lifepo4 battery problem

luvxu

luvxu

1 W
Joined
Jun 4, 2012
Messages
56
hi all
my battery stopped to work and i am looking for some help to fix it if possible. this is a 36v battery that came with my busettii bike. last month i decided to switch it out for a48v one to get a little more speed out of the bike. it has been charged before it was stored away. this is the type of battery that is in an aluminum tube. today i found out that the battery doesn't work anymore. when i measured the voltage at the connection to the controller it only showed19.20v. however when i pulled the cells out of the tube and measured the voltage across all the cells it showed37.89v.

do you know what could go wrong here and how could i fix it?

thank you for your help.

IMG_20120724_221627.jpg

IMG_20120724_221729%20%281%29.jpg
 
luvxu said:
hi all
my battery stopped to work and i am looking for some help to fix it if possible. this is a 36v battery that came with my busettii bike. last month i decided to switch it out for a48v one to get a little more speed out of the bike. it has been charged before it was stored away. this is the type of battery that is in an aluminum tube. today i found out that the battery doesn't work anymore. when i measured the voltage at the connection to the controller it only showed19.20v. however when i pulled the cells out of the tube and measured the voltage across all the cells it showed37.89v.
Click to expand...
First of all, I will wonder how can you update a 36V battery pack in a small aluminum case to 48V by adding cells and update BMS. The image does not show clearly. Can you update better image again? That will help menbers here to check for you and provide you advice.
What's the voltage of each cell right? This will be the first thing to do.
Also you will better start a double check from connection of your new BMS, I think you must change bms from 12S 36V bms to 16S 48V bms. Check if any wire have problem. You will need to check carefully as balance wire may be easy to be a mistake. Odd voltage indication via multimeter mainly cause by wrong connection or short circuit.
 
Where did you buy the battery pack from?
 
Hi Jason27,

I didn't modify the battery or BMS. I just swapped out the 36V 10AH battery for a 48V 10AH battery. I have multiple lifepo4 aluminum tube batteries. So my 36V battery had been stored away for about a month and I decided to check on it to see if it is still working or needed to be recharged. I learned from this forum that one should recharge the lifepo4 battery at least once a month to keep it working. This is when I found that the voltage at the output had dropped to 19.20V. The curious thing is that if I take the battery out of the aluminum case and measure the voltage across all the cells (I think there are 12 cells in series), then I get a reading of 37.89V .

So is this mean that my BMS is not working anymore? Or is there a problem with the battery cells? I measured the voltage across each cell and they are all above 3.1V. This means that the cells are still good, right?
 
I believe that your BMS is working properly and that your BMS is causing the low voltage reading. I think one string is under the low voltage threshold and is cutting out the pack. What remains at the output of the battery is a voltage of part of the pack. Try charging it. I think it will recover.
 
Fivari,
I have put the battery on charge for the last few days now and there is still no change in the battery voltage, it still read 19.20v. Any idea why?
 
what is the output voltage of the charger? is it pushing current?

you can use the ammeter function (10A scale and 10A probe plugin spots) on your DVM to measure the current produced by the charger.
 
37.8 / 12 = 3.15v

assuming that all 12 cells/groups are at 3.15v ,,.... and the BMS output is 19.2v you either have a faulty BMS , it may be in protection mode ( when the BMS trips or detects a fault, it will show low voltage anywhere from 0v to x volts depending on the BMS ) ... a bad connection on the output somewhere.. or the BMS is correctly tripping because one of the cell group voltages drops at the first sign of a load...

more pictures of the pack would be nice..
 
Ok, I will take more pictures and do more measurements. Just for my curiosity, if the BMS is working properly, wouldn't the output be 37.89V instead of 19.20V? I don't know how BMS works exactly so any explanation would be helpful. I was very tempted to re solder the battery connector to the 38.89V leads but I refrained from doing it and went to ask the forum instead. I think if I connect that way then the BMS cannot protect the battery from over discharge anymore, right?
 
check all sense wires are connected and all the pins in the connections are seated in the plastic plug. Good sign that all cells 3.17v and 37v pack.
 
I'm always the one reminding folks to check the obvious, but maybe not so obvious thing. Does your charger work? Broken plugs or wires on the DC side are very common, and maybe you just need to get a charge into the battery to unstick the bms.

If you charged, actually got current into the battery, you should be seeing more than 37v before the bms now.

The problem could still be the bms, but far more likely is the plug on the charger, or on the battery case. Often the problem is a broken wire at the plug.
 
I had problem like this, BMS cutting out, showing lower voltage than the packs voltage. I did disconnect it from battery and then reconnected it and it started charging. That BMS quit working later. Bought one of cellman, had no problems since.
 
luvxu said:
Ok, I will take more pictures and do more measurements. Just for my curiosity, if the BMS is working properly, wouldn't the output be 37.89V instead of 19.20V? I don't know how BMS works exactly so any explanation would be helpful. I was very tempted to re solder the battery connector to the 38.89V leads but I refrained from doing it and went to ask the forum instead. I think if I connect that way then the BMS cannot protect the battery from over discharge anymore, right?
Click to expand...
If you are really updating the 12S 36V pack to 16S 48V pack. Then you can just directly detach the 12S bms and charge 12S lifepo4 pack without bms and restore them to full energy. LiFePO4 cell wil be 3.3V when it stores power. Then update the pack to 16S 48V. It's a way to save thing if you have decide to go for a 16S 48V.
 
ok, so I took the battery out to measure again and here is what I got for each of the cell

1. 3.35v
2. 3.34v
3. 3.34v
4. 3.44v
5. 3.4v
6. 3.47v
7. 3.44v
8. 3.51v
9. 3.34v
10. 3.34v
11. 3.34v
12. .17v

so I figured that the cell #12 is not working right and opened up the cover for inspection. I found that the last cell has a layer of brownish deposit. It looked like it has been leak (see pix). Assuming that this cell is dead, do you know if there is a way for me to buy a replacement for it? Is there a way to remove and replace the cell? I tried to removed it but it is hard so I gave up for now.

IMG_20120727_064436.jpg

IMG_20120727_070513.jpg

IMG_20120727_071110.jpg
 
I recognize those grey cells, some importer guy in the US " os... something " carries packs like this..

A dremel tool with a cutting wheel will make life easier :wink: ,... or, carefully, a hack saw for the white block stuff.

looks like that bottom row may have gotten wet and corroded then leaked... or just shorted out and smoked..

going to have to replace that row of 3.
 
Thanks Ypedal, I have looked on ebay but can't find a similar battery cell for replacement. if someone know where I could buy the replacement cells then that would be great.Once I got them then will find out how I can tackle the disassembling and replacement of the cells later.
 
This may be it. I believe it is a 36650 cell and I too remember someone in the US selling them.
It would be helpful to measure the cell and see if it is 65mm long and 36 mm in diameter.
http://www.alibaba.com/product-gs/287477405/3500mAh_lithium_battery_IFR36650_cell.html
otherDoc
 
I think that must be the battery. But it is all the way in china and the order is a pack of 50 . I just need 3. There must be someone in the US who is selling similar battery 3.5AH 65mm long and 36 mm in diameter hopefully.
 
The closest match that I have found on ebay is this one from vPower

http://www.ebay.com/itm/A123-26650-LiFePO4-Battery-cell-3-3v-2300mAH-3-Pcs-/221080729858?pt=US_Rechargeable_Batteries&hash=item3379703902

It has a little less power 2300Ah instead of 3500Ah but the dimension 66.5x26mm should fit within the original battery 67x32.5mm.

I think I will get a little less power but everything else should work, right?
 
peel the straps back off each end of that end row and get the cells out where you can read what is printed on them. then go google that for the source and you should find them on alibaba.
 
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