Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Motor and alternator in same shaft

  1. Jul 24, 2011 #1
    Should we make both Motor and Alternator on same shaft?
    the Motor will run at 12V and it should not consume >2 Amps and tha same time Alternator should produce 220 V 300watts.

    Please reply
  2. jcsd
  3. Jul 24, 2011 #2
    not sure what you mean by running them on the same shaft... but if you mean to have the alternator power your motor, hooking up 220V directly to a 12V motor will destroy it... you'd need a transformer to drop the voltage and be able to provide enough current.
  4. Jul 24, 2011 #3


    User Avatar
    Homework Helper

    The motor will consume more power than the generator outputs, so it's not a perpetual motion machine. Similar devices are used in some power supplies, relying on the momentum of the motor to provide "cleaner" output to mask variances in the input power. Large ones were used on old mainframes:

    http://smud.apogee.net/comsuite/content/ces/?utilid=smud&id=1586 [Broken]

    There are some audiophile power conditioners still being made using motor + altenator (called power regenators), but I don't know if this is more of a gimmick method than a pratical one.
    Last edited by a moderator: May 5, 2017
  5. Jul 24, 2011 #4


    User Avatar
    Staff Emeritus
    Science Advisor

    A motor consuming 12 volts and 2 amps would NOT produce 300 watts from an alternator attached to it. It would at best produce 24 watts, and realistically produce less thanks to losses.
  6. Jul 24, 2011 #5
    Ultimately, it comes down to conservation of energy, as drakkith said. Power is Voltage times current, so a motor running on 12V 2A consumes 24W of power. A generator powered by that motor (and that motor alone) can produce at a maximum (100% efficiency) only what is supplied to it in the form of mechanical energy IE: 24J/s, or 24W.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook