What do i wrong? @ 18650 Cells

Hi,

i have a few questions about 18650 Cells

I have bought in March 22X 1830 accupacks from docterbass.

after disamble the packs, i have some round the 180 cells left.

after that i cycle(charger) every cell, then i discharge them to 3V - then charge them to 4.1V

the most of the cells come to 1200 a 1450 Mah, so i have make packs 6S with balance conectors and the most even capacity cells by each other.

So i had 3 packets of 6S10P so 14amp ... (i rode with 18S10P)

6S is the limited to my balance charger

BUT after some 15-20 cycles they are unbalanced....

now at this moment i have 14S6P

i have have this building with a new 100W soldering iron from Weller.

So what do i Wrong???????

i thougt that the 2second hand cells the problem whas?

Or must i every cell measuring @ interal resistance????

I whas positieve @ 18650 cells... but now i use most my HK lipo cells from my modelplanes...

Please some help !

I had the same experience with recycled makita cells. Unfortunately unless you do a lot of testing you are going to end up with but cells. I was down to 12s before I gave up and bought new cells.

So what do i Wrong???????


Did you do a 'bleed down' test? ie, did you charge each cell up to 4.1v and let them stand for a
couple of weeks to check they weren't losing voltage? If not, then one bad cell per parallel bank
could be pulling the voltage down and taking it out of balance.

Also, soldering small cells is always a risk - and using a 100w iron is probably too much for this
unless you are very experienced, around one second per connection is enough if you have done
good preparation, much longer and you risk damaging the cell.

I have made many packs with reclaimed sony konion cells and along with any reclaimed cells, they
take a lot of time to check, but once done properly mine have stayed perfectly balanced for 2 years
just bulk charging - limiting max voltage to 4.1v but probably more importantly limiting the minimum
voltage to 3.3v (off load) .

petemarconi said:

Also, soldering small cells is always a risk - and using a 100w iron is probably too much for this
unless you are very experienced, around one second per connection is enough if you have done
good preparation, much longer and you risk damaging the cell.

Click to expand...

that's why you need to use BIG soldering irons. if you play around too long with a small one you will damage the cells. touching the cell with a big iron for a second will do the least harm possible.

Drokz said:

the most of the cells come to 1200 a 1450 Mah, so i have make packs 6S with balance conectors and the most even capacity cells by each other.

Click to expand...

what do you mean with "by each other"? you need to make parallel packs that have about the about the same capacity and internal resistance as the other cell packs you want to put in series. if you got a very good pack and a very bad pack connected in series, the very bad pack will be the weak link in your chain.
when i build my packs it try to even out good and not so good cells to form uniform packs. that way you will get the best performance.
best idea, as already mentioned is to buy a decent bms.
and a question not answered: how far to you discharge those pack?

You have to disassemble the pack to balance it? That's the one thing you are doing wrong I think.

Did you make parallel groups then connect in series? or series packs that are then paralleled?

Either way, you don't need to run take the pack apart to balance it. Just use the balance plug, and your RC charger. Connect by the jst to just one cell, put your charger on 1s, 2 amps. Then fill your low cell groups one by one. It's actually quicker than regular balance charging.

All you need to do this is an adapter. One end is the plug you have on your RC charger, the other end is just bare male jst pins. Find the cell you need to charge, and use the two pins to connect to just that one cell. Easy once you learn which end of your jst plug is the + and which is the -. A cheap DVM can also have the jst pins put on it, so it becomes easy to read cells voltage too.

Staying balanced for 20 cycles is not bad at all really.

i never go down to 3.00v.
do a load test and you will see they fall off a cliff below 3.65v.
i charge when at rest they are 3.80 or maybe i don't get home until 3.75.
this way they tend to stay in balance
plus i watch the LED DVM and a sudden drop means STOP! or nurse it home SLOW!

True for nearly every lithium chemistry, when it goes over the voltage drop cliff, it tends to unbalance the pack more.

If you need it to get home, use it to get home slowly, and figure to need a balance soon. But if you can, stop before that drastic voltage drop and have to balance less.

Kiriakos GR said:

Drokz said:

So what do i Wrong???????

Click to expand...

Use your 6S charger for other use, and buy a proper BMS controller for your battery.

Click to expand...

I Dont Believe in Bms.... chinese crapp??? or sell with no warranty?

petemarconi said:

Did you do a 'bleed down' test? ...

Click to expand...

I have that don, but for 3days.... they max 0.05V drift...

I have bought on the advice of Docterbass a 100 Watt soldering iron.
Because if you have less Watts you have to melt longer thats damage the cell.
Better for power in a second it melt.

izeman said:

what do you mean with "by each other"?

Click to expand...

I mean that i take the most cells with same capacity together.
I have not be able to measure the internal resistance, because I have not for the material there.
And when did not know or that that was important...

I dont trust BMS...
They sell without warranty.... i pass...

I decharge till 3.3V with load. (buzzers)

dogman dan said:

You have to disassemble the pack to balance it?

Click to expand...

NO NO, that is a wrong description of me... (i delete it)
I build the packs in july-august en after many single parallel cells charge because they verry unbalanced.

i balance always/everytime my cells !

i have decided for desoldering the bad cells and repack the cells 18S10P to 14S6P

20 Cycles for 472€ is expensive


before i ride, i calculate the minimun voltage, en keep in mind = 18*3.4V = 61.2V i wil stop elektric riding @62V
after that i turn it off, en i peddle to home

building a battery from bare cells of which you have no idea or even comprehension of the capacity of each cell without a BMS to protect the battery is gonna be a really really expensive experience, and waste of tons of time.

i know.... i would never build an battery with used cells.... i will buy new....

I have been running DrBass Konions in a 14s 12p pack for 18 months. The key is the bleed down test for me. Once I discard the leakers I then do a discharge capacity test, match and solder. I charge to 4.1v and then discharge no more than 3.6v, they stay balanced pretty well with bulk charging.

It takes a lot of time to make a good pack and you need to monitor your cells. Experience will be gained along the way.

Drokz said:

...I Dont Believe in Bms.... chinese crapp??? or sell with no warranty? ...

Click to expand...

but you DO believe in chinese batteries? strange to say at least i have bms installed on all my bigger batteries and still i do check them frequently and monitor them closely. it's a convenience factor as well. plug&play as good as it can get.

After some issues with you having to write in English, I don't see what you are doing so wrong, or even that you have any problem that is not normal.

In use, a pack does get inbalanced. But a pack that is unbalanced every cycle, has cells in it that are failing. Higher internal resistance is the indicator that cells are failing, or just getting too old. When really bad, they will bleed down from internal shorts in the cell.

Could be you have a few cells that did get some damage from soldering.

Could try to patch it. Since you have extra cells, they could be used to boost any parallel pack that is too weak. This would greatly increase the number of cycles before manual balancing.
Or you could drop from 18s to say, 15s, and use those extra cells to add capacity to the weak P's.
Not ideal, but after spending a lot of time and money, might as well get some use out of them.
I would not use any cell that drops .05v in 3 days. The V after 1 day should be the same after 3 days imo. mine stay the same(within .01) after 30 days! (or are duds)

Matt Gruber said:

...I would not use any cell that drops .05v in 3 days. The V after 1 day should be the same after 3 days imo. mine stay the same(within .01) after 30 days! (or are duds)

Click to expand...

i would say this depends on SOC. if you storage charge lipos/licos to 3.85v they will hold this charge for weeks. but they will drop some mV when charged to 4.20v after even a day or so.

he has LIMN not lico not lipo.
Sony V cells.
and says he charges to 4.1 not 4.2 (this could be a cause of running low and going out of balance,since he starts out low, then runs out)
i do have 1 cell in my junk pile that stays at 3.90 for weeks, but refuses to hold anything higher, so i'd say there is merit to the idea, just not with good Konions, which are NOT made in china!
If he rides every day, a slight discharge should not matter much,
More important to see at least 4.15v one hour off the charger, for good range/good life.

Pat Eaton said:

I have been running DrBass Konions in a 14s 12p pack for 18 months.......

Click to expand...

Yes i know, I have been to more testing, that's my mistake.
What charger do you use?

next battery is from fresh new cells... maybe next year.

izeman said:

but you DO believe in chinese batteries?

Click to expand...

some people called Battery Murdering system....
I'd rather have a charger which balances the cells, then a bms that I can't trust ....
idd chinese batteries are in mass production and minimal margin of error.
but what type/brand bms do u use?

Matt Gruber said:

Could try to patch it. ....

Click to expand...

I replace the weak cells... thats the best solution

I charge till 4.1V .
and idd some cells will charge till 4.1V en after charging drop they till 4 to 3.8V..

izeman said:

i would say this depends on SOC.

Click to expand...

What is SOC?

SOC = state of charge
IE,.. Is it fully charged, half charged, near discharged, etc