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Thread: Old NiMHs in a Quark X AAČ: stepdown at first, but full output after a little while?

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    Flashaholic* oKtosiTe's Avatar
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    Default Old NiMHs in a Quark X AAČ: stepdown at first, but full output after a little while?

    When I got my Quark X AAČ, I also ordered an eight-pack of Eneloops for it and my three Wii Remotes. So far, though, I have kept cycling some old Varta 2700mAh NiMHs which may have seen some overcharging abuse in my old two-channel fast charger.
    Almost every time I insert these in my Quark, it manages moonlight, low, medium and high just fine, but when I turn the head to turbo/max, it immediately steps down to medium level output. Switching back and forth between high and max, high consistently has a slightly higher output than max—for the first minute or so. After the light/batteries have "warmed up", max works as it should and is brighter than on high (although possibly still below the output I would see with the never abused Eneloops).

    Can someone explain to me why this is happening? It's not really a big deal, and I don't fault the light for it, but it bothers me just enough to wonder what is causing this behaviour.
    Last edited by oKtosiTe; 07-02-2012 at 09:37 AM.

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    Flashaholic* 45/70's Avatar
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    Default Re: Old NiMHs in a Quark X AAČ: stepdown at first, but full output after a little whi

    Hi oKtosiTe. When your 2700mAh cells are fully charged, partly due to the "surface charge", they are supplying enough power (Watts). The voltage however drops quickly with these old cells, due to their high internal resistance, and the light output begins to drop. As these old cells warm up, the voltage under load rises a bit, and they are then able to deliver a bit more current, thus output improves.

    Generally, the warmer the cell or battery pack, to a certain point anyway, the higher the performance. This is well known in the R/C hobby.

    Dave

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    Flashaholic* oKtosiTe's Avatar
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    Default Re: Old NiMHs in a Quark X AAČ: stepdown at first, but full output after a little whi

    Quote Originally Posted by 45/70 View Post
    Hi oKtosiTe. When your 2700mAh cells are fully charged, partly due to the "surface charge", they are supplying enough power (Watts). The voltage however drops quickly with these old cells, due to their high internal resistance, and the light output begins to drop. As these old cells warm up, the voltage under load rises a bit, and they are then able to deliver a bit more current, thus output improves.
    Thank you. Could this be exacerbated by the abuse they received in the past, or is this an inherent attribute of aging NiMH1 cells? They currently only last for 1900mAh (±50mAh), down from the presumed original 2700mAh.
    Last edited by oKtosiTe; 07-02-2012 at 11:00 AM.

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    Flashaholic* 45/70's Avatar
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    Default Re: Old NiMHs in a Quark X AAČ: stepdown at first, but full output after a little whi

    Quote Originally Posted by oKtosiTe View Post
    Could this be exacerbated by the abuse they received in the past, or is this an inherent attribute of aging NiMH1 cells?
    Yes, any type of abuse is likely to accelerate degradation of the cell and the associated increase in IR that comes with it. Nickel based rechargeable cells will suffer increased internal resistance as they age, but abuse surely doesn't help any.

    They currently only last for 1900mAh (±50mAh), down from the presumed original 2700mAh.
    I'd say the cells are pretty much at EOL. Usually, when a NiMH (or NiCd) cell will only charge up to 80% of it's original capacity, it's time for the recycle bin. Keep in mind that the "2700mAh" rating of even quality cells, is a bit optimistic. Usually these cells test out at the standard 0.2C discharge rate, at about 2550mAh. So, even considering this, your cells are pretty much spent.

    Sometimes the 80% rule is questioned. I have to say that in my experience though, that cells at this point in their life begin to perform poorly. The signs are just what you are experiencing with your cells. They do not hold voltage under load well and really only work adequately in devices that draw very low current. At that, newer cells in better condition would actually work better.

    Dave

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    Flashaholic* oKtosiTe's Avatar
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    Default Re: Old NiMHs in a Quark X AAČ: stepdown at first, but full output after a little whi

    Quote Originally Posted by 45/70 View Post
    The signs are just what you are experiencing with your cells. They do not hold voltage under load well and really only work adequately in devices that draw very low current.
    And seeing as they don't really manage to keep a charge for over two weeks, that kind of use is a no-go.
    I think I will keep cycling them until they become too problematic (step-down to low), since they still last for a good 35-40 minutes (out of 4Sevens' rated 48), but it's nice to have my suspicions confirmed.
    Thank you.

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    Flashaholic* 45/70's Avatar
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    Default Re: Old NiMHs in a Quark X AAČ: stepdown at first, but full output after a little whi

    Quote Originally Posted by oKtosiTe View Post
    And seeing as they don't really manage to keep a charge for over two weeks, that kind of use is a no-go.
    Self discharge actually isn't directly related, although this and high IR often begin to show up at about the same time. Increased self discharge occurs when the separator in the cell begins to "leak". This can happen due to impact to the cell (dropping on the floor, for example), or of course, the aging process.

    I actually have some 1200 and 1800mAh NiMH AA cells that are over 10 years old. They do suffer from an inability to hold voltage under load well, but actually exhibit a very low self discharge rate. While they are close to only 80% of their original capacity (@ a 0.2C discharge rate), they will still hold a reasonable amount of charge for months. I have a hard time recycling these cells, as they are like old friends LOL!

    Dave

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