Hi guys, I'm starting to finish my second e-Bike, and I still have the charger left over from my first one.
I modified a Meanwell power supply for 3A charge current and an adjustable voltage.
The pack I'm going to charge will have 16s5p A123 cells.
The BMS I have is the one in the first image here:
https://bmsbattery.com/bmspcm/323-16s-lifepo4-bms-battery-management-system-bms-pcm.html#/201-discharge_current-50_100a
The one with the aluminium heatsinks.
Normally, I would adjust the charger voltage to (3.6V*16) 57,6V.
However, should one cell bank be out of line, the charging (BMS stopping charge current) will only stop when it reaches 3.9V, and again start at 3.8V, so the cells will be within these voltages until the balancer has bled away enough capacity and the other cells have cought up in voltage and the pack is balanced. I would like to avoid having the cells exposed to this voltage region, which would always happen if the cells are unbalanced and the charge current is higher than the balancing current.
So here is what I thought up: I will adjust the charger to a lower voltage, around 3.45-3.50V/cell. I charge my RC A123 packs to 3.50V/cell with practically no loss of capacity, so the pack should still be pretty much full at this level. To engage balancing, I will then supply a higher voltage, but at a very little current, like 30mA, to allow the balancer to cope with it without the unbalanced cells reaching a higher voltage. For this, I would use such a step-up converter:
https://www.ebay.de/itm/400W-Boost-Konverter-DC-Step-Up-Wandler-Modul-8-5-50V-auf-10-60V-Spannung/302635040733
The converter would be wired to the charger output. Before being connected to the pack, both the charger and the step-up converter would have a diode at the output to prevent current flowing backwards.
So the charging would work like this:
The charger would charge with 3A until (3.45V*16) 55.2V are reached. The current would taper off to nothing (CV phase).
Before it tapers off to nothing, the step-up converter would still push a steady current of 30mA into the pack, until the pack voltage reaches (3.6V*60) 57.6V.
This way, the balancer with a current capability of 70mA will be able to do it's work without cells reaching a voltage much over 3.60V.
Does this sound like a reasonable plan?
Thanks,
Julian
I modified a Meanwell power supply for 3A charge current and an adjustable voltage.
The pack I'm going to charge will have 16s5p A123 cells.
The BMS I have is the one in the first image here:
https://bmsbattery.com/bmspcm/323-16s-lifepo4-bms-battery-management-system-bms-pcm.html#/201-discharge_current-50_100a
The one with the aluminium heatsinks.
Normally, I would adjust the charger voltage to (3.6V*16) 57,6V.
However, should one cell bank be out of line, the charging (BMS stopping charge current) will only stop when it reaches 3.9V, and again start at 3.8V, so the cells will be within these voltages until the balancer has bled away enough capacity and the other cells have cought up in voltage and the pack is balanced. I would like to avoid having the cells exposed to this voltage region, which would always happen if the cells are unbalanced and the charge current is higher than the balancing current.
So here is what I thought up: I will adjust the charger to a lower voltage, around 3.45-3.50V/cell. I charge my RC A123 packs to 3.50V/cell with practically no loss of capacity, so the pack should still be pretty much full at this level. To engage balancing, I will then supply a higher voltage, but at a very little current, like 30mA, to allow the balancer to cope with it without the unbalanced cells reaching a higher voltage. For this, I would use such a step-up converter:
https://www.ebay.de/itm/400W-Boost-Konverter-DC-Step-Up-Wandler-Modul-8-5-50V-auf-10-60V-Spannung/302635040733
The converter would be wired to the charger output. Before being connected to the pack, both the charger and the step-up converter would have a diode at the output to prevent current flowing backwards.
So the charging would work like this:
The charger would charge with 3A until (3.45V*16) 55.2V are reached. The current would taper off to nothing (CV phase).
Before it tapers off to nothing, the step-up converter would still push a steady current of 30mA into the pack, until the pack voltage reaches (3.6V*60) 57.6V.
This way, the balancer with a current capability of 70mA will be able to do it's work without cells reaching a voltage much over 3.60V.
Does this sound like a reasonable plan?
Thanks,
Julian
