Kalkhoff charger output

[Bles31]

I’m trying to sort a problem on my daughter’s ebike - a Kalkhoff Connect Xion 27. The battery seems to have failed and in checking for reasons
I tried to measure charger output voltage. It gives 42v for a couple of seconds, then drops to millivolts for around four seconds then back to 42v... and this sequence carries on continuously. Am I right in thinking that the charger begins the charge process then sensing an unusual load ( multimeter rather than battery) cuts itself off as a safety feature? Or could it be a charger fault?
I think the battery may be six or seven years old and may have sat unused for long periods. It is marked Derby Cycles. It functioned fine for over a hundred miles after the daughter got the bike given to her then died quite suddenly, now providing around 10 volts.
Thanks for any input.

 

[vfr400]

10 volts is probably leakage voltage when it's switched off, not the actual voltage. Some batteries go to sleep if not used for a while, and there's a wake-up procedure. Check the handbook before you get ripped off by whoever is checking it.

 

[Andy-Mat]

I’m trying to sort a problem on my daughter’s ebike - a Kalkhoff Connect Xion 27. The battery seems to have failed and in checking for reasons
I tried to measure charger output voltage. It gives 42v for a couple of seconds, then drops to millivolts for around four seconds then back to 42v... and this sequence carries on continuously. Am I right in thinking that the charger begins the charge process then sensing an unusual load ( multimeter rather than battery) cuts itself off as a safety feature? Or could it be a charger fault?
I think the battery may be six or seven years old and may have sat unused for long periods. It is marked Derby Cycles. It functioned fine for over a hundred miles after the daughter got the bike given to her then died quite suddenly, now providing around 10 volts.
Thanks for any input.

The battery may have reached its end of life. Not proper looking after them, reduces them quickly to being an expensive bit of rubbish.
What you are seeing, is that the multi meter doesn't not draw enough current to allow the charger to get above the 3% charge current, so the charger shuts down.
But it is designed to check the battery every few seconds, which it is obviously doing.
This "checking", which also happens when someone forgets and leaves the battery on charge after full charge is reached, is what drastically reduces the life of a Li-ion battery.
I use a simple mechanical 24 hour time switch, slightly modified so that when the required hours are run and it switches the power off (to the charger in this case), it also switches itself off!
Cheap and effective!
regards
Andy

 

[cyclebuddy]

It gives 42v for a couple of seconds, then drops to millivolts for around four seconds then back to 42v... and this sequence carries on continuously. Am I right in thinking that the charger begins the charge process then sensing an unusual load ( multimeter rather than battery) cuts itself off as a safety feature?

Both my own ebikes' chargers (both different mid-motor systems) behave in this way: The charger applies a pulse and is looking for a response from the battery BMS before starting to charge. Other threads on this forum relating to Kalkhoff charging suggest it'll be similar for you.

It functioned fine for over a hundred miles after the daughter got the bike given to her then died quite suddenly, now providing around 10 volts.

Again, one of my own ebike system batteries "sleeps" when not used for a while as vfr400 suggests: On this system, there's a surface voltage of 16-volts at the terminals. Holding the button down for 5 seconds re-awakes the battery, and 42-volts appears. Yours likely has a similar function.

 

[Bles31]

Thanks everyone. Useful information and some things to try.

 

[Bles31]

Just a bit of feedback - yesterday my daughter turned up on the bike, which was running perfectly. Gave it 12 miles with big hills and it was fine. This morning it turned on at a push of the button! One thing I had done a couple of days ago was to give the handlebar mounted computer a night in my airing cupboard just in case it was damp inside. Sorry - left this out of my first post. Given that the bike is now working I think damp in the computer may have been the problem and that I have been picking up a leakage voltage as suggested above and interpreting the results as a battery problem . (The voltages show up in a digital meter but not on an analogue moving coil meter). It just goes to show what can happen when a mechanical engineer gets his hands on a multimeter !

We’ll see.