38v ceiling?

[timidtom]

After not being used for 4 months I charged our 36v 10a batteries for a couple of hours each. They peaked at 38.x volts. I tried each one on the bike - maximum speed peaked at 9mph (without pedal assistance). Two of the batteries are 4 years old, one is 2 years and the last is just a few months old. Is this likely to be solely a battery problem? Help, please. I am a bear of very little brain and long words bother me ...
Tom

 

[Deleted member 4366]

What bike is it and what type of batteries? If you don't know what type of battery, what's the voltage on the charger, 42.0v or 43.8v.

 

[Geebee]

It would seem strange for all packs to fail simultaneously, my first thought would be a faulty charger, can you measure the output from it?

 

[timidtom]

It would seem strange for all packs to fail simultaneously, my first thought would be a faulty charger, can you measure the output from it?

Thanks - not sure how to measure the output from the chargers but both are marked 42v. Think I'll give each battery 2 hours with each charger and then measure the voltage retained. I'll get back to you after 8 hours!
Tom

 

[KirstinS]

You need a multimeter to measure the voltage - they are cheap to buy online or around 15 quid from halfords and similar

How did you know the packs are 38v ?

 

[timidtom]

You need a multimeter to measure the voltage - they are cheap to buy online or around 15 quid from halfords and similar

How did you know the packs are 38v ?

I have a Maplin multimeter (and limited knowledge about how to use it!)
1 battery has accumulated 38v, 2 batteries have 38.8v and 1 battery has 39.9v after charging for 4 hours (2 hours on each of the chargers). Road test tomorrow (if it's not raining ...)

 

[Deleted member 4366]

Check that your meter is accurate by measuring your car battery. If the battery in your meter is going flat, it'll give false readings.

 

[timidtom]

Check that your meter is accurate by measuring your car battery. If the battery in your meter is going flat, it'll give false readings.

Thank you - I'll do that.
Tom

 

[timidtom]

Check that your meter is accurate by measuring your car battery. If the battery in your meter is going flat, it'll give false readings.

Tested battery in meter and found to be OK. Each of the four bike batteries has had an additional 4 hours charge, 2 hours from each of the 2 chargers I have. Two batteries are now at 39.4 volts, the other two haven't gained any extra charge. I attempted (after I'd completed the last charge) to measure the output of the chargers. I managed to get a reading of 40.2v from one but failed to register anything from the other. Probably prodding at the wrong prongs or something. When the local streets are clear of children (four schools within 1 kilometre of home ...) I'll try a pedal-free ride round the block (about 3 k) and see what happens.

 

[KirstinS]

40.2 is too low - it should be 42v
It explains why you get battery readings just under 40v

Time for a new charger . What does the connector look like and we can suggest some.


I'd say this is good news as a charger is far far cheaper than new batteries !

 

[Deleted member 4366]

Your meter is faulty. It should show 42.0v from the charger. If it's 1.8v out, 39.4v would be 41.2v, which is more or less normal.

 

[KirstinS]

But I believe op has checked the meter already for accuracy vs car battery ?

Bow to your superior knowledge though !

 

[timidtom]

40.2 is too low - it should be 42v
It explains why you get battery readings just under 40v

Time for a new charger . What does the connector look like and we can suggest some.


I'd say this is good news as a charger is far far cheaper than new batteries !

Hi. The charger to battery connection is tube with three prongs inside. I just tried a 3k ride with both batteries and had to pedal all the way round. Drat. New charger then, you reckon?
Tom (fingers crossed).

 

[Deleted member 4366]

Chargers work or they don't. They can't give the wrong voltage. It's 42.0v or nothing. Borrow a meter from a friend/neighbour and start again.

It's clear that you have problems, but we need proper test results to find the causes.

 

[KirstinS]

Hi. The charger to battery connection is tube with three prongs inside. I just tried a 3k ride with both batteries and had to pedal all the way round. Drat. New charger then, you reckon?
Tom (fingers crossed).

No , that was what I thought but d8veh is the real expert here

Borrow/beg/steal a multimeter from somewhere and take his advice

 

[timidtom]

No , that was what I thought but d8veh is the real expert here

Borrow/beg/steal a multimeter from somewhere and take his advice

OK, thanks. Will do.
Tom

 

[timidtom]

Chargers work or they don't. They can't give the wrong voltage. It's 42.0v or nothing. Borrow a meter from a friend/neighbour and start again.

It's clear that you have problems, but we need proper test results to find the causes.

Thanks - I'll try to find another multimeter.
Tom