found a variac... now what?

K

Kindyr

Joined
Dec 5, 2007
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I did quite literally find a variac. sitting all wrapped up like it hadn't been used, in my local junk yard. its a model W20M, so single phase 120.

first question: anything I can do to test that it works? there is a wall plug on the input cord(I assume it's the input cord) and no plug on the output cord(again, assuming the wall plus is correct) Can I just wire up a femal style 110 plug to the output and run a multimeter on it to see if it's varying the voltage in AC?

Second question: What all can I do with this? I know that with a bridge rectifier I can do DC etching, and in AC mode can have it color the etch. I've also seen information on anodizing with one. Does it also work for electroplating? Anything else this allows me to do?

third question, where can I find a good bridge rectifier for this?

if it works(and it only has a couple of scratched from looking brand new) I'm very excited.

And the price? well I got the variac, and some other items and they charged me for 40# of tin. I got out of the yard for $6 total. very good day in the junk yard today.

Thanks for any advice

Kindyr
 
Righto, I use a bridge wave rectifier to convert AC to DC for anodizing Titanium.
You can probably get one from Radio shack. Or might try Ebay. I dont know of anything else you can do with a variac, but righto just slam a cheap multimeter on the output and rotate the dial and you should read in AC the voltage changing.
Chris
 
Hey Kindyr, a simple test can be done with a lamp. Just plug it into the variac and turn the knob back and forth. If the lamp gets brighter and dimmer, you know that it is functioning. You can use a multimeter like blindhogg suggested but you really need to test it under load. If you want your variac tested professionally, I'd be happy to test if for you for free if you cover shipping to and from.

If you need a rectifier, I have several rated at 3+ amps. I'll be glad to put one in your hands for free. Just pm or email me your address.

Randy
 
Please put a fuse in the input line, and it is a good idea to put a protection fuse in the output line.
Stacy
 
You can plug a guitar amp into it, Eddie Van Halen used it to get the "brown sound"! I think Stevie Ray used one too... very cool! I didn't know they had a non tube amp use, I've been looking for one for years.
 
Stacy, can you provide more details regarding the fuse on the input? Like I said, it currently has a three wire grounded outlet plu on the end of the cord. I'm not picturing where the fuse would go, unless I splice a fuse box into the current wire. And would a circuit breaker wire in the same manner provide the same benefits, or is there a reason for a fuse over a circuit breaker?
 
The circuit breaker at the fuse box will protect the wiring in the wall against an overload, but won't protect the variac against a short circuit.The circuit breaker is probably 20 amps. The variac has a power rating (look for the rating on the label) and it should be fused at that amount. Lets say it is rated at 1500 watts. That is 12.5 amps at 120 VAC. A 10 amp fuse in the input line will protect it from frying itself if the output becomes shorted. This fuse is normally a Buss type glass fuse, and can be added in-line or on the cabinet. If the variac is an older one, or the power cord was added by someone not versed in electronics, it may well not have such a fuse. If wired properly, it may well never matter, but if something is wired wrong ( and you sound unsure about such matters), the whole thing may go up in smoke and sparks.

The output side of the variac should have a similar fuse added to be rated at the maximum power drain required. If the variac is going to power a plating device that runs at 5 amps max , then a 5 amp fuse should be used to prevent the plating machine from being burned up if it has a short circuit in the wires.
Stacy
 
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When your making DC, you should use a capacitor. A Bridge rectifier basically flips the other alternation so you get two up humps instead of an up and down hump. If you add a cap, it fills in the spaces between the humps and smooths them out. If its a 140 volt output you need at least a 15000 microfarad at about 300 volts.

Yes you need a fuse in line as well.
 
Nice simple explanation, Frank. I like the humps.:D Made a picture in my head of the waveform. Been awhile since I built a power supply. Etcher coming up.
 
Check the output voltage carefully when first hooking it up, it is possible to wire most variable transformers to provide more than 120 volts out from 120 volts in. Without looking at the connections and a schematic, who knows how the last user left it wired.

Variac is still around. They have online schematics for their products, including discontinued/obsolete stuff.

While you are inside the Variac looking at the wiring conections, look also at the carbon brush. Make sure it stays in contact with the coil at all times as it sweeps around the coil. If it comes away from the coil the slightest bit adjust the spring, or if it is worn short, replace the brush. Once you place the Variac in service listen for arcing between the brush and the coil. If the brush is not in firm contact with the coil, there will be arcing which will pit the contact surface on the coil, and if you let it continue, it will arc through the coil and ruin it. Replacing a brush is less than $20, but the coil costs as much as a new Variac.
 
fourcornersrocks said:
You can plug a guitar amp into it, Eddie Van Halen used it to get the "brown sound"! I think Stevie Ray used one too... very cool! I didn't know they had a non tube amp use, I've been looking for one for years.
Click to expand...
Many a budding young guitarist in the late 70's and early 80's destroyed their amp because they thought that Eddie got his "brown sound" by cranking up the voltage with the Variac. What he actually did was drop the voltage to as low as 90 volts so that the amp would run out of steam even more quickly and he would get more "sag"
 
A Variac and a popcorn popper (old style West Bend's are good ones) make a temp. controlled green coffee bean roaster. If you can stand the fussing and the learning curve, home roasted coffee beats the heck out of just about every other coffee available. http://www.sweetmarias.com

Mike
 
You can get a 8 amp bridge rectifier. a DPDT switch and a small metal enclosure from Radio shack for a few bucks. Install the rectifier and the switch in the box. Run the output of the Variac to the AC legs of the rectifier and a set of wires from the ac legs to the outer legs on the switch. Run wires from the DC legs of the rectifier to the other set of outer legs on the switch. Then off the center legs of the switch connect wires that exit the box and terminate with alligator clips. You now have a variable output AC or DC supply. You can add a capacitor across the DC legs of the rectifier if you want smoother DC. Mark the switch as to AC or DC.

Dial it down to about 12v and use it for an etcher or crank it up to various voltages to get different colors when you anodize. You could also use it to do plating.
 
Something like this one...
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preview_gedc02230.jpg
 
Just thought I'd point out that the contact strip thingy in the middle with all the wires connected to it is totally unnecessary; it can easily be hooked up without it. I was just going by how the fella that did the video on the etcher, plater, anodizer did it in the video.
 
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