For one light I’ve put together I need 7.4V, and since it’s more of a headlamp then a flashlight I’ve stuck with external batterypacks.
Normally I’ve used a battery holder, with a bms for a 2S setup.
However, I want to expand a bit, as this setup got its limitations.
i. For a 2S1P pack it is just two cells and a 2S bms board.
For a 2S2P pack would it be two of these ‘2S1P + 2S bms’ board setups in parallell?
And for a 2S3P pack three of them?
Or would you need another form of bms?
(don’t think of balancing for now, I use the the bms for undercharging- and short-protection)
ii. Since I want to use a standard charger I wonder if I can go and charge each cell individually?
Like use charging leads with magnets, and hook directly on the anode and katode of the idividual cells (they will still be spot welded together at this point).
iii. If ii works, can you charge more then one cell at the time with this method, if you just got more leads?
For #1, the BMS board is configured for the number of series cells- the parallel cell count doesn’t matter. 2s3p will work on a 2s BMS. You only need one board.
charging the cells individually if connected is not recommended. In most series or series parallel battery packs, there is both a protection and charging circuit (like a laptop battery) to keep the cells balanced while charging and discharging. For DIY stuff you usually use a balance charger in conjunction with the BMS. This is for safety and the longevity and performance of the batteries.
get yourself a balance charger that will charge properly. You cab get a BMS with a charging circuit built in, but it’s good to have the charger since the BMS is mainly for monitoring the vents during charge/discharge and isn’t that accurate.
FWIW, I’ve had a number of BMS board go bad and cripple a pack. When taken apart ALL cells were fine when checked individually. I’ve come to somewhat distrust BMS.
All packs I make are pure balance packs, no BMS. I do have an RC charger that will go up to 6S.
If you have access to the +/- poles you can charge cells individually.
In theory iii would work. Cells interconnected in parallel balance each other. Then you charge them as a single large cell.
They do NOT balance in series.
When connecting cells in parallel it is important that they be at least reasonably close together in voltage. If there is a lot of difference there can be a large surge of current as they self balance.
In other words, be damn careful if you try that. One polarity mix up could put some unwelcome excitement in your day.