Battery Cell Issues Pls help

[my.motion]

Hi Team,

I place my 48v Lithium Ion charging overnight but it could only reach 44.2v. This morning I took the battery pack apart (consists of 29 cells (C-Type battery) each measureing 3.7v/3.8) and decided to measure each cell, about 4 or 5 cell measured 2.4v, this clearly indicates that these group of cells have not charged up to max 3.8v Is there anything a can do to get these groups of cells to 3.8v?

There are a total number of 29 cells each measuring 3.8v does this mean that I have more than enough for 48-54v? Should the total power not be 29 x 3.8v?

I soldered some of the connections on the battery does this provide resistance causing the battery to discharge erratically?

I have checked the charger it reads 54.2v

Any comments will be highly appreciated

Thanks for you help

 

[flecc]

These cells are nominally 3.7 volts each like most lithium cells, but their actual fully charged voltage is typically 4.1 to 4.2 volts, hence the 41 volts for the pack. You need the cells to get to a maximum of that 4.1/4.2, 3.8 volts is insufficient. At the other end when the charge is used, the cut-off voltage is about 32 volts, 3.2 volts per cell.

It's the job of the internal BMS (battery management system) to balance and equalise the cell charges during charging, so one of three things has probably happened:

1) The charger cut out before reaching full charge.

2) The BMS is failing to do it's job.

3) Some cells are faulty.

To deal with number (1), try charging again since chargers can accidentally drop out of charge on occasions.

The others are a matter for the battery supplier of course, and there's little you can do about them with an item that's under warranty.
.

 

[my.motion]

Thanks flecc, I also receive a 48v SLA charger, will it be safe to try this charger?

Regards

Motion

 

[flecc]

Difficult one Motion. In theory it should charge the lithium battery to somewhere approaching full charge since it's the battery's BMS that carries out the full charge cutoff, lithium batteries not needing smart chargers.

However, if your BMS is giving trouble it might not be safe to try it, and it won't balance the cells any more than your present charger. Only the BMS can do that.

Your lithium charger giving 54 volts seems high for a lithium battery, those I'm used to output about 44 volts. NiMh 36 volt batteries use 54 volt chargers.
.

 

[Fecn]

Hi Team,

I place my 48v Lithium Ion charging overnight but it could only reach 44.2v. This morning I took the battery pack apart (consists of 29 cells (C-Type battery) each measureing 3.7v/3.8) and decided to measure each cell, about 4 or 5 cell measured 2.4v, this clearly indicates that these group of cells have not charged up to max 3.8v Is there anything a can do to get these groups of cells to 3.8v?

There are a total number of 29 cells each measuring 3.8v does this mean that I have more than enough for 48-54v? Should the total power not be 29 x 3.8v?

There is something odd with your numbers - are you sure it was 29 cells?

29 is a prime number, which means that there aren't any parallel cell combos where it would work, and if they were in series, it would give 107 Volts. I'd expect a 48v LiIon pack to be made up of strings of 13 cells, so 39 cells would make sense. That way, it could be a 3p13s arrangement (with 3 cells in parallel, arranged into a string 13 long.) If the parallel cell groups in threes are not charging up, then it is possible that one of the cells in the group has gone short-circuit/low resistance, and is draining the charge from the other two. If the cell is standalone and still won't charge, then it's dustbin-bound.

 

[torrent99]

Hi Team,

I place my 48v Lithium Ion charging overnight but it could only reach 44.2v. This morning I took the battery pack apart (consists of 29 cells (C-Type battery) each measureing 3.7v/3.8) and decided to measure each cell, about 4 or 5 cell measured 2.4v, this clearly indicates that these group of cells have not charged up to max 3.8v Is there anything a can do to get these groups of cells to 3.8v?

There are a total number of 29 cells each measuring 3.8v does this mean that I have more than enough for 48-54v? Should the total power not be 29 x 3.8v?

I soldered some of the connections on the battery does this provide resistance causing the battery to discharge erratically?

I have checked the charger it reads 54.2v

Any comments will be highly appreciated

Thanks for you help

First of all that measurement of 2.4V on some of the cells, if it is correct, probably means that those cells are very likely to be dead and unrecoverable.

(Lithium cells have a minimum voltage they shouldn't go below otherwise damage results very rapidly)

This low voltage also means that the BMS circuitry is likely suspect as Flecc says.

And as Fecn says 29 is a strange number of cells.

If we are dealing with a Lithium Cobalt/Lithium Manganese battery (for some reason known as Lithium Ion these days) then the nominal voltage in 3.7V.

So for 48V you need 13 (as Fecn says) in series [3.7*13 = 48Vish].

Then to get the required capacity, you parrallel cells together so if your pack is made of 5AH cells to get a 10AH battery you have 13 sets of 2 cells in parallel (to get 10AH) then connected in series (to get the 48V). In this case you would have 26 cells.

Either way Flecc has hit the nail on the head as usual, with the likely causes.

Who did you buy the battery from?

 

[my.motion]

There is something odd with your numbers - are you sure it was 29 cells?

If the parallel cell groups in threes are not charging up, then it is possible that one of the cells in the group has gone short-circuit/low resistance, and is draining the charge from the other two. If the cell is standalone and still won't charge, then it's dustbin-bound.

I will try to post the picture and recount the cells,

This morning I disconnected one of the small BMS wires adjacent to the faulty group and placed it directly on the faulty group that had low charge, and lucky the thing has started picking up the charge . I soldered the two groups metal plate together, and the solder could be creating low resistance? I couldn't wait for the group of cells to fully charge (i left for work when the cells got to 3.1v)

The battery was bought with the kit from luckybdd in china

 

[my.motion]

39

I have now recounted the cells and can tell you it is 39 cells in total. Image below. I am now thinking of return this battery and maybe getting 48v 10A Lifepo4 from ping.

Will this 48v 10A be ok for my 1000w motor?

I have attached the image below

Regards

Motion

 

[my.motion]

Clearer image below

The three colums of battery from right to left are 11 X 3, and the last one is 6 cells (first column on the left consists of 6 cells - where i labeled as soldered)

Thanks

 

[Fecn]

It sounds very much like you have some faulty cells in that pack, so I'd definitely return it. I think you want more like a 20Ah LiFEPO4 pack for a 1000W motor. A 10A pack is only really suited up to about 500W.

 

[my.motion]

so I'd definitely return it.

Thanks Fecn, I am just worried that the seller may not send it back from China, especially that It is working now and I've always fixed it myself. He will try to blame me? I did pay by paypal though. I am not looking to use 1000W yet will this 500W one work for 1k motor or will the controller reject it? My currrent batt out put to 12A

 

[torrent99]

Thanks Fecn, I am just worried that the seller may not send it back from China, especially that It is working now and I've always fixed it myself. He will try to blame me? I did pay by paypal though. I am not looking to use 1000W yet will this 500W one work for 1k motor or will the controller reject it? My currrent batt out put to 12A

Good luck returning it

As far as what motor with what battery size....here's a bit of theory...

Different batteries have different "C ratings". The C rating says how much current a battery can supply as compared to its capacity. So a 2AH battery cell at 1C will be supplying 2Amps at 2C 4 Amps at 0.5C 1Amp etc etc.

Lithium Cobalt and Manganese (often mistakenly called "Li-Ion") usually have higher C ratings in the range of 10-40C I think. [could be wrong on the values but the principle's there]

LiFePO4 based cells usually have much lower C ratings e.g. Ping rates his cells at 2C though most people like to run closer to 1C to be on the safe side.

What does this mean for your 1000W motor?

Well at 48V you need to provide 1000/48 = about 20A of current for 1000W of output.

If you have a 48V 10AH battery that's 2C ( 20/10 = 2).

So the Ping battery would really be pushing it at 100% of its rating, leading to voltage drop and possibly long term damage to the battery. Going to a 20AH battery brings it back down to 1C which means less voltage drop (=more uumph) and less strain = longer life.

You also get higher capacity at lower current draws i.e. at 10AH battery at 0.5A (0.05C) might give 11AH but at 100A (10C) might give only 5AH before it needs charging. So a 20AH battery might actually provide more than double what a 10AH might provide in the same (high current drawing) application.

A **good** Cobalt or Manganese ("LiIon") would probably be OK due to it's higher C rating. However, do you have a good "LiIon"?

Hope this helps...

Cheers

Steve