Charging A Car Battery With A Power Supply

Ken. T: Would it be safe to charge a battery with a mixture of the 2? The reason I ask is because atx power supplies often have a -5v and -12v rail, I would like to add a potentiometer to properly give a car battery a 13.5v charge. But I’m not sure is the negative voltage would have an unwanted effect on the on the battery. I would be using diodes and to direct the flow of voltage. But I wanted your opinion before I attempt. Thanks for the videos!
Clyde A. Lettsome, PhD, PE, MEM Answer: It should be safe to mix the two. However, I would suggest you use two ATX power supplies. Use the +12V and ground from one supply and the +5V and ground from the second supply.  Use the following Figure to configure the circuit.

Note: The negative of each voltage source in the Figure is the ground of the ATX power supply.

Good Luck!

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