Battery shows full charge when tested, bike wont turn on

[sladd]

been having battery issues, first battery has been only charging to like 57.5v max, now battery has full charge but but won't turn on bike, tested battery with volt meter reading 56v

thought maybe controller, did some troubleshooting, then hooked up another ebike battery that I had and everything came on, so 100% this battery, weird how it has a near full charge when tested but won't power up bike, anyone know a reason or cause a charged battery won't allow bike system to turn on, damaged cells?

my other battery was 55v and turned right on.

I tested battery while on cradle on wire end XT90 connector and the metal terminals directly underneath battery both voltage readings are the same

any ideas why a charged battery isn't powering up bike?

 

[E-HP]

Are the batteries lithium ion? What is the nominal/rated pack voltage? Are the two batteries otherwise identical?

 

[fechter]

Possibly the BMS is tripped for some reason. Try placing some kind of load on the battery while measuring the voltage. If the voltage drops out under load, the BMS isn't happy. To test more, you'll need to take apart the battery to get access to the BMS. If any one cell group is out of range, the BMS will trip off.

 

[docw009]

Maybe your bike's controller has a 56-57V overvoltage circuit? I don't believe most discrete controllers put these in, since they can put a 48V label on the box for free. Some middrive controllers have them,

 

[sladd]

Are the batteries lithium ion? What is the nominal/rated pack voltage? Are the two batteries otherwise identical?

both batteries are 52v lithium ion

 

[sladd]

Possibly the BMS is tripped for some reason. Try placing some kind of load on the battery while measuring the voltage. If the voltage drops out under load, the BMS isn't happy. To test more, you'll need to take apart the battery to get access to the BMS. If any one cell group is out of range, the BMS will trip off.

thanks I'll have to consider that as a cause

 

[sladd]

Maybe your bike's controller has a 56-57V overvoltage circuit? I don't believe most discrete controllers put these in, since they can put a 48V label on the box for free. Some middrive controllers have them,

controller is BAC 855 rated up to 72v I believe, set for 52v battery (58.8v)

 

[E-HP]

both batteries are 52v lithium ion

If the pack doesn’t reach the full 58.8v before it stops charging, then there could be one, or more, cell groups that have bad cells, tripping the BMS off. Assuming the other cell groups are able to reach 4.2v, then at 57.5v, the non performing group would be at 2.9v. At 56v it would be at 1.4v, either of which would likely trip the BMS. Partially disassembling the pack in order to measure each groups voltage may be necessary.

 

[sladd]

If the pack doesn’t reach the full 58.8v before it stops charging, then there could be one, or more, cell groups that have bad cells, tripping the BMS off. Assuming the other cell groups are able to reach 4.2v, then at 57.5v, the non performing group would be at 2.9v. At 56v it would be at 1.4v, either of which would likely trip the BMS. Partially disassembling the pack in order to measure each groups voltage may be necessary.

ty for the info

 

[amberwolf]

been having battery issues, first battery has been only charging to like 57.5v max, now battery has full charge but but won't turn on bike, tested battery with volt meter reading 56v

If it has been charging to a lower and lower voltage, that usually indicates the cells inside are not matched to each other so they're getting more and more unbalanced (different in voltage and charge state). At some point, the difference can be enough to trigger a properly-designed BMS (they aren't all) to turn off the output (and often the input) to prevent use of the pack, since enough difference between the cells can mean a serious pack failure that could lead to a fire.

Most batteries are not made of matched cells, but if it has a balancing BMS, leaving it on the charger longer can temporarily correct the unbalance (it doens't fix the root problem, which requires replacing all the cells with ones that have matched characteristics). It can take hours, days or much longer to fix such a problem depending on how different the cells are, and the charger will typically turn off and back on repeatedly during the process.

If there's no balancing function, the imbalance just grows worse and worse until some cells are at full voltage (turning off the charge process) while others can be nearly empty, so any load on the pack causes those near-empty cells to drop below LVC and the pack turns the output off. When the load is removed the cells rise in voltage a bit and clear the LVC, so the BMS turns the output back on, and it appears to be full or nearly full, so it doens't seem like a battery problem.

thought maybe controller, did some troubleshooting, then hooked up another ebike battery that I had and everything came on, so 100% this battery, weird how it has a near full charge when tested but won't power up bike, anyone know a reason or cause a charged battery won't allow bike system to turn on, damaged cells?

my other battery was 55v and turned right on.

I tested battery while on cradle on wire end XT90 connector and the metal terminals directly underneath battery both voltage readings are the same

Is that while the controller is being turned on?

When the controller is "on" it draws more current than when off, and if the battery has a problem where the BMS has turned off the outputs, the "ghost voltage" you can often see on the output in this state will drop (usually rapidly) to nothing or near nothing once a load is applied to the battery.

 

[docw009]

If you can get your voltmeter onto the controllers plus/mnius wires when the battery is turned on, you'll get more clues on what's wrong.

 

[sladd]

If you can get your voltmeter onto the controllers plus/mnius wires when the battery is turned on, you'll get more clues on what's wrong.

thanks good tip