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Get Powered Up! Certified Energy Manager Jeff Yago answers your alternative energy questions

Wondering about a great new energy-saving device
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Charge Controllers for Battery Banks

Friday, April 3rd, 2009


I need to use 2 to 4 12VDC batteries in parallel to achieve the necessary amp-hours required for a project.

Will a Morningstar charge controller (Sun Light 10 or Sun Saver 10, for instance) reliably monitor the voltage and charging current of the battery bank as well as it does for a single battery?


Richard Heiser
Sacramento, CA


A solar charger is sized based on the following –

First, total short circuit amp rating of solar array X 125% .    Note- Under extreme cold and sunny days, its possible for a solar array to reach 156% of short circuit amp rating for short periods and this is used to size solar array wiring.  If your charge controller does not have this temporary surge capacity, you should use the larger multiplier .

This calculation will determine the “amp” rating of the charge controller.

Next, select voltage for charge controller.  This will be total voltage for battery bank.  For example, two batteries of 12 volts in series would require a 24 volt controller.  Four batteries of 12 volts in parallel would require a 12 volt controller.  Four batteries of 12 volts with 2 in series and 2 in parallel would require a 24 volt controller.

The controller doesn’t know or care how many batteries you have or how they are wired, as long as the controller design voltage matches the voltage of the battery bank.

Now that you know amp rating and voltage for controller, select a model with the options you need, like digital meter, low voltage dis-connect, and/or temperature sensor.

Good luck,

Jeff Yago



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