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ac voltage divder

Discussion in 'Electronic Design' started by jabriol, Apr 29, 2009.

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  1. jabriol

    jabriol Guest

    All,

    I need to design a voltage divider, that is going to drop 15vac.
    like 120 to 105 at .385 amps. voltage is running 400Hz

    Any ideas?
     
  2. Guest

    Voltage? Frequency? Aren't they the same??
     
  3. Guest

    As a 'stupid' graduate student I used a capacitor to limit the AC
    current going to the heater of a diffusion pump. It seemed to work
    just fine. Do you need me to calculate the value for you also?

    George Herold
     
  4. HardySpicer

    HardySpicer Guest

    At 400Hz a normal mains transformer is not a good idea.


    Hardy
     
  5. This is under the previous response for a reason. What kind of
    isolation would a 120:15 tranformer give in when properly connected in
    the application suggested by the OP?

    Also, I might point out that most tranformers, and many
    autotransformers, don't have adjustment knobs to alter the turns
    ratio.

    Note that these particular ones are rated for 400Hz operation, and are
    not unreasonably priced ($250 or so), but are a bit overrated for the
    application.


    Best regards,
    Spehro Pefhany
     
  6. Small transformer 120 V primary, 15 V secudary at 385 mA, secundary in series with input
    in opposite phase.



    --------------------------------
    | |
    )|| |
    120 V 120 V )||( 15 V / 385 mA
    )|| |_______________
    )|| 105 V
    |
     
  7. Ross Herbert

    Ross Herbert Guest

    :> All,
    :>
    :> I need to design a voltage divider, that is going to drop 15vac.
    :> like 120 to 105 at .385 amps. voltage is running 400Hz
    :>
    :> Any ideas?
    :
    :At 400Hz a normal mains transformer is not a good idea.
    :
    :
    :Hardy


    The OP didn't say that the transformer was a "normal mains transformer". Perhaps
    it is rated for 400Hz operation?
     
  8. Ross Herbert

    Ross Herbert Guest

    :All,
    :
    :I need to design a voltage divider, that is going to drop 15vac.
    :like 120 to 105 at .385 amps. voltage is running 400Hz
    :
    :Any ideas?

    I wouldn't muck around with fudging a voltage dropper as it will probably not be
    reliable or safe in the long run. Buy a specified 400 Hz step down transformer
    115V to 100V as made by Rayco Electronics Mfg - model 5T6155-11005-X (X= S
    (surface mtg) or P (plugin)
    http://www.raycoelectronics.com/catalog/400Hz.pdf
     
  9. Ross Herbert

    Ross Herbert Guest

    :On a sunny day (Wed, 29 Apr 2009 06:39:13 -0700 (PDT)) it happened jabriol
    :<>:
    :
    :>All,
    :>
    :>I need to design a voltage divider, that is going to drop 15vac.
    :>like 120 to 105 at .385 amps. voltage is running 400Hz
    :>
    :>Any ideas?
    :
    :Small transformer 120 V primary, 15 V secudary at 385 mA, secundary in series
    with input
    :in opposite phase.
    :
    :
    :
    : --------------------------------
    : | |
    : )|| |
    :120 V 120 V )||( 15 V / 385 mA
    : )|| |_______________
    : )|| 105 V
    : |
    : --------------------------------------------------
    :
    :So a 6 VA transformer would do.


    Good solution - provided the small transformer is also rated for 400Hz
    operation. It would probably be just as costly as a new 400Hz 115V : 100V @500mA
    transformer from Rayco. Also a more space consuming arrangement.
     
  10. Nice-- what do those things cost, roughly? lead time?

    I'm looking at some applications that have to run at "wild frequency",
    but it's centered around 400Hz.
     
  11. Jasen Betts

    Jasen Betts Guest

    http://www.raycoelectronics.com/catalog/400Hz.asp

    5T6155-1152-X (115:15 @ 1000mA) from rayco is one third the weight of
    5T6155-11005-X (115:100 @500mA)

    so it would also be smaller and cheaper (if done with comparable parts)
     
  12. Rich Grise

    Rich Grise Guest

    Sure - look up Ohm's law.

    Good Luck!
    Rich
     
  13. Rich Grise

    Rich Grise Guest

    Come on, Spehro - you _must_ knowe how to operate Google!

    In the USAF (and probably commercial aircraft and ships), everything was
    400 Hz; and the transformers were Mil-spec, which means "the same part at
    10X the price". ;-)

    Good Luck!
    Rich
     
  14. Yeah, I know. This is going on an aircraft. I don't think Google is
    going to find any Rayco prices -- am I wrong?

    My rule of thumb is that on price..

    marine: at least 3:1
    aircraft: at least 10:1
    space or rad-hard: could be 100:1 and up
     
  15. Rich Grise

    Rich Grise Guest

    Admittedly, reliability is a major consideration - it'd be a bitch to find
    oneself in the middle of the ocean, suddenly lacking some vital system or
    another. Also in the air, albeit if you're over land, it's possible to
    make an emergency landing. Witness the "miracle landing" on the Hudson
    recently. I don't remember the heroic pilot's name. )-; ) I saw one short
    clip from some security cam; the rooster tails were impressive!

    Cheers!
    Rich
     
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