Question about a revived lithium ion battery pack.

[MorganCMY]

Hi everyone,

I am working on this battery pack that had been discharged to around 2.0V per cell. I was able to boost charge them to around 4.2V and they are holding charge. The issue i am having is the bms shows a much lower voltage than the actual pack itself. The battery is at 58v now while the bms only shows 45v. As soon as i put a load on it, the voltage will drop to 0v. I also can't charge from the bms so i am guessing the bms is locking the battery from being over discharged before. Am i able to reset the bms on the board some how? The battery appears to be 13P14S with 18650 cells.

Thanks in advance!!

 

[amberwolf]

The BMS is probably just doing it's job, and trying to protect you from a fire from recharging over-discharged cells, just as it was designed to do.

Better-designed BMSs will be able to brick the battery to prevent an end-user from doing things that could result in danger to them and others. Someitmes there are factory reset methods but they probably require the factory software and connections to do this, because it would be being rebuilt at the factory to replace all the at-risk cells.

It is likely that if you wish to take the risk and continue using these possibly-damaged cells, that you will have to replace the BMS with a new one (which will probably have to be a generic one that will be less capable / well designed / well built than the original.

Or use them without a BMS, which I really would not recommend (I would actually recommend not reusing overdischarged cells, as you cannot know if any are damaged in a way that could lead to future fire risk; it is safer to assume they are all damaged like that...the first sign you might have of such damage is the smoke coming out of the battery...).

 

[MorganCMY]

Thanks for the quick answer, these are actually brand new packs. I got them from a electric lawn mower that doesn't work. The issue with this pack is it actually has a connector built in that goes into the mower dash info screen. I won't be able to use a generic better quality bms to replace it and have it work like the factory one. I don't have enough knowledge to find what what's all going to that dashboard plug

 

[amberwolf]

Brand new or not, discharged down to 2v is overdischarged for the typical lithium ion cell (LTO operates in this region, but not your typical 18650 cells), hence the risks.

The dashboard plug likely communicates with the BMS to prevent system operation when the BMS is not working or if a non-OEM pack is used, etc. (this kind of thing has been getting more common for a long while, to keep you locked into a brand). I would guess that the system can't be used without this specific BMS operating correctly.

But it probably leaves you with no good options other than buying a new battery from the manufacturer (probably expensive) or sending yours back to them for repair (probably not cheap either)

Some generic BMSs have reset functions in their hardware for cases like this, but not all of them do either.

You might get lucky and stumble upon someone that has seen these packs before, and dealt with this issue successfully...but you should note that even if you do reset the BMS, there is still a risk of fire with the overdischarged cells.


A search for the p/n on the battery case shows a handful of relevant results, but no info on fixing them. Maybe you could buy the ones this guy has

Should I keep these batteries?

I work at a shop and we just had two unit that are basically brand new get scrapped. These unit are electric lawn mowers with 58volt 30Ah 1680wh batteries I have 3 of them at this time. The battery's are good just other issues with the unit. My question is there a way to use the batteries in a...

diysolarforum.com

 

[MorganCMY]

I am waiting to call the manufacture on Monday morning to see what my options are. Thanks for your help!!

 

[electric_nz]

Check the cell data sheets. Many cells are fine down to 1v, but should be disposed of if they go any lower

 

[MorganCMY]

They are from a Cub Cadet mower. I will check on them after I find out what the want me to do with them on Monday. Thanks!

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