Custom Cell balance lifepo4 parallel 48v, 72v

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Last seen: 13 years 3 months ago
Joined: Sunday, May 18, 2008 - 22:28
Points: 17
Custom Cell balance lifepo4 parallel 48v, 72v

So i've been building ebikes/karts for a few years now, gone though about 3 iterations of bikes and most recently a dirtbike frame fitted with a 48v altrax/etek with SLA batteries and and so forth...

ANYWAY the point is, i'm going to be building a full on long range high speed fully lithium motorcycle and i realized....No way to get 72v lithium packs in parallel effectively without risking some life shortage via one pack faster then the other.

I'm in college for mechanical engineering, so i just asked one of my electrical engineering friends to come up with a cell balancer that can monitor voltage/ouput from every cell, and balance each pack in parallel thus creating a perfectly even discharge EVEN, if the cells were not balanced to begin with!

Design and prototype cost for this kind of thing are rather high so we figured we would offer (once we get it working) 48v, 60v, and 72v parallel cell balancers for others so they don't have to spend a fortune (or just not be able to do it at all).

Additionally those wishing to use multiple ping packs for high power applications (as we are) should not be using the ping BMS for discharge (but you can still have it on for charging in our setup) and use something like the kelly motor controller to limit your amps intelligently, so no shut-offs, no re-booting, same current limiting effect.

Just wanted to know what the interest level is on parallel cell balancers, should not only increase range a little bit, but cell life by far. Additionally, you can (probably) order a bunch of cells for a custom pack (ask for no duct tape lol) and make it yourself.
Friend of mine has a ping pack now, and is getting more, so you can bet we will have all sorts of data aq. once we get it running. (cell balancer can even have data logging to an SD card or similar).

I'll be getting several ping packs later when i get some more moolah.

Just wanted to know what the interest level is on parallel cell balancers, should not only increase range a little bit, but cell life by far. If enough people want em, ill invest more and see if we can't have fancy and low tech versions...Fancy versions being able to individually monitor and log data etc etc...

LinkOfHyrule's picture
Last seen: 15 years 1 month ago
Joined: Wednesday, October 17, 2007 - 14:54
Points: 730
Re: Custom Cell balance lifepo4 parallel 48v, 72v

Interesting, but I wonder how you're going to actually manage to discharge them evenly AND efficiently at the same time. This is actually quite hard to do, since you either have to dump the excess energy from the cells or modulate the output from the cells. The former is wasteful and you might as well just have an LVC circuit on the cell with the least capacity; the latter is expensive, since you need relatively powerful components and ICs to to it.

Details when you get them, plz. :D

The author of this post isn't responsible for any injury, disability or dismemberment, death, financial loss, illness, addiction, hereditary disease, or any other undesirable consequence or general misfortune resulting from use of the "information" contai

Last seen: 13 years 3 months ago
Joined: Sunday, May 18, 2008 - 22:28
Points: 17
Re: Custom Cell balance lifepo4 parallel 48v, 72v

Please allow me to update/"correct" information as I am mostly relaying what I understand from my friend about the design.

Also, please forgive obvious typographical and grammatical mistakes...Was pretty tired when I wrote it.

Cell monitoring will not be done on the individual level, as can be seen in BMS systems like this one
Rather they will be done at the pack level *see star below* for obvious reasons [may be subject to change]. Considering the cost of the 16 cell bms, you can imagine how much it would cost to get a few kWh wired up (over 100 cells). I myself plan to have about 2.8kWh in my project (the equivalent of 3 48v20ah packs or 4 36v20ah packs)
Even one 48v 20ah pack has 64? (if i'm not mistaken) cells which would be quite expensive.

*packs will not be in series, rather they will have one string in series followed by other sets in parallel of the same voltage.
For instance, instead of having 2 36v packs in series and 2 36v packs in parallel, they can be re-assembled as multiple 72v strings in parallel. This, (i'm assuming) allows the parallel pack circuitry balancing to operate correctly.

The link above is a more feature rich and ideal method (although i don't have any personal experience with it), but relatively impractical on a large scale. In a perfect world, both systems would be implemented. Either way the point is that the systems are targeted towards different markets.

Anyhow i'll have more on how it will actually work after i've gotten an "official statement" so to speak from my friend. He likes to use alot of words i don't quite get, so hopefully when he has time he will write up something explaining the technical details.
Sorry to leave you tech-junkies in the dark, but thats all I have for now.

Last seen: 14 years 3 months ago
Joined: Monday, May 12, 2008 - 07:33
Points: 13
Re: Custom Cell balance lifepo4 parallel 48v, 72v

Goto this web page and view the self balanced LiFePO4 13C high discharge cells with internal stable can get them with a B.M.S. but it is not will get whats needed for any kind of e-project
email questions [at] for more details

chas_stevenson's picture
Last seen: 12 years 10 months ago
Joined: Wednesday, December 6, 2006 - 17:14
Points: 1309
Re: Custom Cell balance lifepo4 parallel 48v, 72v


Thanks for the info, but we have cells what we need is a BMS for the cells we have.

Grandpa Chas S.

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