Potentiometer or Triac dimmer?

Discussion in 'General Electronics Chat' started by Green Lantern, Mar 14, 2009.

  1. Green Lantern

    Thread Starter New Member

    Mar 14, 2009
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    0
    I recently purchased an AC/ DC hobby transformer for trhe lights and accessories on my Lionel train layout. Its AC output is 19 volts and not variable. The Lionel accessories and lights work with the full votage supply, but I would like to be able to reduce the voltage to prolong the life of the bulbs and motors in the accessories- without buying another transformer with variable AC voltage. Can i buy a suitable potentiometer from Radio Shack or a Triac dimmer from a hardware store to regulate the voltage?

    Any guidance would be appreciated. Thank you.
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    No, adjusting the voltage with a variable resistor dissipates significant amount of heat and the voltage will vary with load. It is better to buy a cheap adjustable or fixed voltage regulator, like the LM317 or LM78xx respectively, and make your job. Of course you need to take into account the current needed by your circuit.
     
  3. Green Lantern

    Thread Starter New Member

    Mar 14, 2009
    3
    0
    Thank you.
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    Your post states you purchased an AC/DC transformer, but are getting 19V AC from it.

    Is the end requirement AC? If so, the standard regulators, such as LM317 and 78xx will not work, as they are for DC only. If your requirement is DC, then those regulators will work.

    Also, the voltage will go down as the load goes up on the unregulated adapter, if the item powered is a light bulb or small motor, it will absorb the initial voltage down to what the Adapter is rated at for voltage at a certain current level (usually 500mA or so).
     
  5. mik3

    Senior Member

    Feb 4, 2008
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    I think he is talking about the voltage just on the output of the step down transformer and before the rectifier.
     
  6. Green Lantern

    Thread Starter New Member

    Mar 14, 2009
    3
    0
    The end requirement is AC. Thank you both for the input. If there is a device that I could use to control the voltage from the output terminals of the transformer please let me know. Thanks again.
     
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