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        Whoops! Does slow charge balance Lipo cels???

#1 rick121x Mar 15, 2005 11:51 PM

Does slow charge balance Lipo cels???
 
I understand, and I may be wrong, that Lipo cels in a stack will eventually become unbalanced.

If so, then each stack is destined to fail because of overcharge - as the charger has a maximum setting, the total of the stack, - and if one cel is lower charge than the other, the charging will continue whether or not the higher one is fully charged - and will cause a failure on that cel.

I have lost several individual cels because they bulged due to overcharge - it was always one cel in a stack...... :mad: But that's better than both...

So, I wonder; if slow charging, say at 50ma, and through a Kokam voltage limiter, would result in rebalancing the stack - as happens in a nickle-type battery.

I would love to hear from someone who has experience with this.

Richard

#2 Larry3215 Mar 16, 2005 12:43 AM

No - slow charging lipos does NOT balance them.

I have tried it to test the rumor (hall woo keeps bringing this up) and it does not work.

You need to use a balancer or charge each cell individually.

Larry

Larry

#3 psycho_klown66 Mar 16, 2005 01:14 AM

Does slow charge put less stress on the battery when charging then?

#4 Larry3215 Mar 16, 2005 01:27 AM

It has been pretty much agreed that charging at .7C or less will extend the life of your packs - or mabey it is that charging at OVER .7C will reduce the life of your packs :)

Larry

#5 rcflyrdon Mar 16, 2005 05:24 AM

The ONLY way to prevent overcharging which results in "puffing" [or worse] is to MONITOR each cells voltage and balance a pack by charging a low cell periodically. I have been doing this for almost 2 years, and have constantly used cells that are this old, with NO problems.

#6 Valid8r Mar 16, 2005 05:35 AM

From what I can read/see in the trade rags is that sometime this year, cell balancers charging systems are going to solve this problem. In this case each cell will be tapped and the tap will run to a unit that is between the cell and the charger.

Is this common opinion?

Thoughts on the topic?

Jon

#7 everydayflyer Mar 16, 2005 06:21 AM

Yes it seems like cell balancers and pack balancing is the theme for this year. There is a good deal of imformayion in this thread.

http://www.rcgroups.com/forums/showp...9&postcount=40

Charles

#8 hall woo Mar 16, 2005 08:49 AM

Lipo Cell Balancing VS. Cell Equalization
 
Normal LIPO packs can be fast charged at 1C using active balancing circuits at constant current chargers and power supplies for people using a single pack.

For the more experienced user, a constant voltage regulated power supply is what I use to charge 5 packs ( 2s & 3s) at the same time.

The current automatically tapers off as the packs reach their clamped voltage levels of 12.6 and 8.4 at around 200ma to 50 ma

This is a slow charging process which cells in the packs have lots of time to EQUALIZE, emphasis on the time factor, not amps in the final AH reading

I have been using this system for a long time and I have salvaged packs that R cooking brushless motors in a ducted fan models

#9 hoppy Mar 16, 2005 10:24 AM

Quote:

Originally Posted by rick121x

So, I wonder; if slow charging, say at 50ma, and through a Kokam voltage limiter, would result in rebalancing the stack - as happens in a nickle-type battery.

Richard

In the whole world there may be only one person who thinks that a low current charge will balance a lithium ion polymer pack. I would go with the majority. On the other hand, it can't hurt anything as long as the voltage does not exceed 4.2V/cell.

#10 hall woo Mar 16, 2005 10:35 AM

I still have to to use 1C fast chargers for repeated runs on the same pack, but I don't want to wait ~ 1 hour charging at the field and lug out a generator which I see the PROs here at RSA doing, so I usually bring pre-charged well conditioned packs to the field most of the time

All my operational packs have more SLOW charging cycles than 1C fast charges

#11 mode1 Mar 16, 2005 10:35 AM

So...how do you charge 1 cell (to balance) of a 3 cell pack that only has one charge line out?

#12 hall woo Mar 16, 2005 10:48 AM

If U have balance worries, then your pack may be bad, do a discharge capacity check of the pack. If 80%, then the pack is almost gone. U may be able to salvage the other two if the capacity of each cell is normal

AF 109 will charge 1 cell if your pack have taps, one at a time.

DO NOT charge balance all cells without an isolated charging system, U'll ruin the charger

#13 luc Mar 16, 2005 10:54 AM

answer to the main question is simple: NO
if you want balanced cells, you can:
have cell balancers inside your packs, or
build your packs in xP and charge them in // (as I do).

#14 hall woo Mar 16, 2005 11:06 AM

4.19V or 4.20V on the Taps
 
All my SLOW CHARGED packs, particularly the Tanic 2S1P 2150 mah packs, 4 of them ( salvaged, converted from 3S packs ) ,show a perfectly fully charged voltage of 4.19V or 4.20V all the time for the last 2 months on the TAPs of each cell.

Flies my Aerobird " PICNIC " fleet up to 15 minutes full throttle doing snap rolls and split Ss in V-tail or Pro-mode, easy fun sport flying in windy afternoon conditions

#15 luc Mar 16, 2005 11:09 AM

good for you...
but this has nothing to do with a slow charge....


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