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Question from mechanical guy

Discussion in 'Electronic Design' started by Wayne Lundberg, Jun 9, 2006.

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  1. I want to change a heavy battery in a mobile unit from standard battery
    power to ultracapacitors and don't have a clue as to circuitry and control.
    I believe a resistor circuit is essential to drain the high powered
    capacitor to feed to a low voltage electric motor. So can anybody lead me to
    a circuit to replace three 12V battery power packs for a 12V motor with
    speed control already in place such as you see in motorized scooters, golf
    carts, etc. Or even a new control system if required.


  2. John Larkin

    John Larkin Guest

    It probably won't work. The energy density of ultracaps is maybe
    1/1000 that of a decent battery, and the cost per kwh is probably
    1000x as much. Or something like that.

  3. Pooh Bear

    Pooh Bear Guest

    You can't *substitute* batteries with an ultracapacitor, it's intended to help
    batteries supply current 'surges'.

  4. OK, so how do those cheap little model airplanes sold at Harbor Freight and
    hobby stores do their dance? I charge a capacitor, then push the switch, the
    propeller turns and the airplane flies with a very light capacitor and small
    resistor as the circuit. This seems like a simple battery substitution thing
    and weighs much less. What am I not seeing?

    Lets say I want 1,000 Watts for twenty minutes max, and I want the
    power/control system to weigh less than one pound. Can this be done with
    batteries? Also, I want to recharge the system in a minute so I can launch
    again with a different 'mission'.

  5. mc

    mc Guest

    I want to change a heavy battery in a mobile unit from standard battery
    No. There is no way to store that much electricity in so little space.

    You are asking for about 300 watt-hours (Wh) in about 0.5 kilogram, or an
    energy density of 600 Wh/kg.

    The energy density of Maxwell ultracapacitors is about 3 Wh/kg.

    The best Li-ion batteries made by NASA come much closer to your
    requirements, at about 100 Wh/kg.
  6. Probably little sub-AA? rechargable (NiCd?) batteries. That's how the
    micro RC cars work, based on what was inside the one the dog chewed
    up. Maybe you think that looks like a capacitor.
    I seriously doubt it. If such a high performance energy storage method
    existed it would be used for electric cars, mobility scooters and so
    I think you're in very expensive territory, if it's possible at all.
    Maybe some kind of microturbine generator and liquid fuel.

    Best regards,
    Spehro Pefhany
  7. colin

    colin Guest

    Interesting, I wonder what the energy/weight of an elastic band is?

    A one pound elastic band would take some winding !

    Colin =^.^=
  8. Pooh Bear

    Pooh Bear Guest

    The Romans used equivalent natural products in some of their weapons.

  9. It wouldn't take a 1-1/3 HP motor 20 minutes to wind it.

    Best regards,
    Spehro Pefhany
  10. colin

    colin Guest

    I gues not.

    When I was a kid I had this balsa wood plane that had a larger than the
    normal elastic band, but had to wind it by hand, took ages to wind but only
    a few minutes to unwind! I put bigger and bigger ones on till eventualy the
    elastic band just pulled the back and front together but generally available
    elastic bands are pretty weak.

    If advances in elastic band materials could match advances in other
    materials like carbon fibre, aramid or polymers I wonder what then. I gues
    it boils down to the energy storage of excess electrons versus inter atomic

    I Like the idea of that solar powered airplane.

    Colin =^.^=
  11. Rich Grise

    Rich Grise Guest

    As a matter of fact, I've got a couple of those, sitting up on a shelf;
    I'd practically forgotten about them - they were about two bucks a set
    at the dime store. 1 set = little tiny car, charging station (that takes
    two AAs), and controller, which is a hand-held transmitter with four
    buttons: "Forward", "Reverse", "Right turn", and "Left turn". And the
    little sucker is _fast_. Also needs something like a gym floor to run
    on (it's got about 1/16" ground clearance ;-) ). But I can see putting
    whatever little battery and motor they have into a little balsa wood
    airplane to run a plastic propellor (remember those gliders, that didn't
    use any power _at all_? Then the rubber-band ones?)

  12. John  Larkin

    John Larkin Guest

    What ever happened to the rubber-band air conditioner?

  13. Thank you... Will put on my learning cap now.
  14. I received a note from Maxwell saying the best bet is to use their
    supercapacitors to extend the life of a standard battery pack by using the
    stored power in the capacitor as a leveling means and use the extra power
    when the drain is high on the batteries, like when the device is going
    uphill. Makes sense to me. And thanks again for your insight.
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