Years ago we never balanced LiPolys but now days balancing is very common and most recomend it for safety if for no other reason. From time to time a discussion comes up as to how many mAhs are bleed off during balancing and how does balancing effect charging time and what will cell inbalance be without balancing. Discussions also include such items of interest as to when is the best time to balance and will inbalance get worse with each cycle if you do not balance. Most of these questions will never be completly answered to everyones satisfaction but here I go with a series of test which may help add to the confusion if nothing else.

A Turnigh nanotech 45C 3S 2200 was discharged at 4 amps. until the lowest cell reached 3.3 volts prior to each charge.
Attachment #1
First charge was at 5amps. with no balancing at all. Charge graph clearly show cells quickly came into balance with just a little charge into them.
Notes on the graphs (lower left hand corner).

Attachment #2
Second charge was also at 5A but with balanceing turned on to start at 3.8V and there was some balancing observed at this point but graph shows cells were already extremely close. . Is this an example of wasted being bleed away unnecessarily?



Discharge #3 1958 mAh out
Balance charge same as above
27:14 - 2,050 / cells at 4.199 / 4.199 / 4.199

Dsc. # 4 1,962 out
charged with no balancing
26:59 / 2,025 mAh cells at 4.199 / 4.199 / 4.199

No I did not get confused . Charge after Dsc#4 resulted in cells perfectly balanced without any balancing and at the same voltages as a balanced charge.

Charles

Originally Posted by everydayflyer

I go with a series of test which may help add to the confusion if nothing else.Charles

Coming from you it should be very usefull information.

YES, YES, YES! I have several old QUALITY packs without balance taps and they still work great.

I'm old school and still like to check my cell voltages EVERY time before and after charge. My "BETTER BRAND" packs require little if any balancing ..... but I still throw in a balance charge on a regular schedule.

Thanks Charles for all the great testing that you do!!

Charles -

Why don't you get REAL BOLD and do something really stupid like balancing the DISCHARGED BATTERY, and then charge it with no balancing during the charge?

Yes, it seems dangerous, and I wouldn't suggest doing this indoors or near anything flammable. And I certainly wouldn't do this with a battery that wasn't destined for the trash bin. But i see people all the time on the forums that think this is a good idea.

Originally Posted by hornet_dave

Charles -

Why don't you get REAL BOLD and do something really stupid like balancing the DISCHARGED BATTERY, and then charge it with no balancing during the charge?

Yes, it seems dangerous, and I wouldn't suggest doing this indoors or near anything flammable. And I certainly wouldn't do this with a battery that wasn't destined for the trash bin. But i see people all the time on the forums that think this is a good idea.

The cells were only off by .005V when he started charging them. So how will balancing them before the charge hurt the battery? What will it make them, .005V off at the end the charge?

As for balancing or not, last weekend a guy had his 10s Volt pack (made up of 2 5s packs) that he runs in his Furion 6. He bought a charger and all the stuff for JST-XH before he bought the Volt pack and so he does not own any TP balance port adapters. As such he has no been balance charging. I happened to have my CellLog there and so we hooked up my pack and checked it after a charge. The lowest cells was 4.150 and the highest cell was 4.197. The others were all over between those 2 voltages. I would guess he had about 20 cycles on the pack. In this case not balance charging resulted in a fairly out of balance pack.

Perhaps I will and in my case I have no issues with doing it inside just like I do all my other LiPoly bench testing. Also in my case not really stupid as I am still using a charger with balancing leads connected which will prevent any cell from exceeding 4.205 volts.

Fact is what I am doing now is no diferent than testing I did 6 years ago other than I now have a very easy means to graph the result,do automated cycles and of course observe the difference in the way newer cells respond to such testing. Being able to charge at higher C rates also enable me to complete X number of cycles much faster.




Charles

The cells were only off by .005V when he started charging them.

?

3.569
3.355

is a difference of 0.214 or 42.8 times 0.005 difference.

Charles

"...No I did not get confused . Charge after Dsc#4 resulted in cells perfectly balanced without any balancing and at the same voltages as a balanced charge..."

Could this be due to the low IR of the cells?

Shoot, I've been thinking about to balance or not to balance for a while and concluded I can balance at night and don't have to balance any longer during fly days and most of my bats are 20c...

Well as I have been posting for around six years now,some Lipolys need balancing when new,some need balancing every few cycles,some every ten cycles ,some every twenty and some never need it.

In have had LiPolys which really needed balancing every charge and some that went over 200 charges without balancing and were still within 0.05 volts at full charge even after their capacity had drop by approx. 20%.

It is easy enough to check if you have a charger that will do a non balamced charge. It is best to use one that lets you use the balancing leadsa and will terminate the charge when any cell exceeds 4.2 volts and also lets you read the cell voltages at least after the charge if not during the charge..




Charles

Originally Posted by everydayflyer

?

3.569
3.355

is a difference of 0.214 or 42.8 times 0.005 difference.

Charles

Whoops I was just looking at the .x9x on both and did not see the .5xx and .3xx. My bad.

One other point is that you never discharge a lipo anywhere near 3.3V resting voltage under normal circumstances, so why do it now? If this test is to be useful in real life the packs should be discharged to approx a 3.7V resting voltage and by looking at the graphs, we would see that they will still be very closely balanced.

Originally Posted by tjinguy

The cells were only off by .005V when he started charging them. So how will balancing them before the charge hurt the battery? What will it make them, .005V off at the end the charge?

If packs are not carefully matched with respect to capacity and internal resistance, balancing them while discharged can create a dramatic and possibly dangerous imbalance when the pack is charged, where cell to cell balance is most critical. It is for this reason that balancing in a discharged state is foolhardy and very likely far more dangerous than never balancing at all.

The fact that many if not most of the manufacturers of budget packs employ no cell matching when assembling packs makes owning a quality balancing charger or inline balancer even more important.

Balancing chargers and inline balancers that have the ability to monitor all cells within a pack and terminate charge if an unsafe voltage is reached have been the single greatest contributor in the dramatic reduction in overcharge related lipoly fires. The fact that they are also extremely inexpensive make it completely foolish to not own and use them, especially if one charges indoors.

Mark

Graph shows non balanced charges 5-9 (10 if you count the from storage one). As can be seen the cells have not became more inbalanced with each cycle as many state they will. I used this pack for these test mostly due to the simple fact that it is not what I consider an extremly well match pack to begin with.

Charles

Excellent graph Charles.

Clearly indicates that if this particular pack (which is poorly matched with respect to capacity) were balanced while discharged, the witnessed imbalance would 'shift' to the charged state and possibly to a unsafe level. This condition would be far worse if the pack were a higher cell count and had several 'higher capacity' cells and one 'lower capacity' cell. Balancing while discharged would drag the higher capacity cells to the same voltage as the lower capacity cell. When subsequently charged, the lower capacity cell very well may be overcharged to the point of ignition. Ignition is bad.

Mark

One other point is that you never discharge a lipo anywhere near 3.3V resting voltage under normal circumstances, so why do it now?

How else can I make the p[oint that I am trying to make? I often discharge well below the 80% point ,charge at higher than approved rates,exceed proper temperature guidlines and such all in the name of science.

There are more that do not follow the 80% rule than those who do. Most Lipoly users never visit a user's forum . Most still fly to LVC and most LVCs are still more appropuate for 6C Lipolys than 20C plus ones.

There are many here on RC Groups who have been members for years who sstill expect a 2200 mAh LiPoly to deliver 2200 mAh even after it has been flown 50 times and stored fully charged since new and it is now two years old.

Most of the small percentage who know and practice good Lipoly management rarely ever post as they do not care for the constat debating that goes on.

There are some experts who still claim that discharging a LiPoly 100% at 1C or even 0.5C down to 3.0 volts per cell does no harm to them.

Charles

Note : I captured the first screen shot early in charge beforee the inbalance point became to compressed.


Bet these results are not nearly as bad as some imagined.

Charles