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Easy current measure/recording in power strips?

Discussion in 'General Electronics' started by [email protected], Mar 29, 2005.

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  1. Guest

    I'm looking for an inline plug-in type of AC current
    meter that will tell me how many amps are flowing through
    a particular power strip - i.e. I'm willing to unplug a
    power strip from a receptacle, plug in a "gizmo", then
    plug the power strip into the gizmo.

    This is a 'temporary' kind of basis... just measurements
    over a short period (5-15 minutes), not a permanent


    I have a number of equipment cabs in my data center than
    have dual 115V 60HZ vertial power strips in them. The
    cords on these strips have 'ordinary' 15A male 3-prong
    plugs and they are plugged into receptacles that are fed
    from individual single-pole breakers back in the PDU
    (power distribution unit). Some of these breakers are
    15A, some are 20A.

    For each cabinet, I want to survey the current draw on
    each power strip when both are on, then each strip being
    the lone power source for that cabinet. Nearly all of the
    gear in the cabs have dual power supplies, with a power
    cable from each to a separate power strip.

    My budget is such that I cannot afford a full-blown
    "Dranetz" analysis/recorder type of device, and that's
    overkill for what I need to do anyway.

    A pair gizmos like a "Watts Up?"
    ( would be great except that it
    is 15 amps max - I may have some strips pulling more than

    Is a device available similar to the "Watts Up?" but just
    a little beefier and (mabye) better quality?

    I guess I could buy/build a simple short pigtail with
    separate wires to enable me to use a clamp-on ammeter,
    but it's not as "pretty" of a solution.

  2. Guest

    There is a similar device (with the same 15 A limitation) called
    a Kill A Watt.
    There are pictures of it disassembled here:
    It looks like the current measuring shunt is a loop of wire in the
    neutral line. Depending on the gauge of wire, it _might_ be OK for 20 A
    for a relatively short period of time. The open question is whether the
    microprocessor is programmed to give up / indicate an error if it sees
    more than 15 A or not. I haven't used one of these, but they seem to
    sell for about US$30, plus or minus.
    If you want pretty, you can buy one already made up
    but these are often only rated at 15 A.

    You could measure the voltage drop across a chunk of wire. I am
    thinking something like some 12 gauge cable, a plug, and a receptacle.
    Wire it up like an extension cord, but also include a 3" pigtail off of
    the hot wire on either end. Measure (carefully) between the two pigtails
    to get the voltage drop in the cable when it is supplying a known load,
    like a few 100 W light bulbs. Then, put the cable in the circuit of
    interest, measure the voltage drop there, and do the math.

    You could even do it by brute force. Look up the rating on the breakers
    involved, then add a 100 W light bulb to the circuit and wait to see if
    the breaker trips. If no trip, add another light bulb. Keep doing this
    until the breaker pops, then calculate the original load by
    (breaker rating - (0.833 * number-of-bulbs)). Yes, this is a moderately
    silly way to go about this...

    Matt Roberds
  3. Guest

    Guest Guest

    Actually, at one time, Amprobe had a model that included exactly this item.
    It had 3 windows in it for various current values and was to do exactly what
    you describe..and it was pretty. The clamp on meter went thru the chosen
    window and then you could read the current on the meter. This is just a
    'pretty' version of the 'multiple loop' homemade device described by others.

    I dunno if it is still available or not...check Amprobe...and check Ebay
    (who knows?!) it is....
  4. Andy P

    Andy P Guest

    If youve got time (you said you only wanted to measure for a few
    mintues) why not jsut use a clamp on multimeter and watch it. load it
    down for peak amps, and then that'll probably give you a good indication
    of what's going on. It's a much simpler way of doing things if ya ask
    me. More time consuming in man hours, but cheap and easy.
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