Can this battery be revived?

[RichB]

Hi RichB . I have been following your thread with interest. I appreciate it will be very frustrating and annoying to you but wonder if I may ask a question out of curiosity?

Whoosh suggested a broken wire. I know very little about ebike batteries but the thought had also occurred to me so I’m interested to know if B14+ back ro the BMS has good continuity. Did you check the wire from its connection to the cells back to the BMS? No loose connections, dry solder joints or hidden breaks under the insulation sleeve?

Hi there,
Yes a broken wire was certainly a possibility but I’ve actually taken a reading directly from the last cell group as well and that is also showing zero volts. For some reason the last cell group has drained down to zero and nothing I’ve done so far has been able to put any kind of charge in it.

 

[Nealh]

Some where along the line there are voltage anomilies, the 13 cells give about 53v and some where there was an other 3v ?

I one removes the 4 cells from # 14 then the battery will become a 13s /48v pack, parallel wise one will still have 20ah as per the original spec of 21700 /5000mah cells.

There will be the one Red discharge wire to solder to # 13 cell group on the positive end of the Buss.

A new BMS is relatively easy to solder on and one doesn't even have to solder the BMS to the pack , simply cut the three BMS wires at the BMS or part way along and solder wire to wire.
The soldered wires don't have to look pretty, strip back 2- 3cm sheathing to bare the wires and tin them fully with solder.
Slide a nice dia of 3 - 1 shrink along the wire, let the wires by pass each other and just melt them together adding more solder as you go if need be. Then slide the shrink over the joint to insulate.

For the sense wires as they are only thin one can simply apply a little heat to the existing solder blob pull the old wire and blob on the new wire or cut the wires and solder wire to wire.

If not sure we can advise which wire to solder where.

Then one will have a nice 20ah 48v battery, the cells look like they say 45a .

 

[Nealh]

What neck of the woods are you in RichB ?

 

[WheezyRider]

What neck of the woods are you in RichB ?

He said near Reading.

 

[RichB]

What neck of the woods are you in RichB ?

I’m near Reading Neal.
I must admit your depth and clarity in your explanations certainly inspire me to stick with it! I’m pretty much ready to give up on it and then you come along with an explanation and it sounds completely do-able, so thank you again for your time!

In terms of replacement BMS is there anything I should be looking for specifically when I get one, ie, would this be suffice?
https://www.ebay.co.uk/itm/394215757273?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=3fsep1zcqcq&sssrc=2349624&ssuid=Bovxo23gRW2&var=&widget_ver=artemis&media=COPY

Thanks again for everyone’s help and advice.

 

[Woosh]

We still don't know exactly where the fault is. I suggest you strip the blue shrink tube and locate the bad cells. See first if you can safely remove them.

 

[RichB]

We still don't know exactly where the fault is. I suggest you strip the blue shrink tube and locate the bad cells. See first if you can safely remove them.

Everything has been stripped off the last 4 battery cells all show zero volts, measured at the cells themselves.
Thanks

 

[Woosh]

what brand and model of cells are the dead cells?
if they are still current, it may be worth replacing them.

 

[Nealh]

A BMS like that would suffice.
Firstly though one needs to know the controllers current rating and then buy a BMS with a slightly higher current rating.

 

[Nealh]

what brand and model of cells are the dead cells?
if they are still current, it may be worth replacing them.

It's only worth replacing if the end user has a spot welder to carry out a proper job.
Also as we know cell age is an issue vs introducing new cells.

 

[Nealh]

For fusing two wires together (with the bypass method) having pre tinned them with ample solder use a croc clip to hold them tight on a flat work surface (I use and old large wooden chopping board) and then apply heat/solder either side of the clip, turn the wires over and ensure the solder has fused well.
Apply solder to the iron tip first before adding the heat to the join for better heat spread and penetration.

Test ones technique on spare wire to get the knack.
Use a good 60/80w basic solder iron (240v) and a nice solder 60/40, 70/30 is fine and a good thickness of approx. 0.8mm - 1.2mm solder. If the sodler wire thickness is to thin is simply goes up in smoke and doesn't supply enough molten solder to puddle the join. Keep the heat applied until one see the molten solder dissipate a little and turns to a nice silvery wet puddle.
Practice is the key.

 

[RichB]

A BMS like that would suffice.
Firstly though one needs to know the controllers current rating and then buy a BMS with a slightly higher current rating.

If it’s saved I’ll be using with a BBSHD with the standard inbuilt controller

 

[saneagle]

If it’s saved I’ll be using with a BBSHD with the standard inbuilt controller

Either the pack voltage is 52.52v instead of the 56.6v you measured, or you have 14 x 4.04v cells, which means they're all good. I pointed that out 9 days ago in post #21, but you still haven't remedied it. Clearly, you have measured something incorrectly. Did you check the switch, and did you re-plug the multi-pin connector like I suggested?