Thursday, May 9, 2024

900VA variac rehabbing

Last month I've found a big industrial enclosure with a giant knob on it throwed away. I've take it home and open it. To my surprise what's inside was a variac.

A variac is a type of variable autotransformer in which the output voltage is varied by twisting a dial.

My variac is the Belotti V-10NA 220V 900VA 4A.

WARNING! - The project described in these pages utilizes POTENTIALLY FATAL HIGH VOLTAGES. Do not attempt to build circuits presented on this site if you do not have the required experience and skills to work with such voltages. I assume no responsibility whatsoever for any damage caused by the usage of my circuits.

In my small home lab I don't have a variac, so I decide to clean it and prepare a new enclosure. The original enclosure was big, and it has disconnected wires. It was all a wiring jam.

I throw almost all and keep the variac. I clean it and then I select an enclosure that I've around.

I decide to built it using a simple circuit.

It has two fuses, one on the mains input rated 6.3A on the rear side. The other on the front side. This last one is useful if someone want's to test some equipment.

I would like to thank Pier Aisa ( that help me sizing the main fuse.

Then I have a main switch. I've around a 25A one. And a de-activate switch, a 16A switch that I use to de-activate the output, when activated a bulb lights up.

The main switch powers the variac, and the two meters I've put. There is one voltmeter that measure the mains line. The other measure the output from the variac. It also features an ammeter. This last one is a cheap two wires meter, for this reason it takes supply from the line and it can not measure voltage lower than 20V. If I want accurate measurements or lower voltage measure I can wire my multimeter on the line output.

It's important not to overtake the limit of 900VA output, otherwise the variac will became hot and eventually burn his coils.

On the output I've put an EU plug, and a couple of banana plug in parallel,

The enclosure I've around it's used so I've to clean it and cut holes. The front panel already has holes, so I've to put a piece of wood in front of it to keep the front clean.

The finish product is pretty good at my eyes, and finally my lab also have a variac.


  • read risk disclaimer
  • excuse my bad english