Replacing Li-ion Cell

[bouncer10]

I have a Wisper 905se but now has limited range, one cell in the 36V 14 AH Li-ion battery stays at 3.6v while the other 9 cells charge up to 4.2v. Has anyone replaced a single cell in this type of battery or where can individual cells be purchased.
Alternatively can a new block of 10 cells be purchased to refill the old case.

 

[flecc]

Changing these cellpacks hasn't been a realistic option since they constantly change with developments, and the internal BMS elctronics are matched to the battery. For example, Wisper have changed through three battery manufacturers for their 14 Ah battery to keep with the best option at all times, so stocking all the different types would be difficult. I suspect the same will be true for individual cells, and it's likely to be difficult to find the right one.

 

[Scottyf]

You could replace the dieing cell.
Its not impossible. Might be impractical - what type of cell is it?
You can buy all sorts of single cells. There a bit pricy but you can do it.

 

[banbury frank]

Hi the cells should all be 3.7Volts Have you asked wisper for a new cell but it need to be fully charged

I bet you it is the first cell

Also It may just need charging on its own it is common for the charger to over charge the rest off the battery's leaving one flat usually the first one we just charge the flat one the run the battery for 4 charge discharge cycles and if you recheck all the cell will be the same we use a bench power supply 2 amps at 39 volts if flat will take 6 to 7 hours to charge

Frank

 

[banbury frank]

Hi sorry missed a point out individual cell should be charged at 2 amps 3.9 volts not 39 v

Frank

 

[bouncer10]

Thankyou flecc I did not realise there would be a difference in the packs i assumed the packs would be very similar characteristics even from different sources

 

[bouncer10]

It looks like i will have to buy a complete new battery in the end so i may try Franks suggestion of charging the first cell (it is first) on its own, i have nothing to lose. I checked the state of the cells using the 11way connector coming out of the shrink wrapped pack as i presumed this was directly connected because the readings increased evenly on each pin. i haven't cut open the shrink wrap yet or do i need to to charge the cell or does this 11way connector come directly from the cells

 

[flecc]

I don't know offhand, though the 11 way probably does, best to cut open the shrink wrap to some extent to check though, since in some batteries there are feeds coming from individual BMS cell mounts.

 

[Deleted member 4366]

I'm sure that 11 pin connector is directly connected to each cell. Check the voltage on each pin when fully charged, and then again when fully discharged and it should show any problem cells, or whether they're all tired. Measure from 1 to 2, 2 to 3, and so on for individual cell voltages.

 

[hech]

I consider that our man Frank mebe due a round of applause here. What he lacks in punctuation he surely makes up for in technical insight. The same first cell in my battery is 3.7v, the rest 4.1v and me thinking its the cold weather slowing the bike down. Will try independently charging it as Frank recommends, but then, surely the BMS s'posed to deal with that sort of thing?

 

[flecc]

The BMS is, and the fact the first cell is down on voltage tends to indicate weakness in it. You may well find that bringing it up to 4.1 volts if possible won't be lasting.

 

[Deleted member 4366]

Sometimes the first cell is used to power the BMS, which can be active even though the battery is switched off. That's why it's important to do an occasional re-charge. A couple of re-charges should sort it to give the BMS a chance to re-balance.

 

[bouncer10]

Thanks for all the advice
I don't know if it is classed as first it is possibly the last at the most positive of the battery. I have started to recharge it individually and the voltage has risen from 3.6 to 3.99 on constant current, I will switch to a constant voltage shortly and see if current drops off, then we can see if it holds a charge

 

[bouncer10]

The cell was still at 4.18 today so i have fitted a small 2pin connector to bring that cell connections outside the battery case and have made a simple test plug with two leds to simply plug in and indicate if nearer to 3.6 or 4.1. I took the bike out for a short ride up a hill where it cut out before and all was fine and when i returned plugged in the led tester and it was still around 4 V. the test will be when i use up the battery and try a full recharge, unfortunately this may not be for a while but i will post update when i do.

Thanks again for all help.

 

[flecc]

Thanks for the update, that does seem promising.

 

[flyingdutchman]

Battery Diagnosis, Repair or Buy

I've had a similar problem. Battery power suddenly stopped mid journey during a rainy day. I can't start the recharge. Maybe a short circuit?

Battery is a Lishen 36V 10ah,15 months old, light to moderate use. See photos.

The static cell readings are: 3.2, 3.54, 3.53, 3.58, 3.56, 3.54, 3.56, 3.52, 3.56, 3.57. Total battery output = 35.3V but BMS output only 9.8V.

So all close except the cell nearest the bms. Does this prevent the charger from starting to charge? Do these reading levels indicate anything else? There is no visible internal damage and all wires are connected.

The options I see are:

1) Re-charge single cell?
From this post it seems that this needs to be done at 4.19V and 1.8A? My charger is rated at 41.9V and 1.8A. Can I use a voltage divider (resistors in series, (R2/(R1 + R2))) to achieve the desired voltage? Do I have to disconnect this cell from the others whilst charging? Do I bring it up to the average(3.54V) then charge all as normal? What are the chances that this cell fails again? Will moving the cell's position to the end (furthest from BMS) help keep it's strength longer?

2) Replace the cell?
The cell terminals are clamped together, so easy to disconnect. How and where do I get a replacement cell? Do i need one at exactly 3.54 V static?

3) Disconnect the defect cell?
Will this solve the problem in exchange for a small loss of power? Seems to be easiest option.....Do i then need a charger rated at 41.9- 4.19 = 37.71 V ? Or is it better to remove more cells?

4) Replace the BMS or charger?
Could this help or is it better to get a more sophisticated charger to ensure balancing?

Thanks in advance for any advice.

 

[Deleted member 4366]

Looks like your BMS has shut down because that first cell voltage is too low. You can charge it with any 5v charger as long as you monitor it. Any current up too two amps should be OK.

 

[flyingdutchman]

thx d8veh,

This worked. Battery and bms now working normal. I used a mobile phone charger for a 5v charge on the one cell. I then had to initially bypass the bms and charge the whole battery with the 42v charger until the battery voltage increased to 39v then the bms jumped back into life.