Building a 48 Cell Li-Ion Battery Pack??

Hi guys,

I need to build a 12s 4p battery pack to power a hub motor for an electric unicycle project. I found that the cheapest batteries with the greatest density are 18650's (the same ones Telsa Motors uses). So, I need to combine them as described above, however, I fear I won't build the pack properly and they may overheat and/or explode.

Even Ladyada warns about putting Li-ion batteries in series or parallel. Her advice is "you should upgrade to a larger battery."

[u]Hub motor specs:[/u]

  • Max current: ~20A
  • Most efficient at 7.5A
  • 48v/1000W (up to 60v max)

I was planning on buying these Li-ion cells since they are the best deal around. Of course, it's eBay, so I ordered a few to test before ordering 48 of them.

I've looked around online and I haven't seen anything on DIY versions of these packs with more than ~8 cells. I briefly looked over Tesla's patents, but they aren't too insightful.

Thanks in advance!

hi, I'm not the expert on this; hope someone here is1

There are 18650's that have built-in overcharge-overcurrent protection that are a little more expensive. But note the discharge limitation. I think you need to get the manufacturer's information directly. Here's a quick translation of one seller's info: ---------------------( COPY )-------------------------- 1, the latest UltraFire BRC 18650 3000mAh 3.7V Li-ion battery with protection, large 3000mAh battery capacity, the highest capacity on the market (according to ultrafire official information);

2, low self-discharge rate, no memory effect, high efficiency, more power;

3, the battery itself with over-current, over charge, over-discharge protection voltage 2.45-4.20V, the battery can be used to ensure safe, secure, xenon flashlight does not support the large current discharge, WF-500, L600, L1200 and other high-power xenon flashlight can not use the battery; -----------------( END COPY )----------------------


There are various suppliers that produce already-built lithium battery packs with protection circuitry built in, and you can also get the far safer LiFePO4 cells in this form. Ping Battery is one name that springs to the memory, there are others.

Yeah, but they're preeeeeeety dang expensive. Does anyone know of Li-Poly or LiFe packs at a decent price?

electric unicycle? holy shit. do you have any links or more materials on that?

fkeel: electric unicycle? holy shit. do you have any links or more materials on that?

Yeah, they've been done a lot before, just Google it and you'll find examples of both DIY versions and commercial products. Some of the best are listed below and I'll post my entire build on Hack N Mod when it's done:

My goal is to replicate this:

I have been doing some research on can't find a light 48v battery pack with enough amp hours at an inexpensive price 48v, 500-1000 watts and 10-20 amp hours is some serious battery power. I can see why you would like to create a smaller one for the uni but dealing with the balancing issues of so many small batteries may be tricky and potentially dangerous. I wonder if a charging system for a more expensive battery array used with smaller less expensive batteries would be an option - just thinking out loud here to spawn discussion / thought.

I too am very interested in creating a petal free electric unicycle and have been mulling it over for at least 10 years. I even purchased an electric motor for this purpose but battery has been the big limiting factor for me as well. If I come up with any power solution I'll post here, please do the same.

If you need any programming assistance with the project - PM me.

Best of luck.