3 Phase 400 VAC 6 A Variac Stack With Voltage/Current Meters

[Mads Barnkob]

Video:

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Story of the project, in text and pictures:

I bought this 6 A variac stack as advertised for 6A (in 2016). But the physical size suggests it could be a 10A model as well. There is no part numbers or data shields to go by. Variacs are usually rated to be able to handle 200% overload for up to 5 minutes and 300% overload up to 1 minute. As the lids and housing was missing, it needed to get built into a new enclosure.


A new enclosure was needed


New wiring was needed


Almost finished


The variac was tested with a 3×400 VAC 9 kW space heater. With the variac set for 400 VAC, the current draw was around 12 A. this gives a total 3 phased power consumption around 8.2 kW.

[Hydron]

Just a heads up for anyone doing this for a single phase variac (or are happy having 3 separate meters like here), you can get some nice cheap panel meters that include an energy monitor chip and thus can do real/reactive power, PF etc. As an added bonus, they can normally be modded so that they are powered by the _input_ mains, but measure the output, so that they will work properly all the way from zero variac output.

[Mads Barnkob]

Just a heads up for anyone doing this for a single phase variac (or are happy having 3 separate meters like here), you can get some nice cheap panel meters that include an energy monitor chip and thus can do real/reactive power, PF etc. As an added bonus, they can normally be modded so that they are powered by the _input_ mains, but measure the output, so that they will work properly all the way from zero variac output.

That is a good point!

I did change a voltage/current meter to work from 0VAC, with a external 12VDC power supply. It was fairly easy, like cutting a single wire inside the meter.

I went for the small meters because of space and there has been a change to Danish import taxes last year. We could import from China, taxfree, if it was below 12€. Now the limit is 0€ and tax is applied to both item price and shipping costs. Usually rendering the "cheap China stuff" into "expensive China stuff" and we might as well look for better quality alternatives that almost end up at the same price.

[rikkitikkitavi]

Is it heat sinks on the external? I have never seen a variac with that. One would assume freeing the winding would help disperse heat.

I wonder how much one could increase the amperage by using forced cooling?

The winding itself lends itself to a substantial increase by forced cooling, but the wiper and contact resistance might be a limiting factor. I am not sure even immersing in oil would help, rather the contrary by reducing contact.

Nice build, with a robust chassi holding it all together.

I am planning to do that to my three 10A (and perhaps my 25/25/20 too) but as I have no threephase socket (yet) I have no immediate need.