Good afternoon,
I inherited this old Variac from my father and after several years have decided to use it. I wanted it to test various voltage fan motors to see if they run OK.
When I first switched the thing on nothing happened
So I stripped it down and found that the "swipe arm" was not making contact with the coil and the top of the coil, the contact point was very dirty. Before I started any work, I tested the coil and all tappings for continuity - everything fine.
I spent the next hour cleaning everything up and adjusting the "swipe arm" so that it contacted the coil all the way round - I then measured the resistance right across the coil whilst moving the "swipe arm" - all good, the resistance increased/decreased as expected .
I then connected the power as shown below and put my volt meter on the outlet points.
Wow...everything worked as it should for a few seconds........ then the coil overheated and started to smoke! The coil overheated exactly in line with the "swipe arm", a neat brown line from the bottom of the coil to the "swipe arm" contact!
I tried the arm in several different positions but every time the same happens!!
The picture of the "swipe arm" is not mine, it is one found on the net but is almost identical
What am I missing?
I inherited this old Variac from my father and after several years have decided to use it. I wanted it to test various voltage fan motors to see if they run OK.
When I first switched the thing on nothing happened
So I stripped it down and found that the "swipe arm" was not making contact with the coil and the top of the coil, the contact point was very dirty. Before I started any work, I tested the coil and all tappings for continuity - everything fine.
I spent the next hour cleaning everything up and adjusting the "swipe arm" so that it contacted the coil all the way round - I then measured the resistance right across the coil whilst moving the "swipe arm" - all good, the resistance increased/decreased as expected .
I then connected the power as shown below and put my volt meter on the outlet points.
Wow...everything worked as it should for a few seconds........ then the coil overheated and started to smoke! The coil overheated exactly in line with the "swipe arm", a neat brown line from the bottom of the coil to the "swipe arm" contact!
I tried the arm in several different positions but every time the same happens!!
The picture of the "swipe arm" is not mine, it is one found on the net but is almost identical
What am I missing?