How do I know if my lifepo4 is wearing out?

T

tbonephile

100 µW
Joined
Jul 7, 2008
Messages
7
Hi,

I have a 48v20ah battery from ping that I have had for almost two years. Its been working great, however this june after not using it for 2 months (I used to use it everyday with my scooter as my daily transport) I noticed a sudden drop in range like almost 40% less riding in the same area and conditions which was weird because I had more range in the winter then I do now during the warmer weather. The other day the LVC kicked in and when I took it home to charge I noticed it only charged 8 ah of power into it before the charger light went off. I thought it might be that it was severely out of balance so I left it on the charger for 2 days to let the bms balance it. I used the volt meter today and noticed that all 16 cells are at 3.58, so it seems the battery is in balance. What could be the cause of the lack of range? Just the battery wearing out? Ironically it charges in the same time it did when I got it new, but it refuses to charge more then 8-10 ah into the battery. Any ideas? For the record I have put almost 14,000 km into this pack! Thanks!
 
I would bet on a weak cell. You might want to check the voltages after you have ridden a bit to see if you have a cell or two that are not playing well with the rest. If not then is the voltage fine and the LVC kicking in early? Brakes dragging, tire pressure low? Lots of things to check on. Good luck.
 
Have you measured the battery voltage VS the cell voltage x 16?
It could be something as minor as a loose soldered connection to a few cells.

Like the previous poster said.. drain that pack a bit and see where the cells are at then. That should reveal some things for ya :)
 
the BMS circuit current will drain down the first 4 cells if you leave it uncharged for a long time. you have to wait until those cells catch up with the others above them over several balancing cycles. just avoid discharging to the point where it shuts down.
 
Well I went for a ride and measured the cells when fully charged off the charger the battery measures 60 volt. Went for a 20 km ride, sure enough 13 cells were at 3.32-3.33, one was at 3.30, another at 3.28 and one at 3.24 Will replacing these three cells solve my woes?
 
When I have the pack charged all the cells are evenly charged around 3.65ish and the pack voltage is 60. I have three cells that a little lower then the others, Can one low cell help to trigger the LVC earlier? Because I'm only able to use 8-10ah of my 20ah pack before it cuts off
 
tbonephile said:
When I have the pack charged all the cells are evenly charged around 3.65ish and the pack voltage is 60. I have three cells that a little lower then the others, Can one low cell help to trigger the LVC earlier? Because I'm only able to use 8-10ah of my 20ah pack before it cuts off
Click to expand...
Absolutey correct.. As the old saying goes, "the weakest link in the chain"

What are the ah ratings on the individual cells?
 
I had one set of cells that were low 48v20ah ping last in line 16 pos. red. took the pack apart and saw one pouch went puff the other 3 cell in parrell look o.k. ? So I replace the end one cell and hope the other 3 are good. I did have the other 3 cells but do beleive in high hopes. It seems better ? Will test with new c.a. first one was defect and replaced 2 weeks later. So time for the test.
 
if you can measure each of the cell voltages when it is fully charged, why can't you measure it when the pack shuts off for LVC?

can you discharge the pack into a fixed load and measure the cell voltages as it drains?
 
O.K., I replaced the one puff cell on the end pos. charged 60.1 not the 61.3v off charger . Rode to 50.7v 18.26ah till the bms cut out is that 838.47 watt/hrs the amount on that one charge. I tried to find a forum ? One cell cut at 3.1v. Now what does all that mean ? Thanks.. it's a 48v 20ah
 
what are the most ah can get out of a 20ah till cut off. I rolled down the hill. then I tested the cell. what the ping cutoff ? 3.1v.
 
the initial pouch should have the ability to store the entire 20Ah. i think yours is close but you got the BMS to hit the LVC when it was under load and that caused enuff sag to pull that cell which reads 3.1V at rest down to 2.1V while under load. so that was why it shut down. imo
 
tbonephile said:
When I have the pack charged all the cells are evenly charged around 3.65ish and the pack voltage is 60. I have three cells that a little lower then the others, Can one low cell help to trigger the LVC earlier? Because I'm only able to use 8-10ah of my 20ah pack before it cuts off
Click to expand...

Absolutely!
http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=17035&start=45#p320679

Measuring 'static' voltages might give you some info, but the real view of cell health comes from looking at voltage under load.
 
Sounds like you are getting your moneys worth out of it anyway. I'd start looking at what you want to do, get another ping, or get into something stronger.
 
You must log in or register to reply here.

Similar threads

riding_on
(Mis)using a Priority Current range extender: should I expect fire damage in my future?
Replies
12
Views
789
calab
C
N
    • Spicy
    • Like
I had a lithium fire (my own fault)
2
Replies
39
Views
2,471
JRP3
JRP3
Skyler
LFP reverse polarity.
2 3 4 5
Replies
105
Views
4,588
DaLanMan
DaLanMan
ERN
I think I may have fried my mind.... help!
Replies
17
Views
1,190
DomW
DomW
H
Why do my DC converters keep dying?
Replies
18
Views
1,009
E-HP
E-HP
Back
Top