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1. How many volts

wondering what would be the max volts to build a panel to charge 12v wet cell battery bank. I know the standard is 36 cells to get 18-20 volts, but what if I used 49 cells to increase the wattage. I need to build to a specific size and 49 3X3 cells would do well.

2. Depends on what kind of charge controller you use. If using PWM or series type controllers anything over 36 cells will just be wasted. For example if you used say 50 cells with a Imp of say 5 amps would produce a panel wattage of 125 watts, but the maximum power out of the PWM charge controller is going to be 65 watts. Use 36 cells panel wattage = 90 watts and the same 65 watts out of the charge controller. So anything over 36 cells is just a waste and gains nothing.

No if using a MPPT controller you get about 95% of the power out withing the input voltage operating range. Some of the better quality MPPT controllers can handle up around 130 volts maximum power point voltage.

3. Interesting. I am using a PWM controller. It says 7 amp max input. Do I need to convert this to watts and say the max voltage of 14.2 output to the batteries to figure the max wattage input. Will the charge controller convert the 24v input to a safer voltage to the battery? Can't afford an MPPT controller yet. I should have only a max of 36 watts from the panel. I figure the charge controller should be able to handle about 105 watts.

4. Originally Posted by chp
Interesting. I am using a PWM controller. It says 7 amp max input.
For a PWM controller input current = output current.

So let's say you build a panel that has an Imp of 7 amps using 36 cells. That panel will have a Vmp of about 18 volts and an Imp of 7 amps, Pmax will be 126 watts. On the output maximum is calculated 12 volts x 7 amps = 84 watts. Using anything more than 36 cells will be a complete waste as the output will always be 84 watts max.

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