# Battery Desulfator - Capacitive Voltage Divider

A few years ago, I posted this video showing my first crude Battery desulfator.

This works like a champ, but I wanted to point out there is a few ways to make this safer. The one in the video had no protection and it put out up to 170 volts pulsed DC at 1.1 amps. This one MUST be connected to a battery when you turned the power on.

I wanted to make it safer and limit the voltage to about 55 volts. This is done without a transformer and uses just run-type capacitors. You could also use a transformer, but, hey...this is just interesting. Besides, you can swap out capacitors to get different currents. Also, a transformer isn't constant-current like this circuit.

 Update - the fuse should be on the hot side.

The top capacitor basically controls the amperage. This one would be 1.1 amps at 120 VAC at 60hz. The bottom controls the voltage. If the bottom capacitor is rated the same as the top, then the output will be cut in half. In this case, there is 120 VAC coming in and the output will be one-third of the input, or 40 volts AC. Actual DC is 1.4 times the AC value, so the full-wave bridge's output will be 56 VDC pulsed at 120 times per second.

Here is a real-world example. Let's say you have lots of 25 MFD run-type capacitors that you picked up from the local HVAC shop. You could use 5 of them as shown below. This gives you one fifth the input voltage that goes to the rectifier.  If you start with 120 VAC, this gives 24 VAC to the rectifier. Multiply that times 1.4 and you get 33.6 VDC. This example could charge any lead-acid battery up to and including 24 volts with no problem. It would do it at 1.1 amps.
 Update - the fuse should be on the hot side.

IMPORTANT: This is not a smart charger. It will keep trying to charge a battery and it is like the terminator, it will not give up. You have to monitor the battery Voltage and fluid levels. You don't want to overcharge or dry out the cells. OR, you could use an Arduino to monitor the voltage for you and switch this circuit off with a relay.

This post first appeared on Renewable Energy For The Poor Man, please read the originial post: here

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Battery Desulfator - Capacitive Voltage Divider

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