How to wire a vintage wattmeter

[Food Scientist]

Oops sorry about that MrMoody - I wasn't expecting anyone to actually follow the thread down the road. I am actually wiring it up tonight and referencing the connections posted earlier.

So I hooked it up as recommended (with one modification) and it sorta worked - the needle moved but in the wrong direction. It was close to 0 to start and pegged the meter below zero. Possibility the polarity is wrong?

I hooked it up as follows:

Hot wire from wall to S
Hot wire from bulb to L
Made a jumper wire from V1 back to my voltmeter that was a common neutral wire (vs hooking up the two neutrals directly to the V1 post)
No new V2 connections.

My thought is to switch the S and L wires so the electrons are flowing in the right direction?

 

[MrMoody]

That's pretty weird. AC doesn't have a "direction," it reverses every 1/120th of a second. Swapping S and L shouldn't make any difference. A DC meter wouldn't say, "1 phase." I can only figure the meter must be damaged internally, like a blown rectifier or mechanically damaged or mis-assembled. How easy is it get open?

 

[Food Scientist]

It looks easy enough to take apart but I figured if it was damaged internally its easier to try swapping the leads and it worked! So in the photo I have only one 60 watt light bulb hooked up. I ran the hot and neutral to the voltmeter and then made a series of jumper wires. Hot from voltmeter to the ammeter, ammeter to the watt meter. Ran both neutrals to the voltmeter from the power source and the bulb, made a jumper wire to run neutral from the watt meter to the voltmeter to complete the circuit.

I made the hot wire connection initially as advised and the needle moved every time I plugged in the cord, just in the wrong direction. So right before I typed this up I switched the leads and it works! I still may take it apart to see the difficulty in adding a bulb, but further down the road. I will have 3 bulbs on the ammeter connected for a total of 1.5 amps, but need to adjust it so it reads accurately.

Thanks so much for your help, I couldn't have done it otherwise. Once I have the entire project finished (library) I plan to start a new thread and post some pictures.

 

[MrMoody]

Oh! I just realized why this is! Because the voltage sense was out of phase with the amperage sense. Now we know you have it right.