sbslider

I am considering adding a circuit board to a 2s2p 7.4v battery pack that is coming with a Cree XML light I bought. It is here: https://www.batteryspace.com/pcbfor74...mit2round.aspx

It claims to balance charde two single cells in series. Assuming the battery pack I receive has the batteries connected in parallel at the center point of the two stacks, is there any reason I could not use this circuit?

Also, any links that will help me learn about charging Li ion batteries would be appreciated. Thanks!!

davidad

https://batteryuniversity.com/

Burton

A 2S1P has 2 cells, wired in series. A 2S2P pack has 4 cells (2 groups of 2S wired in parallel). Unless for some reason you're absolutely stuck using one particular battery format - two larger cells will give the same capacity and performance without all the cell balancing hassles. From what you posted - you'll need two of those and if you have room to add components, I'd think you'd have room to rethink the whole battery pack design and use as little space as possible for battery management and as much as possible for capacity.

sbslider

thanks for the responses. I can see my initial post was unclear, so I will elaborate. I purchased a cheap bike light to supplement the one I have, https://cgi.ebay.com/ws/eBayISAPI.dll...ht_3555wt_1163
I don't plan to buy anything until I get the light a check it out, but I suspect the battery pack 4 18650 cells hooked up to provide the 7.4V required to run the light. I may be wrong and it is 4 cells in parallel, as it does claim to be 8800mA hour. But the listing also claims 8.4V, so there must be a series connection some where in there.

Several years ago I dabbled in RC planes, and had learned a bit about Li-ion batteries, but I was primarily running NiMh. Since Li ion are so prevalent in bike lights today, and I have a bike light battery i suspect could use an upgrade, I was hoping to learn a bit more about the subject. The batteryuniversity website is somewhat helpful, but I did not find details about my specific subject.

I do realize Li-ion batteries can be dangerous, and that is part of my motivation for wanting to upgrade the battery pack by adding a $5-$10 circuit card that will do a better job of charging the batteries properly. Any additional help on the subject, or references to websites that do the job would be appreciated

Burton

Suggest you might be getting a little ahead of yourself. Probably better to wait till you get the light. If they're actually 18650 batteries those are available in different capacities and in both protected and unprotected configurations. Why add something on that can be built in? Never heard of anyone selling products on eBay with quality batteries so you'll probably want to change them soon anyway.

colleen c

I cannot find where the claim of it balance charging two single cell in series. I really do not believe it does that. There is an additional wire connection on the PCB to the common center terminal of the two parallel circuit but that only for low and high voltage sensing for each of the two half of the bank. I do not think it is for balance charging.

I have bought two of these PCB myself in the last year. I own this battery pack from Batteryspace which uses the same PCB like the one you listed. So far I am unhappy with the PCB. I accidently short circuit the PCB twice on two board and both board does not recover from the short circuit protection. I tried to connect a charger back to it with no luck. The only way I found to fix the problem was to replace the board in the pack.

sbslider

You are correct, I guess I read into the description what I wanted to read, not what it said. Thanks for pointing that out.