Bench Power supply, basic question

Discussion in 'General Electronics Chat' started by jgessling, Sep 4, 2009.

  1. jgessling

    Thread Starter Active Member

    Jul 31, 2009
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    14
    Greetings, I'm confused by the simplest things sometimes, so please don't laugh. I got a bench power supply (from the local hamfest) that I think works OK, I'm just not sure how to use it. It has three outputs, Negative, positive and ground. There are two meters, volts and amps and two knobs, volts and amps. When I set the voltage to (say) 5, then the meter says 5 and my multimeter says 5 volts from negative to positive. From positive to ground, the multimeter just jumps all over the place.

    Is this proper operation? If it is, then when I'm building a circuit that shows ground and +5, then do I hook the circuit ground up to the supply negative and the +5 in the circuit to the positive on the supply? What's the supply ground all about anyway? Inside the case, the green wire from the line cord attaches to the case and the ground output.

    Thanks, the next question will be how to use the current knob, does that act as a limiter?
     
  2. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    The supply is operating correctly. The voltage is generated between the (+) and (-) terminal and is floating, i.e. no reference to ground. The ground is a chassis ground and can be used to reference either side to the green wire ground of the house. It is often used for electrical safety. Faults are best shunted to a true ground.

    Your statement of supply connection to a circuit is correct. (-) to GND and (+) to supply.

    The current knob will, as you suspected, act as a limiter for the output current.
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,765
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    Ground is one of those subjects that come up here every so often. It is suprisingly complex, and yet simple in the basics. If you are experimenting with electronics most times you do not need it, but there will be times you do, which is why they left it as an option under your control.

    If you need a postive power supply ground the negitive side. If you need a negitive power supply ground the positive.
     
  4. jgessling

    Thread Starter Active Member

    Jul 31, 2009
    74
    14
    Is that little metal plate I see in some pictures the way to link the minus to the chassis ground? I can fabricate something like that in case I ever need it. Thanks for your help.
     
  5. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    Or just use a piece of wire like the rest of us. :D
     
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