Weak Cell

[expresso]

I have one Weak Cell - on my ADD ON pack its an 80ah pack

its fine other than the fact it takes a long time to balance that one cell - when its not used daily -

i am curious how bad would it be to just leave it and use this way - what happens if one cell does go bad discharges much faster than the rest of the pack - if i dont do nothing to this - what happens to the rest of the pack when in use ?

i have a spare cell and i may just change it out over the winter - i am just curious what would happen if i didnt change it and just used it as is -

this is an ADD On i use with the bounder - if i use it daily and recharge daily - its not too bad to balance the one cell - but when not used often - and winter time sitting for long periods - it takes a long time unless i charge it weekly -

lets say that one cell does die in use - what happens to the rest of the Cells - do they get pulled down faster but still work ?

thanks

[Burgerman]

its fine other than the fact it takes a long time to balance that one cell - when its not used daily -

This is why its essential to test self discharge rate when building a new pack. With headway packs using many small cells, you can shuffle cells around to end up with the same total self discharge. With big prismatics you can buy A grade, or maybe an exra cell. And discard the one with the worse self discharge rate. But if a cell is stored too full, taken over voltage (hello all BMS!) or discharged too deeply as can happen easily on an addon pack, then this can happen later on too.

i am curious how bad would it be to just leave it and use this way - what happens if one cell does go bad discharges much faster than the rest of the pack - if i dont do nothing to this - what happens to the rest of the pack when in use ?

As cells age or deteriorate they do so in different ways. Maybe 1 of these or could be all of them.

1. Self discharge rate. Reduces capacity over time. If used same day its no problem. If used a week or a month later possibly big problem!
2. Reduction in capacity. Your 80Ah cell isnow a 40 or 60Ah cell. Obviously less range as this cell is now smaller.
3. Internal Resistance. As it increases you can pull less and less amps from that cell.

All of these things are accelerated if:
Stored full.
Ever taken to too high a voltage. The further you stay away from top voltage the better. And the shorter time its held at a safe high voltage the better.
Ever taken to too low voltage. The further you stay away from this the better.
Ever taken too much current. So too small pack, too low C rate. The further you keep away from this the better.

What will happen if you keep using it? Same as now. Only will get worse over time/cycles. And I dont know why I bothered to write all this as you will read one line.

[expresso]

i dont expect my ADD ON packs to work as well as others - last year i replaced one cell once i removed the pack and redid it with better connections - the studs on one of them were stripped - so i replaced it and it was fine - but that pack i didnt give the same attention as the full packs - i did a quick build - - so i redid it and changed one cell last year -

i noticed after another cell is weaker - i dont use a BMS on it - the chair has a BMS - not my ADD ON - i may have over done it when i did that 68 mile test ride - the chair BMS i am sure cut off -and i was running off the ADD ON only at some point - either way - i believe that had something to do with it

so unless i charge often daily or weekly at least - it takes too long for that one cell to balance out - during discharge its not that bad - it hangs in there - and i dont even think its the first to drop - its just on the recharge balance where its not good

i will just change it since i have a spare - i was just curious if i didnt change it - i dont do 68 mile rides -i did it that once to see - even on a long ride -i say 50 miles at most - thats all well with in the range - not worried much - about over discharging it - but as it ages - the chair pack also - with the BMS - it my have lost some of its Cap.

on my Full Packs - i dont have that issue - my 6 year old 105ah headways are fine - charge up balance fine just as good as new - even the head ways ADD Ons are better overall - i cant say i got Grade A cells when i got those 80ah cells - the new replacement cells i got from another seller and are Brand New - the one i replaced is the best of the pack - the rest are all even and then one weak one i will replace -

i am charging it now and its balancing - i will see how long it takes - i dont expect it to be too soon - i been too busy with my apt. to deal with it - till now - after this charge - i will discharge it some - leave it alone and change it over the winter before i use the chair again next year

[expresso]

Lets say for example

the ADD ON pack - the weak cell drops down dead during use - below 2.5v or 2v etc, the rest of them are good -

what would happen - does it still work and keep going - i would think it would and the rest of the them would work harder ? till they slowly get bad over time also ?

this pack was one of the first that i had to glue down those studs on top - and in doing so-i have had issues with stripping the hole - i have done a better job with the other packs after i learned better with this one - i didnt use Red locktite on this one when i first did it -and used lockwashers also - it was a quick thing

its been used pretty hard and not built as well from the start which may have caused this to happen - i though it was screwed down good but finding out that a few may have not been and stripped - the one i replaced last year was stripped - could no longer work - it may be still good - but would need to be redrilled the hole etc,

i am not going to bother with it - its garbage for me - and so will this one when i replace it -

[sacharlie]

And I dont know why I bothered to write all this as you will read one line.

LOL
Not me, I just keep reading and reading and reading.

[Burgerman]

He missed this line, so missed all the rest. Then repeated the same stuff over.

[expresso]

pack is removed from chair - will replace the cell this weekend - and test -

from the graphs is one cell #5 - Cell 8 is the new one from last year - thats the strongest - the rest are all about even across - and Cell 5 the weak one has to go

[expresso]

i replaced Cell 5 with a new one i had - i discharged it some since i had the pack discharged some also -

not knowing how much the pack was or the new Cell - i connected it and guess what cell 5 is still the lower one out of the bunch -

i know i have to fully charge it and maybe i do a full discharge just to see how much this pack really is - then do a full recharge - before i worry about it -

BUT in the event when all said and done - and its still Cell 5 same as before - Could that be possible - if so - is there another reason for this i cant think of what it may be

PL 8 showed Cell 5 - weaker - bad - i replaced it with a new Cell - same as the one i replaced last year -

i was not expecting to see Cell 5 lower than the rest now - so i am fearing the worse - that it will end being the same - meaning maybe the Cell i replaced isnt bad - in that case - i am lost for what it can be -

this pack is like a frankincense pack - two different cells - size wise - but same 80ah in Cap -- 6 taller cells - but thinner - two shorter ones new ones - but thicker -

if something is wrong - i either just leave it till it dies - and redo it with Brand new cells -

i will start it tomorrow - recharge - discharge and recharge -

[Burgerman]

I already explained all this many posts ago where you skipped all the words...

You also keep saying weaker/stronger cells. It doesent work like that. As I already explained.

You can have a cell where the internal resistance is high. And yet that can have as high or higher Ah capacity than its freinds.
You can have a cell with high self discharge thats better in internal resistance, and higher OR lower Ah than its freinds.

Theres no such thing as a weak cell unless you are refering to high resistance where it doesent like high currents.

These 3 things are seperate. Resistance, capacity, and self discharge rate. A cell can be better or worse on all of these things seperately.

[expresso]

yes i know that - when i say weak cell - it means its not as even as the rest of the pack - the lines on the graphs

i started off with 8 Cells all the same kind - most likely - not brand new or grade A - now that i know -

they all were fine at the start - i slapped this together quickly and not correctly - in terms of using the locktite - Red - and being gentle with the set screws on top - - so from the start - i had some stripped cells - i managed to make it work - and then used it - and i used it hard that first year with the bounder -

when i started to see on the graphs - i noticed it - i checked it and noticed i had a few loose connections - i couldnt fix one of them - stripped it on top - so i replaced that one - cell 8 - that cell line on the graph sits above them all - stronger than the rest - i say - the new cell was brand new -

i noticed this Cell 5 from last summer also - but i didnt bother much since i used the chair more often and recharged more often - the balance end wasnt too bad - - i ordered a new cell anyway in case to keep here -

i am charging it now for the first time

Cell 8 - pink is new cell from last year - cell 5 green is new cell from last night i replaced - the rest are from 3 years ago - all are 80ah



since i havnt been using the pack much this year - Cell 5 - sits much lower down and weak to balance at the end of the charge - so all the rest of them are at 3.6 - while Cell 5 could be at 3.45 - or something like that - if i leave it - it will catch up of course -

so i decided to just change it - its done - i am now charging it up fully - to get them even balanced - i will try a full discharge - just to see what the pack really is now - in terms of Cap. - and then recharge again and thats it - maybe i discharge it some since it will sit not being used till next summer -

my concern is what if this Cell 5 - acts the same way as the cell i removed - that would mean what ?

what are the odds of two cells acting the same way - one being brand new - compared to the other being older i am sure from the start and used hard a few years -

i dont think they would be the same - so if the graph shows the same for Cell 5 - that can mean only what then ?

connections are good now - there were good from last year also - nothing is loose -

i guess i cant say just yet - i have to do this charge discharge and recharge - to have a better idea - its just i was not expecting Cell 5 to sit lower now - but then it could be that i discharged it much lower than the rest of the pack - i have no idea how much i discharged overall from either - i had it discharged some already before i took out another 20ah - from the single new cell

the pack i believed i removed 20ah also - more or less -

[Burgerman]

But tha graph where you just started to charge shows the pink cell is either higher impedance (bad) or lower self discharge (good) or greater capacity - so that its voltage has dropped less during discharge, but which is it? Same pink cell also odd in that its voltage is falling as it charges for the first 15 mins. That is often caused by a bad connection somewhere. Although some cells do do this which is why balance should never be attempted below 3.45 to 3.5V.

[expresso]

cell 8 was new pink

cell 5 was new - green - both are same cells - from same seller - size etc,


and its the same way - so its NOT the Cell thats bad or weak i dont believe -

i can try changing the wire that connects Cell 5 with Cell 4 - thats where it connects 4 cells to the other 4 cells -

but if that cable is show how the problem - why wouldnt Cell 4 show as bad - or cell 6 ?

its cell 5 only - - i will let it finish now - just to see how long it takes - the cell i removed i will keep now -

if its an connection - grub screws that are locktite down - nothing i can do about that now -

[expresso]

this is an 60ah pack i use on my indoor chair - with lead

these cells are better in terms of solid studs welded in place when i got them - all i had to do is screw it down with the large nut on top thats it - - worse case i can just use this pack on my bounder - i am sure 60ah is enough also to get me thru the day -

the 80ah pack was the first set of cells i used that had to be locktite down - and very fragile to strip etc. i did a quick build then didnt think much of it - i used lockwashers at first and buss bars instead of cable for the connections - being used hard a few years - i noticed Cell 8 was an issue - last year

checked connections - loose - etc, i went to repair Cell 8 but stripped it in the process so - cant use - got a new cell - replaced it - redid the connections - used cables instead of the buss bars - lock nuts etc, all was good - now its cell 5 - i assumed it was the cell - got new cell same as cell 8 - and now its not the cell

cant believe two different cells would act the same way - its got to be something else causing this - either the cable joining them together which goes from Cell 4 to Cell 5 - or the cable from cell 5 to cell 6 - -

but then why wouldnt Cell 4 or 6 have an issue and only cell 5 does ?

[Burgerman]

Cell 8 has bad connection somewhere. Or is very high impednce.
Cel 5 is far from charged for whatever reason. (self discharge?)

[expresso]

this is the 80ah before i changed out any cells after i redid the wiring and used cables instead of buss bars and lockwashers etc, or i may have used the same screws as the headways with blue locktite -

[expresso]

this is how the pack is right now -


with also Cell 5 changed out - same as cell 8

[Burgerman]

Are your balance wires CRIMPED?

Thaat will definitely do it.

[expresso]

Cell 8 has bad connection somewhere. Or is very high impednce.
Cel 5 is far from charged for whatever reason. (self discharge?)

nothing i can do about the connections really - the screws on top are locktite in the Cells - the lock nut is tight - cant be anything else other that its a different cell from the rest and not matched of course

my concern is Cell 5 - thats the issue - i assumed it was the cell - and replaced it with same cell as Cell 8 - but its not the cell then - the one i removed was the same way -


so what are the options if all are tight now - i will wait till it gets cell 5 charged up fully - then what should i check next ? i was thinking of changing the cable joining both Cell 4 and Cell 5 - easy to do and check it again - ?

[Burgerman]

Are your balance wires CRIMPED?

Thaat will definitely do it.

????

And be sure you charge all full before doing any evaluations. Tests. Etc.

[expresso]

Are your balance wires CRIMPED?

Thaat will definitely do it.

yes all my balance wiring i ever done was crimped with those 3M - never had an issue before with them - i usually double up on the wire - fold it in half and then crimp it down and heatshrink is built in -

[Burgerman]

Then there is likely many of your problems. I said dont crimp for very good reason.

We are balancing to a mV.
Do you know what voltage you get when you join copper wires to a brass or zink coated connector? You get 1.1V or if you like 1100mV... Because that forms a battery once it oxydises a bit or the humidity gets into it. Crimping is no use. http://hyperphysics.phy-astr.gsu.edu/hb ... trode.html

How is the charger supposed to display a proper cell voltage or balance a cell, to within .1mV when you are putting little batteries at avery crimp! That can produce as muct as 1100mV depending on damp, oxidation, etc.

[expresso]

i will let it finish now its going


you think i should redo the one balance wire for Cell 5 only ?

i dont want to take it all apart and use a new balance cable now that we cant find them any more - i dont want to waste it if its only one cell -

maybe i can cut it - add new 3M same way - and try that - that would the easiest to try first - ?


or should i do a full discharge and recharge before touching anything else ?

i dont think its going to change the outcome though

[expresso]

Then there is likely many of your problems. I said dont crimp for very good reason.

We are balancing to a mV.
Do you know what voltage you get when you join copper wires to a brass or zink coated connector? You get 1.1V or if you like 1100mV... Because that forms a battery once it oxydises a bit or the humidity gets into it. Crimping is no use. http://hyperphysics.phy-astr.gsu.edu/hb ... trode.html

How is the charger supposed to display a proper cell voltage or balance a cell, to within .1mV when you are putting little batteries at avery crimp! That can produce as muct as 1100mV depending on damp, oxidation, etc.

the only thing i never soldered were the balance wiring - using the 3M connectors with heat shrink built on - seems fine to me giving it wont be stressed etc, - the connectors are not bare copper -

i guess going forward i would have to solder them and heat shrink myself - but for now - you feel it could be just that one balance wire ? or something else also

[Burgerman]

No. First SOLDER all the balance wires. Or everything else may or may not be meaningless.

Then leave to FULLY charge or help the low cell along and then fully charge and balance.

Then do a full discharge to the point that the first cell sees 2.900V or similar.

Then post that graph.

Then do a full recharge. And show that graph.

Then monitor after charge, for maybe 6 hours. And post that graph.

[expresso]

that will take time now - i can do it - but was looking to just savage it as it is for now -

if its just one Cell - i can try just that one balance wire - and see if it makes a difference - if it does - then i know and if it happens again - then change them all ?

to solder them - i have to remove the cabling first - cut off each end - and try to use the same wiring - just replacing the ends - would be a bit shorter but it work that way -

i dont want to waste another balance cable if i can save this one -

[expresso]

forget the charge i was doing

i asked my girl to go check on my laptop - turns out - i dont see PL 8 charging etc, - who knows if my cat walking over it - i am not there -to see it - so just told her to unplug the charge cable and shut the PSU

i have no idea now

i will just go ahead and do the balance wire - either try just cell 5 first alone - or take it all off and redo them again - this is what happens if your not watching this thing yourself

just so happens my BT decided to stop working the other day - so i can keep it near me to watch it - i had to go back to using the FUMI cable now - till i look at the BT setup to see - will make another one when i feel up to it - i know for sure the cable always works - i am just not near it now when i charge -

[Burgerman]

Not watching yourself. Quite.


There are millions of BMS equipped packs that are suffering all kinds of issues. But the user has no idea. Until one day they stop very unexpectedly.

[expresso]

later i may be able to just cut the balance wire on Cell 5 only - replace it the same way - crimped etc, just to see if thats the issue

i would be able to see that quickly with the PL8 - i can do that without taking it apart - if all good i can leave it - knowing what the issue is - its not the cells -

or i can take it apart later time and redo the balance cables only - if i want to know quick - i have to do just cell 5 - and see

[expresso]

Not watching yourself. Quite.


There are millions of BMS equipped packs that are suffering all kinds of issues. But the user has no idea. Until one day they stop very unexpectedly.

there is no BMS on the pack - i dont have any with a BMS other than the bounder

normally i start the charge - its in the living room - my set up - - i am in my bedroom - computer desk - but not easy for me to get up from so once i am here - i stay here for some time till later in the evening -

when the BT was working - i keep the laptop near me so i can see whats going on -

it was either a cell - connection or wiring - i am ruling out the Cell now - the connections are tight - i cant do more with that - so leaves the wiring - the cables are good size -crimped and soldered - i dont think they are bad - which leaves the balance cable only - to be questioned

i was thinking the cable that joins the two cells - why i dont know for sure - but i guess not - if it was that cable - it would affect cell 4 also i would think - and it dosnt -

so to start off - will try cell 5 balance wire first

[Burgerman]

No. Becaue to measure the cell volts you must know the voltage at BOTH its ends. Seriously messing around with ONE cells wires wont tell you anything useful.

Cut off some insulation, solder them in place. Whole thing is about 20 mins. Also use switchcleaver on the PL8 ends, and on the SubD connectors.

Then check any joiners that go to cells with big wires.

Then charge FULLY.