Variac question

[dude]

I picked this General Radio Co. Variac for $50.  Model Type 200-CU, 5 amps. It looks like an uncased model, I assume I need to put a case or frame around it for safety..? The dial was mounted on the opposite of the brushed end, for panel mount.  The instructions said the dial could be switched to the brush side which I did.  Looking at the chart below, I set dial for the 135v side, (table mount, 0-135v) counterclockwise.
With the dial set as above, turning counter clockwise increases the voltage from 0 to 135v. I assume I have this correct?
As for the Line input, which is 123v here, I attach the black (hot) to terminal 1, and the white (neutral) to terminal 4, adding a ground would go to the variac's case?

As for the load output, black (load) to terminal 3, and white (neutral) to terminal 4, adding the green ground from case to load ground receptacle. I planed on mounting a small electrical box (like for a furnace) and having a switch and single grounded plug receptacle grounded. Do I need to fuse the hot side? If so, what rated fuse? Rated current 5 amp, maximum current 7.5 amp, no load loss 10 watts

The brush, looks to be a brass pin, with a carbon brush inside..? and it runs along the coil top which has some wear but no separation of any kind.
Using this without a case would subject one to a shock if they were to touch the coil. Therefore, is it highly recommended to encase the variac?

 

[dude]

One other question: when I switched the dial to brush side there are spring washers that adjust the tension of the dial before the dial is secured, pushing the dial down all the way tightens the resistance in turning, should a just keep the tension just enough to keep the brush in good contact with the top of the coil? as of now I pushed that small spring washer flat, it's pretty thin to start. Turning the dial seems ok, not tight. 

[dude]

One other question: when I switched the dial to brush side there are spring washers that adjust the tension of the dial before the dial is secured, pushing the dial down all the way tightens the resistance in turning, should a just keep the tension just enough to keep the brush in good contact with the top of the coil? as of now I pushed that small spring washer flat, it's pretty thin to start. Turning the dial seems ok, not tight.

[sluckey]

You need a case for safety. Even a wooden box will do, but you should be able to find a suitable PVC box on the electrical aisle at Lowe's.

I don't like the idea of voltage increasing as you turn the dial CCW. There are two ways to change so the voltage increases as you turn the dial CW...

1. Put the knob on the opposite end of the shaft. Like it was originally. Or,

2. Change the wiring. Terminal 5 will be LINE IN HOT. Terminal 3 will still be variable LINE OUT HOT. And Terminal 2 will be NEUTRAL. If this will be in a non-conductive enclosure, simply connect the input green wire to the output green wire. If a metallic enclosure, bond it to the green wires too.

[dude]

I guess put the dial back, as the old wires in side can only turn 320* already are stiff but opposite way. Changing the wiring will work but to twist the internal wires to go opposite doesn’t seem to be an option.
I guess either flip the dial or go CCW. This variac was a panel mounted one

[sluckey]

I guess put the dial back, as the old wires in side can only turn 320* already are stiff but opposite way. Changing the wiring will work but to twist the internal wires to go opposite doesn’t seem to be an option.
I guess either flip the dial or go CCW. This variac was a panel mounted one

Huh???

You don't mess with the internal wires. Simply connect the power cord black wire to #5 lug and white wire to #2 lug. Connect the outlet hot wire to #3 lug and connect the outlet neutral to #2 lug.

[dude]

Ok, yeah, off would be full on, on would be off. What an  l thinking,  .
Thanks, might just change the wiring as it’s easier, not even wired yet.
Thanks again as always

[dude]

Looks like my $50 General Radio Co. Type 200-CU Variac might not have been a good buy after all. The Variac is in excellent condition, body and dial are almost like new..., but the single brushes carbon is down to the brass brush holder touching the top of the coil as it's turned. Needs a single brush new brush, and you guess it, unavailable.

I read in some electronics forums that the brush material needs to be a specific carbon that won't cause arcing..? Below is a pic of the small brass brush holder, inside the round brass brush holder is a small cylinder brush, seems to be glued inside the round brass case, it's worn to down to the brass case's edge. I believe once the carbon extended from the brass when new and was not a circle bit rather ground to the width of the wire winding on the varaiac. So, to contact the a single winding as it's turned..?

I found places that sell brushes or brush material to make my own but only get one chance to get it right. As I'd have to pick out the carbon inside the brass holder and make a suitable carbon piece to glue in the brass holder. I'm looking for advice where to ask these questions, perhaps another forum..?

The directions that came with the variac say replacement brushes are 25 cents, and never let the brass touch the windings as damage will occur, I guess 25 cents in 1933..!

Any suggestions where to find more info, another replacement brush,  info on how to make one and what material should be used, graphite, carbon, copper, etc. 

Appreciate any info or leads to help me get this variac working again, thanks in-advance

[sluckey]

Got no ideas. I feel your pain. Soft moving parts do wear out. Cut your losses and just buy one of those cheap red Chinese variacs. I highly recommend a 10 amp unit. It will outlast you. 

[dude]

Got no ideas. I feel your pain. Soft moving parts do wear out. Cut your losses and just buy one of those cheap red Chinese variacs. I highly recommend a 10 amp unit. It will outlast you. 

Can't cry over split milk, but I have to give it a shot. Seems my best bet is to get a brush and holder that can be modified to fit right over the coil like the original one. I'm sure there are companies out there that rebuild these variacs and resell. I just need to find these companies, so far Google hasn't helped. I assume I need to stay with carbon..?
As always, thanks again.

[TenderTendon]

Don't give up on that. It's a very easy fix. That piece of carbon brush material is very soft and just pressed into that little brass holder. You can simply dig it out with a small screwdriver. To replace it, just get a generic brush with a cross section at least the diameter of the existing brush (something like https://www.amazon.com/Faotup-Electric-Carbon-Brushes-Replacement/dp/B09SCT2BR6) and shape it to fit. These brushes are very soft and can be shaped to a desired size by filing with file, shaving it with a utility knife or dragging it along a sheet of sandpaper (100 grit or so). It would only take a couple minutes to do. Push it in the existing holder and you are done.

[dude]

Found this,$8 shipped.., we’ll
See

[TenderTendon]

Good job finding that. That will save you some time...

[dude]

Got no ideas.

OK, the new brush in last post was too small but I manage to make it fit, you can see the brush below contacting the top of the coil. I cleaned the top contact spot around the coil with 400, then 600 grit wet/dry paper with a little detox-it, came up nice and shinny.

Ohms reading from ends of variac coil is 3.1 ohms, on starting and end pins.  With wiper sweep on meter and other on starting coil, I get about 3.1 ohms, too. Good it's the same. Turning to full a/c voltage 135, meter reads 1.1 ohms, only dropping about 2 ohms.
The variac seems to be working with the new brush but such a small difference in ohms from 0 to full on (seems low to me) but.., I know jack about the resistance in a variac.
I haven't applied line voltage yet, just testing first.  Is the small resistance difference normal from 0 volts to 135 volts?
I can't change the wiring to get the variac to read from 0 to 135 volts by changing the wiring because the "dial is made" to read CCW no matter which wiring ways you suggested.  The only way to get a CC rotation is to flip the brush to the opposite end. This is a panel mount variac, the brush is meant to be on opposite side that I have it now. So, I guess I can reverse the brush assembly to the other end and get CC rotation then wire as you suggested for CC.  All depends on the enclosure I make, if all fits well.

But I'm mainly concerned with the small ohms changes from 0 to 135v before I apply a 120vac line.  These pictures are with the variac set for CCW rotation.

 

[sluckey]

Look at the schematic. That variac is just one long piece of heavy gauge wire. It should be a low reading. Your highest ohm reading should be between terminals 2 and 4. That's from one end of the wire to the other end. Gonna be low.

If you're scared of it, plug it into your light bulb limiter.

[dude]

Look at the schematic. That variac is just one long piece of heavy gauge wire. It should be a low reading. Your highest ohm reading should be between terminals 2 and 4. That's from one end of the wire to the other end. Gonna be low.

If you're scared of it, plug it into your light bulb limiter.

Well, you answered my question, thank you, it's working. 

[sluckey]

Have you tried it with a load yet? Here's a cheap enclosure that might work. Don't know if it's stout enough??? It's big enough to allow switches, digital meter, etc.

[dude]

Have you tried it with a load yet?

Not yet, just works as it should with no load.  One of the enclosures from Amazon will work but I'm most likely to make something out of wood. I can dovetail a nice hardwood enclosure since I have the tools. I'll add a fuse and ground the metal base to a three prong plug. Since the variac is 5 amps, I'll use a 5 amp fuse. I guess I should put a load on it before I waste time making a nice enclosure. The coil looks very good, top contact sweep on coil is nice too, dial looks almost new.
Thinking about flipping the dial to the bottom to read CC but the mounting holes in the steel frame would be harder to rig into a case but not impossible ,this variac was made for a panel mount.
Thanks for the link.
Now, I'm thinking of reforming several old Mallory cans, (if they're not completely shot). I guess I could make a SS rectifier (wonder if I can get DC voltage high enough with only 123vac, might have to use a PT?) and use resistors, slowly bringing up the voltage while I read the voltage across the R. 
 

[shaun]

Thought I would mention the great value that can be added by including a digital meter. Check out this video. It worked a charm, and you're so deep into this that adding the meter should be a snap. You can maybe design your enclosure to include it:

[dude]

Might be a dumb question although if you don't know the answer maybe it isn't dumb  .
Do you fuse the line in, or the load line out on this variac?
I would assume the load gets the fuse but if the fuse blows on the load, the line side has 120Vac on the variac.

I'm using the dial CC rotation table mount, 135v, so pin 1 is line in, pin 3 is load out so fuse pin3 or 1?

[sluckey]

My 10A variac came from the factory with the output (pin 3) fused with a 10A fuse.

[dude]

Thanks, that would be my guess, I'll fuse the load. I assume grounding the Variac's frame would be a good thing too..