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Thread: Storing Li-Ion - would this work

  1. #1
    Flashaholic* Timothybil's Avatar
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    Default Storing Li-Ion - would this work

    Due to upgrades and deals I shouldn't have taken, I have several cells that I am not using on a regular basis. It is the generally accepted wisdom around here that Li-Ion cells should be stored at 3.7v. Now, I have a very nice Xtar VP2 that allows me to set the charging voltage for 3.2v, 3.7v, and the ones that need to be charged to 4.13v. My manual says that the cutoff voltage for charging a 3.2v cell is 3.6v. My question is, would that work for charging my cells to a storage voltage level?
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    Default Re: Storing Li-Ion - would this work

    I donít see why not. I donít see how it can hurt anything. The only issue might be how long it takes. Iíll try and explain.


    I think for the first part of the charge or the CC, LiIon and LiFe charging is basically the same. You pick a current for example 1000mA, the charger charges with that current until it reaches very near or at 4.2V for LiIon or 3.6V for LiFe. The second part or the CV is going to be different. If you are charging a Lion as a Life the current will start stepping down at 3.6V not 4.2V. Way lower than the max voltage. Iím thinking this phase might take a very long time to terminate. I donít know what the termination amperage is on the XP2 but if itís low letís say .05mA or lower this could take a very long time. I am assuming that the XP2 is a cc/cv charger if not this is a non issue since it will just stop at 3.6V.


    Iím going to try it. It seems like a good idea.
    Last edited by fmc1; 07-19-2017 at 07:22 PM.

  3. #3
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    Default Re: Storing Li-Ion - would this work

    Hello Timothybil,

    Recent discussions have indicated that storing at 3.6 volts may be slightly more optimal, but let's take a practical look at this.

    With cells that are targeted for storage only I fully charge them, then discharge them at 1C. After the discharge at that rate the voltage will usually bounce up to the 3.6 - 3.7 volt range.

    With cells that are stored but also act as standby emergency use I store them at about 4.0 volts and understand that it is less than ideal for storage. I offset that by knowing that these cells have about 80% capacity should they be needed.

    Tom
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    Flashaholic* Daniel_sk's Avatar
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    Default Re: Storing Li-Ion - would this work

    If you have free space in your fridge and the wife won't complain then this will reduce the aging of the cells - http://batteryuniversity.com/learn/a...tore_batteries
    But the difference is neglible if stored at 40% charge.
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  5. #5
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    Default Re: Storing Li-Ion - would this work

    Quote Originally Posted by SilverFox View Post

    With cells that are targeted for storage only I fully charge them, then discharge them at 1C. After the discharge at that rate the voltage will usually bounce up to the 3.6 - 3.7 volt range.

    Tom
    What do you use to discharge 3500mAh 18650's at 1C?

    Thanks

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    Default Re: Storing Li-Ion - would this work

    Hello Fmc1,

    I use the West Mountain Radio CBA.

    Tom
    Behind every Great man there's always a woman rolling her eyes...

    Most batteries don't die - they are tortured to near death, then murdered...

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    Default Re: Storing Li-Ion - would this work

    Tom


    Cost wise that analyzer is not an option for me. Your 4.0V storage suggestion is interesting and I totally understand the logic.

    Thank you for your response.


    Frank

  8. #8
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    Default Re: Storing Li-Ion - would this work

    Hello Frank,

    Another option is to pay attention to the run time in your lights. I use the analyzer because I am a geek. You can do the same thing by turning your light on and setting a timer. After a few tries you can dial in how much capacity you take from the cells and pretty much know what the voltage will be.

    For example if you normally get around 2 hours of run time, 80% of that would be 96 minutes. That means that from a full charge you would use the light for around 24 minutes and end up with a cell with roughly 80% capacity left and it should have a resting voltage of close to 4.0 volts.

    Tom
    Behind every Great man there's always a woman rolling her eyes...

    Most batteries don't die - they are tortured to near death, then murdered...

  9. #9
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    Default Re: Storing Li-Ion - would this work

    Tom

    I have an MC3K so when I get home I'm going to make a storage program with a 4.00V target voltage.

    Thanks

    Frank

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