Repair Of An Auto Transformer Chinese Variac
I went to a customers business and he said he was about to ring me. Turns out he had a problem with his Chinese variac.
Unfortunately some of the pictures are web pictures as I forgot to take some photo’s before pulling it apart. This was not purchased from an Australian E-bay site but from a Spanish one. This had multiple problems.
The first being that the voltage was going backwards when using the dial on the top.
The second being that the wiring inside was incorrectly and possibly dangerously wired.
As you can see the Neutral is going through the fuse (normally the active brown wire goes via the fuse, not the blue wire.
I also found under the power wire the active wire was exposed.
So I opened my similar Australian E-bay purchased variac for reference. The first thing was to replace the power cable which I did and put the active wire via the fuse. I also figured out that the Blue wire going to the transformer belonged on the centre tap of the power switch. The thick black wire belonged with the neutral wire from the power cable. The Active brown wire goes to the via the fuse then to the left contact of the power switch.
This fixed the voltage going the wrong way on the dial but didn’t fix the voltage on the digital meter. I had to rearrange the wires going to the meter. Turned out that the black wire coming from the meter went to active not the power switch centre tap I tested it via a light bulb and found the light bulb was triggering the test light so I tried with a non resistive load and it worked good.
This article was contributed by Lee Davey from Hobart Tasmania Australia. He has been doing repairs on electronics and PC’s for around 30 years.
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