I bought a used ebike 350w 36v cheap. The battery is good i tested it and it went for about 20 miles, But i went down all the way to get all the juice out (test), and the battery shuts down at 30v. But when i try charging it, it seems it wont take charge. So i knew the bms shuts completly down at 30v. I charged it directly to battery (by pass bms) with lipo charger, then bms turned back on, and charged fine again with its own charger. Maybe bms bad? How can i avoid bms from shut down, one way to go is charging it at 32v, and avoid bms shut down. I'm planing to sell it back, and don't won't problem with the seller later...
-
Howdy! we're looking for donations to finish custom knowledgebase software for this forum. Please see our Funding drive thread
Bms shuts down at 30v and then won't charge
- Thread starter hamid120
- Start date
kdog
10 kW
I gather this was just a test. It may not be the bms. Some chargers won't start charging unless a voltage is present on the battery leads. If the charge and discharge ports are the same on your bms then the voltage could be too low for the charger to recognise once it trips. I'd charge it gently using an external source, whilst it is on your charger. Then you can see what voltage it turns back on at.
hemo
100 W
32/33v min discharge. The bms will look at total accumulated voltage across whole battery, going to 30v means one cell group or more went below 3v and remained so at rest and bms then wouldn't then allow the charging process to begin.
The fact you by passed the bms to increase the voltage then recommenced normal bms/charger charging indicates this and cell group lvc was too low to allow charge switching.
The bms is fine and doing it's job it was programmed for, the fault is yours for allowing the DOD to go so low.
Ideally you need a controller that allows a higher lvc level of 31- 33v to help protect the battery better, even with cylindrical cells there is little mah left below 3.2/3.3v for any real ebike usage except to use as bike lighting.
The fact you by passed the bms to increase the voltage then recommenced normal bms/charger charging indicates this and cell group lvc was too low to allow charge switching.
The bms is fine and doing it's job it was programmed for, the fault is yours for allowing the DOD to go so low.
Ideally you need a controller that allows a higher lvc level of 31- 33v to help protect the battery better, even with cylindrical cells there is little mah left below 3.2/3.3v for any real ebike usage except to use as bike lighting.
With many BMS boards, once it trips and shuts down, you have to disconnect the load (controller) in order to make it reset.
I have one that won't reset even when you do that and has to be charged through the discharge port to make it reset. This is a design defect. I corrected it by installing a push button the connects the B- to P- through a 100 ohm resistor. If the BMS trips, pushing the button will reset it.
I have one that won't reset even when you do that and has to be charged through the discharge port to make it reset. This is a design defect. I corrected it by installing a push button the connects the B- to P- through a 100 ohm resistor. If the BMS trips, pushing the button will reset it.
dogman dan
1 PW
It could be a poor match between a functioning bms, and a working charger. The charger won't start till above 32v for safety, but the bms lets it get below. Hopefully finding a charger that will start at 30v will fix it, but tell the customer its best if he stops at 33v, or even 34v. He'll need a voltage display to do that though, since the damn bms lets it go too low.
Similar threads
