Here's what I have:
- 24 LiFePO4 nominal 80AH used cells to play with and learn from.
- a 12V 22A charger with adjustable constant voltage
- an inverter & loads, variable from 0A to 18A at the battery
- a JBD 4s BMS with Bluetooth and xiao xiang Android app (Overkill-similar)
- 4 50W 6 ohm resistors, in parallel, for ~2A draw on one cell; ~8A on 4s. I might get more.
- a very good digital multimeter
- time
(I don't want to buy a desktop power supply or other gear I won't use beyond this present compulsion.)
Here's my method so far, without fine details like millivolts and such.
- Assemble a 4s pack with BMS. Start charging.
- Hold back faster-rising cell(s) with resistors.
- Stop the charge or slow it with loading, using the resistors to even up.
- In the 3.5V/cell range and on up, go carefully to take each cell near 3.65, until all 4 have touched that. (BMS cutoff)
- Charge with cutoff set to 3.6V/cell and repeat, using resistors to aim for all cells hitting 3.6 simultaneously-ish.
- Set cutoff to 3.65 and go slowly up to it and if charge current is very small, I have called that Top Balanced.
(I've repeated those last two steps a few times.)
- To confirm, for a little faith in myself, I've discharged a good third or so and charged back to 3.6 or 3.65, all cells together-ish.
- Then I can test the battery capacity down to 2.75V/2.8/3.0, and watch the voltages dance apart and then waltz back together when they get to the top.
It's all very satisfying, but now please tell me the flaws.
It's tedious, yes, but this is a hobby. Bottom balancing seems way easier, but less wise if a BMS is to take over.
I have other LiFePO4 ready-made batteries that are serving serious purposes, but they're quite boring by comparison.
Thanks for any comments!
KJU
- 24 LiFePO4 nominal 80AH used cells to play with and learn from.
- a 12V 22A charger with adjustable constant voltage
- an inverter & loads, variable from 0A to 18A at the battery
- a JBD 4s BMS with Bluetooth and xiao xiang Android app (Overkill-similar)
- 4 50W 6 ohm resistors, in parallel, for ~2A draw on one cell; ~8A on 4s. I might get more.
- a very good digital multimeter
- time
(I don't want to buy a desktop power supply or other gear I won't use beyond this present compulsion.)
Here's my method so far, without fine details like millivolts and such.
- Assemble a 4s pack with BMS. Start charging.
- Hold back faster-rising cell(s) with resistors.
- Stop the charge or slow it with loading, using the resistors to even up.
- In the 3.5V/cell range and on up, go carefully to take each cell near 3.65, until all 4 have touched that. (BMS cutoff)
- Charge with cutoff set to 3.6V/cell and repeat, using resistors to aim for all cells hitting 3.6 simultaneously-ish.
- Set cutoff to 3.65 and go slowly up to it and if charge current is very small, I have called that Top Balanced.
(I've repeated those last two steps a few times.)
- To confirm, for a little faith in myself, I've discharged a good third or so and charged back to 3.6 or 3.65, all cells together-ish.
- Then I can test the battery capacity down to 2.75V/2.8/3.0, and watch the voltages dance apart and then waltz back together when they get to the top.
It's all very satisfying, but now please tell me the flaws.
It's tedious, yes, but this is a hobby. Bottom balancing seems way easier, but less wise if a BMS is to take over.
I have other LiFePO4 ready-made batteries that are serving serious purposes, but they're quite boring by comparison.
Thanks for any comments!
KJU