I week ago i bought a bulk charger for my E-Bike, the idea is to use this to charge the battery fast and then once a week or so use a slower balancing charger to assure that the cells are in balance. I bought the charger from www.bmsbattery.com and they set it up for your requirements.
This is a pretty common china made charger sold at various places under different names. I have seen names link Ping-charger and King Pan charger as well as Kingpower.
The charger uses a CC/CV (Constant Current/Constant Voltage) charging algorithm and i requested the charger to have the current set to 4 A and the voltage 49V with an Anderson SB50 connector for the battery and an European wall outlet contact. They got the current and the high voltage connector right but the voltage were set to 48.8 V and the battery connector was an Andersson Power Pole instead. I had a spare SB50 connector so that one was easy to fix
48.8 V for a 12 cell battery will result in 4.07 V per cell. Since this charger doesn´t monitor each cell independently a safety margin is required but that is a bit to much. I was aiming at somewhere between 4,10 V and 4,15 V per cell. I needed to set the voltage to somewhere above 49 V.
Four screws on the sides held the lid on and after exposing the PCB i was faced with 3 potentiometers.
I would have guessed that there should be one for voltage and one for current. Two of the potentiometers were located next to the current shunt so I guessed that they were for setting the current. Maybe one is for coarse and one for fine adjustment, if anyone knows please leave a comment. The third potentiometer were located below the output fuse holder and that one was my first guess for output voltage. With the charger powered up and a voltmeter connected to the output I tried the last potentiometer and I was right. I adjusted output voltage to 49,5 V resulting in 4,125 V per cell.
Be extremely careful while touching the insides of the powered up charger with a metal screwdriver!!!