100W solar panels of highly similar Voc and Isc values.
2. You had them wired in a 2S4P array.
3. You're looking at wiring them in a 4S2P array.

Your problem will not be solved by reconfiguring your array.

If you deal with shading or partial sun, you may make it worse.

Your fix will be:
1) more solar panels or figure out how to harvest more from what you have (better placement, angle, less shade, etc.).
2) use less energy.

 

[Dennis 1]

OK, let's see if we can help straighten this all out a bit

OK, sounds good. so 4s 100w panels then? 90.4v @ 5.86a

So basically another 4s string that will put out 21.3*4= 85.2v at 5.83a (since mixing panels in series cuts everything to lowest common denominator).

That should put both strings in parallel and reduce the output voltage to 85.2v at 11.7a max

If you're getting that much voltage out of your combiner box there's something wrong. The combiner box should be paralleling the strings, not serial-ing them. You should see about 85v coming out of the combiner box. That's well within the limits of the SCC. Check that with a meter.

If you are getting 175v or so, then go with a Y-splitter and get out of the defective combiner box. With 2 strings you don't need fuses anyways.

 

[Dennis 1]

So if I had another CC I could have one string on one and the other string on the second one. I had a real issue here in Michigan over the winter last year with 4 sets of 2 panels in series coming out of the combiner box keeping my 3 - 100AH lithium batteries charged. I would have 4 panels in series on one CC and the other 4 panels in series on the other one.

 

[sunshine_eggo]

So if I had another CC I could have one string on one and the other string on the second one. I had a real issue here in Michigan over the winter last year with 4 sets of 2 panels in series coming out of the combiner box keeping my 3 - 100AH lithium batteries charged. I would have 4 panels in series on one CC and the other 4 panels in series on the other one.

You literally just posted this and ignored my post. Is English your first language?

The only things the above would accomplish:

1) waste money on a second controller.
2) reduce the effectiveness of two of the HQST panels by 10%
3) potentially harvest even less energy if you have ANY problems from shading or partial shading.

You need more solar or to use less energy.

 

[Dennis 1]

I'll be honest. I'm pretty much lost at the moment. It doesn't matter. One CC or two. You can run 2S4P or 4S2P on your single existing controller with no issues.

Please confirm:

1. You have 8 100W solar panels of highly similar Voc and Isc values.
2. You had them wired in a 2S4P array.
3. You're looking at wiring them in a 4S2P array.

Your problem will not be solved by reconfiguring your array.

If you deal with shading or partial sun, you may make it worse.

Your fix will be:
1) more solar panels or figure out how to harvest more from what you have (better placement, angle, less shade, etc.).
2) use less energy.

Yes everything you said is right. They will get about 5 - 6 hours of sun on a good day, no shade during that time. I thought instead of only 88V coming out of the Combiner box going from both strings to one controller. I thought 1 string on each CC going to the batteries would charge them faster.

 

[Rednecktek]

Yes everything you said is right. They will get about 5 - 6 hours of sun on a good day, no shade during that time. I thought instead of only 88V coming out of the Combiner box going from both strings to one controller. I thought 1 string on each CC going to the batteries would charge them faster.

The draw to using multiple SCC's is when you're either trying to get more panels up than your current SCC can support (a pair of 40a instead of an 80a for instance) or when you're trying to combine multiple strings of vastly different panels (a string of 300w panels and a string of 100w panels for example).

 

[sunshine_eggo]

Yes everything you said is right. They will get about 5 - 6 hours of sun on a good day, no shade during that time. I thought instead of only 88V coming out of the Combiner box going from both strings to one controller. I thought 1 string on each CC going to the batteries would charge them faster.

Your issues are:

Insufficient solar availability (eliminate shade or move panels/add panels where they can get additional sun outside your 5-6 hour window).
Insufficient PV power (get more panels).
Excessive power use (use less kWh/day).

4S2P will perform no better than 2P4S UNLESS you have VERY long wires between the panels and the MPPT.

Adding another charge controller will only cost you money with no benefit.

 

[Dennis 1]

The draw to using multiple SCC's is when you're either trying to get more panels up than your current SCC can support (a pair of 40a instead of an 80a for instance) or when you're trying to combine multiple strings of vastly different panels (a string of 300w panels and a string of 100w panels for example).

That makes sense, Thank You