Electronic/ battery help eekk $100 reward

Hiya guys,
Ok story so far, I’ve got a lithium ion 36v electric bike, that is a year old, it just stopped in the rain, the computer head unit will only turn on for 1sec then straight off again, yes battery fully charged, yes connections good/ clean. I can hear a slight click (like a relay) from the battery that’s it, no more clues…The battery also we have rebuilt once as the case was cracked, so I am laying the blame with me and assuming its the battery, which contains the Li-ion cells, a 5cm square circuit board and not much else…HELP! I am happy to pay $100 cash plus parts for a fix, happy to deliver unit/ bike within a reasonable distance of hackspace, happy to pay $50 cash for your time/ diagnosis, and really need it done asap, as my legs are knackered riding without the electric assist!
Thanks, guys hope someone can take on the challenge. Tim.

Give it long enough, and you might find your legs don’t need the electric assist. :slight_smile:

In all seriousness though… when you say the battery is charged, have you actually measured the cells to see what voltage is appearing? Or are you going by the charger’s behaviour … as they can lie.

The 5cm square board looks like it should be the battery management system… there should be a connection to each “tap” of the battery pack. Measuring between each bank of cells, you should see ~3.2V on each bank.

will check that thanks

Ok found the problem:

I’m the control circuit for regulating the power input and output one of the transistors (the one on the left) gates has much higher resistance at about three mega OHMs and the other three only have one mega OHM of resistance so I think that the left one has blown or is broken. So if anyone knows what the serial number is for the transistor than please respond and tell me as I am finding it hard to find a circuit diagram that shows the serial number for that part. Sorry if this does not make sense as I am not great at fixing circuits.

On the other side of the Transistor, there should be some writing to help you find a replacement part.

I’d de-solder and replace the lot.

  1. places like RS will likely only sell several to you
  2. you don’t know how close to failure the others are

To me that board looks very much like it’s a charging/balancing board for the battery. It’s hard to tell from the photo but it’s likely all those devices are in parallel. Easiest way to tell if that board is working properly or not is to plug it in, try to turn the bike on and measure the output voltage. If it drops to zero, that’s your problem.

It’s supposed to protect against undervoltge, so as the bike turns on the fault may potentially be elsewhere.

I’m happy to have a look at it, will you be in on the weekend?

Paralleling MOSFETs is a black art. Did enough of that in a previous life; fun and games when one MOSFETs ON resistance measures at 1mOhm and its mate measures at 2; guess where the 400A DC goes? :slight_smile:

(If one is not careful… up in smoke with a loud BANG!)

I will be there tomorrow afternoon please tell us a time when you will be there after 1pm

I’ll be in 1pm onwards too.

Ok thanks everyone for helping battery fixed