PowerStat Autotransformer / Variac Rebuild and Repair


Hey there I decided to try something a little
different today I’m doing a narrated slide show on a project
I’m working on Quite a few years ago I picked up this argon
laser head but didn’t have a power supply for it.
I decided to finally get this running and get to building a power supply
and one of the first items I picked up.. uh.. to do.. to do this is this StatPower uh dual
gang Variac I’m going to use the Variac to adjust the
input voltage to the actual power supply itself since I don’t have a switchable boost transformer.
This is a StatPower dual gang autotransformer that I picked up at the surplus shop uh the
other day uhh each section is rated 22 Amps at 120 Volts
and as you can see it’s absolutely filthy It did come with a knob, which is always a
bonus but other than that lots of grime and dirt on everything uhm
The contact surfaces of the winding look terrible as you can see there the copper is just totally
corroded Uhm.. a couple bent windings which are pretty
easy to fix, not a big deal Annd the bake-o-light is in pretty good condition,
terminals aren’t bad, they’re just dirty. Here’s one of the brush uh commutators on
the back Uh, grimey but in general not in bad shape
You can see the uh brush contact surface and here’s kind of a wider out view of the autotransformers
Here’s just a couple more shots of the uh PowerStat before I start tearing things down
and here I’ve already pulled the center shaft out uh it’s pretty easy to do a couple of
set screws and it slides out uh I got it broken in two now and getting
a little closer look at each section uh back plate, commutator with the brush in the upper
right hand corner And that’s taken off, this is one of the contact
rings and this is the actual windings themselves from the top.
And this brush is in pretty bad shape but believe it or not it’s still usable, it’s
just not great. Uhh, here’s another view of how that’s held
onto the uh commutator plate. I’d eventually like to order some new brushes but for now
this will work for testing and my purposes. Uhm it’s not great but it’s liveable.
Here’s some wiping on the uh winding contacts you can see how much stuff is commin’ off.
Here we have the uh windings on the right and the uh insulators and separators and spacers
on the left. Uh, the frame itself actually cleans up pretty
good, this is pre-cleaning on the first winding. Uhm, and.. these are little plastic bushings,
uh, they’re greased and the rod uhm rotating part for the commutator actually slides into
these. Uh they’re a little crunchy, filled with grime
and dirt, but in.. overall they look pretty good, they weren’t corroded.
Uh so I went ahead and pulled those out, cleaned them up and set them aside.
I washed the base plate in the sink and then put it in the oven to dry along with the commutator
and one of the brackets that holds down the windings.
As you can see the results are quite a bit of an improvement and the appearance uhm..
much cleaner. Uh, you can steel there’s still some corrosion but nothing major and this
wiper brush, uh the contact here, uh, cleaned up pretty good with some sand paper.
There’s some dings and digs in the winding surface
I took some sand paper to those and they seemed to clean up okay,uh probably use a little
more work. Uh here’s the back of the windings. uhhm…
as you can see it’s been abraded over time, it’s not supposed to look like that, so I
put some nail polish over those to seal them back up and it should be alright.
Uhhh and we’re getting quite a bit of improvement in the appearance of this project.
Put the phenolic back in and were going to put.. go ahead and put the bracketing.. uh
the.. locating uh parts back in. And here’s the windings back on top of the
bracket. Now this is the first.. uhm.. autotransformer
of the pair and it’s turning out pretty good I’m pretty happy with it.
Of course, for it to work right you have to have both of them, or at least for my needs
gonna have to have both of them working. This point I don’t know if the second one
is in good condition. uhh but here’s a comparison of the two.
Major.. Major difference as you can see and all it took; a little bit of time.
And i got this Variac dirt cheap ’cause it was just thrown in a pile with.. you know..
looked like junk and just a little bit of effort it comes apart.
Here I’ve taken apart the second one.. uhh you can see the locating pin for the transformer
is broken off uh.. I took care of that later on.
Not a big deal. Uh, drill it, tap it and put a bolt in there.
Uhh, all the parts in the sink getting cleaned down.. scrubbed down.
I actually threw these in the oven to dry them out, 200 degrees F for about an hour
or so. This transformer is a lot dirtier than the
last one. Uhm, but.. it cleaned up pretty good.
Can see, uh, we’re back down to copper again. Got all that schmutz off the top.
And i put this in the sink actually and washed it off and scrubbed it down and then put it
in the oven to dry. Here I’m just test fitting the bearings.
Uh, this phenolic sheet was damaged so I coppied the shape onto a piece of FR4.. not the best
copying job, but.. ya know, for this purpose it worked out pretty good.
Uhm, so we got the FR4 plate back down and then the phenolic or G10.
Uhm, and here’s the replacement pin I made, put a ton of Loctite on it. It’s just a 4mm
bolt. Uh, getting the clamps back down
And uh, hey it’s looking pretty good! So now we’ve got two uhm autotransformers
uh commonly known as Variacs although that’s a brand name.
Uh that are both in good shape, they cleaned up really well, they move good, uh electrically
they’re in good shape and so I’ve connected everything now with
these uhm alignment pins that you can see, these.. these gray uh rods that go between
the front and the back Variac uh or autotransformer. And then I ran a piece of rod through that
and everything is a contained, single unit uhm and I now have a working dual gang Variac
for future use. Thanks for watching.

4 thoughts on “PowerStat Autotransformer / Variac Rebuild and Repair

  1. I made my own brushes for my powerstat… Ground old motor brushes to shape on a belt sander. Made my own copper sulphate for copper deposition onto the tops & sides of the brushes. Soldered the new brush into the existing holder with a torch. Saved like $75 and it was a interesting process to learn. 

  2. I love when people bring things back to life. Thanks for the vid. May I suggest you talk a little bit more about your methods in your videos. Information like how you washed in the sink and dried in the oven is super helpful. It would be cool to know if you used contact cleaners or electrical lube and what products were used. Thanks, man.

  3. I plugged a receptacle ground tester into mine and under 60v it's says the ground is fine but anything higher it says it has a bad ground. I even scratched of the powder coat off around the ground lug & it still does it, any idea why?

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