96 volt charge controller

[maurice kezic]

Hi,
Have 40 + 250 watt x 30 volt solar panels.
3 rows of 8 x 12 volt x 300 amp gel deep cycle batteries makes 96 volts.
2 mppt x 96 volt charge controllers x 80 amp output , 200 volt dc input max.

Question:
What would be the most effective way for me to connect my pv array to the controllers?

Thanks in advance.
Maurice - Australia

[Living Large]

Hi,
Have 40 + 250 watt x 30 volt solar panels.
3 rows of 8 x 12 volt x 300 amp gel deep cycle batteries makes 96 volts.
2 mppt x 96 volt charge controllers x 80 amp output , 200 volt dc input max.

Question:
What would be the most effective way for me to connect my pv array to the controllers?

Thanks in advance.
Maurice - Australia

Find the Voc at the coldest temperature you expect, then divide that into 200. 4 strings of 5 in series are candidates.

[Living Large]

I can't edit my post, and it's too late. Welcome to Solar Panel Talk.

Find the Voc at the coldest temperature you expect, then divide that into 200. 4 strings of 5 in series, and 5 strings of 4 in series are candidates. I would shoot for the most in series, to keep the current as low as possible (voltage drop).

[maurice kezic]

So what would I expect from 4 strings of 5 ? 200 volts & 40 amps ?

5 strings of 4 160 volts & 32 amps ?

[Mike90250]

What charge controller do you plan on using to manage all this watts and volts ?

[maurice kezic]

What charge controller do you plan on using to manage all this watts and volts ?

CAP LM-series mttp solar charge controller.
Rated output 96 volts dc @ 80 amps max.
Input 200 volts dc max.

Trying to charge 3 strings of 96 volts ( 8 batteries × 12 volts x 300 amp hour gel deep cycle )

The 3,000 watt 96volt inverter that I have will only charge to 108 volts and never goes above 90%.

Hence the need for this controller to charge to 118 volts.

[Living Large]

So what would I expect from 4 strings of 5 ? 200 volts & 40 amps ?

5 strings of 4 160 volts & 32 amps ?

Let's back up. Your solar panels have specs. One of them is open circuit voltage, Voc. As it gets colder, the open circuit voltage increases. That is why you want the Voc at the lowest ambient temperature, which can be determined knowing coefficients in the panel spec sheets. The limiting factor in number of panels in one string (in series) is the maximum input voltage of the controller - 200V in this case.

There are two ways to determine the maximum Voc. Use NEC table 690.7, which says to multiply by 1.1 for minimum temperature of 32 to 40 deg F, 1.14 for minimum of 14 to 22 deg F, 1.20 for -5 to -13 degF, etc. Or, use the temperature coefficients that are in the spec sheet of the panel.

At Voc, you can expect to get zero (no) amps. That is open circuit. You can figure the current using Isc. Then multiply by number of strings on one controller to find the total current. Also, you need to multiply by a safety factor of 1.25 per the NEC rules for PV source circuits. So if your Isc is 8A, and you have 4 strings, that is 32A. Then multiply by 1.25, or 40A. All of this can be done using a string sizing tool for your controller - if one is available.