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Thread: Turnigy NiZn Cycle Life Testing

  1. #1
    Flashaholic*
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    Default Turnigy NiZn Cycle Life Testing

    A while ago, I did some testing on Turnigy NiZn cells - unfortunately, I never got around to actually posting the results before now:



    NiZn rechargeables have an advantage over NiMH rechargeables in that they maintain a significantly higher terminal voltage throughout their discharge, even when running at heavy loads (around 1.6V versus 1.2V) - this can be useful for devices that are poorly designed and don't work well on the lower voltage of NiMH cells. (Any device that can't work properly below 1.2V won't be able to use a significant amount of the capacity of even regular alkaline cells - with Alkalines, the voltage drops off as they discharge - at 1.2V, they still contain a significant amount of their original energy content)

    The biggest problems with NiZn rechargeables are that they have a bad reputation for high self discharge and that they're quite fragile - many people have reported that they've only managed to get a handful of cycles out of their NiZn cells before they became unusable.

    With this test, i've shown that NiZn cells are capable of performing quite well for a significant number of cycles. It appears though that when they're deeply discharged, that is when they sustain damage - and the damage occurs quite quickly. I performed a similar test with a new pair of NiZn cells and instead of using a 1.3V discharge cutoff, I discharged them down to 0.3V - the cells only lasted for about 80 - 100 cycles before dying in that test - still significantly better than has been reported, but a significant difference compared to the first test. I think that the key reason that the cells still lasted for a reasonable number of cycles in the latest test was because the load was removed as soon as the loaded voltage dropped to 0.3V - many devices will continue to slowly drain the cells in them even when the device has stopped working and has been turned "off" - I suspect that the slow constant drain causes more damage than a quick discharge down to a very low voltage.

    In regard to the self discharge characteristics of NiZn cells, I've seen a wide variety of remaining capacities from cells that have been allowed to sit for a while - some cells seem to retain quite reasonable capacities for a number of months whereas others lose their charge over a relatively short period. Another downside to NiZn cells is that there are often large differences in the capacities between otherwise identical cells - combined with the highly variable self discharge rates and their propensity to be easily damaged when deeply discharged, it's understandable why lots of people have had problems with this type of chemistry.

    In addition to devices which can't handle the lower voltage of NiMH cells, there are also some devices that can't handle the higher voltage from NiZn cells - I've seen reports of devices dying due to this higher voltage. Camera flashes can cycle faster with the higher voltage, but if continued at a high rate, it can end up over heating and killing the flash altogether!

    Overall, I think that if the variable capacities and self discharge rates could be improved with better quality control, there could still be a future for NiZn cells. If they could be improved so that they can better handle deep discharges, then that would also help significantly. Even with these improvements (if they ever come) NiZn cells will still only ever be useful in niche roles - Eneloops (and other low self discharge NiMH cells) are still more than good enough for the vast majority of applications.
    Firmware Developer for the UltraSmartCharger: Open Source Charger/Analyzer for NiMH/NiCad/NiZn batteries.
    http://www.ultrasmartcharger.com

  2. #2

    Default Re: Turnigy NiZn Cycle Life Testing

    Nice, has confirmed what some of us have observed but it does seem the Turnigy NiZn is much better than what PowerGenix came out with. Mind you, most of the NiZn cells for me die when in a pair, or in high drain torches (>2A).

    I still have a pack of PowerGenix cells in the original package, from at least 6 years ago ... maybe more. Might consider donating them to the cause? Would they even be any good after all this time?

  3. #3

    Question Re: Turnigy NiZn Cycle Life Testing

    What's the difference between "slow" and "fast" on the graph? Actual charging current? Is Rev. 06 the presently/shortly available UltraSmartCharger model? If not, is the present one worse or better for NiZn? I really need a reliable NiZn charger and this looks like a worthy contender.

  4. #4
    Flashaholic*
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    Default Re: Turnigy NiZn Cycle Life Testing

    Slow/Fast refers to the discharge rate.

    The revision 6 charger was an early prototype, but the latest version is quite similar. I don't think that there would be any significant difference between the versions when it comes to charging NiZn cells.
    Firmware Developer for the UltraSmartCharger: Open Source Charger/Analyzer for NiMH/NiCad/NiZn batteries.
    http://www.ultrasmartcharger.com

  5. #5
    Flashaholic* Grijon's Avatar
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    Default Re: Turnigy NiZn Cycle Life Testing

    Thank you for the test and write-up, Power Me Up!

  6. #6

    Default Re: Turnigy NiZn Cycle Life Testing

    Not sure how I missed this thread... very interested in NiZn. Thanks for the test.

    An obvious difference between the Turnigy NiZn 1500mAh cells and BPI 2500mAh, PKcell 2500mAh, Ultracell 2600mAh, Ultracell Plus 2800mAh NiZn cells is the advertised capacity. With other chems, esp. NiMh, my experience is the higher the advertised or rated capacity, the more fragile the cell is, the less resistent it is to overdischarging and overcharging.

    I wonder, if the Turnigy cells are indeed more resiliant, that perhaps it has something to do with the lower capacity, i.e. in theory, are lower capacity cells more resilient? Also, just in my experience, cells that advertise lower capacity seem to be more honest about the actual available capacity.

  7. #7

    Default Re: Turnigy NiZn Cycle Life Testing

    I haven't tried the Turnigy NiZn's. I only see them available in AA.

    I'm using PowerGenix NiZn cells in several "low drain" devices and they seem to be doing very well. I had been using Duracell and Energizer alkaline and I get MUCH better run times from the NiZns due to their higher voltage.
    So much so that I rarely have to worry about the batteries any more. I just check them and recharge them periodically.
    Note that I do not use a NiZn specific charger because I've read that those are part of the cause of failure. Instead, I use a CC/CV power supply and charge them to 1.88v @ 100mA
    Works for me.

    It seems to me that the bottom line on these is cost effectiveness. I'm getting so much more device run-time use from the NiZns (mainly because I can recharge them so many times of course) compared to the best Alkalines that the NiZns are an exceptional bargain. One alkaline cell every three weeks vs one NiZn cell once a year.

    17 Duracells at 1.00ea or ONE NiZn at 1.89ea per year. Break even after just 2 re-charges.

    Duracells = $17.00 per year
    NiZn = $1.89 per year

    For me that's the bottom line. I could literally throw away a bunch of NiZn's and still come out ahead compared to buying Duracells or Energizers

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