How do I charge individual cells in a bottle Li-Ion battery?

[alexon]

Hello everyone,

I’m new to this great forum, so please bear with me if I ask some dumb questions.

I have an ebike that I have not used for a few months and when I went to ride it, it turns out that the battery is totally discharged.

It’s a 36V / 9AH li-ion bottle battery that I purchased with an electric kit 3.5 years ago.

Before this problem, I experienced an abrupt decrease in autonomy about a year ago, which meant I had to recharge the battery every 15 miles or so (this sudden drop in capacity points to some dead or disconnected cells, I suppose).

But at least it worked.

Yesterday, when I tried to charge it, the power supply’s green light did not change to red (“charging”) and the battery did not charge. BTW, I checked the charger voltage and it is fine (42V).

From what I read in Spanish forums, it seems that the battery charge may have fallen below the minimum required for the charger to work and therefore the battery is "blocked". I also read that by individually charging the lowest cells, you can increase the total battery charge above that minimum and the charger will start working (for an example, click here: http://perso.maicas.net/ebike/battery1.htm).

Two problems: I do not own an individual cell charger (although I think that a hacked 5V USB phone charger can do the trick) and, what's worse, I do not have ANY IDEA on how and where to connect it to the battery to charge the cells individually (or in groups, because the poles of each separate cell are not directly accessible).

In the attached photo, I have marked in orange the connectors where I guess I should connect the individual charger, but I need someone to please tell me how to do it (the cells are SAMSUNGs ICR 18650-22F of 3.6V, by the way (about 36 in total - three groups of 12)).

Better yet, if by some coincidence someone from Madrid reads this and can lend me a hand in person, it would be awesome .

Thanks a lot for your help,

Alex

P.S. Since I’m a newbie, I probably cannot send PMs yet, so if you want to contact me directly, please send me a message with your email address. THANK YOU.

 

[d8veh]

You have to measure and charge through the multi-pin connector/s that attach to the BMS. There's different BMSs, some of which have strange connection sequences, so show a picture of yours to get more detailed help. It's under the tape at the top of the battery.

 

[dogman dan]

My impression is that this battery has been at 0 volts, and if recharged, could very likely burn your house down later.

So if you fix it, keep it outside. You will at least need a small voltmeter, to identify the + and - of each of the small wires leading to the bms. each wire in the middle of the string, will be the + of one cell group, and the - of the next one.

Overcharging them any at this point will really be playing with fire, so your best approach might be to shoot for getting all the cells to about 3.5 or 3.8v, avoiding the risk of charging them to 5v with the cell charger.

Then connect the bms back up, and let it finish the charge, and balance it.

Again,,, you have an old battery there, not worth much effort. In calendar time alone, its pretty much done. If any of those cell groups are 0v, then you have a ruined battery that is a big danger.

The whole pack may have shown 0v, just because the bms shut it off. I mean if actual cell voltages are 0v, anywhere in the pack, its done.

 

[alexon]

Thanks a lot to both of you for the Info.

Here is a picture of my BMS:

I think I found this exact model online, and here is the diagram for the 11-pin connector wiring (sorry, you'll have to zoom in to read it):

I also purchased an Imax B6 charger, so I guess I’m about ready to start charging the (groups of) cells individually.

Also, Dan, I don’t think the battery is as dead as all that. After I opened it (without doing anything more) I plugged it in the charger and surprisingly the led turned red and it started charging for a while. Then it turned green again. After that, I put the battery on the bike and switched the circuit on. It did start and the accelerator moved the wheel, but the battery charge indicator only showed 2 out of 4 lines, so I guess that if I took it for a spin it wouldn’t last me more than a few miles.

This means, I take it, that one or more of the groups of 4 cells has a lower charge and the BMS and/or the charger have been unable to charge it. This is where “manual balancing” and my spiffy new Imax come into play, except I have NO IDEA how to connect the B6 to the 11-pin connector in order to 1) measure the charge in each group of 4 cells and 2) start recharging them.

If you can give me more detailed instructions or point me in the direction of a Youtube video or a blog explaining this it would be great.

Thanks again,

Alex

 

[d8veh]

That's an easy BMS. Unplug the multi-pin connector, then measure the voltage between each adjacent pair of pins starting with the white and red wires until you have 10 results. You can do a plausibility check by measuring between the two end ones too. The 10 results should att up to that one. You can get your probes in the slots in the side of the connector. Be careful not to short the probes - they'll spark, but no damage would be done so don't panic.

Post the tesults here. Don't attempt to charge yet. The Imax isn't really suitable for this. You need something like a BC168 or a single cell charger.

 

[dogman dan]

That's good, if the cells never went to 0v, then its not such an incendiary device.

B6 a great charger to use to bring each cell group to 4.2v.

Its still old though, and capacity will be low, and it might tend to get badly out of balance every ride. But good idea to use this one as a learning tool for sure.

 

[alexon]

Thanks again.

D8veh, are you sure the Imax cannot charge the cells? Why? (That would suck! :?)

Anyway, I measured the voltages between adjacent pins:

Cell Number____Pins_____________Voltage
___Cell 1_______0-1 (white-red) ___ 3,34
___Cell 2_______1-2 (red-black) ___ 4,26
___Cell 3_______2-3 (...) _________ 3,67
___Cell 4_______3-4 (...) _________ 3,54
___Cell 5_______4-5 (...) _________ 2,96
___Cell 6_______5-6 (...) _________ 4,26
___Cell 7_______6-7 (...) _________ 4,27
___Cell 8_______7-8 (...) _________ 4,16
___Cell 9_______8-9 (...) _________ 4,27
___Cell 10______9-10 (yellow-blue)_ 4,27

What can we conclude from this?

Should I charge all the cell groups that are below 4V? How do I go about it?

 

[999zip999]

Best to check all cells write it down like this. Sart at the neg as cell one.
1. 4.18v
2. 4.15v
3. 3voltage

10. Or ? Xxx volt
Charger voltage and battery voltage.

 

[999zip999]

You can put two pins in the white bms connector check with multi meter. Put a piece of tape to hold in place check pos and neg charge as 1s to 4.2v @ 1a or lower to bring up to 3.4v then at 2a amp. Thats for 4p.

 

[alexon]

Thanks .

Following advice I read in a Spanish forum, I discharged the cells that were at 4.26V / 4.27V to bring them down to 4.20V and now I'm charging those with 3.XX volts to bring them up to 4.1V or so.

What is the next move? Do I connect the battery to the bike and ride for a while to discharge it a bit or do I first plug it to the charger to finish charging/balancing the cells before using it in my bike?

Thanks again.

 

[hemo]

The pack is all over the place and only one cell group (8) looking good. I would check the charger voltage output first as it appears for some reason the pack is being over charged on 5 cell groups/strings. Balance, discharge & charge a few times to see if it stays balanced, if doesn't then the BMS isn't doing it's job well.