PINNED - Lithium battery conversion/info

[expresso]

ok i will have to do that - but i should remove connector plates on those cells both top and bottom so each cell is not connected to each other ?

i am hoping its just a bolt - but we see - i am recharging already now - will start taking it apart tomorrow - not sure when i can have it flipped to get to the bottom though

yes i remember when i did it at first - no balance cable on PL 8 - just leads to each cell with your single cell preset - check each volt monitor first - charge each one - then discharge each one and recharge

do i have to let each cell sit for a day before recharging ? to check which is weaker if any ?

thanks

[Burgerman]

Charge each one first on its own, discharge to 2.9V - that wont be full capacity but will allow you to compare them all. Then charge all back up. If one cell is lower on capacity its faulty. If its capacity falls over time its also faulty. We can test that later if needed. The graph looks like a bad cell.

[expresso]

ok just so i am clear - i will charge each cell - on its own - not connected to the other cells at all - i will have to turn the pack on the side to do that -

after i charge each cell - discharge each cell alone to 2.9v and recharge each cell again - this is with all the connectors off those 7 cells -

and i am looking for what exactly - the amount it takes to recharge - discharge etc, ? i just want to make sure i know what i am looking for during the process -

this is how my cells were when i built it -

[expresso]

two graphs - different times - one was for about 30 miles - and i monitored it that time - was fine -

the other was about 40 miles - with recharge graph - looks fine - so i know it was fine last summer for sure - something happened during winter storage - which i did remove it twice - once to replace end power cables - and then another time to add the breaker - thats it - didnt use it till now -

during the winter i charged it up fully i think Once about 2 months sitting - and then left it till i recharged to use it again now - either i did something during the breaker etc, or the cells went bad in a few months -

[shirley_hkg]

I'd concern the capacity as a whole rather .

First thing I'd do is to discharge the entire pack real down low , say 3.00V unloaded , and to see the readings of all 8 groups .

No need to panic for such tiny Δv , especially when it happens ln the first /last place of the train .

[expresso]

hi Shirly - did you see the graph when i discharged it just today - it dips lower around 30ah discharged - now i am watching it and its about 6 off -

to discharge this thing 90ah will take me a few days - i got about 35ah done today in 10 hours time - i will check the bolts tomorrow - take off the top row - and check the 7 cells - then if all good - put new bolts on - no locktite yet - just to recheck it again - if its fixed - then i can finish it up and leave it alone

if it dosnt fix it - then i can leave it alone and just use the chair watching the pack volt after a long run ? i will try to make the cable for the Cell monitor i got from you -

but first need to get this resovled one way or another - since i have it out of the chair now - i hope to get it fixed or at least checked best i can before putting it back in the chair -

how bad does one cell group have to be before it causes a bigger problem ? i have to continue this in the morning -

thanks for everyones suggestions - will start the take it apart tomorrow

[Burgerman]

The problem is that if one cell is bad connection or bad cell, that GROUP of 7 becomes empty first and you keep driving as you do not know. So all 7 cells end up bad because over discharge.

So best to find the problem, and fix or you will need 7 cells! As it is you likely need one, and you have one already spare.

When you measure you are looking for mAh out as it reaches 2.9v.. One cell will be bad, much less Ah than the others.

[steves1977uk]

expresso, what's the Internal Resistance reading for cell group 1? If it has a higher value than the other 7 cell groups, that would also indicate a problematic connection or cell.

Steve

[Burgerman]

Or long charge cables... group 1 always reads differently on all my packs with long cables.

[expresso]

Or long charge cables... group 1 always reads differently on all my packs with long cables.

my charge cable on the chair is not long - its not longer than 3 feet thats for sure - its maybe 2 1/2 - then the PL 8 is 3 feet - so its not more than 6 feet total charging - i do have two spare cells - i will take it apart today - just enough to free up those 7 Cells and start to test each one - may take some time i would think - will leave the pack flipped on the side so i can get to both ends - this way i can check each bolt also just to see if they are tight - but wont remove nothing just the 7 cells to start with -

[expresso]

The problem is that if one cell is bad connection or bad cell, that GROUP of 7 becomes empty first and you keep driving as you do not know. So all 7 cells end up bad because over discharge.

So best to find the problem, and fix or you will need 7 cells! As it is you likely need one, and you have one already spare.

When you measure you are looking for mAh out as it reaches 2.9v.. One cell will be bad, much less Ah than the others.

I do have two cells in that group that needed more mAh in during the build after resting for 2 months - so those two cells will naturally have more out when testing to 2.9v - in that case - how would i know if they are bad cells or just a bit weaker than the rest - which we know already since it needed more in to begin with -

i guess if its WAY off - then thats the one - - i may need more orange blocks if thats the case - i cant see removing them without breaking them - if i have to change a cell

[expresso]

expresso, what's the Internal Resistance reading for cell group 1? If it has a higher value than the other 7 cell groups, that would also indicate a problematic connection or cell.

Steve

Hi steve - i believe i clicked that tab on the PL 8 but didnt see any information on the IR of the groups -

[steves1977uk]

expresso, what's the Internal Resistance reading for cell group 1? If it has a higher value than the other 7 cell groups, that would also indicate a problematic connection or cell.

Steve

Hi steve - i believe i clicked that tab on the PL 8 but didnt see any information on the IR of the groups -

The IR info is saved with the graph, if you look in the view menu in the graph window you select Internal Resistance vs Time, that will show you the IR of each group.

Steve

[expresso]

BM - i am trying to charge ONE Cell - and the PL8 is giving me a Safety Code 19 - NO PACK - i cant continue - what am i doing wrong ?

i am using your Preset to charge one cell - -

Good news i think i found the Bad cell - i checked each cell in the 90ah pack - all show 3.4 V

the one Cell on the top Row 2.4V - this pack was charged full last night -

i still want to test each cell - why isnt the PL 8 letting me do it ? i have just the bananas in the PL 8 connected to one cell - nothing else connected -

giving me safety code 19 ?

[Burgerman]

Dunno. Did you take a look at the settings? It maybe wont charge a 2.4v cell... If that one is that low and from a full pack then its deceased... Never saw one just die, you must be lucky!

If thats the one, then you can try just replacing it with one of your spare cells (recharge full, re-assemble, and charge, discharge, recharge).

As for error 19? Dont know. Could be cell count error, no balance lead, voltage too low, or bad connection, high resistance -- bad cell , or bad setting, etc. Try reducing charge current to 1A.

[expresso]

its the cell i tried it on the other cells starting to test them now and it works - preset wont start if cell is below 2.55V

thats a dead cell - i wonder how - it seemed fine last summer with the graphs - i will test the rest and the spare - will update when done

thanks

[Gnomatic]

You're unlucky since you got a bad cell it seems, but at the same time, very lucky that the bad one was located in the top row! Only a 1 in 7 chance.

And it was Cell 43, which didn't show much of a static discharge when you initially tested them. Two other cells in that row showed twice as much static discharge! I guess we can determine static discharge isn't rate isn't much of an indicator of whether a cell will be long lived or not.

[expresso]

yes i agree - i would have guessed it was one of the other two cells - very happy that i found it on the top row !!! i managed to get it out without breaking anything

all my screws were tight - and of course i think too much locktite - i guess just very little locktite in one area on the bottom of the bolt may be enough - i over did it -
ordered new bolts - cleaned the connector plates - if this works out- i wont replace any wires this time - i will just have what i need ready in case it comes to that down the line - if the rest of these cells test fine - i will take a chance and put it back together with locktite etc, and test it as a full pack before going back in the chair

this is stressful when things like this happen - makes me think can they last 10 years for real


BM - Can i recharge these cells at a faster rate than the preset it set for ? its set to charge at 5A - - can i raise that to 10A etc?

[Burgerman]

Its best to stay at about 1/3rdC for a single cell. About 5A. You can of course connect all 7 together in parallel and charge all at full power. If you are trying to save time.

You can if you want charge at up top 5C, so 5x 15Ah for 1 cell... It will not charge any faster than say 1C but I wouldnt do it. You end up with a part charge or a very long CV time.

[expresso]

ok i leave it alone then - i should be done by end of week discharging and recharging 7 cells -

[Burgerman]

Use 2 chargers. Do 2 at once, and charge all as a parallel group, then you can do it in a day while watching tv.

That wasn't the cell you had the sparks with by any chance? Never saw that on a cell unless it was allowed to go too low for a long time.

[expresso]

no that wasnt the Cell with the sparks - that happened doing the first ADD ON - before i did the Full pack

this is the first Cell - Discharge - monitor - charge monitor

[expresso]

after charge - monitor

starting next cell - last for tonight - continue tomorrow with rest - by Thursday i be done

please tell me this cell is OK

[Burgerman]

As long as capacity is similar between all the cells then you have no problems. And check with voltmeter after a few days to see all are 3.4xx

[expresso]

Ok you mean if the Cap out during discharge is in the same ball park and recharge etc.. - i should be done by thursday - then i may just pack it back up locktite is - finish it up as if that was it - and then test it again as full pack -

i would have to discharge it for a few days to get it down enough - 60ah - 90ah removed - before i recharge it again - with the bad cell in place - it went down hill around 30ah discharged - started off low and then evened out till about 30ah out and went down hill


any idea how it went bad to begin with ? this got my attention from the charge graphs this year only - if it was bad last year - i was unaware and it didnt show during recharging
this is scary if they can just go bad this fast - - now the winter time is going to make me worry -

[Burgerman]

None of mine ever went bad. So dont know.

Before doing a discharge test, fully charge with termination point temporarily set to 100mA or less to better balance everything and be sure its all correct. Then put it back to where it is now.

You noticed it only because you use a PL8 with a PC and look at the graphs. You need to do this to stay in charge! All those that think otherwise, or use a BMS have no idea what is happening.

[expresso]

ok done two - so far - termination is set to 75 so thats good - but the first cell i used one preset with termination at 90 still good - then i used the other one

both cells are close enough to be OK i believe -

first cell 13 shows a discharge of 13281mAh and recharge of 14069mAh

2nd cell 11 shows a discharge of 13549 mAh and recharge of 14279 mAh

thats it for tonight - start in the morning -

so far are these Two OK ?

[Burgerman]

Yes the way we are testing is not that accurate since we are not fully discharging them, and have a fast termination but they appear healthy. Thats all you need to know.

[Andrey]

Ok, here it is, my charge logs (before and after discharge).



How it looks?

p.s. remove ".zip"

[Andrey]

And my discharge log (had to make it in three times).

p.s. please remove ".zip"