Battery voltage help - not charging

[Planemo]

Gents,

Im in a bit of a pickle, we had planned to go away for a family cycling holiday on Saturday but the Wifes battery is not charging! This will be a problem as she uses her ebike due to a knee injury. Her bike has not been used for a few months due to weather and when I have gone to charge it, it's as if the charger is not seeing that it's plugged into anything. I have tried both her charger and my Oxydrive one, neither are switching from the green to red LED's a second or so after plugging in like my OD battery does. The wifes pack is a 36v 10ah rear rack type and came in a front hub kit bought new a few years back which has been fine up until this. Pack voltage at the charging port is 31.8v, her charger shows 41.9v, mine shows 41.4v. Is it possible that the pack voltage is too low and the charger is not having any of it? The on-board battery meter shows 1 bar (out of 5) and I suspect it was left on by mistake when the bike was last used but surely the BMS would automatically shut it down once it hits a critical voltage?

Please please help, is there any way I can sort this out by end of tomorrow?!

Many thanks

 

[Fordulike]

Gents,

Im in a bit of a pickle, we had planned to go away for a family cycling holiday on Saturday but the Wifes battery is not charging! This will be a problem as she uses her ebike due to a knee injury. Her bike has not been used for a few months due to weather and when I have gone to charge it, it's as if the charger is not seeing that it's plugged into anything. I have tried both her charger and my Oxydrive one, neither are switching from the green to red LED's a second or so after plugging in like my OD battery does. The wifes pack is a 36v 10ah rear rack type and came in a front hub kit bought new a few years back which has been fine up until this. Pack voltage at the charging port is 31.8v, her charger shows 41.9v, mine shows 41.4v. Is it possible that the pack voltage is too low and the charger is not having any of it? The on-board battery meter shows 1 bar (out of 5) and I suspect it was left on by mistake when the bike was last used but surely the BMS would automatically shut it down once it hits a critical voltage?

Please please help, is there any way I can sort this out by end of tomorrow?!

Many thanks

Long shot here, but worth a try. Plug the charger into the battery, before you switch it on at the mains. Also, try it the other way round, switch on at mains, then plug into battery.

 

[Planemo]

Hi, yes I have tried it both ways, lots of times! I know what you mean though, sometimes the charger wont trip into charge mode depending on the order in which things are connected but unfortunately it's not having it no matter what I do

 

[Nealh]

31.8V seems quite low the lowest that my OD batteries have gone are 33.3v, It is possible that the bms has failed or because of the very low voltage will not allow a charge to start. You could try opening the battery and test the cell strings to check they are balanced via the bms ribbon, then try manually to charge each cell string to 3.4 -3.5v so that they are all equal. Once done try a full charge again,
also whilst open check all wiring is intact.

 

[Planemo]

Thanks Neal, I was worried that this would be the only option. I am in the process of pulling the pack apart as I type, time is not on my side with this. All wiring looks OK so far, I do have an IMAX type charger which I use for my RC stuff so I would possibly have the option of using it to try and get some power into individual cells or certain strings. I have never worked on an ebike battery with the multiple strings so I will have to go carefully. I should be able to try and isolate what I can though and see if I can charge from there. From the sounds of it it does seem that the pack voltage is too low for the stock charger to function...

 

[Nealh]

It could be possible that if the battery had been left switched on for a long time that it mat trickled below the lvc.
The bms lvc if it was 31v it should allow charging but expect it is 32 or 33v. I have used a phone charger to manually charge each string via the ribbon but it is slow and had to keep an eye on charging as they go to 5v. Each string may well only need 20/30 mins per string to get to 3.4/3.5v then bung it on the charger to see if it starts. It mght only be one string that is low and once brought up to the others level charging should begin.

 

[Planemo]

OK battery apart and stripped down. All looks OK. I can get to the ribbon plug, I get:
3.8v
7.6v
11.4v
15.2v
19.1v
20.8v!
23.4v
26.7v
29.8v
32.3v

Looks like that one cell might be the problem? Worth trying to put some charge in it with my IMAX? Only problem is I'm not sure where to tap the + and - in to?

 

[Planemo]

OK have found two points accross which I find 1.7v. Going to give it a go with the IMAX, although clearly the cell may well be beyond saving

 

[Nealh]

That 6th string looks shot at only 1.8v I doubt you can recover it, Planemo you have done an accumulating V check/measurement. For single cell and individual charging starting from rhs of the ribbon you get individual string readings for string #1 from pin 1 &2, then reading for string #2 from 2 & 3 and so forth. Neg on pin 1, pos on pin 2 for #1 then Neg on pin 2 & pos on pin 3 for #2 and so forth. The order is serial, hence 11 pin connections. the first is Neg and the last Pos.
You need to place your Neg on pin 5 & Pos on pin 6 be careful they don't touch otherwise fireworks.

 

[Planemo]

Everything after the 1.7v cell seems to be out as well according to the figures:
Cell 7: 2.6v
Cell 8: 3.3v
Cell 9: 3.1v
Cell 10: 3.3v

I am going to bring them all up to 3.8/3.9v as per the first 5 cells, then plug in the stock charger and see what happens....wish me luck!

 

[Nealh]

OK have found two points accross which I find 1.7v. Going to give it a go with the IMAX, although clearly the cell may well be beyond saving

Yep you sussed it before I finished my reply.
Charge to match the others at 3.8v then leave it for 1/2hr then re measure, it will probably bleed back to 1.7/1.8v if shot. In which case the battery has had it unless the string can be replaced.

 

[Planemo]

Ah thanks for the ribbon explanation Neal, I saw your post after I did my last. I had already gone direct to the PCB at the end of the pack of 3 batteries in that bank and it is charging just cell 6 now. Although the stock charger runs at 2a, I am only using .5a on the IMAX just to be careful. Do you think this is wise or should I feed more current (it goes to 5a)?

 

[Planemo]

As as note, I have only just realised that this battery is Li-Ion with the flat, foil wrapped cells like a mobile phone, not the 18650 type cell. Don't know if that makes any difference with the problem I have, just thought I would mention it.

 

[Nealh]

Everything after the 1.7v cell seems to be out as well according to the figures:
Cell 7: 2.6v
Cell 8: 3.3v
Cell 9: 3.1v
Cell 10: 3.3v

I am going to bring them all up to 3.8/3.9v as per the first 5 cells, then plug in the stock charger and see what happens....wish me luck!

The last 3 are out of balance and looks like 6 is dragging 7 down, If 6 & 7 hold up for a while then 8 - 10 should be ok to hold. You should get a charge but in the morning the pack reading may well be only 39/40v or so if they bleed back.

 

[Nealh]

Ah thanks for the ribbon explanation Neal, I saw your post after I did my last. I had already gone direct to the PCB at the end of the pack of 3 batteries in that bank and it is charging just cell 6 now. Although the stock charger runs at 2a, I am only using .5a on the IMAX just to be careful. Do you think this is wise or should I feed more current (it goes to 5a)?

No you are doing the right thing a slow charge, it might even be better to trickle charge at .1 or .2a on the two low strings.

 

[Planemo]

OK thanks have just changed it to .2a and will do the same for the other 4 cells. It's taken around 350mah to get cell 6 to 3.39v, will see how it goes...

 

[Nealh]

As as note, I have only just realised that this battery is Li-Ion with the flat, foil wrapped cells like a mobile phone, not the 18650 type cell. Don't know if that makes any difference with the problem I have, just thought I would mention it.

Not sure what you have there ? Sounds like lifepo4 battery cells to me, which I thought were 3.3v nom and 3.65/3.7v max charge. I think the cells have a much lower V tolerance something like 2v min. Some one like Flecc or D8veh can shed more light.

What is the max charge V you have previously noted on them

 

[Planemo]

Oh!? I only went on what the sticker said on the battery casing - Li-ion battery - EM-3610M - 36v 10AH. The fact it uses the same spec charger as my OD one - 36v 2ah made me think the cells were still the usual voltage. I have never checked voltages on this battery - never had to. It's simply the Mrs bike and until now never had a problem. I do wonder now if the cells are meant to be 3.6v, although why would they show 3.8v on a totally dead battery...and the charger outputs 41.9v...I haven't pulled the individual cells apart...although I can see one of the faces on two of the cells and can't see anything printed on them.

 

[Nealh]

Compared to your OD battery is it noticeably heavier.
Which bike does your wife have ?
When last used did you charge it after use or leave it uncharged ?
If it charges measure the final voltage as the battery bms will halt charging at the set max voltage.

 

[Planemo]

Difficult to say re weight, I wouldn't say I could notice much difference in either but then my wifes battery is in an aluminium case - it kind of slides into the rear rack like a casette. The bike itself is a generic (cheap) full suss with the kit added to it. I think the kit originally came from 8Fun via Ebay. I don't have the listing in my purchase history any more to check but I am 99% sure it was 8Fun. It was left uncharged after last use which must have been 2 to 3 months ago, although it definately wasn't really low as she does very little mileage when we go out. It was charged prior to that ride. I will check to see what the final charge voltage is once I have topped up the dodgy cells.
I know I have been my own worst enemy with regards to looking after this battery - I bring my OD battery indoors over winter (the wifes bike is in a metal shed outside 24/7) and I always make sure that the OD battery does not get too low - I always charge it to full whenever it drops to a minimum of 2 bars. I have learnt what is likely to be an expensive lesson with the wifes battery!