Vbruun said:
I want to be able to have a charger that allows me to adjust the SOC on the battery, when I charge and discharge it.
The charger cannot adjust the SOC during discharge.
The BMS, if it is programmable, can stop discharge at a certain level. Most of them are not programmable and typically only stop discharge when the cells reach the absolute minumum safe voltage level (LVC), completely empty, usually about 2.8v per cell. (controllers usually have an LVC higher than that, at the pack-level equivalent of 3-3.3v per cell).
So to really do what you want, you will need a BMS that is programmable, and you will need to set it up each time to whatever different voltage, etc, that you want the cells to balance at, whenever you want to change what SOC you're charging or discharging to.
If the BMS is reliable, with adjustable top and bottom cutoffs (HVC, LVC), then you don't have to adjust the charger voltage at all, just the BMS HVC, to prevent the pack from charging higher than you want it to. Just make sure the charger does not have a voltage higher than the max normal full voltage of the pack.
You *can* just use an adjustable-voltage charger to stop charging at a certain pack level below the full point, where the BMS balances, but it doesn't have a way to stop at a certain cell level--only the BMS can do that. (unless i'ts an RC charger with individual sense/balance wires hooked up to the cell groups).
So the pack doesn't necessarily stay balanced (definitely won't as it ages significantly, or when it's discharged all the way to empty a lot), unless the BMS is *also* adjustable to balance it at the lower voltage.
At first that won't matter, but it will gradually get out of balance, which will decrease the total capacity available to the lowest-capacity (lowest "full" voltage) cell group's capacity.
Now, if you really just want an adustable-voltage charger, to shut off at whatever pack-level HVC you've decided on, and don't care about the other stuff at cell-level, then you can use a number of things, including those mentioned already in this thread.
I use Meanwell LED PSUs in the HLG series, because they're adjsutable voltage *and* current, and work on 120vac or 220vac input, and are sealed and potted, so can be mounted on the bike without worrying about vibration, shock, weather, etc. I use the HLG-600H-54A, whcih means it's 600w output at up to 54v and is Adjustable. (the non-A versions are not adjustable!) The four I have so far actually go a bit higher, to almost 58v, and 12A, for around 700w of output.
If you don't need that fast a charge, they make them down to less than 100w IIRC, which wil be lighter and smaller. The adjustments are little screwdriver-turned pots under rubber caps (to keep water out), so you'd need to measure with a multimeter (DMM) while adjusting before hooking up to the battery, to verify the final output voltage whenever you adjust them.