1500 or 1000, just WHAT is a cycle ?

[InHisName]

Some of you may have the scientific definition of NiMH 'cycles' so post text or link to def here.

I have had my AAA Duraloops for a year now and have 'cycled' them at 500/400 ma in my C9000. The internal impedance check no was 1.53 when new and is 1.7 to 1.93 now. They have experienced approx 60 cycles so far. Based on what my NexCell s have done, I project that I have about 30 cycles left to go.

They only are used in a frs radio set [walkie talkie]. When new they ran about 33 hours to low battery condition. Three nights at 11 hours each. Then I recharge. Two sets of four. One set per week charged. Average discharge rate is around 22 ma.

Based on the above, I predict that I'll have 90 - 125 cycles before 1st cell goes HIGH. Maybe 155 will send them all to HIGH

I thought I was being nice and gentle with my Duraloops. They seem to be wearing out pre-maturely.

Just what is an OFFICIAL cycle defined as? Maybe its more like charge to 80% then discharge to 30% and repeat. So's the choice might be either 400Mah @900 cycles OR 700Mah @ 100 cycles with 25ma discharge in both cases ? Neither choice gets me very excited.

My NexCell LSDs started hitting HIGH at cycle 40, now at cycle 65+ half are HIGH. I've had these since July 09. The NexCells were used in 16ma radios so took 4 nights to go to low bat mode.

 

[45/70]

Hi In. Most manufacturers consider a cycle as being one full charge and one discharge. That said, most manufacturers also list the amount of discharge during their testing in the data sheet for each battery type. Often, they only discharge cells 80% during cycle tests, for example. For this information, it would be advised to look up the data sheet for the cell you're considering.

It is important to consider that these tests are done in a laboratory in a very strict environment, as well as some facets being merely simulated, and not tested in the field. Therefore the conditions during the tests are in an "ideal" situation and results in actual field use are likely to be far less than ideal.

Generally though, it is considered that discharging a cell halfway twice, recharging fully each time, counts as one cycle. This pretty much applies for all NiMH cells, but again, you should look at the data sheet for the specific cell you are interested in. And again, don't expect "real world" results to fare as well.

Dave

 

[Mr Happy]

I think your real problem is not about the definition of a cycle but about the high internal resistance your cells are developing.

It is possible that this might be reversible. Have you tried running a set of your cells through a break-in cycle on the C9000 to see if that improves them?

 

[45/70]

Another thing you might consider, is that devices like radios, unlike digital cameras for instance, which draw significant current most of the time, tend to run cells to a very low level before the "low batt" indication. It's very possible that you are over discharging your cells, or at least running them to a lower than desirable level each cycle. Also, in these situations it is fairly easy to end up reverse charging one or more cells, if they are used in series, as they are discharged to such a low level.

NiMH cells prefer a less than complete discharge during normal use. Still, even LSD cells should be discharged occasionally, to keep the cells in good health.

Dave

 

[cckw]

These are AAA which do not hold up as well as AA.

Are yours made in Japan or China. That would make a difference too.

 

[45/70]

These are AAA which do not hold up as well as AA.

Humm, I failed to notice In was referring to AAA cells.:candle:

Yes, AAA cells, even LSD's are not as durable as the AA variety. While I've noticed they are considerably more robust than standard NiMH AAA's, they still are not going to hold up nearly as well as their AA brethren.

Dave

 

[InHisName]

I think your real problem is not about the definition of a cycle but about the high internal resistance your cells are developing.

It is possible that this might be reversible. Have you tried running a set of your cells through a break-in cycle on the C9000 to see if that improves them?

Yes it is the high internal resistance. But is it not the end point for the 1000 'cycles' even in the lab ?

I did try several months ago with both the Duracells and the NexCel but did not make much measureable change. I will be doing a break in soon on several of the worse ones to see if that might help now.

 

[noisebeam]

I made the mistake of forgetting (since I read the FAQ long ago) that the Impedance Check should be done when the cells are fully discharged.

 

[Mr Happy]

Yes it is the high internal resistance. But is it not the end point for the 1000 'cycles' even in the lab ?

I did try several months ago with both the Duracells and the NexCel but did not make much measureable change. I will be doing a break in soon on several of the worse ones to see if that might help now.

No, it is not the end point of the 1000 cycles. NiMH cells develop increasing internal resistance just from sitting around or getting gentle use. It is a temporary change and it can be reversed by running a break-in cycle on the cells. It is the reason why it is recommended to cycle and refresh NiMH cells on a regular basis. In between uses in the radio you should probably run some normal full charge/discharge cycles on the cells every three months or so (400 mA charge/200 mA discharge), and run a break-in cycle every six months to a year. NiMH cells are a bit like people -- to keep them fit you need to give them a good workout from time to time.

 

[Battery Guy]

I think that Sanyo cheats a bit when it comes to defining a cycle. Take a look at Figure 9 in the white paper found here.

My interpretation of that chart is that they only completely discharge the cell once per 50 cycles. The rest of the time they are discharging at 0.25C (500 mA) for 2 hours and 20 minutes, which is approximately 1165 mAh of capacity. So each "cycle" is approximately a 60% depth of discharge.

So to say that they can get 1000 or 1500 cycles is kind of stretching the truth in my opinion, when each cycle is only 60% DOD. For comparison, lithium-ion cell manufacturers rate cycle life based on a full discharge and recharge cycle.

Don't get me wrong, I think that the Eneloop is a fantastic product. I have bought my fair share and will definitely buy more as needed. But it seems that Sanyo's marketing department is not above the same snake oil performance claims that we are used to in the battery industry. And it makes me wonder if the "new and improved" Eneloops with 1500x cycle life are really any different from the older Eneloops. Unfortunately, unless someone is willing to devote a considerable amount of time and effort, I don't think that we will ever know for sure.

Cheers,
BG

 

[Sub_Umbra]

I always take it for granted that we are nearly always harder on our cells than we think and therefore shorten their normal lives a little every day. I think one may get all those advertised cycles and more but it would be pretty expensive. With the engineering that goes into satellites they routinely get thousands and thousands more cycles of their NiCads than we could.

While I doubt I'll ever get the cycles listed on the package they always more than pay for themselves when compared to other options.

 

[Bones]

According to the press releases for both the original and the updated Eneloop, their cycle life was determined in accordance with criteria established by the Japanese Industrial Standards Committee.

http://jp.sanyo.com/koho...0511/1101-2e.html

http://sanyo.com/news ... 2009/10/06-1.html

Now, we just need to determine what those criteria are...

 

[45/70]

I think that Sanyo cheats a bit when it comes to defining a cycle. Take a look at Figure 9 in the white paper found here.

My interpretation of that chart is that they only completely discharge the cell once per 50 cycles. The rest of the time they are discharging at 0.25C (500 mA) for 2 hours and 20 minutes, which is approximately 1165 mAh of capacity. So each "cycle" is approximately a 60% depth of discharge.

I don't think this is necessarily cheating, but rather is a close approximation of "typical" use. I'll go along with the idea that this procedure may promote the belief that you will get more cycles out of the cells than you would if you fully discharged them each time, but with NiMH cells you really shouldn't do that anyway. NiCd cells yes, NiMH cells, no. That said, I usually run my NiMH cells down pretty far, but I don't expect to get the advertised number of cycles out of them either. So far, most of my cells have died from old age anyway, not the number of cycles. Hopefully, LSD cells will prove to last longer in this regard.

Dave