Cycle Testing Observations…

[SilverFox]

Hello BackBlast,

Interesting results. Thanks for sharing.

I wonder if the increased capacity of the Ray O Vac cells has anything to do with their drop off of many cycles...

Tom

 

[DynoMoHum]

Very interesting testing... Talk about time consuming... wow.


Now I just finished reading this whole thread, I may have missed a few points along the way... Hope this wasn't already made clear somewhere and I just missed it...

I can't tell if the cycles using the rapid charging were completed in much faster time then the cycles of the slower charging method. That is... Were the same number of cycles per time period conducted with each charge method? or were the high charge rate cycles completed in much less total time?

The reason I ask, is cause I wonder how much a lack of rest time between cycles effected the cell life, in comparison to the effects of the charge rate.

When I was racing RC cars, it was common practice to let out packs rest for a week between charges. It was thought that charging some cells more then once a week was very hard on them. Some of this changed depending on who you talked to and/or what type of cell was being used. Some types of cells were supposed to be able to be charged/used twice on a single race day, others were never used that way, and it was very rare that anyone but novices ever used the same pack more then twice a week.

When reading this thread, I noticed that the Eneloop cells seemed to have the first 100 cycles placed on them in about 10 days or so... which means they were cycled somewhere near 10 times in 10 consecutive days. I know that part of this lack of rest for the cells was in a direct effort to abuse them and/or shorten the total time required to 'see' some change in results. However I can't help but wonder if longer periods of rest between charge/discharge cycles could have effected the over all results, particularly as it relates to the comparison of 'fast' charging vs. the not so fast charging.

 

[SilverFox]

Hello DynoMoHum,

I have also heard that under heavy use NiMh cells seem to do better when allowed to rest for an extended time between uses. The problem is that I have never been able to substantiate that under the loads I am testing at.

You will notice that I am discharging at 1C.

Heat is the main problem with NiMh chemistry. High discharge rates do a good job of heating the cells, and it is a good idea to let them totally cool down after use, but I don't think it takes a week to cool down. With the introduction of cooling boxes, I believe the attitude changed from once a week use to making sure that the cells were cool prior to charging.

The purpose of this test was to explore what happens with rapid charging. This is slightly different from running tests to explore how to optimize rapid charging, or how to optimize charging for rapid discharging at high loads.

If your "wonder" is compelling enough, feel free to run the same tests with extended rest times and report back...

Tom

 

[DynoMoHum]

Umm... I guess my "wonder" level isn't that great...


As you probably know with the RC racing crowd in the Mod classes people would drain 3300 mAh packs in 4 minutes, so the drain was at a extremely high rate. The main reason people didn't run a pack twice in a day was that on the second run the 'punch' or perceived ability to produce that really high output was reduced. With really good drivers they apparently could see the differences in their lap times, particularly in the opening laps of the races.

Several of the battery 'matchers' would also give their recommendations as to how to treat batteries, and they tended to give some indication as to if they felt you could use the packs more then once a night. Now I suppose they could potentially sell more packs if they told you only to use one each race day...

I had always heard that it was not so much a matter of the pack cooling down, but more that the chemicals and such needed time to normalize. In fact I had frequently heard that running fans on them to cool them faster wouldn't help any. The only time I new of people using fans was in an attempt to keep the shrink wrap from melting. Either way I had always figured we were totally abusing our cells the way we used them, and I rarely used my packs more then twice a week, in hopes that they would have the maximum output on the off chance that my car would actually hook the power to the track and I could handle it all.

Now for back yard bashing, I frequently ran packs over and over just letting them rest long enough to get cool . But then I never tried to measure the ouput levels on any of these occasions.

 

[HarryJames]

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