Battery fell out of bike and now having serious issues !!!

[kopngo007]

BIKE : 52V X CLASS WITH A DC MOTO CONTROLLER AND S900 LCD .


Had the bike running great Was getting ready to park for the night and I forgot to lock battery. Battery fell out while I was moving it into my garage . I was walking it as it fell out . THE BATTERY IS IN A HARD CASE .but of course . I went to put it back in and turn on the bike and the display did nothing . I pressed the battery meter button and it don't light up and it don't show full bars like it did before the battery fell .And when I plug charger in
It just stays green .

I decided to take voltage reading at the battery connection terminal ( the terminal pin on the outside that connects to bike)
I only get 2.7v - 2.9v at the terminal ..but I know the battery is fully charged because it was just reading 56-57 v on the lcd display
After getting frustrated over not getting voltage anywhere on bike with battery plugged in
I decided to remove the battery and take apart the hard plastic shell case that protects the cells and BMS and see if connection is loose or broke but it looked fine .
I seen that I could disconnect the battery pack from the pin terminal and it also has a USB port and the voltage battery meter chipboard you can disconnect as well when I check the voltage it reads 50.4 v which is better but still seems not normal for a full charged 52v battery
Now when I reconnect to the chipboard with the battery meter and the USB port
Seems like something is shorting out the voltage because it reads the 2.7 to 2.9v again All I see is a USB port and the battery meter level lcd power wires between the pack and the pin connection and when I disconnect those I get a voltage reading but it still don't power the bike
I Tried reconnect the battery without the USB and battery meter chipboard to see if the 50v reading would turn the bike on but still nothing ..
Could this be a bad BMS or Bad cell from the impact.?

The battery case is super rugged I don't see how a fall from the frame height could cause a problem like this ? But maybe it's poor craftsmanship . And my dumb move for not locking the battery .

Maybe someone could help me diagnose this problem or anything to point me on right direction ! Thanks

I can take pictures if that helps

 

[offGridDownUnder]

bad BMS or Bad cell from the impact.

Do not leave that battery connected or on charge when you are not there to disconnect it and call emergency services.
Don't store that battery anywhere a fire can start.

Unlike most other battery chemistries, several of the most common Li-ion chemistries are capable of a positive feedback loop called "thermal runaway".

You already know it was physically damaged and that something is wrong. Read up on battery fires before you object.

 

[kopngo007]

Do not leave that battery connected or on charge when you are not there to disconnect it and call emergency services.
Don't store that battery anywhere a fire can start.

Unlike most other battery chemistries, several of the most common Li-ion chemistries are capable of a positive feedback loop called "thermal runaway".

You already know it was physically damaged and that something is wrong. Read up on battery fires before you object.

I checked all the cells and they are good . No physical damage and reading the correct voltage . The battery took a fall inside a rugged plastic case . The pack itself was protected and has NO dents , cuts or damage .

 

[docw009]

The BMS will isolate the cells from the outside world if it detects any voltage problems on the 14 cell groups in a 52V battery, You think you read 2.9V, that's just leakage across BMS. On most of them they switch the wire to the outside ground on and off.

The BMS has a harness connecting to every cell group to monitor voltage, It expects the voltage on each cell group to be between 3.0 and 4,2V. If it goes below 3, it shuts off. If one or more wires fall off, it also shuts off, A fall is unlikely to break wires, but it can knock the harness connector out of its socket. Might even crack a BMS circuit board. Who knows.

Working on a battery is risky, Lots of energy in those cells, You know to be cautious. I would check all 14 cell groups for voltage and uniformity. Reseat the ribbon connector if I can. If that doesn't get it working, it's probably the BMS.

There still could be other damage to the battery, which is why we heed offgrid's warnings, Work on it and store it in a place where it won't burn your place down if it goes up in smoke.

 

[kopngo007]

The BMS will isolate the cells from the outside world if it detects any voltage problems on the 14 cell groups in a 52V battery, You think you read 2.9V, that's just leakage across BMS. On most of them they switch the wire to the outside ground on and off.

The BMS has a harness connecting to every cell group to monitor voltage, It expects the voltage on each cell group to be between 3.0 and 4,2V. If it goes below 3, it shuts off. If one or more wires fall off, it also shuts off, A fall is unlikely to break wires, but it can knock the harness connector out of its socket. Might even crack a BMS circuit board. Who knows.

Working on a battery is risky, Lots of energy in those cells, You know to be cautious. I would check all 14 cell groups for voltage and uniformity. Reseat the ribbon connector if I can. If that doesn't get it working, it's probably the BMS.

There still could be other damage to the battery, which is why we heed offgrid's warnings, Work on it and store it in a place where it won't burn your place down if it goes up in smoke.

Appreciate your time writing this . So I checked all 14 white wires coming into the harness connector and I get consistent 3.7 volts from wire 2 to wire 13 the 1st and 14th white wire gives me 3.1 volts on both .. the bms has the same voltage as the packs 50.6 volts so I'm not sure if the BMS is just faulty at this point ? .

 

[amberwolf]

If you see more than 0.1v difference between cells, correctly working and designed BMS will shutdown the whole pack to prevent further cell damage that can lead to a fire.

Cells that are that different in votlage are very different in properties, whether the result of pack aging or of the impact..

The most likely thing that would be a result of impact damage is that there are interconnects between cells within the parallel groups that have disconnected, leaving those groups with less capacity than the rest. Possibly even a momentary or temporary short occured across those groups, discharging them partially (pinched balance wire, etc).

Or that a connector or wire has been damaged.

If your BMS shows the correct pack voltage (from the B+ wire to the P-, and from the B+ wire to the C-), but there is no voltage at the main external pack terminals, then most likely the BMS itself has not shut off and is not defective (though it is poorly designed allowing it to work with that much voltage difference between cells). In that event it's possible that a fuse has blown or been broken or dislodged within the holder, if your pack has one, or a switch or connector has failed internally.


All that said, a pack that has suffered physical impact and ceased working at that moment does have some form of damage, somewhere, and it is not uncommon for there to be interconnect problems or internal cell damage that can cause further problems later on, some of which can lead to a fire.

I would recommend that even if you keep using the pack, you NEVER trust it, and always monitor it when in use or when charging, never leaving it alone, and storing it in a fireproof location away from any residence, etc. Just in case.

 

[docw009]

If you see more than 0.1v difference between cells, correctly working and designed BMS will shutdown the whole pack to prevent further cell damage that can lead to a fire.

Cells that are that different in votlage are very different in properties, whether the result of pack aging or of the impact..

This is likely true for automotive battery controllers, but from what I have seen personally, and also from user posts here, I believe most non-smart ebike BMS do not check for group-to-group variation. They will stay on, as long as each group is above low voltage cutoff.

WHen you have the ability to read individual channel voltages as opposed to simple voltage comparators, then you can make decisions based on voltage differences. It doesn't cost much more to do that, but neither do balance circuits, and many ebike packs don't do either function.

 

[amberwolf]

True, it is likely that the cheapest crappiest packs don't have any of the smarts needed to do the Voltage-delta check, but it doesn't take much of a chip to do this even if there are no balancers. I don't know which BMS chips have this test built in; tried to look them up but none of the usual parts sites use this as a sortable parameter, and I don't have enough time to look up and read thru dozens of datasheets.

That said, there's been a number of battery / bike / etc troubleshooting threads over the years , including for little scooters, where their battery has stopped working and then it's found that voltage measurements exceed 0.1v difference. In some of the cases the person was able to manually recharge the low group(s) to better match the ohters, and the pack woudl then start working again. (often tehy're not capable of doing that for one reason or another, so we don't know if that would fix it and thus if the BMS had turned off specifically for that reason...but it was likely).

I expect that even for ultra cheap packs it's more and more likely as time goes on that this function will be built in even for all the cheapest of the cheap ones where they didn't buy into external parts like balancers, as long as they have a BMS at all.

But we'll generally never really know, as almost no one is willing to dive into their BMS electronics to see what chip it has (and if documentation even exists for the chip) or do detailed testing to find out what the BMS is capable of.

 

[kopngo007]

Thank you all for the replies. I ended up doing a complete diagnosis on all connections and found that one side of the BMS was not getting the right voltage . So I jumped from a lead that was giving me the correct the voltage over to that pin and surprisingly everything was fixed. Maybe wire broke somewhere between the BMS and the pack but that was literally the only wire giving faulty voltage . Every other wire was correct. Thanks again everyone !!!