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Problem Using a DC Power Supply

Discussion in 'Electronic Basics' started by [email protected], Jun 10, 2007.

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  1. Guest

    I have the following Power Supply

    I can adjust the voltage by rotating the knob but I can't seem to do
    the same for the current. When I rotate the knob, the current stays at
    zero Ampere. Is the unit broken or am I doing something wrong here?

  2. CWatters

    CWatters Guest

    Have you got a load connected? If not no current will flow. Try connecting a
    12v light bulb of around 10 to 20W. Set the output voltage to 12V and the
    current limit to max. The bulb should draw around 800mA(10W) or 1.6A (20W).
    Then you can wind the current limit down to see what happens. Note that
    setting a lower current limit than the bulb draws will reduce the output
    voltage. That's how they limit the current.

    Note that you should probably treat the current knob as a safety device to
    limit the power in the even of a fault in the load eg When hooking up a new
    circuit you have built for the first time. It also protects the output of
    the power supply if you accidentally short circuit the output.

    It's not allways possible operate a bench power supply in "current limit
    mode" continuously as some power supplies can overheat. Read the
    instructions for your model. Some models are ok with this.
  3. Baron

    Baron Guest

    CWatters inscribed thus:
    I have one! That is exactly how it works. Current limiting is great
    for testing small thermister's using self heating.
  4. Chris

    Chris Guest

    Hi, Frank. Great question. The easiest way to adjust current limit
    for the two 0-32V supplies is to turn the current limit adjust all the
    way down, short the output terminals, then adjust the current dial up
    to the desired maximum current. You can then use the power supply in
    voltage mode, and be secure that output current will be limited in the
    event something goes wrong or the load becomes excessive.

    Note that this does not work for the 5V supply, which has a fixed 5A
    current limit.

    Good luck
  5. Eeyore

    Eeyore Guest

    Are you sure you're really cut out for this electronics lark ?

    Just a quick test.

    What do volts times amps make ?

  6. Circa Sun, 10 Jun 2007 02:09:48 -0700 recorded as
    First and foremost, do you have a load connected? If so, what is it? That
    will get things started.
  7. Jamie

    Jamie Guest

    THe current setting is only the max load, you need a load on it first.
    Most likely you do not have a function where it shows you the set point.
    the display you have is simply a current monitor not a current set
    point display.
    Most likely the control is near the average spread range for example.
    Lets assume your supply is a 10 amp unit.. set the control at 50%
    should yield you a 5 amp max load before it clips back.
    You may have an option to allow you to see the set point which how
    ever, if so? It should force you to do something else to the controls
    so that you can see the set point? Like push on the knob etc...
    other than that, I think it's like most others.
    Start low, and if you don't get enough current, just bring it up.
  8. Jamie

    Jamie Guest

    A lot of unwanted miss fits?
  9. Guest

    Whatn do you mean. missfits? if you have nothing useful to
  10. To set the current limit, set the current to minimum, and
    the voltage to near minimum. Short the output terminals and
    turn the current up to the desired reading. (Don't let the
    supply in this condition for long, as it generally produces
    quite a lot of internal heat.)

    Then remove the load short and set the desired voltage
    reading. Now the supply will deliver the set voltage unless
    the load tries to pass more than the set current, at which
    point, the voltage will be reduces to something below the
    set voltage that holds the current at the set current.
  11. Jamie

    Jamie Guest

    A man with no sense of humor? or did I get the gender wrong?

  12. Are you cut out for this electronics lark?

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  13. neon


    Oct 21, 2006
    voltage is hereby defined as infinite resistance.
    current is hereby defined as zero resistance.
    now you know where your problem is.
  14. Rich Grise

    Rich Grise Guest

    There will be no current if there is no circuit path for it to flow
    through. Volts is just pressure; current is "how much charge is flowing
    through here", just like in a river - if there's a dam in the river,
    the pressure behind the dam will build up (as the water gets deeper),
    but there is no flow, hence no current.

    The "current limit" is like gates on a spillway - it limits how much
    can flow.

    But electricity isn't exactly like water - it has to have a return path
    to its source.

    Hope This Helps!
  15. Guest

    Why, whats your gender, hermaphrodite I suspect. If you understand,
    then you know what you can go do to yourself don't you LOL
  16. Jamie

    Jamie Guest

    Such a sophisticated mentality you have there. Almost sounds like my
    wife and she knows everything!.
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