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Thread: voltage variance in multiple IMR configurations

  1. #1

    Default voltage variance in multiple IMR configurations

    This is probably a foolish question, but is the issue of close-voltage-compatibility less of an issue in multiple IMR cell lights? I am extremely careful when using multiple protected Li-ion cells in the same light. I am careful with my IMR-fueled lights, too, but I am just wondering if it is as crucial an issue. I normally like all Li-ion cells in a single light to be within .03 volts of each other.

    I have some modified m@g multi-26500 IMR cell lights & multi-26500 IMR cell lights. Is this close of voltage-variance with IMR chemistry just as crucial? Thank you!

  2. #2

    Default Re: voltage variance in multiple IMR configurations

    While voltage can be used as a general criteria for matching cells, you'd really want to know the internal resistance of the cells and match based off of that instead.

  3. #3

    Default Re: voltage variance in multiple IMR configurations

    turboBB,
    Could you please explain this in a little more detail? Thank you!

  4. #4

    Default Re: voltage variance in multiple IMR configurations

    As a general guideline, matching cells by voltage isn't necessarily a bad thing to do (even I'll do this) but the underlying danger is that it can give a false sense that cells are well matched based on that alone since measuring the cells at rest can differ drastically than when measured under load due to differences caused by the level of internal resistance (though in LiIon cells, this tends to change little during its lifetime unless it was exposed to severe over-charging/discharging). Cells with high internal resistance will tend to heat up faster and if sufficiently bad (e.g. under heavy current) can cause thermal run-away hence the recommendation of using protected cells. While LiMn (IMR's) are generally inherently safer than LiCo's due to its chemistry, it's not completely immune to this issue. This was a high-level summary so I'll leave it to the experts at BU to explain further (though they may use non-Lithium Ion cells as examples, the general description of what happens to a battery is relatively the same):

    http://batteryuniversity.com/learn/a...configurations
    http://batteryuniversity.com/learn/a...atch_balancing
    http://batteryuniversity.com/learn/a...nal_resistance

    Cheers,
    Tim
    Last edited by turboBB; 03-11-2017 at 11:57 AM.

  5. #5

    Default Re: voltage variance in multiple IMR configurations

    Tim, Thank you so much for the information!

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