Battery charging problem

[johnebike]

My almost 3 year old, 36 volt pannier rack battery (Cyclotricity) has just developed a problem.
It is partially discharged (measured voltage 39.2) but will not accept a charge - The charger light stays green when connected. The measured charger voltage was 41.8
I hope that someone can explain what has happened and how to get round the problem.

 

[Fordulike]

My almost 3 year old, 36 volt pannier rack battery (Cyclotricity) has just developed a problem.
It is partially discharged (measured voltage 39.2) but will not accept a charge - The charger light stays green when connected. The measured charger voltage was 41.8
I hope that someone can explain what has happened and how to get round the problem.

I would dip a cotton bud in isopropyl alcohol, or spray some contact cleaner on it, then give the charger output connector and battery input connector a good clean.

Sometimes, there can be a tiny spark that occurs every time you connect the charger, and this over time can tarnish the contacts.

 

[Nealh]

Needs opening to check for a loose wire/bad connection.
And a voltage reading from each of the 10 parallel groups,
If one P group is badly out of balance or duff it won't charge if the voltage is too low.

 

[Deleted member 4366]

...or the battery's charge fuse has blown. That's where I'd start.

 

[Nealh]

...or the battery's charge fuse has blown. That's where I'd start.

Yes hmmm!!!! Forgot about the fuse very good point.

 

[johnebike]

Thanks for all your suggestions.
So far I have checked the only fuse I can see on the battery end. This is a 30 amp one and it looks intact. Is there another one I should look at?

 

[Deleted member 4366]

That's the main fuse, not the charging one. the charging one might be inside. You have to follow the wires from the charge socket. Sometimes it's hidden under the handle. without seeing some pictures of your battery, it's difficult to help.

 

[johnebike]

I have now opened the "charging" end of the battery and can see no sign of anything looking like a fuse.
It all looks a bit complex/delicate in there so I am not keen to dismantle any further at the moment
I have included a photo of the opened battery end and also a couple of the overall battery.

 

[Deleted member 4366]

There's no fuse and those connectors are quite reliable, so the most likely cause is a faulty cell.

See the multi-connector in the 2nd photo. Pull it out and turn it over. You'll see slots in the edge with silvery metal in them. User a voltmeter set to 20v scale. Put the black probe in the slot adjacent to the black wire, then probe the voltage in each of the remaining 10 slots. Post the results her.

 

[Nealh]

One thing you can do without going in any further or dismantling is to check the voltage of the parallel groups via the white jst connector with the 11 small sense wires.
Using a volt meter write down the voltage readings of the 10 cell groups to cypher whether you have any low cell groups. Placing the probes on Black and 1st white will give you voltage for cell group 1, 2nd white for group 2 and so forth, the final 10th reading will be black and red which will give total pack voltage. Each reading will be accumulative and will be easy to see if any readings are out.
You may be able to place the probes into the back of the connector to get your voltage readings or you will need to disconnect to se the pin holes.

d8veh beat me to it.

 

[johnebike]

Many thanks to Dv8eh and Nealh for their help in trying to solve my problem.
I have now managed to measure the suggested voltages and hope that they make sense as there was very little exposed wire to work on
The results were

3.94
7.86
11.83
15.78
19.69
1
1
1
1
1 Red

I look forward to your diagnosis.
Many thanks
John

 

[Nealh]

The first 5 readings are fine and are all near the same barring 0.01v so no issue with them.
For the other 5 readings ( > 20v) you need to set your meter dial to the DC 200v range and not the 20v as that's why you only get 1. We need the other 5 readings to see that all looks well and cell groups balanced.

 

[Deleted member 4366]

Yes, sorry, that was my mistake. I normally move along the connector measuring adjacent pairs to get the single cell voltages directly rather than the cumulative. Set it to 200v.

 

[johnebike]

This morning I suddenly realized my stupidity with the meter readings and now have the proper numbers

3.94
7.86
11.83
15.78
19.69
23.5
27.4
31.4
35.3
39.3

Sorry about that!
Thanks

 

[Deleted member 4366]

They all look OK, so nothing there to stop the bike from charging. The most likely explanation now is that there's an interruption in one of the routes between the charge socket and the cell-pack.

I'm looking at that join between the black and yellow wire, which doesn't look quite right. I think you should wiggle it a bit to test that the two sides are actually joined. After that you need to trace the voltage, which means stripping the insulation and glue off the back of the socket and check the voltage there with the charger plugged in. If it shows 39.3v, it's not connectedto the charger. If it shows 42v, it's not connected to the battery. Be careful not to short the two terminals when stripping them because they should have live battery voltage on, which will make a bit of a spark.

 

[johnebike]

Thanks D8veh for your latest comments and suggestions which I have tried to follow
I managed to uncover the black wire at the charging socket but was unable to do this safely for the red wire. However there seem to be joins in the red cable just up from the socket so I exposed one of these and used this point for my readings , point B in the photo
The readings I got were as follows
A - B 39.3v
A - B while charger on , 39.6v. I also noticed that the red charger light showed.
The charger measured at 41.9v

 

[Deleted member 4366]

If the red light went on on the charger, then you've disturbed the fault so that it's gone - maybe temporarily. The charger will show 42v until you connect it to the battery, which will bring it down to the battery's voltage. It should then rise slowwly.

 

[johnebike]

I continued charging for 2 hours after wiggling the suspect wires about without any problem. I then replaced the insulation and reassembled the battery before completing the charging (green light) taking another hour, giving a final voltage of 41.3.
Hopefully this state of affairs will continue for a while but if/when it recurs I do not have the expertise to replace the wiring, if required. Can anyone suggest where I might get this done? ( I live in Derby)
Thanks to D8veh and Nealh for helping with this problem

 

[Nealh]

Good to hear the battery is charging again, somewhere along the line there is probably an intermittent wire fault may be a solder join. Looks like one of the charge wires and wouldn't be surprised if it was the B/Y one d8veh spotted.
Alternatively it may be that the bms needed resetting and if you disconnected the jst/sense lead this may have worked.

41.3 v is showing the cells a little unbalanced and this is borne out from the voltage readings a couple of charge/discharges should balance things up a bit better.