Help needed to change the analog volt meter on my Variac to digital.

[Ken from ontario]

Now that I had a chance to sleep on this. I'm going by the schematic or diagram here. The black wire is connected just like the meter wire to neutral. The yellow wire (sensor wire) is connected to the output like other meter wire. The red wire (power wire) is connected to the fuse or reset circuit breaker (good idea). If you put the red wire on the switch side of the fuse, if the fuse goes the meter will still be on but go to zero. If you put it on the other side of the fuse, the meter will turn off.
I have two older models of these variacs, very useful devises. Just curious, what do you plan to use this for? For many years back in the eighties, I repaired many solid-state amplifiers and power supplies. Ran an AC ammeter, in this case a 5 amp, in series on the hot line. If the rated input current was at let's say 1 amp, I turn the voltage up till the meter reached 1 amp. It made it really easy to trouble shoot without worrying about maximum smoke.

I installed the 3 wire digital volt meter but couldn't find a dedicated power source to run it so had to go for the second option which was to tie Red & Yellow wires to positive, black to neutral, now the variac DVM starts to light up at 20 volt, but it's fine with me because I always turn the knob to half way (50-60 volts) for my use so I can live with it the way it is, I tried different source for power i.e. yellow wire to the fuse (+) side and also, red to positive side of on/off switch but the DVM would show zero and as I turned the knob, it would show voltage in revers(130V,129,128 etc.) and would dime as I turned further.
Anyhow I'm fine not to have zero to 20volts, I also installed the 20 AMP circuit breaker and took a couple of pictures. thank you all for your inputs , Silence dogood, thank you for finding a a variety of options to connect this thing properly, I'm 100% sure you would have figured it out in no time if the variac was sitting on your bench .

 

[silence dogood]

Ken, I'm glad that you got it workingand thanks for the compliment. I had been working in electronics for over 50years. Clear back to the tube days. I would like to commend both Bill and Tq60 for filling in the gaps that I left out. By the way, the instructions that Tq60 gave you for adjusting the pot are excellent.

 

[WobblyHand]

I installed the 3 wire digital volt meter but couldn't find a dedicated power source to run it so had to go for the second option which was to tie Red & Yellow wires to positive, black to neutral, now the variac DVM starts to light up at 20 volt, but it's fine with me because I always turn the knob to half way (50-60 volts) for my use so I can live with it the way it is, I tried different source for power i.e. yellow wire to the fuse (+) side and also, red to positive side of on/off switch but the DVM would show zero and as I turned the knob, it would show voltage in revers(130V,129,128 etc.) and would dime as I turned further.
Anyhow I'm fine not to have zero to 20volts, I also installed the 20 AMP circuit breaker and took a couple of pictures. thank you all for your inputs , Silence dogood, thank you for finding a a variety of options to connect this thing properly, I'm 100% sure you would have figured it out in no time if the variac was sitting on your bench .
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Nice work. That's some fancy variac! How much does that one weigh?

The two I have are the classic death traps - no shields, no switches, no fuses. Everything is exposed. But they are useful at times. I will have to dig up a picture of the larger one.

 

[Ken from ontario]

Ken, I'm glad that you got it workingand thanks for the compliment. I had been working in electronics for over 50years. Clear back to the tube days. I would like to commend both Bill and Tq60 for filling in the gaps that I left out. By the way, the instructions that Tq60 gave you for adjusting the pot are excellent.

I do appreciate everyone who posted on this thread,, the problem I have is, I could not understand the instructions for adjusting the pot, (I'm just being honest here), and don't want to be a pest by asking too many times to explain a simple task, even the explanation might not be clear enough , but I do appreciate everyone who chimes in.

Nice work. That's some fancy variac! How much does that one weigh?

The two I have are the classic death traps - no shields, no switches, no fuses. Everything is exposed. But they are useful at times. I will have to dig up a picture of the larger one.

Thanks WobblyHand, it was a nice and simple enough project and very satisfying to see it work, even though it could have been a little better if I could make the volt meter to start powering up from zero.
You asked how heavy ? it weighs ~ 15 lbs, heavy enough that I have to find a permanent place for it, but it is worth having one around, I also have smaller version of it (3 Amp) that I use daily with my grinder.

 

[tq60]

Adjusting the pot is easy.

Get a good voltmeter and measured the voltage and compare to what your new one reads.

If same good.

If different then you decide if it matters.

If you want to adjust, unplug from power and with a tiny screwdriver insert it in the tiy slot in the pot and turn is just a bit, either way, remember how much and which way.

Plug back in and measure again.

If you went the wrong way unplug And turn it back, or if closer turn a bit more.

It may take a few tries t get it right.

Also check at different voltages.

It also may not matter that much, if off by 1% you can make a label to remind you.



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[Ken from ontario]

Ahh, I see what you mean by adjusting the pot, I actually did that yesterday , my mind was so wrapped up about the dedicated power source, I automatically thought you were talking about a way to make the display work from zero, my bad.

How I adjusted the display was not exactly as you described above but the end result was exactly the same, ( I did notice the adjusting screw in the picture on the listing). I disconnected the variac, used a an eyeglass repair screwdriver, turn the screw on the back of the DVM, plugged the variac back on, did that twice to get it right on, only after I did all of that, then I verified with a proper multimeter and it was spot on.(+,-1V)
Having said that , I still appreciate your thoughts and your help( and Bill Husdson, Silence dogood) even though I sometimes don't follow the lingo which makes me slower to understand but you all took the time to respond which means a lot .