BMS and larger battery capacity

[PaulD1]

Hi All,
I am currently replacing the cells in a 24V Ebike battery. The existing cells are Samsung IRC18650 22FM (35 of them), if I use new cells of a higher capacity (for example Samsung 25R from Cell Supply) will this effect the BMS. Or is the BMS only looking at the voltages? Also would there be any down side to putting in even larger capacity cells.

Will the charger work okay with larger capacity cells.

Also Cell Supply seem to have good reviews, do you think they are a good supplier?

Thanks in advance.

 

[fechter]

Right. The BMS is only looking at the voltages (and the current). Larger capacity cells should be no problem assuming the controller isn't pulling more current. Charger will be fine also, but take longer to fully charge.

 

[Packman]

This is fine to do, yes the BMS is only looking at voltage. Using cells of any capacity will be fine. As for the charger it will just take longer to charge the battery if you run the battery flat of course. I have never heard of cell supply but I have found NKON to be reliable and cheap.

 

[Ralph31]

Good information. I am currently in the process of bringing back to life two Genze e101's batteries. Neither battery will take a charge. They have five, 6 cell packs (30 18650's) providing 42 volts from the batteries. I can easily remove each 6 cell pack and evaluate/charge them separately using a dual output regulated power supply. It appears I may have enough good packs to fully rebuild one.
I will be looking at building a new 30 cell pack and may need to replace the BMS. Looking for information on how the BMS functions. No schematic or theory of Op on how the stock BMS works... The 2 wires that connect to each pack senses voltage but are those same wires also used to provide the appropriate current to each pack?
Thank you

 

[PaulD1]

Thanks for your help. Much appreciated.

 

[docw009]

Good information. I am currently in the process of bringing back to life two Genze e101's batteries. Neither battery will take a charge. They have five, 6 cell packs (30 18650's) providing 42 volts from the batteries. I can easily remove each 6 cell pack and evaluate/charge them separately using a dual output regulated power supply. It appears I may have enough good packs to fully rebuild one.
I will be looking at building a new 30 cell pack and may need to replace the BMS. Looking for information on how the BMS functions. No schematic or theory of Op on how the stock BMS works... The 2 wires that connect to each pack senses voltage but are those same wires also used to provide the appropriate current to each pack?
Thank you

I found this picture of a Genze 101 battery, Five modules, with each module holding six cells. I expect each module is arranged with two groups, each group holding three cells in parallel,


That would give you ten groups in series, 3 cells in each group arranged in parallel, commonly called a 10S-3P. I would guess it uses 2900 mah (2,9AH) cells, The AH of a battery is the P number times the cell AH. Here, P is 3. If you use 2.9AH cells, then 3 x 2.9 = 8.7AH, which is the advertised number for this battery,

If the original BMS has balance circuits, I would keep it but it's hard to determine this, In any case, a replacement will connect the same 11 wires already going to the cells. Make a note of them.

While it will be educational to rebuild using what cells still work, you're working with old cells and good performance is unlikely, Not a good idea to mix new cells with any of the old ones. The battery will not discharge uniformly and it will tend to go unbalanced,


This is a simple schenatic for how a BMS is wired. It just happens to be a 10S-3P. X4 and X2 represent transistor switches that connect the ground of the cell stack to the corresponding grounds of the charge port and discharge port,

The BMS monitors the cell voltages with those wires. If the cells go much below 3V, it won't allow discharge or charging. When the cells reach 4.2V, the BMS inhibits charging. If everything is working right, all ten cell groups reach 4.2V at the same time, and you have 42V coming out of the 46V battery,