Is this normal? Headway cells.

[Spacey]

Having had a lot of trouble with a couple of not working bms's I have had to run the 12ah 48v 16 cell Headway cell without one.

Now the cells were all balanced before I rant the pack for a run yesterday.....I then charge the pack up as normal. Now 3 of the cells I. The end of the pack were registering around 3.8v whilst the rest were either 3.2 or 3.3.

Took the bike for a short 1ah ride and measured the cells again. All were at 3.2 volts. Is this normal for some cells to register high volts then settle down on use?

Also if I leave the charger on without a bms will the pack eventually balance out?

Many thanks in advance

[dnmun]

nope you will just damage the cells that overcharge.

[eva-michael]

That's because the internal resistance of each cells will have some difference. Even though the cells are good match. But there still be more or less difference.
Apparently, the difference of internal resistance of cells make the 16S lifepo4 charger can not put each cell with exact same charge power. And without the function of bms, the energy between cells can not be keeped in a balanced. Some cells are coming full faster when others still not full(difference is very small). faster full cells may overcharge.
what you saw after a little bit discharge and then cell become matched, that's because the cell will maintain in 3.3-2.9V for long time when it discharge. When discharge, the cell will drop back to 3.3V from 3.8V very fast since cell is only poped up to 3.8V and not the feature of lifepo4 cell(a little over charge).
Anyway, the difference will become bigger and bigger after use time after time without control of bms. Finally it may demage by overcharge or overdischarge of some cells.

[Spacey]

Cheers for the help.

Michael, the last battery order I made from you (12ah 48v headway pack with bms), if that has not been sent yet do I have time to order a decent bms ....like the one you include with the 12ah 48v battery pack?

The cells do all settle down to 3.3 volts as soon as it is used, but really do need a bms. I'm not having much luck with the last two bms I bought......should have bought them from you Michael lol.

[eva-michael]

Hi Spacey,
Yes, just let me know qty and bms you need.
Also I just sent you a email for the information of your last order.

Have a nice day.

[Spacey]

Cheers Michael,

Have not received the email yet but have sent you an email with the details of the bms needed.

Basically I have one of your 16 cell 48v 12ah Headway packs and will be using an Infineon 40 amp controller, so pop one of those in the package and let me know what I owe you before I damage my headways lol.

Many thanks

Spacey

[dumbass]

Cheers Michael,

Have not received the email yet but have sent you an email with the details of the bms needed.

Basically I have one of your 16 cell 48v 12ah Headway packs and will be using an Infineon 40 amp controller, so pop one of those in the package and let me know what I owe you before I damage my headways lol.

Many thanks

Spacey

Your using a 40a charger on a 12ah pack? No wonder you have BMS problems. I'm no ezpert but that seems a little (a lot) of an over kill.

Bob

[Spacey]

Need to put your glasses in dude or I'm mumble typing again It says 40 amp controller....but wouldn't a 40 amp charger be nice lol.

[BIG BEAM]

I have found Headway cells to be very robust.I was charging 12-10ah cells all at once without a balancer and one of the batts went to 4.04v.It settled down to 3.33v over night like the rest.I label all my cells(an old R/C thing)and that one was 9698 before I charged it to 4.04vI used the pack for a few times and didn't notice anything.Last weekend I cycled that cell all by itself to see if I did any damage to it.It did 9713 so it didn't seem to affect the cell for now.I don't know what the long term affect will be but I did mark that cell so I could keep track of it.I balance my pack every 2 weeks or so.When I take the bike out I look at the mah I use and charge it most of the way back up.Like if I use 3mah and my charger puts out 2a I'll chareg for an hour or so and reset the CA.It's not full but more that enough for the riding I do.Every 2 weeks I'll take the pack apart and charge with the balance taps(I use alligator clips to balance).My charger only does 6 cells at once.

That being said, if you need all the juice in a pack I would balance all the time every time.If you ride like I do 15% one night 25% the next and then charge I think it's OK to balance once and a while.

Remember if you only charge 90% and dicharge to 80% the batts will last longer.

The balancing charger I use is EZ on cells.It only charges to 3.60v

DON

[jondoh]

Spacey,

What are you charging your cells to? I understand Lifepo4 charge to 3.65v per cell usually. If yours is higher, maybe this is why you are seeing differences. Brand new cells may start out different but start to even out over time. Also helps to not discharge past 80% DOD.

I don't think leaving it on the charges helps balance out the cells as maybe a weeks worth of charge/discharge cycles.

I think the bms balancing helps your batteries if you're trying to get every amphour you can out of your cells, otherwise, if you not discharging completely every time, it's not really necessary.

[Spacey]

Your help is very much appreciated on this subject as I am still learning.

My charger charges at 58.4volts I think (not near charger to see) and it charges at 6amps an hour. My journey to work should use between 6 and 8 ah and my battery is a 12 ah pack. It gets charged as soon as I get to work and also again as soon as I get home. I never go past 10 ah so always 20% left in battery.

Do the cells balance themselves then with use?

[jondoh]

16 x 3.65 = 58.4v

So your charger is just right.

I've heard from a number of places-- including this board that Lifepo4 do "settle in" and become more balanced after a few cycles. If your pack is new, you should see an improvement-- even without a balancing bms. My experience is that this is true as well.

On the high side, I think these batteries can be charged to up over 4v and still be ok. After settling down, cells should be above 3.3v. If some are below... maybe they are not fully charged? I don't know.

[dnmun]

lifepo4 chemistry is resistant to the overheating/thermal runaway/fire scenario of lipo when it is overcharged.

the lifepo4 crystalline structure does not have a source of oxygen available for the combustion, but lipo does not have the crystalline structure and it sill break down and use the oxygen available in the polymer to burn.

it is now clear that the fire that took down the UPS 747 freighter in dubai last week had a lipo fire. this is gonna change the rules permanently. the fedex freighter that burned on the runway in atlanta was on the ground when it caught fire so the crew evacuated. this crew could not fly the plane after smoke filled the cockpit. it is really too bad, almost criminal that they did not get the crew back on the ground immediately and let them fly for an hour after the fire broke out. 2 men gone, that is too much for the pilots union.

[BIG BEAM]

I think these fires will spell the start of the demise of shipping lipos.

They are great batteries but they do pose a hazard.
DON

[icecube57]

They dont seem to be balanced.... or they could be.. Did you tie all the cells in parallel to balance them before you put them in series. You should have tied them all in parallel and let them sit for a few hours and let them truely equalize to the same level and then assembled your pack. It seems your balancer was not able to keep up on the post charging balancing.. If it was able to sit long enough it eventually would have brought the cells in line. I understand that you charged each one individually but they self discharge or loose their float charge and losing this suface charge is enough to get the cells out of balance. Due to the cells having different IR they self discharge at different rates.Even if its just 20-30mah. Its enough to cause problems in post charge balancing. I had the same issue with my Thundersky Cells. There were some cells that rose higher than others because of the lower internal resistance but after spending 30min to an hour on the balance they all balanced out to 3.7v. They kept doing this despite balancing every cycle. Its the cell IR thats causing the back to appear unbalanced but give it time on the balancer and they will level out.

My Thundersky Cells had a wide charge voltage range so it was safe for the cells to rise up to a certain voltage before the balance bleeded them down and allowed other cells to catch up. Im sure headways have a little breathing room also but not alot.

I also like the 80% discharge rule. But Ive come to find out for myself with my TurnigyLlipo. Even if I did a full discharge and the cells appear to be out of balance. They maybe a deviation of .25v. When I put them on the charger with in a few minutes they even out and terminate charge with a 0.02v deviation. So in some chemistries a full discharge causes a imbalance in voltage but they all charge to the same capacity in the end.

[Eclu Lardbut]

it is now clear that the fire that took down the UPS 747 freighter in dubai last week had a lipo fire. this is gonna change the rules permanently. the fedex freighter that burned on the runway in atlanta was on the ground when it caught fire so the crew evacuated. this crew could not fly the plane after smoke filled the cockpit. it is really too bad, almost criminal that they did not get the crew back on the ground immediately and let them fly for an hour after the fire broke out. 2 men gone, that is too much for the pilots union.

Apparently they were offered Doha but declined
http://www.arabianbusiness.com/597136-u ... nd-in-doha