Old Lithium Ion 48V battery pack, and bad BMS, and a solar charge controller

[WorldwideDave]

Hi,
I have an old lithium ion 48v battery pack that has been sitting for 2-3 months. I need to charge it back up - no idea what voltage is right now, but sure it is getting low. It was from an electric bike.
The BMS that is in it went bad. The cells appear fine and I have tested the pack by charging and discharging with various small loads.
Because I have the raw cells with no BMS, and it is getting low, I had considered the following:
Rather than hot wire an aftermarket charger directly to the battery positive and negative, and plug in and charge, which could overcharge the pack, I thought about not replacing the BMS right away, and instead using a solar charge controller, set to 48V, and connect it to PV to charge the battery instead.
I have a victron 100/20 I'm not using, and I think I can turn the amps down to 2.5 amps, which is what the factory charger does (2A just to be safe?), and let the sun charge it up. I could even set the voltage to be maxxed out at 51.2 V instead of the normal 53 V or whatever it is.
I think that this plan isn't totally safe, but at least the solar charge controller will lower the current as it gets close to the top, and throttle the current going in from 20 A down to 2A. Also I think that once the SCC sees that it has reached its voltage, it will stop sending current from the PV to the battery, and I can't say that the aftermarket charger will do that.
What do y'all think?

 

[hybe022]

i suppose it's 13s x 3.7V nominal = 48V
li-ion tops at 4.2V
normally, charging voltage is 13s x 4.2V = 54.6V

Charging the pack even at a lower 51.2V regardless of current without BMS
can cause one of the strings with low resistance to overcharge past 4.2V,
leaving strings with higher resistance with less SOC.

if it was me i'll charge using a cheap step down DC-DC buck 4.2V charger
and charge the strings one at a time.
or disassemble and buy 2-3 chargers, makes charging 2-3x faster.

 

[rodrick]

Lithium ion + no bms = up in smoke thread

 

[WorldwideDave]

OK fine. I will buy a BMS.

 

[WorldwideDave]

i suppose it's 13s x 3.7V nominal = 48V
li-ion tops at 4.2V
normally, charging voltage is 13s x 4.2V = 54.6V

Charging the pack even at a lower 51.2V regardless of current without BMS
can cause one of the strings with low resistance to overcharge past 4.2V,
leaving strings with higher resistance with less SOC.

if it was me i'll charge using a cheap step down DC-DC buck 4.2V charger
and charge the strings one at a time.
or disassemble and buy 2-3 chargers, makes charging 2-3x faster.

I’m looking to buy a charger, but more importantly of BMS for this 13 S that has Bluetooth. What do you recommend.

 

[hybe022]

I’m looking to buy a charger, but more importantly of BMS for this 13 S that has Bluetooth. What do you recommend.

can't recommend on what's a good bms but a quick amazon search shows that these are popular.
most of them have a big working range. 8s-16s some are 8s-24s.

 

[WorldwideDave]

I did that same search. But I can buy a new battery with a BMS for that price on Amazon. And I don’t think that most electric bike batteries have BMS’s that are this large or need to handle this much current.