Building A123 cells into parallel modules

[A1234LIFE]

Hi all,

I have been riding an electric bike for about 6 months. It was built from a Crystalite kit. You can see more about it if you follow this link.

http://home.comcast.net/~steveandbeck/ebike.htm

I just stumbled onto this site and was very impressed. I noticed a name from my R/C days. I actually got great advice about bikes several months ago from Gary Goodrum on the ezone forum.

Anyway, I am working on replacing my 48V lead setup with a 15s4p pack of A123's. After reading through some of the information here, I am thinking about taking all the cells apart and creating 1s4p packs. They would be flat packs with 4 cells side by side, using equal lengths of 16 gauge wire to connect the four + terminals to a 10 gauge piece of wire for the main lead. Same process for the negative terminals. It seems like 16 gauge should be enough for the parallel connections, since I don't expect to draw more than 10 amps per cell. My controller is the 4840, unmodified. Using APP connectors, I could easily put the cells in series to create my 15s4p setup. I will probably build one more so that I have a 16s4p pack and just charge the entire thing with a 48V Lead Acid charger. If I stick with 15 I have a Schulze charger that will do the job. I really like this design, because I can easily disconnect the modules and charge the 1s4p packs individually to keep them balanced. It also makes it easy to add more voltage by just adding another 1s4p pack in series once I modify my controller.

Any thoughts on my plan?

Thanks,

Steve

 

[cerewa]

A1234LIFE-- your plan sounds okay.

I'm wondering if you are aware of the range you'll get with that many A123 cells. If you use them with reasonable efficiency (as in, don't use the motor at its least efficient rpm range, ride at close to normal bicycle speeds) you'll be able to get about 40 miles per charge without pedaling. If you don't need that kind of range, you can certainly go for fewer than 60 cells. On the other hand if you want such a snazzy overpowered battery pack, go for it-- why not?

 

[fechter]

Welcome A1234LIFE,

More is always better...

What about balancing the cells during charge?

You should also probably monitor individual cell voltages on discharge.

If the cells stay balanced, then it might not be a problem, but with the cost of the batteries, I'd want to protect them as much as possible.

 

[Jozzer]

A1234LIFE-- your plan sounds okay.

I'm wondering if you are aware of the range you'll get with that many A123 cells. If you use them with reasonable efficiency (as in, don't use the motor at its least efficient rpm range, ride at close to normal bicycle speeds) you'll be able to get about 40 miles per charge without pedaling. If you don't need that kind of range, you can certainly go for fewer than 60 cells. On the other hand if you want such a snazzy overpowered battery pack, go for it-- why not?

40 miles? That would be at less than 10wh/mile. I'd say closer to 20 miles if you are carefull, and 10 if you blast it (30mph+ or lots of hills)
anuvva Steve

 

[A1234LIFE]

Thanks for the replies. I did some more investigating and I think I understand why this is a bad idea. It seems with cells built in parallel, like my proposed 1s4p pack, it would be perfectly fine to charge each 1s4p pack alone. This was actually where I was heading, I was going to get fifteen of the 2A wall chargers so that each 1s4p pack would have its own charger. I could just disconnect the series connections and plug in the chargers to each pack. If I then connect these packs in series for my 15s4p configuration to discharge the packs and I have a bad cell in one of the parallel strings it will not show up as a voltage loss but it will have a loss in capacity. Over time this would probably destroy the entire 1s4p pack before I could spot the problem. It looks like I need to keep them in series first and get the desired voltage and then connect them in parallel to get the desired capacity.

I do consume about 40Wh per mile, so I will still have about the same range as my current lead acid batteries. I should have more available power with the A123’s and certainly much less weight.

Steve