Can I Build a 3-Phase Voltmeter for Testing Motorcycle Alternators?

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A user is attempting to build a 3-phase voltmeter for testing motorcycle alternators, specifically for Honda Goldwings, to simplify the process of measuring unloaded AC output. They plan to use three digital panel meters powered by individual 9-volt batteries, as isolation between the power input and measurement leads is a concern. A three-position switch will allow selection between the phases for measurement. The project is primarily for personal use and experimentation rather than practical necessity, although the user acknowledges the potential benefits of having such a tool. The discussion highlights the ease of creating custom tools and the growing affordability of meters.
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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:

http://www.ebay.com/itm/Blue-AC0-500V-LCD-Digital-Volt-Panel-Meter-Voltmeter-/111161235696?pt=LH_DefaultDomain_0&hash=item19e1b9d8f0

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.
 

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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...
 
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Likes Jeff Rosenbury
Can you solder ?
this three position switch
http://www.mouser.com/ProductDetail/CK-Components/A20303RNZQ/?qs=sGAEpiMZZMvNbjZ2WlReYqS7wnWG8l9O54StjK1Q2yQ%3d
upload_2015-7-25_9-58-45.png


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
http://www.mouser.com/ds/2/60/A_Rotary_30juyl14-38283.pdf
upload_2015-7-25_10-0-32.png

except it won't have terminals B and D

here's how to wire it
3pswitch.jpg


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.

upload_2015-7-25_10-3-48.png
have fun !

old jim
 
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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.
 
XZ923 said:
I freely admit it's more of a project just to do it than for actual practical value.

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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