Getting sparks

[Chinolatino17]

Hey guys

I bought a new battery pack for my Xiaomi scooter but realized the connectors were different. I cut the connectors from the old batteryand tried replacing them into the new battery pack. I was able to connect the discharge plug wires but when I tried wiring the charging plug wires I got a big spark and smoke . Can someone tell me what I am doing wrong ?

 

[lifepo4ever42]

Hey guys

I bought a new battery pack for my Xiaomi scooter but realized the connectors were different. I cut the connectors from the old batteryand tried replacing them into the new battery pack. I was able to connect the discharge plug wires but when I tried wiring the charging plug wires I got a big spark and smoke . Can someone tell me what I am doing wrong ?

you just blown the bms

 

[harrisonpatm]

Triple check polarity. This can happen when the battery is connected to the controller incorrectly

 

[Chinolatino17]

Triple check polarity. This can happen when the battery is connected to the controller incorrectly

I just checked and the polarity is correct but it’s showing 40 volts . The battery is a 36v

 

[99t4]

I just checked and the polarity is correct but it’s showing 40 volts . The battery is a 36v

Might be OK. Assuming it's a Li-ion battery, fully charged is 42v.

Some charts:

Li-Ion Ebike Battery Charge Charts

Whats an 80% charge on a 48v battery? These charts give answers to questions like this on common ebike battery voltages: 36v, 48v, 52v, 60v and 72v.

talesontwowheels.com

 

[Chinolatino17]

Ok thank you for sharing. Should I attempt to connect the wires again ? Should I start with the positive first ? I don’t recall which one I started with the last time .

 

[amberwolf]

Hey guys

I bought a new battery pack for my Xiaomi scooter but realized the connectors were different. I cut the connectors from the old batteryand tried replacing them into the new battery pack. I was able to connect the discharge plug wires but when I tried wiring the charging plug wires I got a big spark and smoke . Can someone tell me what I am doing wrong ?

If it happened while *wiring* the charging plug, then the most likely thing is an accidental short between the wires with your tools or the wires themselves.

If it happened while connecting the charger to the charging plug, the most likely thing is wrong polarity in the wiring somewhere, or the wrong voltage battery being connected to the system (too high for it).

WHere *exactly* did the spark come from, and *exactly* where did the smoke come from? Those are extremely important, because they tell you where the problem is.

 

[Chinolatino17]

It happened while wiring the charging plug (the one on pic). The spark and smoke both came from the wire at the connection point .

 

[amberwolf]

If the plug wasn't connected to anything at the time, then either the two wires touched, or your tools connected the wires, or there is a short between the two wires inside or at the entrance to the connector itself.

If the plug was connected to something at the time, then it could be wrong polarity or whatever it is connected to is shorted somewhere along the wire path within the cable sheath between your connection and the connector.

There's no way to get a spark (meaning current flow) without an electrical path, so the path would have to go from the wires you're connecting thru a short somewhere between the wires you're connecting and the end of the connector or whatever it was plugged into.

You can measure just the connector and it's two wires, not connected to the battery, with your multimeter set to 2 ohms or continuity. Doesnt matter which lead is on which wire. You should get no beep or tone, and a maximum reading, usually 1. or OL or similar (check your meter's manual for what it shows on open circuit). If you get anything else, it means there is a short between the connector pins or wires, so you would need to fix that before you can connect it to your battery.

If the spark was large, with smoke, it almost certainly left arc flash or heat damage at the short circuit point, so you can carefully examine the cable and connector for this to find the short.


If the short was sufficient current, it could have damaged the battery's BMS, as they usually have no protection against reverse current (discharge) thru the charge port. Usually this failure is stuck on, so you'll probably still read correct voltage at the charge port, but the BMS won't be able to turn that port off anymore when charging once any cell reaches HVC, so it could then overcharge cells.

Just to be careful, I recommend monitoring all the cells during charge the next few times you charge it up, to make sure none of them exceeds HVC (usually 4.2v or less for Li-Ion), and that the charge port turns off (the charger usually shuts off too) when any cell does reach that point.

 

[Chinolatino17]

Thank you so much for your detailed answer. I did check both the plug and wires for continuity. I got a reading of 1. I then inspected all the wires for arc flash or heat damage but did not notice anything at all. I can only assume that somehow I must had created the short while connecting the wires . I just can’t recall doing it but if there is no other way then that must have been it . Thank you again for your help on this .

 

[Voltron]

Just checking, you're sure the positive/ negative polarity is right using your meter?

 

[amberwolf]

It's good to check that, but per their other post they had the problem just wiring up the connector, not plugged into anything, and polarity would not matter for that.

 

[calab]

Open the battery up and triple check the votlage at the battery itself, not any wire.
Look for black spots
You might have friend the bms, in that case take the bms off, reattach the battery wires and see if it will work.
Remember to be safe and triple check everything, confirm the positive red side voltage right at the battery, same with negative black voltage. Check each string of battery if there isnt stuff glues to the tabs. If there is stuff glued, you can slightly press and wiggle the probe to make contact with the tab but thats were I would start. Check polatirity at battery, with no wires or bms inbetween. Check battery to battery connector continutuity.