# Does anyone make a balancing system for lead-acid batteries?



## speculawyer (Feb 10, 2009)

Well now . . . here is someone that created their own simple battery balancing circuit and seems pretty happy with the results:

http://axiom.anu.edu.au/~luke/xr4000batbal.html


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## Technologic (Jul 20, 2008)

speculawyer said:


> Well now . . . here is someone that created their own simple battery balancing circuit and seems pretty happy with the results:
> 
> http://axiom.anu.edu.au/~luke/xr4000batbal.html


My understanding is it's just not that necessary... undervoltage cutoffs for the entire pack is all you'd need.

overcharging LA's don't "generally" have serious issues like with lifepo's. Of course that's only to a point, but most standard battery chargers have a cutoff while charging.

You don't want to just keep charging LA's for many hours after they're full, but for 1-2 hours additional it doesn't really do anything.

Undervoltage is important to make sure they don't drain past about 50% DOD (at least if you want 25,000 miles out of a pack)


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## speculawyer (Feb 10, 2009)

Technologic said:


> overcharging LA's don't "generally" have serious issues like with lifepo's. Of course that's only to a point, but most standard battery chargers have a cutoff while charging.
> 
> You don't want to just keep charging LA's for many hours after they're full, but for 1-2 hours additional it doesn't really do anything.


Indeed . . . after some research, this is what I learned. Lead Acid batteries are to some degree 'self-balancing' since you can overcharge a cell or battery without ill effects. Thus when one battery is overcharged, it kinda just passes the current along. 

However, it is isn't perfect. A battery balancing system can make a lead-acid system work better and use the batteries in a more optimal manner. But the increase in performance is probably not worth the effort.

And at this point, screw lead-acid. LiFePO4s are more cost efficient in the long run now. (Yes, they have a much bigger up front cost . . . but they'll last much longer than lead-acid such that the cost of 2 or more sets of lead-acids are more than the cost of 1 set of LiFePO4s.)


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## Coyote X (Feb 22, 2009)

http://www.electric-lemon.com/?q=node/151 that circuit seems like it would work. It would just take someone who is good at that stuff to sit down and get the numbers nailed down good and post a complete ready to use schematic.

If not the schematic he built his off of should work as is. It will just be more expensive and a bit more complicated. It is linked from that page if you want to look at it.

I planned on building something like that so a standard 12V solar panel could be used to boost pack voltage or at least keep the batteries topped off.


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## EVMAN (Jul 26, 2007)

Have U checked out the LTC6802 battery monitor IC??
Looks like it will do everything that U want.
T


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## speculawyer (Feb 10, 2009)

EVMAN said:


> Have U checked out the LTC6802 battery monitor IC??
> Looks like it will do everything that U want.


Woah . . . Now there is a nice chip for enabling a cheap BMS system for Li-Ions to be built! 
http://www.en-genius.net/site/zones/greenpowerZONE/product_reviews/grnpowp_101308


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