The new toy

[AlexanderHun]

My new toy, 22 kg, variable toroid transformer 
Input 220v, output 0-240  6000va
Max current, 27.5a

[Mads Barnkob]

Very nice, it is a power house and practically indestructable!

I got a 3 phased version of almost the same, 3x25A variac with motor control.

Never used it and it is super heavy!

[AlexanderHun]

This is the big toy !!!!  Compared to that, mine is a toothpick, I do not use three phases but it is an impressive piece! 

[DashApple]

Very nice varices both of you : D

I too have a three variac unit , though mine is configured for 230V single phase with balancing chokes 75 A continuous 90A max


I am a fan on the linear style varias mainly , though i havent seen many past 13A

[AlexanderHun]

90 Amps?  Jesus, what do you want to operate an electric locomotive?      Do you have pictures?

[Hydron]

Looks like a good score!

If you want a nice meter for the new toy, then I'd recommend poking around on ebay/aliexpress for a panel meter with current/voltage/power/VA/power factor, like this:
https://www.aliexpress.com/item/4000098834279.html
(that's the first one I found, there are some other styles too, haven't tried them though)

These meters use the same sort of chips that the plug-in wattmeters meters use, and will at least attempt to give a "true-RMS" type current reading, not just one based on peak current, plus will also show some other useful info such as power and VA use. What you will find is that being self-powered by the measured voltage, they rely on the input voltage being above a certain amount before working properly, which can be annoying when using with a variac. They can normally be modified however to cut the connection between the powering voltage (which can be connected to the 120 or 240V variac input voltage) and the measured voltage (connected to the variac output voltage). I've done this to a couple of different meters and they have both worked very well.

[AlexanderHun]

Thanks, I don't trust Chinese panel meters, especially at such a high current.  Even at low voltage, maybe 100 amps?  I don't even look 30, but I can be wrong.  Thanks for the tip!

[AlexanderHun]

"Measure range:

  AC voltage: AC 80-300.0V/200-450V

  AC current: AC 0-100.0A"

Unfortunately, the lower limit of measurement is not enough

[Hydron]

They use a CT for the current measurement, so 100A is perfectly reasonable. And given that the output of a Variac is to be treated as live mains regardless of setting I'm not so worried about how much I trust it, though one should always be careful with cheap mains powered kit! The biggest issue I see with these is the use of a capacitor, which may not be an X rated one, to do the bulk of the voltage dropping for powering the meter. You could always put another better capacitor in there (or in series externally) if you're modding one though.

[Hydron]

"Measure range:

  AC voltage: AC 80-300.0V/200-450V

  AC current: AC 0-100.0A"

Unfortunately, the lower limit of measurement is not enough

From the live terminal on the mains input of these meters, there is the connection to the voltage divider for the measurement circuitry, and another connection to a capacitor used as a voltage dropper as part of the power supply to the meter. The 80V limitation is from the latter - if the input voltage drops too far it doesn't get enough current to run. If you split the two into a measurement connection and a power connection, and run the power connection from the primary (input) of the variac and the measurement connection to the secondary (output) then the meter will measure all the way down to 0V (with neutral being shared, as it is in the variac). When I have done it all that was needed was a track cut and the addition of another wire for (power) mains input.

[T3sl4co1l]

Lovely ones

The most interesting one I saw was in the open back of a piece of test equipment.  I don't remember what it was (some manner of AC source), but it was this type of design: https://5.imimg.com/data5/TestImages/HJ/VN/PS/SELLER-1853729/radiotone-double-layer-roller-contact-vertical-variable-autotransformer-500x500.jpg

I wonder what the tradeoff is, if those are better because of scale (core savings?) in the 20kVA+ range, say?

Tim

[MRMILSTAR]

Which company makes that variac? I've never seen roller brushes like that. It doesn't appear to use the full face of the windings.

I have a General Radio variac made back in the 1970s rated for 25 amps at 240 volts. That device is engineered incredibly well. It uses a full face of 6 linear brushes on the outer circumference. In addition, the contact winding faces are silver plated to inhibit corrosion and improve conductivity. I gave (yes, gave) one of these to a fellow tesla coiler. I spoke with him a few days later about his progress. I was telling him about the engineering features of the GR variac including the silver plating. He sounded surprised and said that I was glad that I told him about that because he kept polishing the winding face expecting to see bare copper and he just kept seeing that silvery surface! I told him not to rub too much or he would remove the silver plating. 

[DashApple]

I to haven't seen many with round brushes , I have three linear variacs used in lighting rated for 13A , two of them use one round brush in the centre  and the other with a round widnding uses 2 , I believe they are German made .


My 30A Tri stack uses British made transformers with full brush coverage and what looks to be brass coated windings ( goldish colour ) .

AlexanderHun Heres the picture , It was too good to pass so i got it : D .

[MRMILSTAR]

I to haven't seen many with round brushes , I have three linear variacs used in lighting rated for 13A , two of them use one round brush in the centre  and the other with a round widnding uses 2 , I believe they are German made .


My 30A Tri stack uses British made transformers with full brush coverage and what looks to be brass coated windings ( goldish colour ) .

AlexanderHun Heres the picture , It was too good to pass so i got it : D .

Are those 2 devices that look like transformers actually current-sharing inductors for the 3 variacs?

[DashApple]

Are those 2 devices that look like transformers actually current-sharing inductors for the 3 variacs?

Yeah , I need to look and see how they wired them in