Friday, January 15, 2016

The Variac That Took Us To The Moon

I generally don't have much work around the Christmas holidays going into the first few weeks of the New Year.  I have time to repair gear, and make some new projects.

Here is one of my new projects; a 20 amp variac.

This is an old General Radio type W20 that is in perfect condition.  It came from an old 3-phase lab bench type variac; cool but not suitable for use on a set.  I've had the parts for it sitting around on a shelf for the past couple of years.  I just hadn't found time to work on it until now.

I love old electric devices like these.  The design is simple.  The construction is excellent.  Devices like these were designed to exceed their rated capacities and last a long time.

One of the hardest parts of turning this into a studio-use variac is just finding an enclosure that it will fit.  Then there is cutting and drilling to fit the variac into the enclosure.

On the bottom of this variac is this awesome ID label from NASA.  This could be a variac that took us to the Moon.  Maybe, or not.

Not having the original insulated shaft for rotating the brush assemble, I substituted an acrylic rod.  This assemble is energized when the variac is on.

Here is the finished "Moon" variac complete with it's original ID plate.  I have added a breaker and a power-on indicator light.  I also like to use indicator plugs.  These are very handy allowing you to see at a glance if there is power.

Testing the new variac, I was surprised with it occasionally popping a 20 amp circuit breaker at the electric panel.  Carefully checking the assemble for a short, I found nothing wrong.  With further research, I found that this is a common issue with these large variacs caused by the in-rush of current.  It is more a problem on-location when breakers tend to be of a quick-acting type versus studio equipment which seems to have slower reacting breakers.


This "new" 20-amp variac is a great addition to my gear.   Now I have 1-7.5 amp variac, 2-10 amp variacs, 2-20 amp variacs, and 1-50 amp variac.
My 50 amp variac in a unistrut cage

I can't say my variacs have made me a lot of money, but they have more than paid for themselves with reliability.  I found many times over the years, variacs from rental house are often unreliable.  And this is not surprising.  Variacs are fragile.  One drop or dent is enough to irreparably damage it.