Looking for a variable-frequency 120 VAC power supply

Discussion in 'General Electronics Chat' started by SumGuy98, Oct 31, 2009.

  1. SumGuy98

    Thread Starter New Member

    Oct 31, 2009
    4
    0
    I need to generate a pressure waveform or signal of about 2 to 4 psi (a square or sinusoidal signal would be fine) and the frequency needs to be variable, from 1 hz to maybe 25 hz. I've thought about running a small hobby motor connected to a piston pump or bellows (the pressure can be conducted through air or a fluid like water). I basically want this pressure signal to be delivered through a flexible tube to a pressure transducer.

    One off-the-shelf item that sort-of does this is an aquarium air bubbler. These things have a bellows that's articulated or vibrated with the help of a small magnet that moves back and forth across an air gap of a transformer that is connected directly to the main 120 V ac power. What I'd like to do is power this thing with a variable-frequency power supply. I'm thinking the current is relatively low - maybe 100 ma.

    I know this looks a lot like I need a signal generator, but I think I need more drive current (and a lot higher voltage) than your typical signal generator.

    Any ideas?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    How about a speaker with a waterproof diaphragm?
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Well, those type of AC-powered devices are designed to operate over a fairly narrow range of frequencies; usually 47Hz to 63Hz. If you tried using a lower frequency, the coil would rapidly enter saturation, and it would "look" like a dead short to the AC input. You would then have a blown fuse, or smoke. Maybe both.

    I like your "hobby motor driving a bellows/piston/diaphragm" idea much better. If you have a bass speaker in an enclosure sitting around, that might work.
     
  4. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    Some of the "higher end" aquarium pumps are actual piston pumps with a crankshaft and motor. Replacing the original motor with a small DC motor and using PWM to drive it should give you what you need. Or better yet, try one of these....http://www.aquariumguys.com/battery-pumps.html
     
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