Lithium battery suddenly reverse polarity and changed voltage!

[Victor B]

I just bought this cart yesterday and was giving it a good test out today. It was running great for about a half mile, and then suddenly it stopped dead. Before taking off, I had checked the voltages of the system and the individual batteries, and all was normal. After it died, I tested the batteries right then and there with my voltmeter I had with me, and the last battery is now reading -24v. This means that it reversed polarity and changed voltage.

I have zero experience with lithium batteries and do not even know how this is even possible. The cart was running great when this happened. How can a battery suddenly change its polarity and voltage? Can it be fixed or is the battery bad?

[rngilliland]

This is just a guess, but the bms may have shut that battery down. The voltage you are reading is the other two batteries in series. Some lithium batteries need to have the bms reset if they shut down. Some batteries have a switch or button to turn the battery on. Some of them I think you plug the charger in to reset the bms.

I would call Allied battery and ask them.

[Volt_Ampere]

The BMS has shut down on that battery. I don't like that setup and I don't know how you reset the BMS on those but you need to get them charged properly. Contact Allied.

[scottyb]

Another redflag is that battery cable to the cart frame. Never, never, ever, connect a battery to the cart frame. DO NOT put or charge this cart in your house or barn until you fix this and other problems.


As for your original question. Lithium batteries can change polarity if due to an imbalance some cells drop voltage more than others. THis can also change the voltage of the battery.


I agree with Volt - call Allied asap

[Pat911]

As others have said, the BMS on that battery has shut down. This is due to your 12v batteries becoming out of balance over time. This is why I never recommend 12v series connected lithium batteries. The BMS should reset once a charger is connected to it.

Get a 12v nominal (14.6v max) lithium charger and charge each battery individually, or better still, remove all batteries from the cart, connect them in parallel and then charge with a 12v charger. Once charged leave them connected in parallel for a few days. This will equalise the charge in the batteries. You may need to do this procedure twice a year depending on use.

BTW, once disconnected, that one battery will read either 0v or around 12v if the BMS self resets. If it still reads -24v when disconnected (very unlikely) then call Allied, actually I would discard the battery at that point.

Cheers
Pat.

[Victor B]

Originally Posted by scottyb

Another redflag is that battery cable to the cart frame. Never, never, ever, connect a battery to the cart frame. DO NOT put or charge this cart in your house or barn until you fix this and other problems.


As for your original question. Lithium batteries can change polarity if due to an imbalance some cells drop voltage more than others. THis can also change the voltage of the battery.


I agree with Volt - call Allied asap

Thanks, will do. I bought this cart from an Engineer who did the upgrade himself. No wonder it is wrong. LOL!

[scottyb]

A little knowledge is a dangerous thing.
Buddy has pallets of those batteries he tried to give me. I'm sorry but - they are garbage, as he attested to. And Allied comped all the batteries in his shipment and won't send a call tag.


All did some type of cut off like yours and had to be disconnected from the cart and reconnected to auto reset. You can try it... that's what he told me. He was an Allied dealer.

[Pat911]

Originally Posted by scottyb

As for your original question. Lithium batteries can change polarity if due to an imbalance some cells drop voltage more than others. THis can also change the voltage of the battery.

Hi Scotty,

A “battery” can only be forced into reversed voltage from an external source during charging. Individual “cells” can be forced into reverse voltage by other higher charged cells in the pack during discharge.

Lithium “batteries” cannot change polarity unless the BMS is faulty, or no BMS is used AND a charger is connected in reverse polarity.

The scenario you describe would also require a failed or non existent BMS but would not result in a polarity change of the “battery”. Individual “cells” could change polarity during discharge, resulting in an overall reduction in battery voltage though.

Either way, the battery would be toast and should be safely discarded.

Cheers
Pat.

[Volt_Ampere]

As scottyb said, there should NEVER be a connection between the battery system and the cart frame. That is a serious safety hazard and anyone working on a cart should know better. You need to get that cart sorted and if you don't know what you are doing electrically, get help!

[Victor B]

Originally Posted by scottyb

A little knowledge is a dangerous thing.
Buddy has pallets of those batteries he tried to give me. I'm sorry but - they are garbage, as he attested to. And Allied comped all the batteries in his shipment and won't send a call tag.


All did some type of cut off like yours and had to be disconnected from the cart and reconnected to auto reset. You can try it... that's what he told me. He was an Allied dealer.

I took the body cable off and reconnected the battery normally. The battery reset itself and is now reading 11.9V. The other two batteries are reading 13.6V. I put it on the charger and will charge it up to full and take it for another test drive. Hopefully, it will do better next time.

The cart runs great, so I know it is just a battery problem. I got it for $2,500, so I am hoping I got a decent deal, even if I have to replace a battery.