Abnormally large spark, burned me. What's going on?

Back in January 2013, I was visiting the Bafang factory when Yonree showed me a new prototype - the BBS01. Riding it in suit and tie in freezing weather, I asked him to sell me the first production model when it came out. Three months later, they sent me serial number 17, which I wrote up in this forum. After 6 months testing, we did a group buy of 27 motors with EM3EV batteries. I had to convince Paul to give Bafang a second try (helped by introducing him to Yonree - in China it's all about who you know), and had the motors sent to him for shipping along with the batteries. All were 36V except for one 52V that I wanted to try.

Fast forward to 2020, and the 36V batteries are all giving up the ghost, but the 52V had a different problem; the charger quit. Paul sent me a new charger and better connectors than the six-year-old versions, and yesterday I finally got around to putting it all together on a 1999 Mercedes belt drive bike I picked up online.

All was going well until the final link, connecting the positive battery wire to the positive motor controller wire. Using gold bullet connectors, it did not just spark, it gave me a welding-level blue flash that turned my hand black and raised a nasty burn on my thumb. First took some aloe vera growing by the garage to deal with the burn, and then tried to work out what was going on.

I took very heavy battery switch from a jumper pack and wired it in line. Replaced the burned bullet connectors. Battery tested 57V. I tested the positive battery switch feed by grounding the voltage tester to the negative battery bullet connector: 57V as expected. Wearing welding gloves, glasses and welder's jacket, outside in case something blew up or caught fire, I turned the switch on. It made a slight sound but nothing happened. No fire, no heat, very anticlimactic. Pressing the display power-on button, the display did not come on. Turned it off, using the voltage tester, turned the heavy power switch on: zero voltage. At that point, I quit, removed the battery and motor, and cannibalized one of the guest bikes 36V motor and battery which works fine except the power stops if I draw full power (old battery problem).

Does anyone know what would cause such a flash? The flash was like what happens when accidentally touching positive to negative on a car battery, except that should have overheated or melted down something when the heavy on-off switch was switched on.

I am mechanical, but not electrical-oriented. I know the basics of using electrical testing equipment, but not confident to take apart a battery or do more than simple soldering. It may be that at 6 years, I've got my money's worth out of the group buy (I did buy a new 52V battery/BBS-HD kit from Paul when the charger problem cropped up, so my main commuter bike is running fine), but I would like to keep these guest bikes going if I can.

A bad controller perhaps, like maybe it had some internal component damage like in a filter array on the pcb.

My guess is you managed to discharge a large capacity capacitor somewhere somehow.

That big POW has happened to me on several occasions where I plugged the battery charger in to the 110 outlet prior to hooking up the charge lead. After the second time, I don't do that anymore! I plug the charger into the battery PRIOR to plugging the charger in to the wall outlet.

AHicks said:

My guess is you managed to discharge a large capacity capacitor somewhere somehow.

That big POW has happened to me on several occasions where I plugged the battery charger in to the 110 outlet prior to hooking up the charge lead. After the second time, I don't do that anymore! I plug the charger into the battery PRIOR to plugging the charger in to the wall outlet.

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Hopefully that was a good quality built charger, hate to see what would have happened with a cheap charger.

When you have a welding spark high enough to burn your hand it is not only charging a capacitor, it is a short. Something is shorted inside and you must not try to plug it again, not before you had solved the problem.

Yep, you plugged into a short. Classic KFF.

Maybe the controller was wired backward? More likely it was just defective. Bet if you open it up, you see where the short was. Sounds like the stray blob of solder rattling around in there melted, and no longer is shorting the now killed controller.

The spark was not the charger. It was reassembling a bike where the final step was to plug the battery cables into the BBS02. The first time it sparked and I instinctively pulled back. Figuring I was going too slow, I tried again, controlling the instinct to pull away, and it turned into an arc welder. But when I then wired in a very heavy battery switch, nothing melted or flashed. If it was a proper short, I would have expected smoke (which is why I did the test outside, wearing heavy protective welder's gear). Except for a slight noise when turning the heavy switch, nothing happened. No heat. No smoke. But when I pressed the BBS start switch, no joy.

Since it is a 2013 version motor, I may be better just adding it to the ever growing pile of dead motors (four so far) rather than try to replace the controller.

I also am accumulating quite a collection of 2013 dead batteries. They still work, but the draw then shuts off the motor. Probably a few cells are too weak and the BMS kicks in. None of the batteries have a lot of cycle hours. It appears they die from age rather than use. We have 6 bikes, some for house guests, and are down to one remaining good 36v, one marginal 36v that works until I press the thumb throttle which draws too much power, and a new 52 volt just bought from Paul at EM3EV that is amazing (albeit heavy). Any idea if a battery guy can take the old stock apart and replace cells, or are these batteries ready for recycling?

Your switch is hiding the spark/short (inside the casement of the switch) everytime you use the switch, the switch will not last long.

Your battery pile needs to be looked at, ask yourself why the batteries are not lasting. Are you charging to fast, are you discharging the batteries to much, are you buying quality batteries.

I thought it was non working now, and the spark went away.

Thats cuz the short melted away, and or killed a circuit inside. Bet it was a loose blob of solder in the controller housing.

Yes it’s a dead short. I’ve had this a couple of times with my 27ah 120v pack. And they give some nasty burns. One from a controller failure and the other on the charge cables were obviously to close in connector. It blew the terminals to nothing both times.

Do they not believe in fuses in China?

A 5 cent 40A car fuse would have prevented this.

Comrade said:

Do they not believe in fuses in China?

A 5 cent 40A car fuse would have prevented this.

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Yeah thats the running joke that EVERYTHING in China is generic/counterfeit/junk, which is obviously not true there are tons of high quality products coming out of China. Most people do not want to spend the money, which is why Walmart and Dollar/rama/tree are so popular. Even products like this, I am sure are being made in China.

In any integrated mechanical units, where (in that particular case) controller, motor and gear reduction are enclosed in a compact casing, there is a higher risk of failure. Just swapping 2 different screws in assembly can result in a short, for an example. Those BB drives are toys, often not worth the repair.