Thompson K2

[dylan]

Hi Guys
I have been given a Thompson K2 electric mountain bike.
It's basically new from 2007 & has just been left sitting unused in a garage.
The NIMH 24V 8Ah (20 cell) battery pack appears dead & I am hoping to revive it.
After plugging in the charger the red charging led on the charger turns green after a few minutes.
The battery voltage is only around 1V on the battery output terminals.
I have stripped off the battery shrink wrap cover & have included some pictures.
There is also a tiny black sensor (thermocouple?) in the middle of the battery pack, connected between negative battery output terminal & pin 3 (of four) on the charger socket
There is also a small silver component (fuse?) between the positive charger socket & battery positive terminal
The charger output measures 40V when not connected to the battery - is this correct?
What is the best way to go about sorting this problem out without spending lots of my hard earned money on a new battery pack?
Thanks Dylan

 

[amberwolf]

Check the cell voltages. If they all seem very close to 0V (which would be about right for 1V pack level) then you may be able to manually recharge them, slowly, with a current-limited power supply at low mA levels. It'll take a while, but it might revive them.

However, cells could be dead, internally shorted by dendrites/etc., and may not recharge at all. I'd just keep checking cell voltages as they recharge, and if you see ones that stay well below others then they could be bad.

NiMH will be about 1.2V nominal fully charged, 1.4V or more during charging when near full. (voltage drops at end of charge, causing heat, which is why it has a thermistor in there, so the charger will know when that happens and can turn off charging so it doesn't destroy the pack or cause a fire).


FWIW, if hte charger continues to output voltage/current even a trickle after it goes green, then you can just leave the pack on it whenever you are there (take it off if you leave, just in case) and see if eventually it charges the cells any.

 

[wesnewell]

First, I'd get 24v to the bike some way to make sure it still works. If it does, I'd throw that 7 year old pack in the trash and buy a new 24V lithium pack. It was only 8ah to begin with. Even if you revive it, it probably will be less than half that in capacity. A single $50 5000mah 6s lipo pack would probably work better. Sometimes crap just isn't worth saving.

 

[agniusm]

Agreed with above. 5ah of new lipo is way better than those past age nickel cells. As above, 10ah pack would cost you 100$. Its still better than spending hard earned cash on alcohol, smokes or some stupid pop concert.

 

[dylan]

Well guys I finally got round to doing something with this bike.
I have spent around £15 & now it's sorted into a stealthy backup electric bike.
I purchased from Ebay a seat post rack & a small toiletries bag.
I borrowed my 48V 10 Ah battery pack from my everyday electric bike.
This battery can now be transferred in about a minute from bike to bike as the rack, bag & wiring stays put on each bike.
I removed & junked the original dead battery & all the original centre frame plastics.
I cut the bottom out of a water bottle which hides the controller & cables.
Acceleration is very slow, requiring a bit of peddling to get going, & top speed is around 18mph (as tested by my 14 year old Son who loves it).
I do find this bike too slow as I'm used to my daily BPM 500W bike doing 28mph with strong acceleration.
I could buy a new controller that will push more amps through the motor.
Or I'm good with a soldering iron so I could open up the controller & look into doing a shunt modification (never done this - is it easy & would it go much better?)
I have included a picture of the bike.
Best regards to you all.
Dylan