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bench power supply

Discussion in 'Power Electronics' started by dbyrd26, Aug 16, 2014.

  1. dbyrd26

    dbyrd26

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    Sep 16, 2013
    I have an old Mallory adjustable power supply at work. The supply is not constant though. For example, if I set the supply to 12 volts and hook it up to a thermoelectric device the voltage on the meter drops to 6 volts or so, maybe less. Do I have to compensate for the loss? And turn it up to 12 volts after the device is hooked up to the supply?
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Sounds like you're overloading the power supply. The power supply is designed to give you the voltage you adjust it to, but if you connect it to something that draws too much current, that will drag the output voltage down.

    Find out what output current the power supply is rated for, then connect a multimeter on the 10A range (you need to move the red lead to the 10A socket on the multimeter) in series with the load. That will tell you how much current the load is drawing. If the current you measure is greater than the power supply's rated output current, then you need a gruntier power supply.
     
  3. dbyrd26

    dbyrd26

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    Sep 16, 2013
    The power supply is rated at 6 amps but I'm only drawing 1.6 amps.
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Oh. Well, there's something wrong with the power supply.

    It's a regulated power supply, is it? Do you have a model number or a link to any information on it?
     
  5. dbyrd26

    dbyrd26

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    Sep 16, 2013
    The model is 12 RS 6D. Its a mallory rectopower supply. The electronics inside are very minimal. Theres a transformer WITH a potentiometer built into it and 2 very large capacitors. They look like motor start capacitors. Also another component i cant identify but that just appears to be attached to the current gauge And that's all besides a couple switches and gauges.
     
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    OK, it's an unregulated supply. So yes, you will need to adjust the supply to get the voltage you want with the load connected. The voltage will vary as the AC mains voltage varies, and depending on the current drawn by the load. If you need an accurate or stable voltage, you should get a regulated supply, or add an external regulator to that one.
     
  7. dbyrd26

    dbyrd26

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    Sep 16, 2013
    Thank you. I thought so but I didnt want to turn it up and accidentally fry my peltier.
     
  8. BobK

    BobK

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    Jan 5, 2010
    Are you basing the draw of the Peltier on it's specs or did you measure it? I have a little refrigerator based on one, and it blew out 2 power supplies because it was drawing way more than the spec.

    Bob
     
  9. dbyrd26

    dbyrd26

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    Sep 16, 2013
    I measured it. It actually reads 2.75 amps at 12 volts. It was lower before I turned it up to 12.
     
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