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3-phase voltmeter

  1. Jul 24, 2015 #1
    Hi, I'm trying to build a voltmeter that will simultaneously measure all three phases unloaded of a 3-phase permanent-magnet alternator off a motorcycle (Honda Goldwings mostly, not that that's relevant...) The way these are typically checked in the industry is to set a voltmeter to measure AC, disconnect the stator and measure the unloaded AC output Line 1-2, 2-3, 3-1. This is sometimes a pain to do in the garage so I'm looking to make a tool I can simply plug into the 3P outlet and read all three at the same time. The meter I use already is this:


    I've used this successfully as a single-phase meter for a while, so my though was to tie three of the together, powered by an independent 9-volt battery (when it says "power supply needed" the spec is 8-15VDC). I've attached a PDF of my proverbial tool and was just looking for input as to any design mistake I've made.

    Attached Files:

  2. jcsd
  3. Jul 24, 2015 #2


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    Staff: Mentor

    I'm not sure, but I think you need 3 separate power sources for the 3 meters. I doubt they have isolation between their power input and the measurement leads...
  4. Jul 25, 2015 #3

    jim hardy

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    Gold Member

    Can you solder ?
    this three position switch
    http://www.mouser.com/ProductDetail/CK-Components/A20303RNZQ/?qs=sGAEpiMZZMvNbjZ2WlReYqS7wnWG8l9O54StjK1Q2yQ%3d [Broken]

    wired to a connector that mates with the stator plug
    will let you select the phase to be measured.

    its bottom will look like this
    except it won't have terminals B and D

    here's how to wire it

    on the front panel of whatever you mount it to
    Label position 1 AB (or 1-2)
    Label position 2 AC (or 1-3)
    Label position 3 BC (or 2-3)

    now you can use any meter
    myself i prefer analog meters for you can judge by the needle movement how much fluctuation you're getting.


    have fun !

    old jim
    Last edited by a moderator: May 7, 2017
  5. Jul 25, 2015 #4
    Thanks for the input. Berkeman, I appreciate the input and I will adjust the panel to give each meter it's own individual 9V power source. Jim, the 3-position switch was actually my first thought on the subject, but I went for the three-digital-panel design simply for aesthetics sake since to be honest I'm really building a tool simply for the sake of the tool. I freely admit it's more of a project just to do it than for actual practical value. Maybe I'll make both designs and see which works better.

    Thanks again guys.
  6. Jul 25, 2015 #5

    jim hardy

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    I predict you'll wonder how you ever got along without it.
    At bottom of my avatar is a home-built special purpose test box.
    Making your own special tools multiplies your rate of 'getting things done' .

    Meters have got so inexpensive it's hardly worth buying a switch.
    Whichever you do, your work-mates will want one too...
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