Lee Hart, an EV guru on battery maintenance and equalization, has graciously e-mailed with me regarding the best way to equalize batteries. He's currently working on upgrading his battery balancer (see link at right) to handle a wider range of battery technologies and applications.
Lee convinced me that the flying capacitor approach that I originally thought would work is not practical in real world situations. I think Lee's battery balancer design would do a great job; however, I'd like to cost reduce it to something more suited to my own needs.
My plan is to create a relay board like Lee's that only handles 10 amps per relay instead of 30. If I costed out the parts and boards correctly, I can probably get that down to $100 per relay board vs. Lee's assembled cost of around $200. For the main controller board, I plan to use a similar design, but simplify the design to meet a narrower set of needs and replace the high-cost components with lower-cost, harder to use components.
For example, instead of a $80 complex STAMP controller, I'll use a $6 PIC that has more flexibility but will require more complex programming. Instead of the $150 Vicor BatMOD module, I'm using a free 100-watt 32-volt isolated power supply from an HP printer and making a current controlled buck converter to step down the voltage and charge the batteries (about $10). Instead of the $60 Radio-Shack meter, Lee is working on using an LM331 voltage to frequency converter to measure voltage and current of the charger which should cost around $10.
Many of these components will be harder to calibrate and program, but I'm willing to do that to lower the cost and reduce the size of the system. I don't know how this will end up, but I'll learn a lot and that's the point.