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

[XZ923]

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.

 

[berkeman]

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...

 

[jim hardy]

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

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

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

 

[XZ923]

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.

 

[jim hardy]

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...