With all these open source projects... It seems the only two things we are missing are batteries and battery management... I'm not capable of initiating a conversation about planning open source DIY batteries, but I do believe that a BMS is important.
I am no expert on this subject, and much of what I think I know may be wrong. Please don't hesitate to interject and/or correct.
The three types of BMS I know of are:
1) Passive and isolated, like a zener lamp. At a certain Voltage current is shunted to a resistor (a bulb in the example i read). Limits overcharging.
2) Passive but interactive. I can't remember the example of this very well, but it sat in between batteries and shunted current between the two batteries until they are equal in voltage. IIRC it was a passive device, not actively moving current.
3) Active. like Lee Hart's (
BalancerLand - Intro) I see a couple ways of doing this.
a) have a microprocessor watch voltage (and temp) of each battery and move current from the highest to the lowest etc.
b) have a microprocessor watch voltage (and temp) of each battery as it charges and remove batteries from the string as they reach a defined voltage for that charging phase
i) this would require a very smart charger or that the BMS work hand in hand with the charger. (you do have to reduce voltage when you remove a battery right? you can't charge a 24volt pack with 120 volts?)
ii) technically this isn't BMS, but if you are charging a pack every night and every night it is equalized, it's darn close to BMS (until a battery goes bad).
What I want out of a BMS:
Effective
inexpensive
average joe can build it
I would love for it to actively display individual voltage readings to a backlit dashmounted lcd, but I wouldn't pay an extra $100 for it.