Battery issue.....but not the normal variety.

[chubbygordito]

Hi all.

I have my ebike with a bottle battery installed, one of the 36v 10ah samsung celled ones.

Anyway, the problem is, within 20 seconds of setting off, the battery cuts out. If I switch it off and on again, it powers up fine.

BUT....it even happens when the battery is off the bike.

Last night I fully charged it.....up to 41.7v. This morning, I switched it on in my front room, and it was dead. Flicked the on/off switch a few times, and the leds on the top lit up. Left it for 5 minutes, came back, there was a brief flicker of the leds, and then it died again. Flick the switch a few times, worked again, still full voltage.

On my way to work it cut out around 5 times.....not even when using power particularly......cycling slightly downhill on a smooth road, it just switched off. Had to stop and turn the battery off and on again.

This evening it was even worse.....it died every 5-10 seconds.....then 10 minutes no problem....then died again. I tried switching it off and on several times, each time the leds only lit up for a second, then went off.....so obviously getting full voltage at first but then drops off.

I've taken the casing off, and no obvious signs of damage or dodgy wiring.

I was thinking either a faulty switch or the circuit board on top??

 

[chubbygordito]

I've checked the switch and its fine. I've checked all the cells, and they are all full and balanced.

When the battery is switched on, on the circuit board, from the last cell output pin #10 (43v), across the circuit board to the main discharge cable there is 43v.

However, when the battery doesn't work, it drops down to 22v, though there is still 43v from the cells.

So, it looks like somewhere in the circuit board there's a problem.

In the past there has been condensation inside.....so maybe its done some damage?

I've ordered a new circuit board....so hopefully that should sort it.

 

[Deleted member 4366]

The 22v isn't a real 22v. It's zero volts. As soon as you connect anything other than a meter, it'll drop straight down. Your BMS (circuit board is switching off. Find where the switch wires connect to the circuit board and bridge the pins/pads to see if it stays on like that. If no improvement, check that the multipin connector (11-way) is properly plugged in. Unplug it and re-plug it anyway.

Some have a temperature sensor that will be connected to the circuit board by two wires, Check the connection to that too.

 

[chubbygordito]

I've bridged the switch pins and it works, 43v output. I then left it for 5 mins without touching a thing....and it had stopped working.

I measured the voltage as I bridged the pins, it jumped up to 43v for less than a second and dropped straight down to 22.

Did this a few times and it suddenly started working again.

I've also unplugged and checked the multipin connector....all looks fine.

All the other connections look fine and I can't see anything obvious.

 

[Deleted member 4366]

Probably a dry solder joint on the PCB. Start with the two switch pins and follow the tracks. Check all the pads along the path - both sides of the pcb if you can.

 

[chubbygordito]

Unfortunately I couldn't trace the tracks.....the underside had a pad glued on to it....no way it was coming off.....and the top side was covered in a black hard glue of some sort....nearly all the connections were covered.....tried to remove it, but it was rock solid.

Anyway, I got an electrician at work to wire up the new circuit board.

It worked for about 20 mins, then smoke started to come out from the middle of the battery pack.

We had a look and it looks like one of the connections inside the ring of cells had corroded and set the plastic wrapping on fire.

I contacted a couple of people who repair these type of batteries, and both said that they won't touch the round bottle style batteries with a barge pole.

Took it to a local bike shop that sell ebikes, he had a look at it, and confirmed the whole battery was pretty shoddily put together....instead of cell connections spot welded....most were just dabs of solder. There were 3 "rings" of cells, one on top of the other, and the connections between each ring were already breaking up with the vibration.

So, I've ordered a custom made battery. Its being made in this country, with genuine Samsung cells, a decent BMS and a 5 year guarantee. Plus its around 50% more capacity....so range should be a lot better as well.

Hopefully within the next few days I'll be back on the bike.

Thanks for your help and advice.