Sunday, February 18, 2007
Battery Equalizer Schematics Rev 1.0
I'm currently working on a battery equalizer for the 914 EV based on the whitepaper at the following link:
The above two schematics show the circuit that I'm experimenting with using 12V batteries. It seems to work fine on my bench. The circuit above costs less than $10 per battery in parts and I hope to make this available to everyone to help people make their batteries last longer.
By clicking on the images, you can get a much larger version of the pictures. Any feedback on how to improve the circuit would be welcome. I'll have to modify the circuit with a voltage doubler in the final stage to work with 8-volt golf-cart batteries for the 914 EV kit. Big thanks to Max at and all the other supportive engineers at HP for designing this circuit.
ADDENDUM: recently, many people have been asking me about this circuit and how well it's working. After some experiments awhile ago, I found that the capacitors simply do not transfer enough current to make this circuit viable, especially for the large amp-hour batteries needed for an electric vehicle. I currently drive an electric Civic and use resistive shunt balancers on it that seem to work well. The large 3-ohm shunt resistors are mounted away from the batteries on an aluminum base as a heatsink since they dissipate quite a bit of heat. The shunt balancers were purchased from Belktronix, but you could probably make them yourself with a low-current comparator that drives a FET to switch in the power resistor at a specified voltage (like 14.4V).