Battery voltage dropped to 2 VDC and is not "seen" by charger?

[Rapidrob]

38120S cell in a pack of four for 12 VDC under load. The battery is new as of January 2024 and was fully charged. I went to use it today and the battery pack was reading 6 VDC. I took a reading of the four cells and found the new battery was only showing 2 VDC. ( should be 3.3 )
When I hooked the pack up to my AIR-8 charger the battery number two shows no voltage. And the charger will error out after a minute of so. The error is " this function is not supported"
Is the cell dead or can it be revived? There were no loads put onto the pack and it was sitting with a BMS hooked up waiting to be used to power a radio.
Did the battery fail and cause this or did the BMS cause this to happen?

 

[sunshine_eggo]

Cell = a single element in series with others to form a battery. In this case, I would guess you have 4 cells in series to form a 12.8V LFP battery.

Battery = a collection of cells or other batteries.

Please clarify what is happening using the above two definitions.

Is the battery or cell new?

How do you know it was fully charged?

 

[Rapidrob]

It is one cell of a four cell battery. When installed into the pack-of-four, the pack was charged to 13.4 VDC.
The pack dropped to 6 VDC in one month, not used, in reserve.
The pack was dissembled and each cell was tested, one cell showed 2 VDC, the rest, slowly settled at 3.2 VDC after the 2 VDC cell was removed from the pack and BMS.
The pack was reassembled and the 2 VDC cell is shown by the AIR 8 charger as NOT BEING THERE. The pack will not charge.
Does this clarify what is going on?

 

[MisterSandals]

Does this clarify what is going on?

Yes.
I have a couple ISDT chargers so i think your Air8 can charge a single cell. Charge the one cell to about 3V and the Air8 should recognize it with the balance wires. You do not need to disassemble the battery to charge one cell.

I suspect your BMS drained your battery.

 

[time2roll]

It is one cell of a four cell battery. When installed into the pack-of-four, the pack was charged to 13.4 VDC.
The pack dropped to 6 VDC in one month, not used, in reserve.
The pack was dissembled and each cell was tested, one cell showed 2 VDC, the rest, slowly settled at 3.2 VDC after the 2 VDC cell was removed from the pack and BMS.
The pack was reassembled and the 2 VDC cell is shown by the AIR 8 charger as NOT BEING THERE. The pack will not charge.
Does this clarify what is going on?

Pack should have held good voltage for six months. Low in 30 days.... something is defective.
Need to disconnect and test while separated. Yes good chance there is an issue with the 2 vdc cell.

 

[MisterSandals]

Pack should have held good voltage for six months.

Agreed but a little 8Ah cell (8Ah x 3.2V = 25.6Wh) may not last long with a BMS, especially with bluetooth or other connectivity.
Thats about 3 months x 30 days/m x 24h/d = 2160h

25.6Wh x 4 cells = 102.4Wh

102.4Wh / 2160h = .05W

If the BMS uses more than .05W that is enough to fully drain your battery in 3 months.

 

[sunshine_eggo]

It is one cell of a four cell battery. When installed into the pack-of-four, the pack was charged to 13.4 VDC.

So you replaced a cell? What was the state of charge of the cell you installed?

What were the states of charge of the other cell.

charging to 13.4V is too low to ensure fully charged.

2V may be too low for the charger to register the presence of a single LFP cell.

With the main leads only on the single cell, use the charger on NiMH @ 0.1A. It will push current regardless of voltage. Once you hit 3.0V, switch back to LFP.

 

[Rapidrob]

When I charged the "pack" each cell was showing 3.4 VDC after settling down and placed on a shelf for two weeks. I went to use the pack for POTA ( radio activation) and the pack had dropped down to 6 VDC. I dissembled the pack and found the one cell was 2 VDC.
The cell replaced originally was leaking.
I'll try the single-cell charge as you posted.

 

[sunshine_eggo]

I re-read the thread.

IMHO, you either have defective cells or a faulty BMS that is draining them, or bad balance settings that are triggering passive balance when they shouldn't.

Cells at rest should not drop below 3.30V. To see one at 2V and the others at 3.2V after a couple weeks of sitting on a shelf says either they can't hold charge, or something is draining them.

BMS can eventually drain a battery.

If you are able to get all cells at or above 3.40V, disconnect the BMS sense lead connector from the BMS when you place it in storage. Check cell voltages weekly

 

[Rapidrob]

The Air 8 won't "see" the single battery battery. I rigged up a 13.8 VDC power supply to see if the battery will charge and hold the charge. I'm pretty sure the cell is bad.
I ordered 8 new cells and they arrived yesterday and out of the 8, two are completely dead! As in less than one volt. The seller is refunding the money for two cells. He says they are Headway, but they are not marked as such. so now I have no idea what the batteries came out of or even how old they are, let alone the maker.
If one of the two BMS's are bad , this will be the third one that has failed. They are rated for 60 amps and my radio draws 22 amps at full load.
I need to find a brand that is more reliable if it is another failed BMS.

 

[sunshine_eggo]

The Air 8 won't "see" the single battery battery. I rigged up a 13.8 VDC power supply to see if the battery will charge and hold the charge. I'm pretty sure the cell is bad.
I ordered 8 new cells and they arrived yesterday and out of the 8, two are completely dead! As in less than one volt. The seller is refunding the money for two cells. He says they are Headway, but they are not marked as such. so now I have no idea what the batteries came out of or even how old they are, let alone the maker.
If one of the two BMS's are bad , this will be the third one that has failed. They are rated for 60 amps and my radio draws 22 amps at full load.
I need to find a brand that is more reliable if it is another failed BMS.

Given that you're not purchasing new cells from a reliable supplier, it's impossible to determine if the cells or BMS are at fault.

 

[MisterSandals]

The Air 8 won't "see" the single battery battery.

It definitely does support a single cell:

Air8 support 1~8S Life, Lilon, Lipo, ULiHv batteries,
even includes the ULiHv battery with 4.45V/cell.
and it also support 1~12S Pb battery and 1~16S NiMH/Cd battery.

 

[Rapidrob]

The bad cell was not "seen " by the AIR 8. I did some more test and the cell is shorted/ or a component in the cell internally has failed.
If it is charged it overloads the charger ( not the Air8) and the cell gets very warm ( less than 2 amps max charge )
Is the correct way for one cell:
BMS Positive to the cell +
BMS Negative to the cell -
Charge sens wiring harness Red to Positive
Is there a wire to use for Negative from the charge harness for one cell only? If so is it number 2?
Thanks for the reply MisterSandles.

 

[sunshine_eggo]

The bad cell was not "seen " by the AIR 8. I did some more test and the cell is shorted/ or a component in the cell internally has failed.
If it is charged it overloads the charger ( not the Air8) and the cell gets very warm ( less than 2 amps max charge )
Is the correct way for one cell:
BMS Positive to the cell +
BMS Negative to the cell -
Charge sens wiring harness Red to Positive
Is there a wire to use for Negative from the charge harness for one cell only? If so is it number 2?
Thanks for the reply MisterSandles.

If you're asking me, I don't understand these questions.

 

[Rapidrob]

I'm asking for a Single Cell wiring connections to the Air 8 charger.

 

[MisterSandals]

Remove the balance wires and set the cell count to 1. Then charge. The voltage range is narrow, probably 3.6 to 3.65.

 

[Rapidrob]

It turns out the BMS is bad. I have one cell that is positive .2 VDC higher than the others and will not balance out. 3.32 VDC on three cells, 3.52 on the one )
I've read that this can destroy the BMS? Is this true?

 

[sunshine_eggo]

Why do you think the BMS is bad?

Hundreds of people have posted deviations on the order of 0.2V on an imbalanced battery. That doesn't mean the BMS has failed. It means the cells are imbalanced.

Passive balancing can take a really long time and requires the balancing criteria be met the entire time. It can take weeks for cells to balance passively.

Did you balance charge it with the Air 8?

 

[Rapidrob]

When the 4S 12 VDC pack was hooked up, I get an error " unexpected voltage " even though the voltage is 13.1VDC at the plug. Wiring is not the issue.
I have two of the same 4S packs and the identical BMS. One works just fine, the other causes an error after a few seconds of charging.
The Air8 displays the balancing mode is not supported.
I ordered a specific balancer today for my batteries. They had been balanced originally, then two of the batteries failed due to leaking.
The remaining batteries were then no longer in balance to one another when the new batteries were installed, and needed balancing.

 

[Rapidrob]

I took a few photos of what I'm seeing:

This 4S pack has one cell that is higher than the rest. No matter if I go through the BMS or straight to the pack cell one will always be high.
If I try to charge the pack, it will error out in a few minutes with an "abnormal voltage".
The same type BMS and the 2nd pack has no issues charging either through the BMS or strait to the pack.



2nd pack




The Air8 does not have a balancing feature.