PINNED - Lithium battery conversion/info

[Burgerman]

China. Large manufacturer other products/cells too. http://www.headway-cn.com/en/about-us.php

http://www.headway-cn.com/index.php

[steves1977uk]

Imagine building a pack using these cells... http://www.headway-cn.com/en/showproducts.php?id=1752 But I noticed they're only 0.5C rated instead of 10C like the 12Ah cells.

Steve

[Burgerman]

2C max I think. But wrong size/shape.

[Irving]

Just got off phone with General Sales Manager @ VES. They are a Venture Capital group who have acquired a number of companies in the EV arena with a view to creating a UK design & engineering centre of excellence for EV technology. They already do some interesting stuff (Williams Formula E car is but one example of many). They don't manufacture batteries/cells but work with electrochemical companies to develop same to customer needs. They don't sell batteries/cells commercially and, although he wouldn't confirm it outright, the Goodwolfe cells were probably manufactured by the same EC company as the Headway ones. It would have been for a specific customer project so the added value I guess would have been matched cells or similar. The other interesting fact is they have a motor manufacturer joining the group.

Anyway, there is mileage in continuing the discussion and we've agreed to set up a face to face meeting in regard of supporting the charity-led Research programme, but if I can spin other stuff out of it that would benefit WCD members, I will. Won't happen overnight but watch this space.

[Andrey]

Got my headways 12Ah recently (I decided to build 8s7p/12Ah pack). Charging cells and have some doubts because some of them, #3 have very different behaviour.
After full charge I try to discharge it (minus 1Ah) with 5A and cell #2 shows graph like this, which I think looks good:

But cell #3 with 5A discharge had only 2.97V and hits it almost immediately after discharge started, also with 2A discharge graph looks like this (3.17v) which of I'm very concerned:

Is it Ok or not?

Cells are new, just arrived. Should I check it somehow (how?) before "calibrate" by full charge and -1000Ah discharge to measure self-discharge?

Thanks!

[Burgerman]

1. Did you FULLY charge each cell to 3.6V before you started? Do so!
2. Are these Loose cells, or already assembled intom a pack?
3. Discharge cell for a few minutes directly after a full charge. Discharge at the same Amp rate, and watch the volts. All should be the same voltage about 3.3x after a few minutes discharging at say 2 to 3A. Is that the case?

If not you have a problem. Seems unlikely as I have never had a bad cell. Or you have a bad connection...

But cell #3 with 5A discharge had only 2.97V and hits it almost immediately after discharge started, also with 2A discharge graph looks like this (3.17v) which of I'm very concerned:

Was it fully charged?
If so it may have a fault, or been discharged too low, or overcharged, or you have a bad connection. Where are the cells from? A reliable source?

[Andrey]

1. Did you FULLY charge each cell to 3.6V before you started?
2. Are these Loose cells, or already assembled intom a pack?
3. Discharge cell for a few minutes directly after a full charge. Discharge at the same Amp rate, and watch the volts. All should be the same after a few minutes discharging at say 3A. Is that the case?

If not you have a problem. Seems unlikely as I have never had a bad cell. Or you have a bad connection...

1. Yes, I did.
2. Single cell connected directly to a charger.
3. I'll try again and write back.

How should voltage drop on "absolutely healthy cell" under load of... 3A or 5A?

Was it fully charged?
If so it may have a fault, or been discharged too low, or overcharged, or you have a bad connection. Where are the cells from? A reliable source?

Yes, I charged it to 3.6 and waited for 20-30min more. Cells are from evassemble.com

[Andrey]

So, I did the following:

1. Charged to 3.6v with 2.5A:

2. Discharged with 2.5A for 12minutes, voltage drops to 3.15v:

3. Charged again to 3.6v with 2.5A:

How does it looks? How it should look?

[Andrey]

And one more time discharge with 5A, voltage drops to 2.98v in few minutes:

[Burgerman]

The charger discharges in pulses mostly, and then stops for a few secs to see UNLOADED true voltage.

As long as all cells behave the same theres no problem. If only 1 or 2 cells do this then there is a problem. The difference between high peaks and low points under load represents resistance of cell, wiring, connectors.

[Andrey]

The charger discharges in pulses mostly, and then stops for a few secs to see UNLOADED true voltage.

As long as all cells behave the same theres no problem. If only 1 or 2 cells do this then there is a problem. The difference between high peaks and low points under load represents resistance of cell, wiring, connectors.

I understand that, my concerns are about if it is ok that voltage drops to 2.9x in few minutes under 5A load. Isn't it too low if 3.00v is a cut-off for 80% DOD? When this cell is not loaded it shows 3.3x.

[Burgerman]

It depends on if this is cell resistance, connection resistance like a loose screw, and if its different to the other cells. Do the other cells behave the same?

The voltage under load isnt that important. Its going below a certain state of charge that is the problem. The unloaded voltage.

2.9 = end of play for any normal use.
2.5 = end or discharge for max capacity measurement.
2.0v or = less damage. UNLOADED.

So again, do the other cells perform the same?

[Andrey]

I didn't tested all cells yet. Will continue charging and see. Thanks!

[Andrey]

Just finished to charge all 57 cells, took me 5 days. All cells behaviour are same, some has lower voltage when resistance higher, that is understandable, and seems because of connection (i used crocodile connectors).

Sorry for my early panic, had no much experience with DIY

Now wait two weeks and get ready for next steps...

p.s. Thank you for so much info and extremely useful experience.

[Scollard]

You should probably consider waiting at least 4 weeks. The cells are generally pretty good and hold their charge well. If you want to balance your pack more accurately you need to have some self discharge to measure. I waited 4 weeks and I had a number of cells that were < 10 mAh returned.

[steves1977uk]

http://www.evlithium.com/Headway_Battery/51.html 16Ah 10C cells, might use these in my next build

Steve

[expresso]

nice find - if those are the same size as the 15ah i used - i can use those also for my next pack - i need them to be the same size all around - using the same orange connectors - that would be great - if the cost is good also -

[Burgerman]

They are the ones you used. But 8mm longer 1Ah bigger. In response to people complaining that the 15Ah cells were lower c rate than the 12Ah and 10Ah ones...

[expresso]

whats the difference then - this C rate ?

longer but same size - same orange connectors as the ones i used 15ah ? cost ? i dont see them on the EV site -

[Burgerman]

Not yet. They have a higher C rate, greater Amp capability. It wont worry you on your chair!

[expresso]

https://endless-sphere.com/forums/viewt ... 14&t=41877

[expresso]

Not yet. They have a higher C rate, greater Amp capability. It wont worry you on your chair!

what do you mean - it wont worry me on my chair ? now i feel cheated -

So Far - cant complain - i love it - and i notice a difference now from the ADD ON Chair to the Full pack -

[Burgerman]

I mean because your battery is big, the C rating of the ones you have far exceeds its requirements already.

[expresso]

Ok now i feel better

by the way - i was thinking of those fatter front tires today - 9 x3 etc, - what section was that we can post about those ? i dont want to post it here - off topic - thanks

[Burgerman]

10 x 3...

[expresso]

did you read that story from the link i posted - Headway cells fire on bike - - reading that section making me worry now - should i be ?

i dont feel they know what they are saying - all guessing what happened - but most likely the BMS started it ?

in Our case - on our Chairs - the Pack i just made and using should be Safe - ? vibration shouldnt be a issue i hope ?

[Burgerman]

These fires are always bms failures, with a nest of cables and pcb on fire shorting everything out. You are safe. At least as safe as lead.

This is one of the reasons I wont have a BMS in charge... Every lifepo4 fire you will ever see is inevitably a wiring/BMS issue. There are some experts that build electric cars that wont have an EV in their workshop with a BMS on it... Same issues set fire to a boeng dreamliner, and many laptops, and recalled lithium camera batteries.

EVERY EV forum is endlessely discussing battery problems which inevitably turns to BMS problems. You wont have any...

i dont feel they know what they are saying -

Correct. Same on every forum everywhere when it comes to batteries. Everyone is an expert but when I read it, almost every one of them hasnt a damned clue.

Theres 3 lithium chairs in my house. If they had a BMS on each, they would be stored in the garage...

[expresso]

Ok - i read about the orange blocks that crack at the thinnest part - from vibration which then the two cells touch and rub - till the blue coating wears off and shorts them out - all kinds of scary things i picture in my head -
something about the older orange blocks were made of a different material and the newer ones are better - i dont know which ones i got - newer or older blocks -

in the chair - there is going to be bumps vibrations etc, for sure - i know for sure that my wiring is solid - everything was checked and doubled checked twice , three times -

i dont even want to read anything on those other forums - i feel like i know more than them - i was itching to join and sign in and post back - to tell them - if this is always happening - stop using the BMS !!!

they keep talking about how bad the cells are - etc etc, but dont focus on the real problem
wiring - cheap thin wiring - connectors - packing etc, they mention about having to put them or should put them in a fire proof packing

meanwhile we dont use anything - our cells are done right - and connected once thats it - charged - used- charged - no problems -

[Burgerman]

i dont even want to read anything on those other forums - i feel like i know more than them - i was itching to join and sign in and post back - to tell them - if this is always happening - stop using the BMS !!!

they keep talking about how bad the cells are - etc etc, but dont focus on the real problem

Because they all *know* you must have a BMS as it says so all over the internet, and every pack or laptop or ebike you buy has one... Even airliners, engineers KNOW you gotta have one...

Even though you dont.
As long as you have other things in place to do the all the same jobs properly instead.

A BMS allows you as a lithium battery manufacturer or supplier, to sell lithium batteries to dummies to fit in the wrong situations. It protect the cells from over charge, over discharge, over current etc and balances them when charged with a dumb charger. All extremely badly!!! And not required in a well thought out setup.

[shirley_hkg]

NOW , I'm more convinced that we should put as many AH in it as we can ; so that we can spare 10% at both ends ……… UNUSED.

3.48V is 98% charged already . Can't get you nowhere with that extra bit.

Lithium does need our T L C.