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74VDC to 12VDC

Discussion in 'Beginner Electronics' started by Emory Lehman, Dec 31, 2006.

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  1. Emory Lehman

    Emory Lehman Guest

    I'm planning to work on a new project for use in my work. On the console
    of a locomotive there is a 74VDC plug and would like to step it down to
    12VDC for use of other electronic devices that would plug into a car
    lighter plug. I though of using a 7812k but I see the max input voltage is
    only 30VDC. I then though of using a step down transformer, but I really
    don't want it to be to big and bulky since I have to carry it in my work
    bag with me all the time.

    What does anyone recommend? The current draw should not be too much like 3
    amps at the most. This would be used to power cell chargers, PSP chargers,
    etc.

    Emory Lehman
     
  2. PeterD

    PeterD Guest

    Want the truth, or can I lie to you? <bg>

    Say 74 VDC, 3 amps, 12VDC output. That's a 61 volt difference, at 3
    amps, or about 183 watts of power (HEAT!) to get rid of. Major work,
    fans, all kinds of stuff like that. Fans, big heat sinks, the works!
    Not small enough to slip into the pocket.

    You would be much better off with a switching regulator (more complex)
    with this kind of difference in voltage levels. Would be much smaller,
    more efficient, etc.

    It is perhaps possible that a computer powersupply could be reworked
    to make it work at that voltage... You would proably have to rework
    the input circuits (so it takes DC, and at a lower voltage) to do that
    however.
     
  3. Jack

    Jack Guest

    Scanning the available devices I see that the highest input voltage spec is
    60 volts (LM 2575HVN-12, a 1 Amp device).
    This makes me wonder what would happen if you wired several of these in
    series across your 74volt input to provide 3 separate 1 amp supplies. They
    would all have different ground potentials so you couldn't wire the outputs
    in parallel to get 3 amps into one load but you may not care if you just
    want to be able to charge a few small batteries at the same time. Just a
    thought.
     
  4. jasen

    jasen Guest

    google for "DC-DC converter"
     
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