is the voltage of panels important for the battery bank?

[salve]

how do i wire 4 100W (12V) panels so that i can add that to my current system that already has a 300W (24V) panel attached? does the voltage add up between panel sets and become a problem for the battery bank (200ah, 12V)? I'm going to use another mppt controller for the 4 panels. I'm mostly confused about what the voltage should be for the panel array, how them all coming from two different controllers matters in terms of its connection to the battery. is there like a limit of voltage for the battery bank? or should the voltage be a specific amount?

 

[Bud Martin]

What is the full spec of the 100W panels?
What is the max PV input Voltage of the MPPT controller?
The so called '12V' panel will have the Voltage higher than 12V, the Voc may be 20 ~ 22V range, and the Vmp may be 18 ~ 20V range.
You need to make sure the total Voc of the panels is not higher than the max PV input Voltage, and you also to factor in +15 ~ 20% head room since the Voc will go up up as temperature goes down.
MPPT will take high Voltage and low current from the panels and converts it down to charging Voltage and higher current to charge the battery.

 

[sunshine_eggo]

You need to make sure the total Voc of the panels is NOT higher than the max PV input Voltage, and you also to factor in +15 ~ 20% head room since the Voc will go up up as temperature goes down.

Fixed.

Had to read it a couple times before I caught it.

 

[rmaddy]

Batteries will never see anything related to the panel voltage or amps. The job of the MPPT SCC is to take whatever power is coming in from the panels and to convert that to battery charge voltage and associated charge current. So your two arrays with two different charge controllers can have whatever incoming voltage and current it can provide.

So don't worry at all (with an MPPT controller anyway) about the panel voltage versus the battery voltage. And don't worry about the two different arrays with two different controllers. They do not need to match at all.

The main concern is that the temperature adjusted Voc of your panel array must not exceed the max PV input voltage of your SCC.

With two charge controllers you also need to make sure the combined battery charge current of both does not exceed the max charge current of your battery bank.

 

[Bud Martin]

Fixed.

Had to read it a couple times before I caught it.

I just caught my typo, thanks.

 

[MichaelK]

On a practical note, very doable, but first we need to know the exact panel specs. I would guess that your 300W panel most probably puts out 8A at ~37.5V. Your 12V panels MIGHT be 5.5A at 18V. So, if you created two parallel strings of two 12V panels that would make 5.5A and 5.5A at ~36V, and then put those two strings in parallel with the 300W panel.

+So, what you would essentially get is 5.5A + 5.5A + 8.0A at ~ 36-37.5V. The difference between the three strings is only 1.5V, which is less than the 5% tolerance that is OK for string voltage mismatch.

Keep in mind that the voltages/amperages in the example above are assumptions. We need to know the real panel specs before a final conclusion gets made.

If you do it this way, you only need one controller instead of the two you are suggesting. The final issue to focus on is the total amps going into your battery. Let's assume that at best you'll be getting about 85% of the theoretical amperage, so the math works out to be.....
{[(5.5A +5.5A + 8.0A) X 36V]/13Vcharging} X 85% = 44.7A.

So, a little too much for a budget 40A controller, but a single 50-60A controller while handle all the panels just fine.