Replacing a single LiPO cell from a commercial 14s battery

C

cheatas

100 µW
Joined
Mar 14, 2014
Messages
8
A week ago I was lucky to get a free Lipo battery. The previous owner thought it was dead, because the voltage given by the bms was only 36 V, instead of the 48V+.
The bms is replaced but this didnt solved the problem. The first thing that I did after opening the battery was measuring the voltage before the bms, it was 50v.
After measuring all the 4packs (parallel lipos ) I came to the conclusion that one of those four packs only gave 0.7 volt instead of 4.1. The bms must have seen this
as a reason to shut down the battery pack. This battery pack is brand new and very pricy, I would like to repair it.

My questions are:
Is it possible to replace one of those cells and which cells can I use?

At Hobbyking I found some single cells(5000mah 40C), unfortunately the dimensions were different from the cells in my pack, The cells in the battery pack are approx:
130x63x8, they are clear with only a small barcode. I also have no idea what the brand or manufacturer of the battery pack is.

An additional question, is it wisely to take the cells apart and make 14 1s 4packs? This would be very convenient as the lipo battery doesnt fit in my "frame battery case".

the bad cell:
1.jpeg


the complete battery pack:
2.jpeg

3.jpeg


my excuse for my grammar, English is not my native language.

I would appreciate any idea or answer!
Thanks,
Guido
 
Step one would be to find out exactly what chemistry you have. Lipo is the name used often for lithium cobalt, but it could be lithium manganese or some other type.

14s 48v means it's not very likely that it's lifepo4. With a new bms and charger, you could have a 36v battery. Cutting it into three good 12v sections could work too, depending on what you plan to do with it. I don't see a reason to separate the still good cells into 1s. Looks to me like it's in 3p groups.
 
i doubt if you will find a direct replacement, but you can hack it down in series count.

do you have pictures of the labels on the charger and a picture of the BMS? do you have a soldering iron and know how to use it? two is better to remove the solder on the top of the tabs.

you can hack it down by only one if you wanna to 13S. then save the other pouches for spares to use later.

EDITED: you only have 13S so you would have to hack it down to 12S. who told you 14S?
 
You can charge the low cell to 4.1v and let sit to see if it can hold a charge after 48hrs. Before thinking of cutting it up. Don't over charge. Don't over charge ever. You must sit and watch and not walk away.
 
I'm confused.

OP claims 14s 4p but were counting 13s 3p.

Your looking up 5ah cells because you think it's 20ah made from 4p I think. They are too big for 5Ah cells, I reckon they are about 6.8ah In line with it being 3p not 4p.

What do you want to do. Drop an S or a P. You can keep your 20Ah and drop from 48v too 44.4v, Or alternately keep your 48v and drop from 20ah to 14ah. In size terms, that is shrink 1/13th or 1/3rd. If it is the latter you can just get on with it, but the former needs the bms looking at before you go dropping series cell counts.

edit: If you pull a third out, you are pulling out a 12s 6.8ah pack that still works. Well, It's all a bit perhaps, but maybe.
 
I think Dnmun is quite correct, that cell with a huge hole in it is not usable. It's gotta go. Most likely the cells that are paralleled with it are also gonners.

Pare it down to something smaller if you cannot find identical cells, whatever they are.
 
I counted the cells, and it is a 13s 4 pack, the owner told it was a 14s so i was confused about that.
I dont have a charger for the battery, I will have to buy one. Can I use a conventional charger when i go to 12s?
And do I have to use a programmeble bms for that?

Here is a pic of the bms:

image.jpg
 
that is the original BMS or is this the one you replaced it with? the label say 13S, 10A charging, 50A discharge.

so you never had the charger? is it possible he has more info about the charger or who made the battery?

if it is the original BMS then we could determine if it is for lifepo4 or for lipo/limno2 by watching for the voltage where the balancing shunt transistor turn on.

do you have a soldering iron or two? we can go ahead and hack to to 12S and you can find a 36V lifepo4 charger that is capable of being adjusted on the output voltage so we could push the charging voltage up to 50V.

but it may be possible to find some of those pouches, but i expect every one of those in parallel with that one is also dead from being over discharged somehow since that is usually why they swell up and split. except this one may have split by itself. not sure since no history.

even if you can find some pouches, it is gonna cost money to buy just a few like that, plus shipping, so you are already talking $70-100 and it is not worth that. so that is why i would recommend going to 12S with a modified 36V lifepo4 charger to determine if the battery still has any life left in it. the limno2 packs seem to flake out fast and i think that is what we are looking at.

also by hacking it down to 12S you can save those extra two pouches in case another one blows later. plus since it is gonna be in pieces now, you can figure out how to arrange the pieces so they fit in your frame and then run the sense wires to the cells wherever they end up. so it would be an optimal solution for your needs.
 
That is the original BMS, I will ask the previous owner about the manufacturer and post it on ES.
I have enough soldering irons, and quite some experience to solder them apart.
Will a 36V Magic pie Li ion 1.8amp charger work? Or is it just to dangerous to use a non lifepo4 charger?
Will it be safe to run the 12s pack without a bms?
 
no need to run the pack without a BMS. that one will work i expect or we can show you how to hack it to 12S. open up the charger you have and show a picture inside so we can see if it has an adjustment trimpot for the output voltage. you may have to add a resistor to the feedback loop to reset the voltage to 50.2V from the 44V now.
 
if you look at how the board is split along those holes, there is one single 4 legged IC that goes across from top to bottom sides. on the bottom there is an 8 pin IC soldered on the side that goes on the front end, but if you look on the other side from there in the back end, behind that 4 legged IC, there will be a few resistors on the front side of the pcb, next to the legs of that 4 legged IC, or close by and connected. look for a trimpot. but if some of the little surface mount resistors are stacked 2 high, take a picture there.

that is where we need to look. then we can figure out if we can change some of the resistors and make the output voltage change so you charger would work on the new voltage for 12S.

make sense?
 
4 cells costs $25+P&P if they are 5Ah each. They won't be as big though, and I don't actually agree with mix&match packs, although it's commonly done. They are 130x40x10 or thereabouts. I have a nagging feeling though, as the energy density is off. I'm still unsure if you have a 20ah pack.

I'm not sure if that charger will move from 42v to 50.4v but if it does it will still be toss. It's just too small. There are not enough hours in the day.

I think you looking at a bmsbattery order for a charger, so you might aswell cough another $20 on a new bms. $100 delivered for the pair.
 
Its been a while ago but I bought a new 5A Kingpan charger and I disconnected the group with dead cells. I opened up the charger and saw the pontentiometer in the corner to regulate the voltage.
My next question and a problem that was also mentioned before: can I "hack" or fool my bms that the non existing cell is still there?
 
cheatas said:
My next question and a problem that was also mentioned before: can I "hack" or fool my bms that the non existing cell is still there?
Click to expand...

possibly, but a picture of the bms is required to assess (picture of the inside pcb) :eek:

have fun
 
should be possible to convert that BMS from 13s (now) to 12s in order to accomodate the missing cell group.
prerequisite is that you have a healthy 12s series of cells and that the relative sense cables are sequentially
connected to the BMS. The last sense cable will be disconnected.
After this it is to alter minimally the PCB of the BMS to make it not to care about the 13th cell.
You will need some skills to desolder- solder few SMD components.

have fun!
 
I resoldered the battery and the bms wires. The 13th wire is not connected. On the battery I measure 49 volt and on the output of the bms I measure 44.3 volt. Should I try to charge it? Or do I have to desolder things of the BMS?
 
you could try charging- discharging, but if the bms is good it should not work, since it is still
configured for 13s. and it would sense a fault to the last cell. :|
proper course of action should be to disconnect the main lead (positive) from battery to bms, than detach the sense connector, to be able to modify the bms. converting the bms to 12s via desoldering the last optocoupler closer to the smd resistor and to solder the same resistor in place of the desoldered optocoupler.
than, in order to be sure, if I were you I would wait to know from other members to know if the procedure is correct,
since I just guessed and I never had to repair this specific bms. :mrgreen:

have fun!
 
Thanks for the reply! I will try it but will wait for other members. Can anyone confirm the described modification on my bms?
 
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