# Battery Balancing



## Manntis (May 22, 2008)

it's far more critical to balance lithium ion batteries. 

Sealed Lead Acid batteries can be balanced by a controlled overcharge, eliminating the need for a dedicated balancing device - shunt or otherwise.


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## frodus (Apr 12, 2008)

http://www.powerdesigners.com/powercheq_specs.htm

12V modules.... so you'd only be "balancing" packs of 2 6V's.

and you don't need a ton of current to equalize, it'l equalize over time... so overnight, you're batteries should balance.

most of the modules out there are 12V, or made for Lifepo.... well, the ones that I know of.


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## mattW (Sep 14, 2007)

Hot juice electric have a BMS that was made for AGM/lithium cells but it would work on floodeds... They cost $30 each.


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## joseph3354 (Apr 2, 2008)

put a shout out to lee hart on the EVDL,he is the resident battery god.he has built equalizers for lead acid packs.

here is his evalbum page: http://www.evalbum.com/213


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## VDubber (Jun 2, 2008)

FYI, Lee Hart's balancer is an open-source kit, available here:

http://www.geocities.com/sorefeets/balancerland/

It is a current-transport style balancer, that moves charge around the pack to equalize all the batteries without wasting any energy.


And here is Lee Hart's simple and cheap shunt style zener balancer:

http://www.seattleeva.org/wiki/Zener-lamp_regulator

With part numbers and mods to work at 6V here:

http://teva2.com/projects.htm


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## joseph3354 (Apr 2, 2008)

great job! these links should be in the wiki !


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## hardym (Apr 2, 2008)

I've started a Wiki page about Battery Management System, and have included these links, thanks

http://www.diyelectriccar.com/forums/showthread.php?t=14778

What I am trying to figure out is how the Chinese duct-tape packs are balanced or what features their BMS is providing. 

There is also a small BMS as part of Cyclone LiFePo4 kit that looks very intersting:
http://www.cyclone-tw.com/lithium.htm

Mark.


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## VDubber (Jun 2, 2008)

hardym said:


> What I am trying to figure out is how the Chinese duct-tape packs are balanced or what features their BMS is providing.
> 
> There is also a small BMS as part of Cyclone LiFePo4 kit that looks very intersting:
> http://www.cyclone-tw.com/lithium.htm
> ...


Like many of them, that one is fairly simple and limited:

OVERCHARGE DETECT DELAY TIME - 1.50s
OVERDISCHARGE DETECT DELAY TIME - 9.9s
OVERCURRENT DETECT DELAY TIME - 9.9s
OVERCURRENT & SHORT RELEASE - REMOVE LOAD
BALANCE STARTING VOLTAGE - 3.55V
BYPASS CURRENT FOR BALANCE - 250mA

So, it bypasses up to 250mA once each cells voltage gets to 3.55V during charging, and during use if a cell internally shorts or discharges too fast, the BMS just sends a 3/5V signal on a wire. The user is supposed to use this signal to turn off the controller or something along those lines.

And what is with that 10 second overcurrent detect time? I assume they are letting the peak current go higher, and that is the "10s max current" rating of the battery.

OT, notice the electric car on that site. It uses a Hybrid battery pack - 20Ah LiFePo4 for acceleration and peak current handling, and a 120Ah SLA for range. This seems to be getting more common...

Also, this has to be the trippiest bike I have EVER seen. A true example of function overtaking form and beating it upside the head with a 2X4:


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## VDubber (Jun 2, 2008)

Wow, do we have good timing or what?

This just popped up on the EVDL - A 2 year review of the Lee Hart Zener balancer! (On a pack of used, surplus AGMs no less)

http://www.diyelectriccar.com/forums/showthread.php/evdl-zener-regs-report-after-using-15106.html



> ...Overall though I would give the zener regs a massive thumbs up. The
> batteries are not gassing, they have lasted two years past any rational
> point of end-life, and aside from the clunkers are still doing very
> well.


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## Nodd (Jun 6, 2008)

Hey folks,

Thanks a ton for all these great suggestions. Thanks to you guys hopefully I won't be one of those noob EVers who kills his first pack in six months. Much appreciated.


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## rkonnen (May 29, 2008)

Anybody have a current link for Lee Harts balancer? This link seems to be inactive.
Thanks,
Richard
http://www.geocities.com/sorefeets/balancerland/

It is a current-transport style balancer, that moves charge around the pack to equalize all the batteries without wasting any energy.


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## dtbaker (Jan 5, 2008)

Nodd said:


> I recently purchased a used EV & just ordered a fresh set of 20 6v 242Ah wet cell batteries (Interstate U2300). I'm still recovering from the sticker shock. I read that battery balancing is important for insuring long pack life. I'd like to protect my investment.



if your charger has a built-in over-voltage cycle, that should do it for floodies. The MUCH more important aspect is proper watering.... I learned the hard way because I put off watering once or twice as it was such a pain, and I think my nice battery packis dying after just a year. :sigh:

A couple months ago I installed a 'Flow-rite' watering system which is basically special cell caps with floats and a linked irrigation system. best investment EVER. Made my 1-1/2 hr watering chore into 2 minutes. I documented the install in my gallery..... link below.


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## alvin (Jul 26, 2008)

This link has the battery balancer on it.
http://www.evdl.org/lib/index.html#chg


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