Hi there, I recently picked up 2 micro go m8 electric scooters. Whe I brought them home, neither one would take a charge. When I read the output xt60 I get a reading of 37v. I have tried direct connecting to charger thru output, I ha e tried using bench power supply, and nothing seems to work. I then proceeded to open the battery pack. I will supply a pic . Once I got into it, I noticed the b9 wire from the bms is not attached. I have no idea where it goes on this pack as I have never seen this type of set up before. The battery case says it is 10s2p, but I don't know much about the end to end connecting. I tested the pins for all of the red wires, with b10 giving a voltage of 39.9 volts, so I am kinda stumped. I don't imagine it is at lvc with 37v respectively at the output connector, so I don't know. Any help here would be greatly appreciated.
Bms help needed
- Thread starter doublej74
- Start date
A broken sense wire from cell to BMS means the BMS won't be able to read that cell group's voltage.
If the BMS detects a problem with the pack, such as a cell or cells that are no longer matched with the others, or overcahrged or overdischarged, it will turn off the output and often the input to protect the packs against damage that can lead to a fire.
Some BMS that are poorly designed can't tell a sense wire is broken and will read that as a functioning group with whatever voltage is detected and/or it just ignores the group, which can lead to actual cell damage and eventual catastrophic failure in worst-case scenarios. Yours has probably shutdown because of the broken wire. Before trying to fix it:
If you are *certain* the cells are not damaged, and they aren't overcharged or overdischarged, you can troubleshoot the pack and repair it. to make sure they aren't:
The first thing to check is each of the cell (group) voltages, starting at the most negative one, and listing them so you can see them all next to each other. If they are not identical, then the pack is imbalanced, which means that the cells are different in characteristics from each other, and will perform differently. If they are *really* different, by more than a tenth of a volt, the BMS may have shutdown just because of that.
if any are above full charge voltage for that cell brand/model, or below empty voltage, they are damaged and the BMS shutdown because of that. What that damage is and whether it is dangerous is impossible to know until something catastrophic happens, which is why it does this, and why it is not recommended to try to recover such cells.
Once you know what voltages the cells are at, then we can proceed with what to do from there, such as figuring out the physical cell configuration so you will be able to reconnect the wire, etc.
If the BMS detects a problem with the pack, such as a cell or cells that are no longer matched with the others, or overcahrged or overdischarged, it will turn off the output and often the input to protect the packs against damage that can lead to a fire.
Some BMS that are poorly designed can't tell a sense wire is broken and will read that as a functioning group with whatever voltage is detected and/or it just ignores the group, which can lead to actual cell damage and eventual catastrophic failure in worst-case scenarios. Yours has probably shutdown because of the broken wire. Before trying to fix it:
If you are *certain* the cells are not damaged, and they aren't overcharged or overdischarged, you can troubleshoot the pack and repair it. to make sure they aren't:
The first thing to check is each of the cell (group) voltages, starting at the most negative one, and listing them so you can see them all next to each other. If they are not identical, then the pack is imbalanced, which means that the cells are different in characteristics from each other, and will perform differently. If they are *really* different, by more than a tenth of a volt, the BMS may have shutdown just because of that.
if any are above full charge voltage for that cell brand/model, or below empty voltage, they are damaged and the BMS shutdown because of that. What that damage is and whether it is dangerous is impossible to know until something catastrophic happens, which is why it does this, and why it is not recommended to try to recover such cells.
Once you know what voltages the cells are at, then we can proceed with what to do from there, such as figuring out the physical cell configuration so you will be able to reconnect the wire, etc.
OK so I have read the cell voltages, and they are as follows
B1=3.9
B2=7.9
B3=12
B4=16
B5=20.1
B6=24.1
B7=28.1
B8=32.2
B9=36.2
B10=40.3
I figured out where the broken wires go, I am just hoping those readings are OK and the bms shut off due to the broken wires. If someone could confirm whether or not those readings are OK, that would be great.
B1=3.9
B2=7.9
B3=12
B4=16
B5=20.1
B6=24.1
B7=28.1
B8=32.2
B9=36.2
B10=40.3
I figured out where the broken wires go, I am just hoping those readings are OK and the bms shut off due to the broken wires. If someone could confirm whether or not those readings are OK, that would be great.
docw009
1 MW
Looks good to me. Your measurements indicate that there would be no reason for the BMS to work when the broken wires are connected to the proper spots. The allowed range for the voltages is between 3V and 4.2V. Full charge is 4.2V. Minimum charge is 3V.
The BMS stops charging when any cell reaches 4.2V. It stops discharge when any cell reaches 3V. If the cells happen to go below 3V, it stops any future charging. Bt the way, there should also be a low voltage circuit in your scooter controller. It looks at total battery voltage and will shut off the scooter if the total
battery voltage drops close to 30-31V, See how the math works? You had ten cell groups. 10 x 3 is 30 volts,
Hopefully, the BMS resets when you re-attach the wires. Sometimes you have to unplug the connector for the balance wires.
The BMS stops charging when any cell reaches 4.2V. It stops discharge when any cell reaches 3V. If the cells happen to go below 3V, it stops any future charging. Bt the way, there should also be a low voltage circuit in your scooter controller. It looks at total battery voltage and will shut off the scooter if the total
battery voltage drops close to 30-31V, See how the math works? You had ten cell groups. 10 x 3 is 30 volts,
Hopefully, the BMS resets when you re-attach the wires. Sometimes you have to unplug the connector for the balance wires.
If you do the math to get the actual voltages for each cell (group) from your numbers, and they are within the safe limits for your cells, and equal to each other (no difference between them), or at least <0.1v between them, then the BMS probably only shut off because of the broken wire.
If so, then fixing the wire will fix the pack.
If it doesn't, then we'll have to do further testing to see what's going on.
