Hailong 36v 21Ah battery fault

[Phil H]

Good morning all and hoping for soe help please.

36v 21Ah coupled to Bafang 250w mid drive, 850c display on a Boardman hybrid frame. Have done thousands of miles on it. Love it.

I left it on charge over night. Don't normally but forgot to switch off before bed. Green light in the morning anyway but the battery has not worked properly since. I was thinking over charged!

Battery powers on and off. Got 42.7v at the output. Put it on the bike and get the briefest 'hello' and then nothing.
Tried with my wife's 15Ah Hailong - perfect.

Googled and thought BMS. Bought one and fitted at the weekend. Quite a faf but done and the battery works. Popped it on the bike - perfect but.... went less than half a mile and boom - nothing. Brief flash of 0% battery and since just the 'hello' and then off. There is an audible click when trying to power on from the display

What's going on please? Really unhappy without the bike and would prefer to avoid buying a new one if possible!

Many thanks
Phil

 

[addertooth]

If you have replaced the BMS, you are pretty much down to bad cells, or a bad connection, possibly where the battery slides into the base, or where it plugs into the controller.

 

[Phil H]

Many thanks for the reply. What’s the test for bad cells? I am reasonably practical and understan electrics but unsure how to test without taking all the cells apart.
Maybe that’s what has to be done?
What am I looking for for a cell to be bad?
Kindcregarfs
Phil

 

[Phil H]

mmmmm. We live and learn. Wondered about the connection, an easy fix if it was. Put my knee into the side of the battery and presto. Have popped some tin foil into the sockets and we would appear to be running.
Thankyou for the suggestion. Annoyed I did not check this myself first of course. Getting all the silicone away to replace the bms is not a trivial task and it would appear something that did not need doing.
If anyone wants tips on replacing though I would be delighted to comment
Regards to you all and especially addertooth.
OAO
Phil

 

[addertooth]

You might consider improving the bond between the "foil" and the cells. If it was intermittent before, it will be intermittent again. There are inexpensive "battery spot welder" products on eBay.

p.s. sorry for not responding to your follow-on questions. Where I work during the day, we are not permitted recreational use of our computers. For responses, this leaves early mornings before work, or the evenings (if my spouse does not have need of tasks performed).

 

[Phil H]

No apology needed and thankyou for the replies.
The fault was between the battery and the bike itself - the fitting the bttery slides into. Agreed the foil solution has potential to be troublesome and will do something more elegant when I can. In the meantime I am carrying a strip of foil just in case!!
All the best to you
Phil