PINNED - Lithium battery conversion/info

[Burgerman]

Cell 8 group, looks like theres a cable or cell or bolt problem somewhere. Why is discharge in 3 parts?

And on charge it looks inconsistent. Are you sure all the bolts are tight? The green line looks like you get with long cables or bad connections, thin charge wires. Or a pack split in two with extra connections.

Do another discharge/charge and watch. Lines should all be together or extremely close.

[Andrey]

Cell 8 group, looks like theres a cable or cell or bolt problem somewhere. Why is discharge in 3 parts?

And on charge it looks inconsistent. Are you sure all the bolts are tight? The green line looks like you get with long cables or bad connections, thin charge wires. Or a pack split in two with extra connections.

Do another discharge/charge and watch. Lines should all be together or extremely close.

In 3 parts because I had to move the chair (also it is my only wheelchair for the moment), I was sure that all bolts are tight, but... now to be sure I have to check, for sure. Will do in next few weeks I hope.
Balance cables are 20AWG, could be too long, but not much, I will measure later exact length. Pack is single but there is extra connection, I use MPA charger board to connect the pack to the charger because I made XH-connector (maybe I will cut it off later to change for cellpro).

[Burgerman]

What about main charge cables? Balance start should be set to 3.500v not lower or set to balance at CV only.. Balance while discharge should be off.

[Andrey]

What about main charge cables? Balance start should be set to 3.500v not lower or set to balance at CV only.. Balance while discharge should be off.

Main charge cables are 12Awg, I use your setup attached above (start at 3.50V), balance while discharge is off.

[Burgerman]

Well theres something odd...

[expresso]

BM -- I am on my last two cells - will be done today - should have it back together by friday to start testing the whole pack again - what should i expect once together and how far down should i discharge the pack before recharging ?

i checked the dead cell and its showing 1.8V now - good thing my spare is 3.4v all the rest of the cells i tested so far are more or less in the same ball park - some a bit more returned when charged - anywhere between 13999 ah to 14500 back in during the recharge -

i checked back at the graphs from last year - everything seemed fine - this year once i started to use it again - the very first ride and recharge shows OK also - and then on the next ride recharge - i noticed it was off a bit - 3 more rides after and recharges - became more pronouced that something is off - looks as if i caught this just in Time before it spread to the other Cells in the group -

lets say - i had a GOOD BMS on this pack - would it have helped at all somehow ? to keep that Bad cell from overcharging or under discharging etc, ? i have no intention to add a BMS - just curious since thats the purpose of the BMS in the first place to try to prevent this from becoming a problem and taking the whole pack down with it

i am starting to see many many more lithium batteries now that are drop in models - of course with a BMS - and double the cost of what we can do it for ourselves - at some point - someone has to make a GOOD SOLID BMS that would do its job correctly ?

[Burgerman]

lets say - i had a GOOD BMS on this pack - would it have helped at all somehow ?

nope, it would have cut power totally at some random point in the future as that group died due to low voltage, and would have failed to keep it balanced with its feeble 50 to 100mA balance capability. Leaving you stuck. And with 7 ruined cells.

i am starting to see many many more lithium batteries now that are drop in models - of course with a BMS - and double the cost of what we can do it for ourselves - at some point - someone has to make a GOOD SOLID BMS that would do its job correctly ?

nope!

A bms has to know what our exact requirements are, and hows it going to know this? Its also got to communicate with the control system, and reduce current proportionally as required instead of cutting off power suddenly. And the controller already does this ans has the required current limiting etc.

And it would need to control the charger rather than keep disconnecting it, so it doesn't bounce the cells up and down for hours at charge end/balance. Which the PL8 does already...

[expresso]

Once i get the pack together again - How much should i discharge it to test it - how far down before recharging ? i can get about 25ah to 30ah a day discharged - not looking to leave it overnight and can start it again next morn.

should i discharge down to 3v on the PL 8 cell groups etc, ? keeping it about 90ah at most discharged just to be safe ?

[Burgerman]

Charge full, repeat a few times to be sure its balanced. Then discharge about 40Ah and recharge before refitting. Should be fine as you found a faulty cell.

[expresso]

ok you mean first thing to do is fully charge - then discharge about 40ah - recharge and repeat - discharging 40ah again etc, ?

you say fully charge repeat a few times - do you mean charge full - and charge full again a few times before ever discharging at all ?

just to be clear - i want to do it right -

thanks

[Andrey]

And again, my today's discharge and charge (about 22Ah).


I understand that it is not good. But is it safe for cells if I use no more than 30-50Ah from 84Ah pack with such behavior?

It will take some time for me to disassemble it and try to find what could be wrong.

p.s. didn't attached graph file because it has overlimit size.

[expresso]

Hi Andrey - - i am going thru a similar situation and from that graph - it looks like you need to check the cells on group 8 - i had a BAD Cell in my group 1 - my graphs looked a bit better than yours and it turns out it was a BAD Cell for me -
at least so far as i can tell -

your taking a chance if you keep using it this way - it will work but can take the other cells down with it if thats your problem also - Wait for what BM suggests - i am always in the learning stage here

[Burgerman]

Are you building a new pack?
Did you test all cells and charge before assembly? Because you would have found a bad cell before this point?
Are you sure its not a long thin CHARGE cable issue?

If not then you either have a bad connection like a bolt that you have missed and that is not tight, or a bad cell, or something.

A bad cell or bad connection / loose bolt will show in a full discharge test, as group 8 will discharge and drop off earlier than all the others. So do a discharge test. Set to 2.9V, and balance off. It will take a long time. Or undo all the bolts and connectors on one end of the cells in group 8. And test those alone, and test with a volt meter for obvious failure.

And before any of that it possible but unlikely that the charger itself is out of calibration. So if you have a GOOD volt meter with 3 or 4 digits after the decimal place, you can measure all 8 groups individually as it is discharging to be sure that what you see on screen is real. Must be good to measure a couple of mV. The figure you see will be different to the actual numbers on the charger because the charger charges and discharges in a high frequency pulse with breaks. And it measures unloaded voltage where you will be measuring the average. So ignore the difference between charger and volt meter.

Yes its safe to use. Has it just started to happen or is it a new pack? Does the voltage of group 8 fall faster than the rest after charge, if you choose to monitor?

[shirley_hkg]

Do you have 2 X 115mm headroom for these 55Ah cells ?

Around @ £15.00

[shirley_hkg]

This has total length of 275mm inclusive of terminals . Too bad .

[Burgerman]

Sadly not. All these cells are always just the wrong shape!

Only those 125Ah cells from sinopoly are perfect. But I cant find a supply.

http://www.sinopolybattery.com/userfile ... /125AH.pdf
http://www.sinopolybattery.com/en/products.aspx?cid=10
http://www.fdgev.com/en/sp_fa41255bm/

Need 8 of those. But dont speak chinese!
4 together, is 175 tall, 255 long, and 162 wide.
So correct height, 5mm less length, and 8mm less wide than a grp 24. Easy to fit 125Ah where a grp24 came from.

[Gnomatic]

Do you have 2 X 115mm headroom for these 55Ah cells ?

Around @ £15.00

Nice find, Shirley. I could probably fit those in my chairs. Only 110Ah, but that's a heck of a price!


Keep posting these as you find them, Shirley. I'm no good at searching Taobao. If the timing and deal work out at some point, I might give something like these a try for my backup chair.

Thanks!

[Gnomatic]

What do you think of these cells, BM?

Seems they would be a VERY tight fit in my battery area. 173mm x2 so they need 346mm minimum to fit in my battery compartment. I only have room for 347mm MAX in my chair. Probably not a good idea.

[Burgerman]

A bit too long. And not new..

[expresso]

i got the pack together - BUT it dosnt look good at all - actually looks worse than before - not sure what the deal now

i am discharging it now - wont be done tonight - will continue to discharge tomorrow before a recharge

i did use Cell 25 instead of Cell 31 - for some reason i felt it was better - seemed to discharge and charge better - Cell 31 showed 3.3V today -

so i went with Cell 25 instead - maybe it was a bad call or they are both not good ? this worries me if the cells are going bad this way -


i wasnt expecting a perfect line at this point but wasnt ready for this wide a gap between them - what do you think BM - and whats the next step -

i dont feel this will fix itself

[Burgerman]

Dont know. You wrote many words, but no idea what you are describing.

You reassembled the pack.
You fully charged and tested those 7 cells. You now have 7 good ones. And all connections are also tight.
And then you fully charged the pack.???

Correct?
And now discharging? The screenshot?

If so you didnt do some of the above correctly...

Or you didnt charge it yet??? Or is that chart just monitoring?

Not enough info. You MUST charge and balance the pack before discharge.

[expresso]

OH -

I put it all back together and then connected to the PL 8 - and monitor - - that screen shot was a monitor before i did anything at all -

now i am discharging it - i may have a chance that it will fix itself - ?


all screws were checked - all of them - i used new screws on the cells i removed them from - replaced the bad cell - to best of what i know - i believe i did it correct -

i did not charge it fully before i started the discharge - i thought i had to discharge it first -- then fully charge balance it - then discharge it again and repeat a few times ?

its a hour in the discharge - should i stop it - charge and then start discharge again or just leave it now ?

[Burgerman]

OH -

I put it all back together and then connected to the PL 8 - and monitor - - that screen shot was a monitor before i did anything at all -

now i am discharging it - i may have a chance that it will fix itself - ?

Stop discharging it will accomplish nothing useful yet!
Charge fully. When it stops, do it again half a dozen times so we know its properly balanced. (or as I said in a previous post that you ignored) set termination to a LOW level so the cells balance properly. Read back!
Set termination to 500th or 1000th C and for 3.65V for this one charge to correctly balance everything. 1000th C means 105mA on a 105Ah pack. Set anything between 200mA and 100mA. THIS charge ONLY! (150mA good choice)

It will hold all your cells FULL for long enough to ensure that the whole pack is fully balanced.

Then and only then, monitor it. And if that looks OK, then do a discharge test. You will likely find that swapping that one cell means its fixed!

[expresso]

Ok i changed the charge to 3.650V - term. 150mAh - and started the charge - for this charge only - then change it back to 3.6V charge and Term. was 200mAh - or leave it this way for the first 4 or 5 recharges before putting it back to the way it was ?

sorry i misunderstood the steps

[expresso]

first charge - now will set it back to 3.6V and 200mah term.

[expresso]

ok after 6 charges - the graphs looks OK for the 2nd charge up to the 6th - then i monitor it - and i dont think its holding up -

i will start to discharge it till i go to bed - then start again in the morn. and do a recharge - then a monitor again - but i dont think its going to fix it -

looks like i have to take it apart and replace all 7 Cells to be on the safe side - ?

[shirley_hkg]

Found one similar , 100Ah rated 2C , tested @98.5Ah .

@ £25.00

[shirley_hkg]

Found this too , and think you'd give it serious thought .

Look at the super low internal resistance , and tested capacity .

I'm quite confident that you can fit 16 of them in it , and that's 150Ah .

Should be good stuff . 0.36mOHM @ 2.65V That's really good , itsn 't it ?

@£17.00

[Burgerman]

1st one ok, but prefer the 125Ah one.
2nd one too tall...

[Burgerman]

Expresso, charge all, remove connections on all 7, replace the cell that falls lower... You dont need replace any that are ok.

What maybe happened is that one bad cell allowed all those to go lower in charge in that one group last summer.