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Check my Insight build thread. I built a grid charger, and explained in brief how they work.

Posts #73 and #74 are a good place to start:

http://ecomodder.com/forum/showthrea...tml#post441979

Quote:

How grid charging works, as I understand it:

Basically, your maximum usable capacity is determined by the difference between the "worst" and "best" cells in your battery. Some cells may have a low capacity due to degradation, and will have a limited voltage range. Other cells may just be low because they're out of sync with the rest of the pack, and may only, for example, be 75% charged when most of the other cells hit full charge. Cells are most likely to drift apart when left to sit for extended periods, but will do this to some extent even if used daily.

The current theory on grid charging is that even a healthy battery that's driven daily will benefit from an occasional grid charge (maybe once every 6 months), because the onboard systems have no way to balance the low cells with the rest of the pack. Charging too often may result in earlier degradation of the battery as a whole though, because in order to achieve a balance, you overcharge the full cells until the low cells are also full.

It's commonly held that a deep discharge will maximize benefits of a grid charge but my system isn't able to do that, and as I understand there are some dangers to deep-discharging this type of battery system.

It's also possible to restore the capacity of degraded cells somewhat with this system, but not to the extent of a unit that reconditions individual cells by cycling them.

Some considerations - a slower charge will produce less heat, which is the worst enemy of these batteries. Even charging at 300ma I'm going to be running the battery cooling fan.