(7) Zero to 132 Volts AC or DC !




About: Been To:1) All 50 states 2) Guam 3) Adak 4) Hawai'i, Mo Bettah. The only good thing about snow is that it goes away...Would that it never comes.

I was walking home with my wife one day after lunch in one of the many Asian restaurants we have in Oahu.
Walking is a good thing.
Gets your heart working harder, you break a sweat, and you lose some weight you did not need to lug around in the first place.
While Hawai'i is a very beautiful place, we have many shopping carts parked around the island filled with garbage.
Nobody really knows who fills up the carts, but there they are beckoning the attention passers by.
Sometimes they are way too gross to bother with.
And then there are the times when there is a little gem just sitting there begging to be claimed..................

I had found a piece of electronics lab equipment. A variable bench power supply with a giant Isolation Transformer in it.
The thing was covered in oil, water, and other forms of grunge you would not want to get covered in.

After bringing the thing home I hated to even touch the thing, it was so dirty and greasy.
So I put it into the tub and got busy with a screw driver.
I removed the sides as this was where all the screws were that held it together.
The top fell off when the sides were removed.
My hands were filthy.
I was grossed out.

When I set the unit on its feet my jaw dropped.
There sitting before me was an Auto-Transformer looking as new as the day it was made.
Also included was a meter that had four scales with LED's to indicate the scale being used, a nice bezel for the meter that needs painting, and various switches with cement resistors and diodes.
No real heavy electronic circuits one would have to be an engineer to figure out.

The heavy transformer it came with was cooked. Covered with oil and dirt and water, I was not gonna touch it.
Transformer went to a re-cycler.

Step 1: And Parts Is Parts

Ground Score:
One Staco Energy Products Type 291 Auto-Transformer for free. Worth +/-,   $150
One Dixson, inc. Meter with 4 scales and 4 LED indicators, 1 for each scale.

Junk Box:
0 to 150 Volt DC meter
4 gang DC binding posts

Lauan plywood 12"x18"x3/8"
3/4" plywood

9/7/11 I went to a Ham Radio flea market over the weekend and found 2 more
           Variable Transformers that were Motorized for a dollar each !

Step 2: Panel and Box

This is a basic box made from 3/4" plywood. The sides are 12"x18".
The Lauan panel is screwed to the edges of the 3/4" plywood with 1-1/4 drywall screws.
Glue it if you want, I don't because if I need to make the box deeper than 6", I want to be able
to remove the panel without destroying it.

Various holes needed to be cut to accommodate the parts I want to mount and use.
I cut the holes with an Exacto Knife because I don't have saws to do the job. I like it better
because I can get a better fit for the parts.

Step 3: Panel Nomenclature

See notes on picture........

So far this thing only takes the 115VAC out of the wall socket and transforms it 0-115VDC with the use of a full wave rectifier after the transformer. The variable DC power goes to the Red and Black power taps.
It also transforms 115VAC from 0-132VAC [+/-] and sends it to the AC outlet to the left of the DC power taps.

The Auto Transformer is rated at 4 Amps so until I get an Amp meter on this thing I have to watch what I plug in. On another identical transformer I plugged in an electric iron and heard the crackling of transformer windings. Fortunately I was able to pull the plug in time to save it. The Ammeter got Pegged on that one.

The big 0-150VAC meter still needs a resistor to keep it from smoking the inside of its casing. Smoked meter is not very good unless you add salt and pepper. This meter will measure the voltage at the AC outlet.

The dark AC outlet will eventually have its own ammeter.

The Lighted Switch has a Ne2 Neon bulb in it to indicate AC on to the transformer.

Step 4: Schematic

Schematic is done on TinyCad.com it is a free CAD program.

Everything I used in this little project, I Found.



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    9 Discussions


    5 years ago on Introduction

    Nice but a small quibble:

    An isolation transformer is often a safety feature. ( see Test Gear: The Isolation Transformer from Salvage https://www.instructables.com/id/Test-Gear-The-Iso... )

    Your transformer is a autotransformer, and shares a connection in common with the mains which can be dangerous for that reason. I would use this with care and:

    only use a 3 prong plug

    consider a indicator between ground and neutral to indicate danger

    add a true isolation transformer ( probably a bit expensive )


    Reply 7 years ago on Introduction

    Thanks pfred2.
    All told I found one and purchased two more @ $1.00 each.
    The dollar ones were motorized with sixty rpm clock motors so I also got some nice inch and a half standoffs out of the deal.
    There is something to be said for Amateur Radio Flea Markets.


    Reply 7 years ago on Introduction

    I'd imagine if someone decided they didn't want a Variac anymore the things are little boat anchors. So they'd let them go for cheap instead of carrying them around like the stones that they are. I do a lot of sales and stuff but I never seem to run across them. I'd like to get a higher current one than the one i have now, but I guess the one I have now is doing what I need it to do. I've both input and output fused on it, so if I try to draw too much one should blow I hope!


    Reply 7 years ago on Introduction

    Gotta get the caps first. Under the small white meter there are two binding posts.
    The red and black on the right are un-filtered DC and the other two will be filtered with caps. I still need a resistor for the bigger meter so I don't smoke it.


    7 years ago

    This is a great Instructable, but you need to add a main image of the final project to the intro step. Please do that, and leave me a message when you have so that we can publish your work.