I have a vintage Westinghouse AC Voltmeter that I had intended to wire into an Edison Lamp. My thought was to have this AC voltmeter come to life when the lamp was toggled on. My problem is that I'm unsure on how to wire the voltmeter up....but also unsure about whether or not it can handle the direct wiring to 110 or whether or not a resistor is needed. There are three posts on the back: one has both a + and -, the one directly across says 1500v, the one at the top says 15v. I planned on using a terminal block for my wiring to clean it up. I don't know whether or not the gauge works but the needle does float. Thanks for any guidance anyone can give!

 

You may have to remove the back cover to find out the resistance of the meter, this can be seen by the value of the resistor used on the 1500v scale terminal, then a suitable resistor can be calibrated to use in series with the 15v to convert it to 150v FSD.
Max.

 

Max,

Can you elaborate on the part about calibrating the resistor to use in series w/ the 15v to convert it to 150v? Not sure I understand why there are two terminals anyway.

 

There are two terminal to produce two scale values, one for 15v and the other for 1500v, I assume you want to make a range of 150vac?
Max.

 

Correct.....
I suppose this is really just for the aesthetic effect....I plan to backlight to gauge but would be great to have the needle measure the voltage once the lamp is on. Once the meter is open and I can verify the resistor used on the 1500v terminal would I just wire in a resistor between the incoming voltage and the back of the gauge?

 

It will require changing or placing another resistor in series with the present 15v one to increase the scale to read 150v.
A pic of the rear when you have it open will help in further assistance.
Max.

 

Thanks Max...I'll post a pic when I get home this PM.

 

You probably don't need to open the meter. With a DMM, measure the resistance (a) between the +- terminal and the 15V terminal then (b) between the +- terminal and the 1500V terminal.
The second measurement value will probably be about 100 times the first. If so, then the external resistor to be placed in series with the meter can have a value about ten times the first value.

 

Thanks Alec.....I'm learning! Wish I'd paid attention to this stuff when I was younger.

 

Being an AC meter, If there is any kind of internal rectification it may distort the reading.
http://www.allaboutcircuits.com/textbook/alternating-current/chpt-12/ac-voltmeters-ammeters/
Max.

 

From the face of the meter, I'm gonna guess that 1500 terminal was originally 150.
Just a guess.

 

I would connect the AC between the 1500V terminal and the ± terminal and see what it reads.
I'm thinking it might be mislabeled and the 1500V terminal is actually 150.0V.

 

Would I need to step down the voltage before hooking to the 1500v terminal?

 

Being an AC meter, If there is any kind of internal rectification it may distort the reading.

True. But judging by the non-linear scale, my money would be on the meter being a moving-iron type, with no rectification.

 

Would I need to step down the voltage before hooking to the 1500v terminal?

No.
Either the meter will indicate about 12V on the upper scale if it actually is a 1500V range, or 120V if it's a 150V range.

 

Thanks! I'll try it...
Magic smoke here we come....

 

OK, here's how it went: Wired it up to the 15v terminal and got the needle to move all the way to the right. Then generated lots of smoke so cut the power. Tried the 1500v terminal, no movement from the needed but again lots of smoke. Suppose this gauge may be old and nonfunctional? THANK YOU!

 

You may have blown it by putting 120v on the 15v terminal!!
The suggestion was to use the 1500 only.
Open it up and see, nothing to lose.
Max.

 

Well, that's great. OK, I'll open her up this PM.