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

Vehicle Alternator Output

  1. Oct 28, 2008 #1
    Hello everyone,

    I have a question that I have been unable to find an answer to. I am interested in salvaging a vehicle alternator in an attempt to create a homemade generator. I understand that household electronics' needs are measured in watts, but I can't seem to figure out how to calculate the theoretical output on a given alternator's output. From what I understand 1kw requires about 1.3hp, but I am lost on the rest.
  2. jcsd
  3. Oct 28, 2008 #2


    User Avatar
    Science Advisor
    Homework Helper

    Electircal power is volts * amps.
    Vehicle alternators will have a rectifier and regulator built in to put out around 13-14v DC, a typical modern car unit generates about 50A.

    The AC part of the alternator (if you can get at it) generates 3phase AC at low voltage - it's not going to be that suitable for running houshold electricals.
  4. Oct 28, 2008 #3
    Alright, so if I have 50amp * 13v, that would mean I would have a theoretical output of 650w? What I am planning on doing is connecting the generator to a series of car batteries. Then the batteries will be connected to a 1-1.5kw Inverter.
  5. Oct 28, 2008 #4


    User Avatar
    Science Advisor
    Homework Helper

    Sounds reasonable - if you are planning to run it continually you want to look at cooling. It might also be better to get a heavy duty alternator from a truck or bus.

    Search the alternative power websites - they have a lot of info about the best junk-yard solutions.
  6. Oct 28, 2008 #5
    I really appreciate all the help. Are there any particular alternative energy sites you would recommend?
  7. Oct 28, 2008 #6


    User Avatar
    Science Advisor
    Homework Helper

    No, sorry - I remember reading one about windpower that made their own generators out of a Volvo wheel hub, some super strong magnets and their own coil windings.
    There was some reason why car alternators weren't suitable - mostly their lifetime if run continuously, volvo wheel bearings apparently run for ever!
  8. Oct 28, 2008 #7
    I think I should throw out a big part of my plan, just to see what everyone thinks. I am planning on testing this wacky magnetic motor design [link deleted]. I really don't think it will work, but I want to try it. If it fails I am planning on using a standard Gasoline Engine as the driving mechanism (not much wind where I plan on using it, and mobility is a must).
    Last edited by a moderator: Oct 28, 2008
  9. Oct 28, 2008 #8


    User Avatar
    Science Advisor
    Gold Member

    Do you understand that the field windings in an auto alternator requires that you provide them a voltage inorder for the unit to give an output? So your batteries will need to be able to supply the winding voltage. Not very efficient for wind generation. You should try to find a dc generator instead.
  10. Oct 28, 2008 #9
  11. Oct 28, 2008 #10


    User Avatar

    Staff: Mentor

    It is a pretty obvious hoax.
  12. Oct 28, 2008 #11
    the only thing i can imagine that might make that work is if it sets up an oscillation in the hand, and minute amounts of force from his muscles are transfered to the disc. a bit like using a treadle to power an old sewing machine wheel, but with a magnetic instead of mechanical linkage.
  13. Oct 29, 2008 #12
    To be honest, I have little to no understanding of this field. I am a hands on kind of person. I am planning on using the alternator as a component of a home-made Gasoline-engine generator (after the expected failure of the magnetically driven motor, I don't find any harm in at least trying.)

    I am not saying it is true, just that I don't understand why it can't be. He seems to present a valid demonstration, at least to the uninformed such as myself. Is there any theoretical reasoning you can demonstrate as to why it wouldn't? Maybe you'll save me money and time that I would otherwise have wasted. Any help is appreciated.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?