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NiCd batteries

Discussion in 'Power Electronics' started by bobmart32, Jul 7, 2015.

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  1. bobmart32

    bobmart32

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    Jul 7, 2015
    so i'm researching the effectiveness of Nickel-cadmium as an electrical source, and this coming from a beginner chemistry class, one of the things that is weird to me is that nickel and cadmium are supposedly both positively charged, so how is it that nickel hydroxide is a good anode and cadmium hydroxide a good cathode? to me, they look like balanced chemicals and therefore shouldn't be feeding electrons.

    Thanks in advance.
     
  2. Gryd3

    Gryd3

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    Jun 25, 2014
    You are forgetting about what's in-between ;)
     
  3. bobmart32

    bobmart32

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    Jul 7, 2015
    Well, potassium is positivel charged, but only +1. and i'm told that the potassium hydroxide only acts as an electron carrier, so again that confuses me, how does that affect the cathode and anodes to create a charge?
     
  4. bobmart32

    bobmart32

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    Jul 7, 2015
    Oh, redox...nvm....so if the KOH breaks down in H2O to form K+ and OH-, presumably the OH- is feeding the electrons to the anode, but what is happening the K+. does it react with the nickel, or it just stays in the water?
     
  5. Gryd3

    Gryd3

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    Jun 25, 2014
    Well.. you sound hands down more into chem than I ever was.

    Perhaps this helps? https://en.wikipedia.org/wiki/Nickel–cadmium_battery#Electrochemistry
     
  6. bobmart32

    bobmart32

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    Jul 7, 2015
    haha well thank you, perhaps it's the wrong forum, but i'm trying to build a battery to supplement my electronic engines, based off nickel cadmium, i figure this would be a good way to at least see how variable power affects other electronic components and logic circuits
     
  7. Gryd3

    Gryd3

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    Jun 25, 2014
    Well. There are some pretty smart guys on here. Perhaps one of them knows what you are after ;)
     
    bobmart32 likes this.
  8. bobmart32

    bobmart32

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    Jul 7, 2015
    sorry internet is bad
     
  9. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    The electrical potential of Ni and Cd depends on the chemical environment. Unfortunately in the English edition of the Wikipedia this is not clearly explained. The German edition goes a bit more into detail, stating:
    • E(Cd/Cd2+) = −0,81 V (in alkaline solution)
    • E(NiO(OH)/Ni(OH)2)= +0,49 V
    Which nicely makes for a potential diffference (voltage) of 1.3V as expected.
     
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  10. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    You are aware that NiCd is no longer the preferred chemistry for rechargeable batteries, are you? For one it suffers from the so called "memory effect", second Cadmium is a substance that poses health hazards. NiMh or LiIon is the current state of the art.
    You should provide a voltage regulator between the battery and your electronic circuits. Not many electronic circuits tolerate the varying voltage from a battery. Erratic an unpredictable behavior can be the consequence.
     
  11. BGB

    BGB

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    Nov 30, 2014
    however... NiCd can generally provide more peak amperage than NiMH, and is cheaper than LiON.
    so, at least in the US, they aren't really dead yet. they are one of the more common battery types for lower-cost cordless power tools (with LiON being more typical for higher-end models).


    decided to leave out a longer description in favor of being more compact:
    PbAc: lower cost, high current, low (useable, *1) capacity
    NiCd: lower cost, high current, medium-low capacity
    NiMh: medium cost, low current, medium-high capacity
    LiON: high cost, medium current, high capacity
    LiFePO4: high cost, high current, medium capacity

    *1: the actual raw capacity of lead-acid isn't particularly bad, per-se, however only part of the capacity can be used without causing damage to the cells. if drained too far or left discharged, the battery may be effectively destroyed. in contrast, NiCd and NiMH are much more tolerant of being discharged and/or left in a discharged state.

    approximate best per application (values relative to price):
    small device, high current: NiCd, LiON (ex: power tools)
    small device, high capacity: LiON, NiMH (ex: consumer electronics)
    large device, high current: PbAc, LiFePO4, LiON (ex: engine starting, back-up power)
    large device, high capacity: LiON, NiMH, LiFePO4 (ex: robotics, *2)

    *2: both LiON and NiMH seem roughly break-even in a capacity-vs-price sense.
    for a custom-built high-capacity pack, NiMH is cheaper. for premade batteries, LiON is cheaper.
    for similar capacity, the NiMH pack would tend to be bigger and heavier though.

    a drawback for LiON is that they have a risk (if not charged/discharged safely) of going into a thermal runaway and catching fire and/or exploding (LiON packs generally use built-in controllers to make them more-or-less safe).

    could be wrong, this is mostly based on observation.


    if the goal is to make batteries by hand, than NiCd or NiFe (nickel-iron) should be easier to make.
    commercially made cells though generally use sintered plates, and using plain metal plates results in much worse performance. so, much beyond proof of concept, it is probably much better to buy batteries.

    NiFe mostly differs in that iron-oxide is used instead of cadmium.
     
    Gryd3 likes this.
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