Capacity loss 48V16Ah. LiFePO4 battery

[Jaak]

Hallo everyone,

I am new to this forum as a writer, but as a reader I am a frequent visitor. Thanks for all the information and pleasure that I have had when visiting it.
The reason for starting this topic is that my 48V16Ah. battery (16 x cell EP1181245, Vcharge=3.65V, Vcut off.=2,4V, Vtypical=3.2V) is loosing capacity after 3 months of use and 30 charge-discharge cycles from a proven more than 15Ah. to a 10Ah. now, and it is still getting worser.
The stop charging voltage is 58.4V and after the BMS cuts off the power, the battery voltage remains 51.6V at zero load.
It seems that the battery voltage (at a 10A draw off) is becoming lesser after time, from a firm 51-52V when it was new to a 49-50V now after starting my ride after full charge of the battery.
I’m not sure, but it seems that the voltage is slowly increasing after a few kilometers ride. (according to my cycle analyst)
The cut-off voltage of the BMS according to my cycle analyst is about 45V, but I am not sure if this is a true value as I wonder if the responding time is fast enough too catch the lowest (cut-off) value.
I have already informed my supplier (ecitypower) and they support me well.
Their first advise was to put the battery on 24h. of charge.
Thus I did, but without improvement.
They now advise to open the pack and measure the voltage of each individual cell just after full charge and also after the BMS cut off and asked me for submission of these data.
I was wondering if anyone of you had ever faced a problem like this and would share their knowledge wit me and help me out of this problem.
Thanks so far for your info.

 

[recumbent]

You definately have to check your batteries voltage individually, because your voltage drop indicates a rogue cell. I have a similar pack and the voltage should rest at about 53volts after charging and left to rest for a day.

Do exactly as you stated your supplier said at the bottom of your post. When you find your low cell (or cells) just charge them seperately with a single cell charger. Or drain the high cells using automotive headlights. Use an old cell phone charger with clips if you monitor them carefully.

What you are essentially doing is manually balancing the cells, then all should be fine in a perfect world.

Also, remember that if your bike is outside and the temperature has dropped below zero "C" your batteries will show a lower value.

 

[dnmun]

post up some pictures.

actually measure the voltages as it is charging and see if you can tell which cell is highest right at the point where the BMS shuts down the charging, record every cell #1-#16 so you don't forget.

then record every cell immediately after it shuts down for LVC. record them so you can keep track of them.

i discharge into a 100W light bulb so it takes about 24hrs.

you can buy a digital voltmeter at harbor freight for $3 on special sales.

 

[Ultraman]

I had some issues with my ecitypower 48v12ah pack. I tested the individual cells and found a weak one, which continued to be weak after individual charging. Jack Du has offered to send me a cell and some packaging to put the pack back together after it's replaced. Looks like yours might be in worse shape than mine though, I was getting 10.6ah out of my 12ah pack after about 30 cycles. Check out page 18 of this thread for a similar discussion. http://endless-sphere.com/forums/viewtopic.php?f=14&t=9054

 

[Jaak]

Thanks all for your replies.
I did already do the test and I have attached the results in a photo.
Pay attention to cell 14.
I also have attached a photo of the dismantled batterij and the Trice it is used for for your info.
Results are already mailed to Ecity power and I am waiting for their instructions.
Keep you informed.
All the best.View attachment results measurements.JPG

 

[Jaak]

I want to close out this with a recap of what happened in the past year:
I came into contact with Ecitypower (Jack Du) and send my battery back to him in October 2009 for a warranty repair.
Their diagnostics revealed failing cells, also as a result of transport damage they stated.
They replaced 4 cells, 2 on their costs and they charged me for the other cells.
After having received the battery and having charged it, at my first test ride the BMS cut off at 11Ah, which is still 5Ah less then the original capacity of 16Ah.
After another 20 cycles, the BMS cut off came in at 6.5Ah and was still becoming worser every cycle.
As it was a very time consuming and unpleasant experience (see below relational details) to get my battery back, I was very reluctant again to contact Ecitypower and I decided to open up the battery myself just after the BMS cut off. (I luckily ordered some spares)
It appeared that 1 cell had a significant lower voltage than all the others.
After replacement of this cell, the BMS cut off came in at 11Ah.
Now, about 4 months and 60 cycles later, the BMS cut off remains at that capacity value.
So far the technical details, now the relational details with Ecitypower.

Jack Du from Ecitypower (he left the company a few months ago as they told me) was a friendly person, but his Email responding behaviour was sometimes provoking me.
Promises on information about the diagnostics, repair proposals and shipment were not kept and the weekly Email contact had always to come from my side.
It took more than 3 months before I had the battery back home and I wonder if this would not be longer if I did not threaten him with addressing the story to the Endless Sphere forum.
Now 1 month ago, I informed them about the battery and I requested them to offer me for some spares that will enable me to repair the battery myself.
They replied me saying that the battery was out of the warranty period of 1 year, which in fact is true, but counting for the period it has been in my possession, this is still lesser than 1 year.

By closing this thread, I think that I have learned the following from this buying cheap and light Lifepo4 Chinese battery including the accessories.
- Cheap. I could not afford spending more money.
- As you may believe from other threads, other similar batteries (Ping) and manufacturers will do
better.
- I have learned some of the essentials of Lifepo4 batteries and repairing them which was very
interesting and satisfying.
- I cannot prove, but threatening with addressing names of man and horse to the ES could help getting
things afloat.
- Once you bought, you are stuck and delivered to them for spares and replacement parts, so I am
now going to order new parts and keep them smile.

 

[dnmun]

from your original measurement of the pack, it appears that the only cell that was bad at the time was #14. if they replaced other cells and not that one you would still have a problem. in fact they really should not have charged you to replace anything if that was the one they replaced originally since it was self discharging pretty fast then. maybe it was simplest for them to replace 4 at once but there is no way to know. i doubt if jack even had any contact with the people who repaired it. they would have sent it back to the people who build packs for them to get it repaired and those people may have had no clue, or have access to your your data for analysis. imo

this pack has the v1 signalab for BMS or the ecitypower BMS?

 

[Jaak]

I don't know.
Here's a photo.
Rgds

 

[dnmun]

do you know which cell is low now? are you gonna attempt to unsolder the old one and insert a new one? are they glued together?

#14 would not have been damaged by handling, but maybe when it was returned to them they thought that was what the problem was if it was damaged in return to them.

do you know which cells they replaced and how do all the voltages compare when it is discharged down to where it cuts off at 6Ah where they are now. this is 2 pouches for each 16Ah?

 

[Jaak]

I don't know what cells they have replaced.
I will not open up the pack again until the BMS cuts off at 7Ah. (It now cuts off at 11Ah.)
7Ah is what I need for my single home-work ride.
Each single cell is 16Ah. (see photo)