Newbie - Need help sizing a charge controller

Hi, I have a simple system that consists of 3 solar world 70 poly/RHA panels with rated voltage of 18.1 amps each and short circuit voltage of 3.pp amps each, they are run in series ad drive a one horse DC well pump. I would like to add batteries which are Roll Royce 6v batteries, what size controller and what is the configuration of batteries to achieve the proper 12V output. Currently the system has only an on-off switch and a lightning resistor attached. I tried to add a 20 amp controller and did something wrong because it smoked it. Help.


  • BB.BB. Super Moderators, Administrators Posts: 32,319 admin
    Welcome to the forum Drgossomer.

    I am not really sure what you are trying to do... There are some pumps that can be run by direct connection to a solar array--And if you only need water when the sun is shining (pumping from well to holding tank, irrigation, etc.)--That is a wonderful way to do it. No Batteries, no AC inverters, no Charge Controllers, etc..All of those add costs, maintenance issues, etc.

    But if you have 210 Watts of solar panels driving a 1 hp pump--That seems to not be a good match. 1 HP would take something >1,000 Watts of solar panels to run near full power--Of course, if your pumping application does not draw 1 hp from the pump motor (low head, low volume, etc.)--Then that can work OK too.

    What would help is a link to your solar panels (sounds like Vmp=18.1 volts, Imp=3.87 Amps).

    Also, a link to your pump+motor... A 1 HP @ 12 VDC or @ 36 volts is not common (unless you have some sort of pump controller involved).

    And a bit more about your needs... For example, it can be a very nice system where a well pump + solar panels pump into a cistern. And a second above ground pump + 12 volt (or other) (i.e., RV or Marine water pump) pressurizes the plumbing for domestic needs.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • drgossomerdrgossomer Registered Users Posts: 2
    Hi BB,

    The pump is a phased dc gundfos pump. in Sunlight is runs at full power pumping 15 gpm. I am trying to add batteries to allow it to work 24/7 this is where I running into issues.
  • BB.BB. Super Moderators, Administrators Posts: 32,319 admin
    Can you supply a link/model number for the pump?

    Please note that to pump the same amount of water, you may need 2-4x the amount of solar panels because of battery and controller losses.

    An alternative may be to use your Gundfos pump to fill a cistern, then use a small (RV type) 12 or 24 volt DC pump to pressurize the house. They DC system to power a smaller RV pump can be quite small compared to a well pump (particularly if the well is fairly deep).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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