Does slow charge lipo = balanced pack? - Page 2 - RC Groups
Dec 31, 2006, 03:48 PM
Southern Pride
Quote:
 I've watched cells go from a state of being out of balance by several hundredths of a volt to being within a hundredth after a quarter of an hour at a quarter of an amp...and at the end of a normal charge past that point, they reached normal terrminal voltages without damage...as actually witnessed on my DVM.
I can fully understand this however my point is that the same thing would have happened even if they were being charged at 1C.

What purpose does a balance serve? Make less than perfectly matched groups of cells connected in series safer to charge and lets one squeeze a bit more performance and life from them. A balancer can also prevent a cell or cells from being damaged by an overcharge.

Charles
 Dec 31, 2006, 03:58 PM Permanently Banned that usually depends on how much the imbalanced cells have been overdischarged and overheated and they usually R < 80% DIMINISHED CAPACITY now U can compare that with a normal healthy pack using a AFI watt-hour( or WATT-SEC ) meter to measure the " PUNCH " that the pack can deliver
Dec 31, 2006, 04:07 PM
Registered User
Quote:
 Originally Posted by roidspop ... I've watched cells go from a state of being out of balance by several hundredths of a volt to being within a hundredth after a quarter of an hour at a quarter of an amp...and at the end of a normal charge past that point, they reached normal terrminal voltages without damage...as actually witnessed on my DVM. Nothing about the internal condition of the cells changed, but going by the only criteria I've got...measured voltages...those cells balanced. ...
From several hundredths of a volt to a hundredth of a volt is a pretty fine measurement for typical home measuring devices, so there's obviously a +/- factor to be considered. Ideally, you'd run similar tests at various charge rates to see if the variance was due exclusively to the rate of charge. It will never be as accurate as a climate-controlled lab with the best (most expensive) calibrated measuring devices. But careful home testing can yield reasonable results.

The danger, of course, is to imply to someone with no measuring devices at all that slow charging Li cells can produce a balanced pack. This could create a false sense of security and lead to safety problems. So any answer to the original question should leave no room to be interpreted as a "yes."
Dec 31, 2006, 04:13 PM
Suspended Account
Quote:
 Originally Posted by Rodney The answer is an unconditional "NO", you can not balance a LiPo by slow charging. The highest voltage cells will be overcharged and most probably ruined by trying this.
My practical experience proves this incorrect. My packs without balance taps have been charged many many times and if slow charging hasn't helped these packs then it certainly hasn't hurt them.

Also, my prolites and extremes are often "slow charged" and very rarely go out of balance. I was beginning to question my balancer until I checked packs w/DVM.
 Dec 31, 2006, 04:35 PM That's a funny word Possibly I can illustrate this in an opposite sort of way. I'll start out by saying that a slow charge (or any charge)will not cause the cells to self balance (like a nickel pack) The reason they are appearing in balance at the top is because they were never out of balance at the top. They are only out of balance at the bottom. Now for illustration: Balance the pack perfectly at the bottom (at 3.5 - 3.7 voltsper cell) When the pack is in it's discharged state and in perfect balance it will stay "in balance" until it is charged and the opposite will occur. A slow charge will now unbalance the cells when they are full. In fact any charge will unbalance the cells when they are full. This can be easily observed and repeated. So, I can say that a slow charge will "unbalance" my series cells every time I charge them because when I am done with the run and check them they are in perfect balance. The answer has been to either use a balancer or to use exactly matched cells. If exactly matched cells are put together in series they will be balnced at the top and the bottom. If this doesn't illustrate then I have a demo using clear cups of water of varying size to illistrate it. My NIckel demo cups are either the same size with slightly different sizes "leaks" in them and they are all nailed to a common board simulating a series charge or discharge The Lipo cups have tiny tiny leaks that are insicnificant, but are not all exactly the same size and will show the balance very visually.
 Dec 31, 2006, 05:10 PM Space Coast USA 1. If a lipo pack is balanced, it doesn't make any difference if it is slow charged or fast charged, it will end up balanced. 2. If a lipo pack is unbalanced, it doesn't make any difference if it is slow charged or fast charged, it will still end up unbalanced. A pack that when charged has all cells within +/- 0.03V is a balanced pack. This is true whether the pack reached that state by itself, by parallel charging, by using a "blinky", or by using a balancing charger.
 Dec 31, 2006, 05:56 PM Registered User There are two separate issues being discussed, and they have two different answers: Yes, it is believed by many that conservative charging and/or conservative discharging will be less likely to cause a Li pack to go out of balance than aggressive charging and/or aggressive discharging. No, slow charging an out-of-balance Li pack will not cause it to get back into balance.
Dec 31, 2006, 06:02 PM
Permanently Banned

Normal Cell Internal Resistance

can better be reduced and maintained during SLOW CHARGING becuz each cell in a pack will become more voltage stabilized when it reaches close to 4.2v and charging current is at zero

a VOLTAGE CLAMP will give U these results and not any standard commercial LIPO charger balancing or otherwise and that's why I use it most of the time
when not 1C charging at the field

I have used most of the common commercial LIPO chargers and not one of them will stabilize a lipo pack at 12.6V at zero charge current like the VOLTAGE CLAMP