New Ebike battery bms completely dead or overcharge?

[500w_Of_Power]

I fully charged my brand new never run ebike battery, and let it sit for a week, the charger says its fully charged, but no voltage is coming out of the battery- nothing turns on, checked with multimeter, nothing! Other batteries turn it on.

It is a Cao MM 48v 20a battery.

 

[calab]

where are you measuring the voltage, at the battery or at the bms?

 

[500w_Of_Power]

From the Battery.

 

[500w_Of_Power]

The battery has voltage, but it is being cut off from the negative wire.

 

[glennb]

If the charger’s definition of charged is when the current drops below a threshold, rather than battery voltage having risen to a threshold, the battery is not necessarily charged (fully/properly).

It’s too early to tell where the problem lies. I’d recommend starting with the following steps:

1. Measure the charger output.

If it’s less than 13 x 4.2 volts you’ll need to perform further charger troubleshooting.

If it’s slightly higher, connect it to the battery again and confirm that it indicates that the battery is fully charged. (If it indicates charging, wait for it to finish).

2. Disconnect the charger and measure the battery voltage.

If it measures less than [(13 x 4.2) -2] volts, the BMS is likely detecting a bad (low) group of cells, and you’ll need to perform further battery troubleshooting.

If the battery is around 13 x 4.2 volts, you’ll need to perform further BMS troubleshooting.

 

[docw009]

I believe the Cao MM 48v 20a battery is a shrink wrapped pack. Do those guys offer any warranty support? I wouldn't cut it open yet, as that might kill any warranty, although I would be surprised if you get much support.

Possible causes if you have to open it up.

-Bad connection to one of the BMS balance wires or maybe a thermal switch. These could be fixed.
-One of the 13 groups is out of range on voltage. BMS detected it and shut off. You don't want the battery if this happened.
-Defective BMS.

 

[500w_Of_Power]

I believe the Cao MM 48v 20a battery is a shrink wrapped pack. Do those guys offer any warranty support? I wouldn't cut it open yet, as that might kill any warranty, although I would be surprised if you get much support.

Possible causes if you have to open it up.

-Bad connection to one of the BMS balance wires or maybe a thermal switch. These could be fixed.
-One of the 13 groups is out of range on voltage. BMS detected it and shut off. You don't want the battery if this happened.
-Defective BMS.

I will check the BMS wires, too late to open the battery. As glennb mentioned, I will check the charger. I don't thing the voltage is too low, I plugged in a 36v battery and it turned on. The BMS is not getting a connection from one wire. Also, what is 13 groups?

 

[500w_Of_Power]

Oh its the 13 groups of cells in the battery.

 

[E-HP]

Is there voltage at the charging input of the battery pack?

 

[500w_Of_Power]

I will check, I am in school right now so it will be a while until I can look.

 

[500w_Of_Power]

Ok, I am back, I get 6.5v out of the discharge port, Bms plug is fine, What do I do next? How should I measure voltage?

 

[500w_Of_Power]

I just returned the battery I don't wan my house to burn down if I screw up.