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Life Expectancy of Tenergy Li-ion Cell — Parallax Forums

Life Expectancy of Tenergy Li-ion Cell

doggiedocdoggiedoc Posts: 2,245
edited 2011-12-12 03:39 in General Discussion
I have a dead Tenergy cell. I would have expected it to last longer than this. Any one care to give me any insight into how I may have damaged it. The last thing I was doing with it was powering a breadboard that I was testing capacitors on using another Li-ion charger/pack in series with it.

:frown:
Paul

Comments

  • PublisonPublison Posts: 12,366
    edited 2011-12-10 09:30
    I'm just guessin' here Doc, but the Tenergy Cells that Parallax sells has a internal PCB to prevent overcharging. Using another charger might have damaged that circuit? The cells will not charge in the Parallax charger anymore?
  • doggiedocdoggiedoc Posts: 2,245
    edited 2011-12-10 09:39
    It has never left the original charger. (Until I swapped it into the other Parallax charger I had to test it). I can't think of any reason for it to die.
  • doggiedocdoggiedoc Posts: 2,245
    edited 2011-12-10 10:22
    UPDATE: ok, I have determined cell is not "dead" as I STILL get 7.96V from the pack. But I have determined that the Cell Status LED does not come on in any position for with the one cell. If I move it to position A - that Cell Status LED does not light indicating a charge. Puzzling.

    Jim you mentioned that each cell has internal circuitry. Perhaps this is where the problem is with this cell?

    Paul
  • PublisonPublison Posts: 12,366
    edited 2011-12-10 10:41
    I know some have and some have not. I have not taken the dive into that realm yet.

    Time for Ken to say "Send it back and I'll have Matt look at it, in the mean time here's a new one" :)
  • doggiedocdoggiedoc Posts: 2,245
    edited 2011-12-10 10:55
    I've got spares. I just need to be comfortable I'm not going to fry them all. Perhaps this is my fault. :D
  • doggiedocdoggiedoc Posts: 2,245
    edited 2011-12-11 04:33
    False alarm! I Connected my Spinerette last night and let it run from the li-ion pack all night - thus completely discharging both cells. When I plugged it in to charge this AM - Viola! both status LEDs light up indicating charging.

    Yay!
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2011-12-11 06:57
    Li-ion cells are easily damaged by excessive discharge. The general rule of thumb is that you have to discharge only to above the specified 'depletion threshold' of the output voltage rating. A short circuit or using to drive a motor without the logic for a smart cut off will harm them. I am not sure the internal protection prevents excessive discharge.

    For the most part, well-taken Li-ion cells really last much longer than other chemistries. In fact, the Li-ion FE technology just gets better with age.

    In your case, you may have triggered a 'false alarm' with the inner protection board. Or one cell may have discharged much faster than the other and by letting it rest, it came back to a functional range. Overall, I suspect your batteries will mellow with use.

    From the Lithium ion battery Wikipedia.....

    Prolonging battery pack life

    * Depletion below the low-voltage threshold (2.4 to 2.8 V/cell, depending on chemistry) results in a dead battery which does not even appear to charge because the protection circuit (a type of electronic fuse) disables it.[96]
    * Lithium-ion batteries should be kept cool; they may be stored in a refrigerator.[96][97]
    * The rate of degradation of Lithium-ion batteries is strongly temperature-dependent; they degrade much faster if stored or used at higher temperatures.[96][98]
  • PublisonPublison Posts: 12,366
    edited 2011-12-11 13:44
    doggiedoc wrote: »
    False alarm! I Connected my Spinerette last night and let it run from the li-ion pack all night - thus completely discharging both cells. When I plugged it in to charge this AM - Viola! both status LEDs light up indicating charging.

    Yay!

    Li-Po's are funny animals. Glad that worked out.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2011-12-11 20:41
    I did a bit of research. The Tenergy Li-ion cells that Parallax sells seem to have over-voltage protection, under-voltage protection, and short-circuit protection in a little printed circuit attached to the negative end of the battery.

    So it may be that you just hit a trigger due to an excessive discharge and the battery reset after a delay.

    BTW, the low-voltage limit is officially 2.437 Volts and nominally 2.5 Volts. At that point the cells apparently shut down until recharged.

    And there is thermal protection as well.
  • doggiedocdoggiedoc Posts: 2,245
    edited 2011-12-12 03:39
    Thanks Loopy - it is working normally now. I must have triggered the protection circuit somehow.

    Paul
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