48 Volt 12Ah LiFePO4 replace cells or new battery

[nailsnglue]

Hoping this info and pictures can also help someone else troubleshoot problems.

For a long time my bike has sat idle in the garage dripping with disappointment that I purchased it. From new, the battery cut out on hills. Cycling the battery on and off restore it working until another heavy load applied. Battery recharges to 53 volts. Today I set about running some battery tests to determine if there was a problem with the battery. On testing each cell I get 3.98v to 4.06v. It wasn't until; I applied load that it was apparent there are massive problems with the battery.

A = no load
B= load applied with bike on bicycle resistance machine as shown in picture. Load was applied increasingly until LVC occurred. Lowest voltage shown. 

B1-B2 - A:3.9v  B:2.87v (BAD)
B2-B3 - A:3.98v B:3.4v
B3-B4 - A:3.98v B: 3.4v
B4-B5 - A:3.98v B: 3.4v
B5-B6 - A:3.96v B: 3.4v
B6-B7 - A:3.97v B: 2.4v (BAD)
B7-B8 - A:4.01v  B: 3.53v
B8-B9 - A:3.88v B: 2.7v (BAD)
B9-B10 - A:4.04v B: 3.65
B10-B11 - A:4.06v B: 3.63
B9-B10 - A:4.06v B: 3.64

QUESTIONS:
Could someone please comment as to whether I should replace the battery or just the cells. If just the cells - where do you purchase these from at a good price?
I have search high and low. Does anyone out there actually know what the LVC of the BMS is?

[Pwd]

Hello,

judging by the pictures, it doesn't look like you have a LiFePO4 battery. When did you buy the kit? The main reason I suspect is not the LiFePO4 is the charger voltage. What is the voltage output on your charger? I also know that the older cells were orange (cylinder shape) and the LiFePO4 are blue (rectangular blocks).

[nailsnglue]

Charger voltage is 54.6v. Cells are orange. You are right. It is liion

[Pwd]

Here is a topic on replacement cells for your battery:

http://goldenmotor.com/SMF/index.php?topic=2984.msg17965#msg17965

However, I would highly recommend the lifepo4 battery instead. I have the same older pack as you and basically the same thing has happened (would cut-out under load). When my friend bought his kit with the lifepo4 battery, I swapped batteries with him and immediately noticed the difference. More punch and runs at a higher voltage.

[nailsnglue]

Thanks for your help. Will my old charger charge the lifepo type or do I need another charger also? If you buy the lifepo battery from golden motor does it ship with charger or is that extra?

[Pwd]

No problem, glad I can help.

The lifepo will not be able to use your charger as it puts out 54.6V and the lifepo's charging voltage is 58.4V

The GM battery should come with the charger, it should be in the item description. FYI, this is where I got the one for my friend from:
http://www.goldenmotor.ca/products/48V10AH-LiFePO4-Aluminum-Cased-Battery.html

[Bikemad]

I thought I'd better mention that you have not tested all of your cells. You have only checked 11 groups of cells and there are two other groups of cells that will also need to be checked if you are still considering replacing individual cells (or cell groups).

The following diagram shows why these two groups have not been measured:



You need to measure the voltage between "B-" (not "C-" or "D-") and pin 1 on the balance plug connector to measure one group, and between pin 12 and "B+" to measure the other group. If you use "C-" or "D-" instead of "B-" you may get incorrect readings caused by voltage drop across the MOSFETs.

Unless you are going to replace all of the 39 cells, it probably isn't worth the hassle of repairing the battery pack. The existing cells (good and bad) are all the same age and have been subjected to exactly the same number of charging cycles (and discharge loads) and I think it would be fair to say that more of the good cells are likely to fail soon after you start using the pack again. Especially when you consider that they are likely to be much weaker than the newer replacement cells.

Alan
 

[nailsnglue]

Yeah I have gone with  a new battery. The battery is old but has only been charged about 100 times. It broke very early on and my communication with Golden motor did not achieve resolution.