Battery help

[philmalaguti038]

The battery I don't have near me for the next few weeks but it is a 72 volt 50 aH that came from a rumble air ss ebike that had a sabatron 150 controller in it.. ... I was wondering with out seeing what the cells are at the moment is there any way of knowing what the amperage range of the battery could possible be with the right bms in it?? Like if it had 50c cell or some other cell.. I'm just curious if I brought a to small bms at say 80 amps if the battery could be up in the 150 to 200 nominal output with the right bms in it? Thanks for any help

 

[amberwolf]

if the battery came built on a prebuilt company-m,ade bike it is usually safe to assume the cells are barely capable of what they were already being asked to do.

what was the current limit of the system originally? i'd assume that's all it can do, especialy if it's used or aged (not absoutley brand new just manufacturered) as the cells will have degraded from their factory capabilities.

same with all of the internal battery interconnects, wiring, etc.

 

[philmalaguti038]

I got the bike from a friend who only had it for like 3 months but someone happened and when I got it I figured out the stock bms something happened cause it discharged the battery to a point where it wouldn't register.. So I took that bms off and used my hobby charger and charged so the groups back up then installed a bms and it has been working fine.. so it was a pretty new battery considering.. but I think the BMS i put in was to cheap and I could possible have more amps if I put a better bms with Bluetooth too. The Bike was a Rumble Air SS 72 volt 50aH.. I couldn't find much info online about the setup.

 

[99t4]

I was wondering with out seeing what the cells are at the moment is there any way of knowing what the amperage range of the battery could possible be

No way to know, we'd just be guessing.

it discharged the battery to a point where it wouldn't register..

OK here you have to start getting really careful because the cells could have discharged beyond their safe limit, which means possible fire and explosions in future charging and discharging usages.

 

[amberwolf]

the stock bms something happened cause it discharged the battery to a point where it wouldn't register.

Or...something was already wrong with the cells, and the bms turned off the pack to protect you from damage that can lead to a fire.

 

[philmalaguti038]

No way to know, we'd just be guessing.


OK here you have to start getting really careful because the cells could have discharged beyond their safe limit, which means possible fire and explosions in future charging and discharging usages.

Which when I disassembled the battery I took it out of the aluminum case so I could use my multimeter and test the cells.. I charged each group with my hobby charger to 4.2. I did that 20 all the groups and waited a few days to see if they ask stayed at the 4.2 which they did.. So then I put a new 80 amp bms just some cheap no name one on it.. The battery works but I'm wondering if I should replace the BMS again with a better one. The battery is made out of 21700 cells I know that..

 

[amberwolf]

Which when I disassembled the battery I took it out of the aluminum case so I could use my multimeter and test the cells..

What were the cell voltages measured before any thing was done to them?


As far as replacing the BMS, that depends on the functions you already have vs the ones you want.

Either way, you wouldn't want to put a higher current BMS on it than it started out with from the factory, unless you know *for sure* that the cells were designed to take the higher current.

 

[philmalaguti038]

I just got the bike back and looked at the cells "Lishen 21700-LR21700SA 12A Flat top 4000MAH" any help figuring out the max amps from that for me.. Please and thanks for the help

 

[BatteryMooch]

I just got the bike back and looked at the cells "Lishen 21700-LR21700SA 12A Flat top 4000MAH" any help figuring out the max amps from that for me.. Please and thanks for the help

The datasheet (below) rates them at 12A at room temp up until a bit warm and 6A above that with a 60°C max temp limit. In a pack it’s easy to get hot enough (45°C) to need the derating down to 6A continuous.