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PSU watts reading

Discussion in 'Hardware' started by Frank, May 9, 2004.

  1. Frank

    Frank Guest

    Hi all,
    Anyone knows if it's possible to monitor or take a reading of how much watts
    the psu is giving out. I have a 400W psu and I would like to know if I'm
    running it at full capacity or if it's just giving out 50% of its capacity.
    Reason is the fan pulls out air which is 2x hotter that my case fan which I
    would suspect the psu is in demande. But how much? Volts I can figure out
    with a meter, but watts? How do I take a reading. anybody know?
    Thanks
     
    Frank, May 9, 2004
    #1
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  2. Frank

    jamotto Guest

    I think most of those meters also can read ampere if it does then

    Volts * ampere = Watts
     
    jamotto, May 10, 2004
    #2
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  3. Frank

    Aaron Guest

    You would need an anmeter (spelling?), which is an instrument that
    measures amps. Then you can multiply amps by volts, and you will get
    watts. Maybe you could measure at the wall plug for total draw, but I
    don't think that that will show output power. Anyone know how to do
    that without working individually on each plug?

    Aaron
     
    Aaron, May 10, 2004
    #3
  4. Frank

    Don Taylor Guest

    Almost all commonly available DC ammeters need you to put them in series
    with the load, maybe that is feasible for him, maybe not.

    One alternative that may or may not help him is a "clamp-on ammeter."
    These usually test AC amps, not DC. They look like a large pair of
    pliers with jaws that open. You put ONE of your AC power lead wires
    between the jaws and close the tips to encircle the wire. The current
    flowing through that wire create an alternating magnetic field that
    induces a magnetic field in the jaws and this can be measures without
    needing to bare any wires or insert a meter in series with your load.
    That would give you a measure of the total current flowing into your
    computer but not the current in any of the individual low voltage DC
    cables to processor, drive, etc.

    I think Radio Shack had a cheap clamp-on meter at one time. Some other
    cheap meters like that are sometimes available.

    Now, if you really want to get picky about it, there is the voltage
    sine wave and the current sine wave. When those are lined up perfectly
    all this works just fine. But those two waves can have a phase shift
    between them, and when that happens you can measure large currents and
    the expected voltage but the product of these will be bigger than the
    actual power. If you want to get precise about measuring things then
    can actually use watt meters, some of which take all this into account
    and give accurate readings even when voltage and current are not
    perfectly in phase. You can build things like this if you want to
    go there, using 4-quadrant analog multipliers, little chips that
    multiply two inputs and give you an output that you can then measure.
     
    Don Taylor, May 10, 2004
    #4
  5. Frank

    jamotto Guest

    Well, hopefully the OP is still watching this tread so he can read you post.
     
    jamotto, May 10, 2004
    #5
  6. Frank

    Mike Walsh Guest

    It is easy to measure input wattage. Measure the line voltage. Cut one wire of an extension cord and insert an ammeter to measure current. Volts X Amps = Watts.
    It is much more difficult to measure power supply output wattage; you would have to measure the current of each output wire. Power supplies are not very efficient, which accounts for the warm air coming out of the power supply. You will never be able to run a power supply at 100% of capacity. To do that you would have to have each section, 5V, 3.3V, 12V, etc. running at peak output. The maximum output is usually rated at a relatively low temperature for a short time. Continuous output when warm will be less.
     
    Mike Walsh, May 10, 2004
    #6
  7. Frank

    Frank Guest

    Did not think it would be so difficult. I do have an amp metter however I'm
    not too keen on monitoring my components with open wires. To easy to have 1
    of them touch the case and boom. I'm trying to monitor the total output
    watts so the best would be to cut the main 12V wire going to all components
    but again, I don't want to screw up my psu. I think I'm going to try that
    clam meter or see at radioshack if I can maybe find something. Anyways,
    thanks for all the help guys.


    wire of an extension cord and insert an ammeter to measure current. Volts X
    Amps = Watts.
    would have to measure the current of each output wire. Power supplies are
    not very efficient, which accounts for the warm air coming out of the power
    supply. You will never be able to run a power supply at 100% of capacity. To
    do that you would have to have each section, 5V, 3.3V, 12V, etc. running at
    peak output. The maximum output is usually rated at a relatively low
    temperature for a short time. Continuous output when warm will be less.
     
    Frank, May 10, 2004
    #7
  8. Frank

    willah Guest


    You would probably have to crack it open and go before the wires exit
    the housing, I dont know if all the wires attach to a single area in
    the PS though. Theres got to be a way to do it without that "death by
    electrocution" problem. (The capacitors of the PS retain power even
    when its unplugged, so I'm told anyway)
     
    willah, May 10, 2004
    #8
  9. Frank

    TechnoPaul Guest

    A clamp on amp-meter is a HELL of alot safer than doing the cut the
    wire method. . You are exposing yourself to electrocution for no
    reason. A clamp on meter can be bought at Radio Shack and just clamps
    on to the main power cord of your computer. THEN you can use the
    formula :Watts=Clamp on meter's reading ( in amps) X 115 Volts. I pick
    115 volts because that is a typical reading in an average home. If
    you want to get a more precise watts reading you can measure ( if you
    know how to do it safely) the AC voltage at the outlet the computer
    is plugged into, then multiply that by the meter reading to get the
    number of watts.
     
    TechnoPaul, May 11, 2004
    #9
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