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I am working on a senior design project and just wanted to ensure the following charge configuration would work. I have a 12V solar panel that I plan to run its' output to TWO separate PWM solar charge controllers. Despite the vehicle running off a a 24V system, I would like to charge the batteries separately. I think that I need some sort of changeover relay to alternately charge the two 12V batteries .I think I need some control for the relay . Could I use just one PWM charge controller if I employ the relay ? Do you think that my concept will be cheaper than 2 solar arrays and 2 PWM controllers? Just wanted some input from those who have more experience than me with solar energy. Thanks for the help and sorry for the rotated picture!

Circuit Diagram

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  • \$\begingroup\$ Usually the charge controller is responsible for powering the load, what charge controller are you using? What is your load? What solar panel are you using? \$\endgroup\$ – Josh Jobin Jan 2 '16 at 19:05
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    \$\begingroup\$ Test your charge controller with an ohmmeter. If Solar "-" and battery "-" terminals are connected together, as they are on mine, it should be obvious that this won't work. \$\endgroup\$ – Brian Drummond Jan 2 '16 at 19:05
  • \$\begingroup\$ The regular charge controller is simply a single MOSFET that switches the solar cell on and off the battery, depending on its state of charge. So B- is shorted to Cell-, and B+ is periodically connected to Cell+. You'll have to disconnect the batteries from each other completely first. \$\endgroup\$ – tomnexus Jan 3 '16 at 1:44
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You can do that only if the outputs of the solar charge controllers are fully isolated from the inputs.

If the controller output grounds are directly connected to the input grounds (as is likely), you would be shorting the "bottom" battery through the ground leads.

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  • \$\begingroup\$ Ahhh. I assumed the inputs and outputs were completely isolated. But I agree, if that is not the case, the second battery will be shorted out. Thanks for pointing that out! \$\endgroup\$ – Brandon Peter Jan 2 '16 at 19:42
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best answer is probably to use a charge cintroller that outputs 24V from a 12V panel and charge the two batteries in series.

search: lead acid boost charge controller

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  • \$\begingroup\$ That was our original design plan actually! Problem is the controller we were going to use runs around $170. Combine that with the price of a flexible 12V 100W solar panel, most of our $500 budget is taken! \$\endgroup\$ – Brandon Peter Jan 3 '16 at 13:44

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