[alex]

Is a BMS for lithium battery charging only critical when charging the cells in series?

If one were to come up with a clever switching "mechanism" to charge the cells in parallel, and use them in series, would that negate the need for a multi-segment BMS?

thanks,
jp

So what? a 3.2v charger system?

Don't you get the battery balancing problems whether you do it in series or parallel?

 

[alex]

Would it really be?

I've already got a simple switching mechanism I made up with relays that can switch 3x 12v batteries between parallel and series for different speeds.

I'm thinking this would be a hell of a lot cheaper than a BMS. Is there anyone who can qualify this idea?

There is no mention of parallel in the BMS wiki http://www.diyelectriccar.com/forums/showthread.php?t=14778

 

[alex]

As per the image with my MS Paint skills...

Without power connected to the relays, the NC circuit is connected (series). When power is connected, the top relays are turned on, so the NO circuit is closed.

THEN the bottom relays are turned on, and you go from having a series circuit to a parallel one. The catch is that each TOP relay would have to be rated for max Voltage/Amp use plus you have to wire up all of those relays.

But, depending on the price of a high amp, 3.2v charger - this might be a poor man's BMS (eg my kind of BMS )

 

[alex]

Heh, lets not jump to conclusions!

Ok, so for 144v we're looking at 45 cells. Ouch

So that is 44 high current relays ($???) + 44 lower current relays. Suddenly a ~$1000 BMS is looking cheap.

I guess for someone using 12v lead acid, it might be more practical? :/

Back to the drawing board


Maybe I'll go for the water powered car instead