Ping battery problem - is it the cold weather?

[frank9755]

I've read the reports of battery problems which several Kalkhoff owners have reported recently with some concern. This morning it was my turn.

My Ping LiFePO4 battery has been in the garage, but unused over the recent cold spell. The sun was shining this morning, so I gave it a top up and connected it to my bike. I lifted the motor wheel up and it worked fine. but repeated and it didn't work.

The fuse had blown. I replaced it with another 20A fuse. This one blew immediately on reconnection without the throttle being opened - ie should have been zero load.

Does anyone know what is wrong with it? Has the cold weather done something to upset it (like all the other batteries being reported)? Could I have over-charged it? I've brought it inside to let it warm up properly and might have a play tomorrow, but would welcome any suggestions!

Frank

 

[Fecn]

If it's blowing fuses then it may not be the battery to blame at all. Any cold weather effects I'd expect to see from the pack would be reduced range or weak performance.

 

[flecc]

Like Fecn I feel the battery would be much less likely to give problems when cold Frank. More likely a short circuit somewhere.
.

 

[eddieo]

moisture, condensation? bring it in for a while and let it warm up?

 

[frank9755]

Thanks,
I'll check my connections for shorts and report back!

 

[frank9755]

I've opened up all my cable joints and connectors and checked for shorts, but it's still blowing the fuse as soon as I connect it. I guess there could be a short in either the controller or the motor. Presumably most likely to be the controller. Luckily I do have a spare Tongxin one so will give it a go and see what happens.

Update:
I've now changed the controller and it works!

 

[RobinC]

Did you figure out what might have caused the controller to die?
A bit worrying if they can keel over for no good reason, I'm think of doing a Tongxin project soon.

Robin (1st post)

 

[frank9755]

I should say it wasn't a Tongxin controller. It was one I sourced from another supplier - who used to deal with Tongxin but stopped when he had so many controller problems! He tracked this one down in China and has offered it as an alternative to his customers who have had Tongxin ones fail.

I've emailed him and he's suggested I open it up and see if there's evidence of a mosfet having blown, which I shall do.

I've now fitted a Tongxin controller, which I got from JohnP recently. I've not heard of failures with the recent batches of controllers so am hopeful this one might work for a bit longer.

Frank

 

[RobinC]

OK thanks, that is reassuring. Some of the other failures I read about could possibly be explained by overheating or some other excuse but in this case I couldn't see any good reason.

Has anyone experienced controller failures after zooming downhill?
Someone on endless-sphere claimed:
"...One note on the [Tongxin] controllers, they are vulunerable to high levels of back EMF. If you go down a steep hill, the voltage generated by the motor will burn up the mosfets, I suspect because the internal diodes are conducting. The work around is to add some protection diodes on the three motor leads, to GND and Batt+."
An extra 6 diodes shouldn't add much cost so maybe Tongxin already do this on more recent controllers.

 

[Tiberius]

I wouldn't worry about that too much Robin. That downhill back EMF problem only applies if there is no freewheel in the motor. With motors such as the Tongxin, eZee, etc, the wheel can't drive the motor (unless you roll down the hill backwards).

Even without a freewheel, its not a problem unless you go very fast. And even then, its not a problem unless the controller can't handle it. The mod described is not generally necessary.

Nick