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I designed a simple PCB but it's not really doing what I'm looking for. It has 3 motor controllers connected to it. I want the motor controllers to be able to pull current from either the 12V lead acid battery or the power supply. When the motors stop extra voltage is sent from the motor controllers back to 12V-B and I want to make sure the diodes block that from going into the 12V-PCIE and instead the power gets dumped into the batteries.

When I turn the switching power supply off the battery is sending power back from 12V-B to 12V-PCIE and makes the fan in the power supply run. Shouldn't the diode block power from going that way? I feel like I'm missing something really simple.

The blue is the ground plane. In the top of the board are the two 12V planes separated by the diode.

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You probably need to add a couple of diodes so that forward current can come from either the battery or the supply but reverse current (i.e. that generated by the motor) only goes to the battery.

If you had a better schematic we could more easily help.

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