LiFePo4 / chargery one cell dropping fast

[dudeinthewoods]

I've got a 48v LiFePo4 280ah and chargery 16t.

For some reason cell 13 has been dropping while the rest are staying full. I looked and it was at 1v while the rest were more or less the same. I pulled it and bypassed so I'm on 15 cells right now which doesn't excite me either. The 15 are holding up better than the 16 were.


Cells all just arrived a few days ago from xuba.
Chargery BMS seems setup right.
Nothing is loose or oxidized etc.

Just not sure why #13 dies so fast. Could have shipped me a bad cell? What to try balance them up and see if it happens again?

 

[snoobler]

#13 dies because you didn't balance them before build, or you got a bum cell.

 

[Steve_S]

#13 eh. Hmmm
Did you Bottom or Top balance prior to installing ?
Have you swapped cell positions, meaning swap #13 with say #6 and is the behaviour the same ?
The BMS Balance leads, is the #1- & #1+ on the last cell where the main NEGATIVE comes off the cells as shown below (16S example)

 

[dudeinthewoods]

Thanks both of your for the feedback.
I let them sit and equalize but didn't connect a power supply and verify it. I probably screwed it up.


I'm going to do it right now and hopefully don't need to buy any new cells. Could have got a bum cell but probably my fault.

Edit: thanks Steve, verified it is hooked up right and no didnt swap cells just going to balance now.

 

[snoobler]

What do you mean by "let them sit and equalize?" Did you parallel all of them and leave them that way for several days, or did you just have them sitting there in series?

I wouldn't be so quick to take the blame. New cells should be charged to a very similar state of charge.

 

[dudeinthewoods]

I should have been more clear.

I checked every cell and they were what I thought was close enough 50mv or so.

Then hooked the BMS up and let that sit.

I thought I was good to go. Worked fine the first 24 hours then #13 crapped out.

 

[snoobler]

That clarification suggests it's highly likely you got a bum cell unless 1-2, 14-16 were all the same and #13 was the only .05V outlier. When #13 is at 1V, what do the others read?

 

[dudeinthewoods]

The others were all 3.24 - 3.26.


I may have. I'm going to try a complete top balance of the whole thing make sure it's all dialed in perfectly and see if it fixes it. I may have rushed it but didn't think so at the time.

 

[snoobler]

Sorry, is that the as-received voltage, or the cell voltages when #13 is sitting at 1V?

 

[dudeinthewoods]

While #13 is at 1v

Sorry trying to work as fast as possible its TX without AC I'll work on my clarity haha.

 

[snoobler]

Bum cell.

 

[dudeinthewoods]

Yeah what I'm afraid of.

Bought 16 from xuba
14 arrived waited for the other 2
2 lost probably not their fault
Bought 2 from Craig (thanks)
Bus bars from xuba didn't arrive so they shipped air (thanks)
Now one is bad this just hasn't gone smoothly haha

 

[snoobler]

Personally, I never trust anything that comes from Ali/China. I will always test something to verify it meets spec.

 

[Xerxes]

Are you in the USA?
Did you use an American Credit Card to pay?

If so then you should have given XUBA the opportunity to replace the two missing cells as they are responsible for you receiving them.
Its one of the few times that ALIBABA sides with the buyer instead of their Chinese Countrymen, and withholds payment if there is no proof of delivery if you complain.

For the bad cell XUBA should replace that as well-if it is their cell that is bad.

But from your last posting it sounds like two of the cells are not matched to the other 14 so such behavior is predictable if the Craig is battery #13.

You should have definitely top balanced (if your BMS is set up to do top balancing management) to take into account two different sourcing/age/possibly different manufacture.

Do not try to series balance as there are too many members here reporting they do not have the patience for this (bloating)-parrallel balance only and watch it diligently-there are no additional safety factors if one step/procedure/component goes south on you.

 

[Ampster]

..........

Do not try to series balance as there are too many members here reporting they do not have the patience for this (bloating)-parrallel balance only and watch it diligently-there are no additional safety factors if one step/procedure/component goes south on you.

If i remember correctly three examples of bloated cells were from overcharging in parallel. Series top balancing is usually done by the BMS.
My take on this cell is that it has gone south. There is nothing that balancing can do for a cell that drops to 1 volt while in a series string. The OP can try to charge it up and capacity test it individually. I would not put it back in the pack in series until I know it has similar capacity to other cells.

 

[CaptainDenmark]

I suggest you find out if the chargery draws power from #13.
I found one of my packs had a 0.00v cell after a longer storage, (turned off) made no sense.
So I measured the balance lead for the cell, and sure enough, it draws 35mA even when turned off.
Defekt Chargery, fracked up my entire pack.
Pretty lame as it is supposed to protect my investment.

 

[snoobler]

Long term storage of a battery with the BMS attached is folly unless you KNOW the BMS cuts itself off at some threshold. They need power to assess the battery.

 

[CaptainDenmark]

Long term storage of a battery with the BMS attached is folly unless you KNOW the BMS cuts itself off at some threshold. They need power to assess the battery.

Now I know.
The BMS was shut down, the other pack was fine.
It is the short circuit Thad messed up my cell.
Take a good look at the picture, what is going on there is not right.

 

[Ampster]

They need power to assess the battery.

I guess that is one advantage of more expensive BMSs like the Orion that are powered separately. That may speak more to their typical use in EV applications where the BMS is turned of unless the EV is charging or driving.