Digital voltmeters 3 wires

[BigDaddy]

I bought a few of these on Ebay to go with the buck voltage regulators I bought previously.  I figured I could more precisely dial in a voltage for lighting.  Yes I know they have those regulators with voltmeters, but I have what I have.

I thought I was buying a 2 wire volt meter, but there are 3 wires.  Testing with a 9V battery, it reads 0 unless the red and yellow are connected together. 

Red and Yellow at the + terminal and black at the - will read 9V.  That will work for my purpose, but why is there a 3rd wire?

 

[RR_Mel]

I have several three wire meters and the way I hook them up is 12 volts to the red and black wire and the measured voltage is between the yellow or white wire and the black.

 

The reason is the meter needs a bit over 4 volts to operate.  The yellow or white wire is for the measured voltage.  A two wire meter can’t measure a lower voltage than its supply voltage, the three wire configuration allows 0-20 volt range.

 

Clear as mud?

 

Mel

 

 

My Model Railroad   

http://melvineperry.blogspot.com/

 

Bakersfield, California

 

I'm beginning to realize that aging is not for wimps.

 

[gmpullman]

I bought a bunsh of those for the same use. 

IMG_6337 by Edmund, on Flickr

Mine have amperage readouts, too. Wiring diagrams were provided by the seller (it was maybe four years ago?) but most are the same. Higher amperage requires a shunt.

meter-hookups-LCD by Edmund, on Flickr

Good Luck, Ed

[BigDaddy]

RR_Mel

The reason is the meter needs a bit over 4 volts to operate. The yellow or white wire is for the measured voltage.

So I would wire red and black to the input side of the buck regulator and the yellow wire to the output (red side)?

[rrinker]

 That would work. The negative side of those modules is straight through, at least on the two types I have, so there is a common between the input and output. 

                                --Randy