How long does it take to balance charge your pack?

[wesnewell]

I didn't balance charge the pack. That's why it was off that much. And I never run my pack down to 3.5v. The lowest I've gone so far is 3.63 per cell and they were all within .01v. Not sure where they started at that time, but as I almost never balance charge, I'm sure they were off a lot more than .01V to start.

 

[wojtek]

ok my knowledge is limited, but thinking logical, the only reason why one cell would charge faster than others, is that it has somehow limited/ reduced capacity comparing to others.
So there is no way this cell will discharge same as others. At some point at the end of discharging, it HAS TO drop in voltage below others.
Sorry im 33yo, cant believe in miracles anymore.

 

[Ypedal]

All cells self discharge, lithium does this much slower than Nicad for example... and not all cells self-discharge at the same rate within a pack.. in a perfect, ideal world, they would all be exactly the same and would remain in ballance while sitting for long periods of time.. however.. this is not the case in real life.

1- you may have one or more bad cells, causing imabllance.... depending on the degree of " bad " .. the call may still work fine in daily use, or may need to be replaced.

2- the pack may have been sitting in storage for a long period of time and the higher self discharge cells simply need to be refilled to provide their rated capacity...

only testing will confrim witch you have.

 

[wojtek]

thanks guys to take your time for the responses
by "bad cell" you mean lower capacity [ah] or there might be other reasons behind BAD cell? i guess it is hard to answer?

 

[Ypedal]

A bad cell can be a few things, either it has " puffed " and should be retired.... or it canot deliver it's rated capacity witch is not too bad depending on how much capacity it lost..

a 5ah cell that delivers 4.8ah is ok.... if it can only deliver 3.0 ah it's really bad.

a cell that delivers less and less capacity on a weekly basis is bad... one that delivers 4.8ah and 2 months later still delivers 4.8ah is tollerable..

 

[wesnewell]

ok my knowledge is limited, but thinking logical, the only reason why one cell would charge faster than others, is that it has somehow limited/ reduced capacity comparing to others.
So there is no way this cell will discharge same as others. At some point at the end of discharging, it HAS TO drop in voltage below others.
Sorry im 33yo, cant believe in miracles anymore.

During discharge, each cells potential will equalize. I doubt that's the right terminology, but that's what happens in my limited testing of this. It's fairly easy to see for yourself if you start with a non balanced pack then discharge it down to 50% and then check the balance.

 

[neptronix]

If you guys want solid answers and not just speculation, pick up a charger that can monitor cells while charging or discharging, and provide you graphs.

You will learn a hell of a lot.
Examples would be the iCharger line or hyperions.

I can yammer on all day on the forums about how lipo balance acts in real life, but the best way to understand it all is to see it for yourself.

Celllog 8S's also have this functionality, so that's a cheap way to get into it. Make yourself a discharger and hook the celllog8 up to your pc, connect to it with logview and watch what the cells do while being discharged and charged.

http://www.logview.info/vBulletin/content.php?10-english&s=e7a2925afe47a35067ca88524474ae4c

http://www.hobbyking.com/hobbycity/..._Name=Cell-Log_Cell_Voltage_Monitor_2-8S_Lipo

 

[liveforphysics]

ok my knowledge is limited, but thinking logical, the only reason why one cell would charge faster than others, is that it has somehow limited/ reduced capacity comparing to others.
So there is no way this cell will discharge same as others. At some point at the end of discharging, it HAS TO drop in voltage below others.
Sorry im 33yo, cant believe in miracles anymore.

During discharge, each cells potential will equalize. I doubt that's the right terminology, but that's what happens in my limited testing of this. It's fairly easy to see for yourself if you start with a non balanced pack then discharge it down to 50% and then check the balance.

You must be talking about LiFePO4, or some other buffered charge plateau chemistry.

 

[wesnewell]

Balance Test 14s1p 5ah 15C Zippy lipo

Starting cell voltages
4.14
4.15
4.13
4.13
4.11
4.14
4.14
4.13
4.05
4.13
4.13
4.13
4.13
4.13
.09V gap

Check at 79% charge
4.02
4.03
4.01
4.02
4.00
4.02
4.02
4.01
3.95
4.01
4.01
4.01
4.01
4.01
.08V gap

Check at 17% charge
3.71
3.72
3.72
3.72
3.70
3.72
3.72
3.72
3.67
3.72
3.72
3.72
3.73
3.73
.05V gap

 

[neptronix]

Ah, good thing that is only one cell.
Once you hit the cliff, that one outlying cell becomes your problem. 3.7v/cell is close to the cliff, but not enough to see the difference.

So if you wanted to discharge down to 3.5v/cell resting, that one will be much lower.
If you ever go down to 3.3v/cell, that one will probably be below 3.0v.

Make sure you get that cell up to where all the others are.
If you balance charge it and this disbalance occurs again, you've got a cell that could be a problem down the line in the next dozen or hundred cycles.

I've had a few funky cell packs like that. I set them aside for other uses. I know i will get complacent with checking the balance, so i think it's a good policy to not keep packs with cells like that cycling through daily use.

 

[Ypedal]

When you look at a discharge curve of lipo, the top and bottom ends have a steeper slope, the middle part is flatter, this is why you see a smaller level of high to low voltages in the pack, nothing more nothing less.

 

[wesnewell]

When you look at a discharge curve of lipo, the top and bottom ends have a steeper slope, the middle part is flatter, this is why you see a smaller level of high to low voltages in the pack, nothing more nothing less.

That's the terminology that fits.

 

[wesnewell]

Ah, good thing that is only one cell.
Once you hit the cliff, that one outlying cell becomes your problem. 3.7v/cell is close to the cliff, but not enough to see the difference.

I normally don't let the gap get to .09V or normally go as low as I did this time. I would consider a .09V gap extreme. Usually try and keep it to under .05V at 95% charge. The SLA charger seems to actually keep the balance better than doing a non balance charge with the lipo charger. Probably because its only a 2-3A charger, while the lipo charger is set for a full 1C at 5A. Had I started with just a .05V gap, it would have been down to a respectable .01V gap at the end of the test. I realize once you hit the cliff, all bets are off. Balance will quickly go out of what by more than .1V. That's why I never get that close to it.