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Old 03-24-2003, 10:56 AM   #31
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Not sure, but I always thought that flex charging or reflex charging or whatever companies call them is used for "burping" NiCds. It is suppose to break the crystals that form inside the cell and release some gas build up. NiMh has different chemistry and don't need this. Can somebody add to this?
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Old 03-24-2003, 11:09 AM   #32
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Default Charger comparisons

Guys;

I haven't had any need to use the Flex charging feature. Most of my packs are less than a year old.
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Old 03-24-2003, 12:28 PM   #33
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Default Flex and pulse charging;

This site http://www.repairfaq.org/ELE/F_NiCd_Battery.html is the most informative and the most reliable (at my opinion), I've found so far;

By reading the below text from the site, there's some interesting factors: Cells are different. So on some cells flex and pulsing is an advantage and on others, there seem to be no difference. Another factor, is that these techniques can be implmented in very different ways. Like frequency, discharge rate, discharge time...

My own charger is the pulsing type. It pulses at 300 hz, which seems to be way too high, according to the below...

I wish some of the RC Car magazines would do a serious test on this. By using a discharger, which produces graphs. Then use a series of 5 packs from Sanyo, 5 from GP etc.... Also add some track testing and get 5-10 chargers to the test bench.

From the site:

"Pulse charing is a hot topic that alot of people are trying stake out patents. There seems to be some advantage at the highest rates 15 -30 minute charging to this technique for nicds. The Cristie charger was designed for Lead-Acid systems, where liquid phase stratification was a big problem. It is quite helpful in "stirring" the acid in the big cells they typically market. There is also some evidence that the pulse charging changes the morphology of the cadmium electode, in an advantageous way. High rates and current reversals tend to give higher areas and better utilization. This is good, expecially for cheap plastic roll bonded cadmium electrodes found in your average commerical cell.

The comments about storage shorted or trickle charged is right on. What wasn't said is the benefits of keeping them in the fridge or frezzer. Keep them above -20f and you'll be sure not to freeze the electroltye.

Jonathon was asking about bubbles and charging and heat. It sounds like you got some sales literature thrown at you. The bubbles are oxygen, and you don't shake them loose, you electro- chemcially recombine them. Bill, they are generated at the Nickel electrode. The real solution is to not make so many of them. You do that by controlling the cell potential, and thus the driving potential on the positive electrode. Pulsing may do that by relaxing the proton diffusion gradients in the postive electrode, or it may not! Like I said, at high rates, good idea. The effect on dead cells can be to burn out the cadmium shorts and give you a few more cycles. Jon, I could tell you what to look for but then I'd have to kill ya! :-)

The circuit that Gerald posted seems to be working off 60 hz AC. I am not sure, but I think that is a little fast for optimal results. (So move to europe 50 hz :-) The problem is that at two high a frequency you just access the doulbe layer capacitance in the cell and you don't exercise the main reactions, or the overcharge ones. I seem to remember 15 hz as being indicated by the work of McBreen on the Zinc electrode."
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Old 03-24-2003, 12:48 PM   #34
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Default Off on another path

Guys;

When Charging at the Track, how many of you use a Fan to keep the pack cooler (while charging) and do you see any noticeable advantage in doing so?

Thanks,

Last edited by popsracer; 03-24-2003 at 07:45 PM.
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Old 03-24-2003, 01:36 PM   #35
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I dont use a cooler. This is because I believe that cells dont like fast changes.
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Old 03-25-2003, 02:00 AM   #36
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Alyee, I tend to find the Jaycar report quite true. This is because most parts are very reasonably and are in accordance with most others sources. Then there's the part about flex charging; I wont doubt that the NASA and US military have tests that prove that flex charging, double life time of batteries. But they probably got way better batteries, than consumers like us. And the use of batteries, might also be a lot different.

To me, it seems that flex charging is an advantage with certain types of cells, probably the cheaper ones.

If flex-charging really gives an improvement with all types of batteries and with all types of use, then all chargers would charge this way. Especially in a demanding hobby like ours.
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Old 03-25-2003, 02:24 AM   #37
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Cole, I don't have a charger with PC interface for curve display, but now I'm really curious how the discharge curve will be like for both linear and flex charging on the same battery pack.
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Old 03-25-2003, 04:59 AM   #38
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Me too. I aint got a flex charger, mine is the Apex Sigma Plus. Hmmm. There's a method without using those chargers / dischargers with graphical interface. One can simply monitor the voltage during discharge, and then take samples for a fixed interval. That is, for each 100 mAH measure the voltage. Or for each 20 seconds. Write them down. Afterwards, it's possible to draw the discharge graph. It's a little time consuming, but it can be done.

Preferable, it should be done for several charges / discharges at each method, to ensure the reliability. For example like 5 runs for each charge method. The time schedule should be the same for each test. for example charge, 15 minutes pause, discharge, 24 hours pause, next phase...
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