Category: Safety transformer V3

Safety transformer V3

I came across an ad form Stefan Haesen, he had a bunch of transformers and motors for sale at a low prize. I reacted and a few days later the trunk of my car was full. Thanks Stefan!

Between the transformers there as a 1000VA safety transformer and a 1500VA variac. I decided to build a variable safety transformer with these. For the case I used an old pc case in which I made a chassis. I also have put some wheels underneath it. The measuring print will be the same as in V2.

Because this transformer is big I had to build something to limit the inrush current.


PC case with reinforced bottom and wheels:

Scheidingstransformator V3


Scheidingstransformator V3

Front panel almost finished

Scheidingstransformator V3


Inrush current limiter

inschakelvertraging schema

Scheidingstransformator V3

The power supply:


I build all the pcb’s in the case of a pc power supply. This way it is easy to mount in the big case.




I’m still going to finish my safety transformer V2 because that version has a current limit and this version doesn’t. I have taken V1 apart for the parts.

Safety transformer V3 – Update

The electronics of the measuring pcb from this project is exactly the same as that from the safety transformer V2 project. Therefore I could now finish this design too.

The finished result:

Safety transformer V3 – Update

After a few months of using this project it turned out that the solid state relays where not as reliable as first thought. One time the power relay stayed stuck close, but the resistors where not shorted by the other relay. This caused the resistors to get too hot (they are not calculated for continuous load).

The burned pcb:

After this I decided to build a new version of this pcb. This time with mechanical relays:

Circuit diagram:



The firmware in the microcontroller stays the same.