LFP from Docan failed + the warranty experience

[princesse]

Hi all,
I bought 16 EVE LF280K cells from Amy Zheng in April 2022. Recently I discovered that at least one cell in my 8S battery had failed. Everything looked fine until the night before, the SOC was 60%. The next morning we opened the fridge and noticed it was dark (off). That’s when we checked the voltage of the battery cells. The 12V fridge was the only load on the 24V LiFePO4 battery via a 24V-to-12V converter. After measuring the voltages of each cell, we disconnected the cells to protect healthier cells. Then we took a video showing the voltage of each cell to send to Amy. The voltages were

2.664V
2.625
1.921
0.660
2.649
2.652
2.660
2.728

3.385 – This last one is from another (healthy) battery.

We were using a BMS, so not sure why the voltage went so low. The BMS manual shows the low voltage protection setting range is 2.7 to 2.9V. This means a user cannot adjust it to 0V by error. The manual says the delay for the protection is 1 to 3 seconds. Perhaps if there was a short circuit within a cell, in 3 seconds the voltage got lower and lower?

Before the purchase, I requested their warranty info, which Amy sent me in a pdf. The warranty details were the same as what you see on their webpage, except they’ve added one more sentence at the end of their web version.

Return & Refund Policy

DIY battery pack must get the cells balanced (same voltage ) before assembly. Later if there happens don't know how to assembled or wrong assembly is not accepted refund. Professionals will detected voltage/resistance/appearance and other issues before every shipment, we can only ensure that the sin

www.docanpower.com

The warranty says, “Warranty period: 3 years (from the date of successful delivery), if the single battery capacity less than 80% initial capacity, take the test pictures or video to us, we will replace it or give satisfied solution.” I hope Amy will keep her promise and provide a free replacement because as far as we know, there is no user error involved here.

I am seeking help in 2 areas:

1) I would like to hear other people’s experiences with the Docan warranty. Please share on this thread.

2) Assuming the lowest voltage cell is dead, how should we try to safely revive the 7 other cells?

Thanks

 

[Bud Martin]

So you made two 24V battery packs?
I am surprised that one of the cell keeps discharging down to 0.660V even after the BMS has gone into Low Voltage shutdown.

 

[Alkaline]

What BMS were you using, are you sure its not loose connection wire, if its not then yeah 0.66 = Dead as a doornail not reviving it but you also have a 1.92 that is pretty bad as well.

These 280Ks ...

 

[Alkaline]

send some pictures I never seen a LFP cell this low, I think you have a BMS connection problem. Are you using a DALY bms by any chance? If so then I'm not sure I would be blaming Docan on this, those are known to do amazingly stupid things.

 

[Rednecktek]

Assuming the lowest voltage cell is dead, how should we try to safely revive the 7 other cells?

Have you tried a top balance on them then checked with a DMM to see if they held?

 

[princesse]

So you made two 24V battery packs?
I am surprised that one of the cell keeps discharging down to 0.660V even after the BMS has gone into Low Voltage shutdown.

8S + 2 x 4S. We wondered if the voltage went below the minimum converter input voltage, which stopped further discharge. In that case the BMS has not gone into Low Voltage shutdown , i.e., defective.

 

[princesse]

What BMS were you using, are you sure its not loose connection wire, if its not then yeah 0.66 = Dead as a doornail not reviving it but you also have a 1.92 that is pretty bad as well.

These 280Ks ...

JBD AP21S001, no loose connections.

 

[400bird]

Either the cell is self discharging or the BMS is hosed and discharged that one cell and the one next to it.
The BMS seems like the more likely culprit to me, as a failed, self-discharging cell #4 should have no effect on cell #3. But a BMS gone pear shaped, easily could have tanked one cell and pulled the one next to it down some.

8S + 2 x 4S.

Wut?

 

[Bud Martin]

8S + 2 x 4S. We wondered if the voltage went below the minimum converter input voltage, which stopped further discharge. In that case the BMS has not gone into Low Voltage shutdown , i.e., defective.

8S + 2 x 4S. ?????
You have 16 cells, so 8 cells in series, 8s, = one 24V battery pack with one 8s BMS, if you make two pf them then you have two 24V battery packs connected in parallel to make a 24V battery bank.
Or If you make 2p8s battery pack so you will end up with just one 24V battery pack with one 8s BMS.
Can we see the picture?

 

[princesse]

Have you tried a top balance on them then checked with a DMM to see if they held?

I ordered a power supply to try that following the instructions on the pdf from https://diysolarforum.com/resources...ls-using-a-low-cost-benchtop-power-supply.65/

 

[Bud Martin]

I ordered a power supply to try that following the pdf from https://diysolarforum.com/resources...ls-using-a-low-cost-benchtop-power-supply.65/

So did you do top balance when you first got the cells last year?

 

[princesse]

re 8S + 2 x 4S, we are in a transition to 2 x 8S.

 

[princesse]

So did you do top balance when you first got the cells last year?

No, they were all the same voltage.
Edit - It was a year a go, there may have been a 0.001V difference, so practically the same. One thing we also remember is the first time we reached 100% SOC the XiaoXiang app showed all cells in green, indicating all cells having the same voltage. So we were not concerned to top balance.

 

[Bud Martin]

No, they were all the same voltage.

Same Voltage does not mean the cells are at the same SOC (State of Charge), this is due to flat Voltage curve of the LiFePO4.

 

[Alkaline]

POST PICTURES.

Posty posty, we need to see what you are doing. I have used 3 JBD also 8s config and never had an issue, also looking at a 16s JBD for a future build.

 

[Gavin Stone]

If you haven’t top balanced the cells then that’s one issue. Voltage means almost nothing, at least in the center range, because of the flat voltage curve as mentioned above. They should be brought up to at least 3.5 together in parallel. The other issue does sound like a bad connection to the bms.

 

[Alkaline]

Maybe hte BMS is reading the voltages wrong? Can you check with a volt meter, there was some alabama coach guy who posted about his JBD getting wrong readings and it turned out to be an issue with the BMS not reading voltages correctly.

 

[augiedoggy]

Hi all,
I bought 16 EVE LF280K cells from Amy Zheng in April 2022. Recently I discovered that at least one cell in my 8S battery had failed. Everything looked fine until the night before, the SOC was 60%. The next morning we opened the fridge and noticed it was dark (off). That’s when we checked the voltage of the battery cells. The 12V fridge was the only load on the 24V LiFePO4 battery via a 24V-to-12V converter. After measuring the voltages of each cell, we disconnected the cells to protect healthier cells. Then we took a video showing the voltage of each cell to send to Amy. The voltages were

2.664V
2.625
1.921
0.660
2.649
2.652
2.660
2.728

3.385 – This last one is from another (healthy) battery.

We were using a BMS, so not sure why the voltage went so low. The BMS manual shows the low voltage protection setting range is 2.7 to 2.9V. This means a user cannot adjust it to 0V by error. The manual says the delay for the protection is 1 to 3 seconds. Perhaps if there was a short circuit within a cell, in 3 seconds the voltage got lower and lower?

Before the purchase, I requested their warranty info, which Amy sent me in a pdf. The warranty details were the same as what you see on their webpage, except they’ve added one more sentence at the end of their web version.

Return & Refund Policy

DIY battery pack must get the cells balanced (same voltage ) before assembly. Later if there happens don't know how to assembled or wrong assembly is not accepted refund. Professionals will detected voltage/resistance/appearance and other issues before every shipment, we can only ensure that the sin

www.docanpower.com

The warranty says, “Warranty period: 3 years (from the date of successful delivery), if the single battery capacity less than 80% initial capacity, take the test pictures or video to us, we will replace it or give satisfied solution.” I hope Amy will keep her promise and provide a free replacement because as far as we know, there is no user error involved here.

I am seeking help in 2 areas:

1) I would like to hear other people’s experiences with the Docan warranty. Please share on this thread.

2) Assuming the lowest voltage cell is dead, how should we try to safely revive the 7 other cells?

Thanks

This should have never happend even with bad cells, unfortunately something else was to blame here (bad wiring or bms) If it were me I would not warranty this (Sorry, just being honest) defective cells dont just all fail at once on the same cycle and they would never go below the minimum voltage set by the bms overnight like that.. Something else caused this.

 

[Alkaline]

Agreed we are not getting the full story here.

 

[princesse]

Slow down people, I didn’t want to go outside and take pictures at night. You must be all younger than I am

Attached are …

pics showing BMS wiring, taken early Feb,







the app showing SOC 60% the night before the cell failure,


taken today, some BMS wires are removed after the cell failure.







We are stationary for the winter. The aligator clip is a temp solution, we had to do something quickly after the cell failure to connect the fridge to the 12V battery. I know some wires are too long, as I said, we are transitioning …

 

[princesse]

Hope we can figure out potential causes to prevent future problems.

 

[Bud Martin]

1) Looking at the pictures, I cannot tell how all the 16 cells are connected and you only have one BMS. I do not see any cells connected in parallel to get 8s2p. I see top row cells are connected in series, same for the bottom row so I cannot see how you use one BMS for two 8s-cell configuration.
2) The BMS (21s) is rated at 3.7V for Li-ion, not for 3.2V LiFePO4. Can it be configured for LiFePO4? And are you wiring the BMS as 8s?
3) The way you are using the battery busbar for connections, it does not look good, not much clearance.
4) What are those 50A fuses on the cell terminals for?
5) You you draw out the wiring diagram of your battery?

 

[wattmatters]

pics showing BMS wiring, taken early Feb,

What are all those thin wires connected to one battery terminal doing?

Those lugs on the BMS look dangerously close to shorting to me.

 

[augiedoggy]

I see what I think are 2 bluetooth modules which means there may be 2 bms modules. I also see 2 bms heatsinks.

. I see cell c4 is connected incorrectly but I assume because your started disecting the pack.. I will stand by my statement that if any component failed here to bring all those cells down the way they did it would have to have been something other than all the cells like the BMS, and why are these 3.7v nmc bms and not the correct 3.2 lifepo4 version?

 

[augiedoggy]

What are all those thin wires connected to one battery terminal doing?



Those lugs on the BMS look dangerously close to shorting to me.

The bulk of extra wires on the #7 cell in an 8 cell pack is correct with this bms..