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Old Oct 14, 2010, 03:16 PM
Southern Pride
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Haralson County GA. USA
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Idea
Yet another parallel balancing by dumping one battery into another one.

OK not balancing the cells but rather bringing two batteries to the same voltage for storage or for parallel charging.

Others have done this by using resistors or even by not limiting the current at all but as I had some Poly fuses on hand I thought I would give a 2.5 amp. one a go.

First run was with two 4S A123 2300 packs 2.367 voltage difference ,one fully charge and other one empty.

Second run with two 3S 2200 LiPolys one discharged to 10.3 and other charged to 12.6 or 2.3 volts difference. Both of these are rather severve and the Lipolys have lower Internal Resistence so greater flow was expected.

The discharged LiPoly is rated 10C charge so this rate was not really severe for it.

No graph but one 3S LiPoly at 11.2 and the other at 11.9 . Initial flow 6.48 A and down to less than 3A in one minute. This is more of a spread than I would ever have with flown packs.

Charles
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Old Oct 14, 2010, 03:18 PM
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I think you need a disclaimer to "not try this at home" and leave this to the professionals.

Waiting for results.
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Old Oct 14, 2010, 03:36 PM
Southern Pride
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But I did do it at home.

As of late there have been a bunch of Threads / post on parallel charging and some of them show just randomly connecting Lipolys without giving much if any thought to the state of charge of them. I have paralleleld charged for years but have always limited the voltage deferential of the packs.


I only did these extreme examples to show how much current can flow even though it was being limited by a Polyfuse rated for 2.5 amps.

Charles
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Old Oct 14, 2010, 03:44 PM
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Charles I know your a knowlegeable person beyond belief about batteries. You know what your doing.
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Old Oct 14, 2010, 05:57 PM
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Joined Jun 2005
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So some sort of current limit in the parallel harness looks like a good idea, or just be careful about the state of charge of the two or more packs. The cross charge will occur through the balance harness as well won't it?
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Old Oct 14, 2010, 06:01 PM
Southern Pride
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Haralson County GA. USA
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Quote:
The cross charge will occur through the balance harness as well won't it?
Yes but as they are much smaller gage wire they would not handle the current without becoming hot or melting.
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Old Oct 14, 2010, 08:38 PM
The blade numbers go up to 11
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Sydney, Australia
Joined Aug 2002
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Funny, when I mentioned that just connecting packs in parallel for parallel charging was a dumb idea, people jumped on me as if I was an idiot.
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Old Oct 14, 2010, 09:05 PM
Southern Pride
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People tell me the same thing about playing the Market.

Parallel charging can be a real time saver for some but there are pitfalls which many are not aware of . I first started parallel charging around six years ago when myself and son were mostly flying 1320 3S packs on flate plate foamies. balancing was not practiced back then and I did not have a pile of chargers so I charged 5 packs at atime on a AF109 and on occasion another 3 or 4 packs on a couple of Tritons.

With LiPolys capable of being charged at 3 to 10C and the chargers that can do this I rarely parallel charge these days. There is really little point in it and with each cell of each pack being charged,balanced and monitored I feel better.

Charles
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Old Oct 15, 2010, 12:09 AM
Frankenstein recycled packs
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USA, AZ, Gilbert
Joined Jan 2006
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I sold some of those same poly's to a RCG'er and he saw something like 12A initial and slow to decrease amps.
I am going to send him some 1.1A poly's. In the meantime I asked him to cut the top off to reduce the amps. It works but it is a grind, measure, grind... till you get what is needed.
Mee thinking the resistor method may be a better way to go but not sure which is cheaper. At least the resistor is constant.

Rick
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Old Oct 15, 2010, 08:13 AM
Southern Pride
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Haralson County GA. USA
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Quote:
At least the resistor is constant.

Rick

How's that?

Ohm's Law is constant however every time two or more packs of different voltages are connected the current flow will be different.

The simple solution is very simple. Purchase a $4 HF DVM , install an extra charging leads set to it,use it to check pack voltages to insure there are no major differences.

Alternate means is to just blindly connect them together and hope for the best. This will work for most due to the simple fact that even a 20C rate charge of under a couple of minutes duration will not likely damage their LiPolys any worse than other abuses they subject them to.

Charles
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Old Oct 23, 2010, 07:03 PM
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Interesting test, Charles...thanks for the info. I thought poly fuses stopped current flow but I guess I wasn't informed. How exactly do they work?
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Old Oct 23, 2010, 08:12 PM
Southern Pride
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Haralson County GA. USA
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They increase resistence as the heat up. They have a nonimal rating whic when exceeded heats them up and thus they then reduce current flow, as they cool down flow increases.

http://mouser.com/ProductDetail/Litt...NKox994Q%3d%3d
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