lipo balancing

[joeling]

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Hi,

I have a few older Kokam lipo batteries without the balancing taps. Just wondering how difficult is it to add the balancing taps myself ?

I have some basic electrical knowledge (used to DIY tube audio amplifiers etc.) and also handy with the soldering iron.

I am curious how the cells are attached (soldered together). I am under the impression that alumiunium solder is used.

Thanks.

Regards,
Joe Ling

[MetalMan]

You might not have to deal with aluminum solder. Some cells have nickel strips welded onto the aluminum tabs, so standard solder can be used. I have no idea if that's the case with Kokam packs, but that's how it is with the Electric Power pack that I just got.

With the type of solder aside, you can just solder wires onto the PCB (circuit board) that the cells are attached together by. For a wiring diagram, take a look at this:
http://www.rcgroups.com/forums/attac...hmentid=724240
That's for a 4s Electric Power pack, and the wire colors do not matter (except for the red and black). This is the standard way to wire a pack for compatibility with most balancers.

[joeling]

Dear Metalman,

Thanks for the input. U have just given me an excuse to open up my pack to have a peak.

Regards,
Joe Ling

[MetalMan]

Good luck! Just be careful of metal objects near the PCB...

[joeling]

Dear Metalman,

I took courage & opened up the heatshrink. Well, there is a circuit board where the cells attach to & it will be easy to solder additional wires for use as taps for balancing purpose. I took a reading of the cells & they were 3.69V & 3.35V respectively. What a big difference ! :026: :002: To the best of my knowledge, I have run this set of 2S lipo less than 5 times ! Now I am scared to run any of my cells because of this. I will have to solder some taps & charge the cells one at a time while I wait for the balancer & associated wiring to arrive.

Regards,
Joe Ling

[MetalMan]

You may not have to worry about that imbalance. It could be due to different cell capacities, and if it is, this imbalance *could* go away if you charge the pack. As long as you monitor the voltage of the cells during the charge you don't need to worry about it. If one cell reaches 4.20v before another, then just terminate the charge.

[joeling]

Dear Metalman,

Thanks for the insight. Shows that I still have a lot to learn about lipo. I must give the battery the respect it deserves. Time to prep the aluminium container to be used as battery container during charging.

Regards,
Joe Ling

[MetalMan]

Another thing to consider for a charging "safe" is a ceramic pot/container of some sort. Generally these can withstand high temperatures, and are inexpensive to obtain.

[Scott711]

I've taken to using a ceramic pet food bowl for charging lipos. I also keep a fire extiguisher close by just in case.

[Dafni]

A bucket of sand makes a good and inexpensive fire extinguisher. Perfectly suited for this kind of (chemical) fires.