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Ni-cad discharge

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Stockweld, Sep 8, 2017.

  1. Stockweld

    Stockweld New Member

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    I'm discharging a 20 volt battery through twelve, one-ohm, 10 watt resisters. I would like for it to stop discharging at 9 volts by relay to prevent battery damage. What is the easiest way.
     
  2. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Isn't the safe discharge voltage for cycling NiCd's about 1.0 V per cell? How did you calculate 9 V for the 20 V pack?
     
  3. Stockweld

    Stockweld New Member

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  4. dave

    Dave New Member

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  5. Stockweld

    Stockweld New Member

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    It's actually 18 v pack, 12 cells. Measured full charge was 20.1 volts. Paper said optimum discharge to one volt per cell. Trying to "exercise" seldom used pack. To keep it from going south. Have already lost two good packs this way, through lack of use. Thanks for any advice.
     
  6. Stockweld

    Stockweld New Member

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    Measured volts on pack when used up was 9.0 volts.
     
  7. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Maybe that is your problem for a 12-cell pack, not lack of "exercise."
     
  8. Stockweld

    Stockweld New Member

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  9. Stockweld

    Stockweld New Member

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    Forgive my lack of clarity. I'm using 18 volt DeWalt equipment once a year. New packs going bad. Won't take a charge.
     
  10. Stockweld

    Stockweld New Member

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  11. Stockweld

    Stockweld New Member

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    Used only a few times and stored with full charge. Five years old but otherwise "new."
     
  12. Stockweld

    Stockweld New Member

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  13. Stockweld

    Stockweld New Member

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    Online article said ni-cad batteries need to be used and recharged every one to three months for maximum life.
     
  14. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    The major problem with NiCd's is their fast self discharge rate, unlike modern NiMH cells. They do outperform NiMH in some other respects, though. If you let a NiCd sit for a year, it is killing itself. You need to periodically charge them so they do not over discharge.

    Are you aware of the Battery University site? It has a lot of useful and accurate information.
     
  15. Stockweld

    Stockweld New Member

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    Thanks. I'll see if they are fully self discharged every month. And just put in charger more often than I have been. Doesn't sound exactly like what I've been reading. But I'll check out that site as well.
     
  16. Stockweld

    Stockweld New Member

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  17. Stockweld

    Stockweld New Member

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    Battery University appears to favor or be specialized in lithium-ion. Not much on Ni-cad. Other sites have very good specs and advice on maximizing life of batteries. They emphasize the need to charge monthly but also the need to deep DISCHARGE and recharge every one to 3 months depending on use of course. So you can't help with a discharge circuit and I'm left with having to needlessly wear out my drill taping the trigger on ???
     
  18. Stockweld

    Stockweld New Member

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  19. Stockweld

    Stockweld New Member

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  20. Stockweld

    Stockweld New Member

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    There are several other good sites for ni-cad batteries. Technical data repeatedly mentions the need to yes "exercise" ni-cads. There is a definite need for a device that you can plug one into that will do this for you. Simply charging monthly doesn't do the job! Manufacturers are more interested in selling new batteries than helping you preserve the ones you've already bought !!!
     
  21. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Whatever you are doing is not working for keeping for keeping your NiCd's alive. Generally, that is considered as a signal to change what you are doing. I disagree that NiCd's are the preferred choice for modern power tools. But whatever, that is your choice. Allowing your NiCd's to go to 0.75 V per cell is not a good plan.

    John
     

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