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Using a motor or alternator to generate electricity

  1. Aug 12, 2015 #1
    I'm looking into building a 7 1/4 gauge Diesel Electric Locomotive

    I will be using 4x 1hp (or 1 1/3hp) 24vDC permanent magnet motors for the traction motors. What I am looking for is someway of generating 24vDC with a 100-150A max output. (Im using a 3cyl 16hp Diesel engine to drive a motor/generator/alternator). Im struggling to get my head round how to generate such a voltage/current and then be able to control it's output. Can anyone point me in the right direction please?
  2. jcsd
  3. Aug 12, 2015 #2


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    Are you absolutely set on the 24VDC motors? The motors that are used in the new cloths washers and dish washers are 3 phase motors driven with a VFD that is powered by 120 or 208 or 240VAC single phase depending on country of origin and size. Finding a generator that gives normal mains voltage will be easier than trying to get 24VDC. The VFD will allow more precise control as well. You might be able to find some used appliances and salvage the motors and drives you need.

  4. Aug 12, 2015 #3
    Alas, it has to be low voltage DC because of the track circuits, and the smaller motors fit nicely in the back to back of the wheelsets. I know some have used car or lorry alternators without the rectifier, but you have to get them with external rectifiers which are like hens teeth to get hold of, I'd like something that can be easily replaced. I wondered if using a motor as a generator would be better/easier, but I'm unsure of its limitations...
  5. Aug 12, 2015 #4
    Hmm. That's a lot of current.

    The obvious first thought would be to build a big liner supply, big step-down transformer with huge rectifier diodes and a enormous cap. You don't need much filtering for a DC train motor. But these components wouldn't be easy to come by. And efficiency would be questionable. 150A across a 0.6V diode would dissipate 60 watts. A switching supply would too complicated. I think low-tech is the way to go.

    The other option would be a motor-generator set like what you are already describing. But if you are here then your current setup in inadequate and you would need bigger components than you already have. That sounds like more sourcing trouble.

    What kind of duty cycle do you need? Just a high current burst, to get the train moving, and then lower power? Does it have to run all day, or only for a short periods of time? You make be able to get away with using a bunch of deep-cycle lead-acid batteries (aka "boat batteries"). Wire them in series-parallel to get what you need. Then recharge them a night using a 24V charger. You would easily be able to find all of the lugs, heave gauge wire, and miscellaneous bits at local automotive and marine stores. And please, REMEMBER FUSES!!! A short in that system would be all kinds of bad news.

    Golf cart batteries would also work. Their normal use more closely resembles you're purposes than something that was built for a trolling motor.
    Last edited: Aug 12, 2015
  6. Aug 13, 2015 #5

    jim hardy

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    I often see alternators from large trucks at my metal salvage yard.

    Would something like this help ?

    http://delcoremy.com/Images/55SI/55SI-pad-mount.aspx [Broken]

    http://delcoremy.com/Images/55SI/PerformanceCurve-55SI-24V-250Amp.aspx [Broken]
    Last edited by a moderator: May 7, 2017
  7. Aug 13, 2015 #6

    jim hardy

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    You might experiment with an automobile alternator.
    You need one without a voltage regulator but with brushes.

    The rectifiers in 12V alternators are plenty hefty to make 24 volts
    you'll just need to spin it somewhat faster to get that 24 volts.

    With constant current to the field it'll make voltage in proportion to RPM
    and its inherent current limiting will give you somewhat of a soft start

    old Chryslers used external regulator
    one might remove the internal regulator from a newer one and bring wires out from the brush-holders.

    i find these dual voltage military alternators at my metal salvage yard
    but i'm afraid they're brushless

    C.E. Niehoff & Co, Alternators,
    p/n: 3043161,

    200 amp dual voltage, 12/28 volt outputs

    any good scrap yards in your vicinity ?
    Last edited by a moderator: Apr 18, 2017
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