This is my BMS. It started out based on the original McRee/Goodrum circuit.
The criteria I wanted over and above the original design was:
Use any voltage source, not a specific SLA charger.
Unit was to shut down when charging was complete.
To this end, I used 2 constant current sources. These have a negative temperature co-efficient, so the current decreases as the heat rises.
Initially, in bulk charge mode, both current sources are on. Any Shunt Low turns off the higher current source. Charging continues on the second, lower current source.
Once all cells are full, All Shunts Low triggers a time delay before switching the R/S flip flop, which shuts down both current sources. And lights the Charge Complete led.
Bulk charge starts at 4 amps, and settles down to 2.7 amps as it warms up. Trickle charge is about 400mA.
The charger comprises 3 x 24 volt, 6.5 amp Meanwell power supplies. These have a voltage adjustment pot, and the DC supply voltage is about 62 volts. The charger has a diode in series with the output, so the batteries don't power up the supplies, and also a 12 volt regulator to power the BMS logic.
The charger is housed in a recycled server computer power supply case. The BMS also has a 12 volt input from the scooter, to power the LVC to ebrake circuit. This has not been tested yet.
The Mark One version looks a bit prototypish. Mark Two will have a better case, better pcb layout, and I'm working on a switchmode current source, which should allow more current and less heat. Works great in LTSpice, but not built yet.
First photo is the battery pack, 16 x TS LFP 40 AHA.
Second photo is the underside of one pcb, containing the per-cell circuitry for 5 cells. Mostly SMD.
Third photo is the BMS enclosure. 2 x 10 led dip bar graph for the per-cell indication, and a hard disk drive cooling fan for, well, cooling.
Fourth photo is the whole lot on my workbench.
Fifth photo is inside the BMS.
Sixth photo is a closeup of the current sources, showing the little TO92's superglued to the fets (thermal feedback).
And last, but not least, the circuit diagram in pdf format.
Now to install it in my EVT scooter.
EVT-4000e. 16x TS-LFP40 and custom BMS
= massive EV GrinChopper
with 180 Watt Cyclone kit & 8x 20AHr Foxx LiFePO4 and custom BMS