the welder-o-doom
an arc welder built completely from assorted junk that actually works and has produced genuine artifacts.

by Ralph Klimek Copyleft 2007 based on work done sometime around 1992
copyleft. Copying is permitted but not recommended

The welder-o-doom was created when some twenty years ago my friend Dave Stuart VK3ASE gave me the much coveted "melt 'formers". This extraordinary device was purchased for one dollar from "the Curly wharehouse" in Wallan, which was sharing a pasture with some moo cows.  It served its initial purpose as a telephone exchange battery rectifier transformer, then found its second life in melting things and testing consumer durables to destruction.  Having tired of this, it found its third life in my garage waiting for some time and inspiration. It then grew up and got a job!

Inspiration finally arrived when my first child appeared and we needed a new front gate to keep our toddler from testing her luck with the traffic .  I looked carefully at this monsterous transfomer and thought that it would make the heart of a practical welder.  Its secondary voltage was 80 volts which is just a bit too high, 50 volts is the ideal consumeable electrode arc welder open circuit voltage. There was no doubt about the secondary, it could source about 60 to 100 amps continuosly. To get the secondary voltage down I wound extra turns on both the primary and secondary to oppose the voltage and this gave me 55 volts which is ideal.  I did not want to disassemble the frame and core and unwind the primary. The primary winding was wound over the secondary and this precluded simply removing secondary turns to get the voltage down. Besides that the secondary was wound with material resembling copper bar stock and unwinding this would require more physical strength than I possess.

A welder must run from a constant current source and for a AC welder this is done with a moveable core inductor. I had no such thing, but I did have a couple of extraordinary heavy DC iron core chokes from an old mainframe power supply.  I had to experiment a bit with the air gap to get the right inductance, but the final result was a functional welding choke.

An electrode holder was constructed from brass and aluminium 3/4inch rod and insulated with PVC pipe. After a couple of interations with an electrode, I finally got the choke right. I then went out a bought a proper welders mask,  my eyes had got very sore watching the arc, just for a few minutes whilst testing to see even if my concept would work.  The heavy duty cables were all recovered from a scrapped mainframe computer DC power supply lines. 200A cable is hard to get. I notice that it is now possible to get 4 gauge cable in handyman lengths sold as 12volt garden light cable. It also make a cheap substitute for loudspeaker monster cable.

In practice with the the fixed choke I can use 2.5mm and 2.0mm electrodes. There is not quite enough current to light up a 3.0mm electrode.

The welder has proved to be extremely usefull, I never would have bought a real one untill I had tried this.

The construction practice of mine requires me to use it when there are no bystanders or looken-peepers because there are bare electrical terminals at mains potential directly exposed.  The device is worthy of Baron Frankenstein's laboratory and probably should go and stay there!

I had a dedicated 15A heavy duty power feed installed to the garage to feed this monster.  I have found that using a spot light to illuminate the work really helps. It stops the "welders' salute", whereby you must allways flip up the visor to see where the elecctrode is in relation to the work. The GPO outlet on top is where the spot light gets plugged in.  There is also a heavy duty metal oxide varistor on the primary winding to absorb the mighty inductive surges this thing creates.  The transformer magnetizing current is about half an amp, so a power factor correction capacitor will help just a bit.

I installed a couple of ferrite suppressor chokes in series with the secondary current near the handle.  When using it to construct the gate I discovered that my right arm had become very hot. It had turned bright red and wasnt feeling great. The reason was the very large RF currents being induced by the arc were being shunted by my hand capacitance and heating up me, (as in radio diathermy)  The suppressor chokes stopped this unpleaseant effect and permits my neighbours to watch TV whilst I melt metal.

It took a little while to learn to make good quality welds with this device as just about everything is text book wrong with it. The lack of good current control is its main deficiency.

I am no longer afraid of steel as a constructional material. It used to be hard to cut, get and angle grinder, it was hard to drill, get cobalt tool steel drills and it used to be hard to join so get a welder! Where I used to see a pile of junk, these days I just see raw material waiting to be cut and welded!

I would not bother doing this thing again, these days you can get an adequate handyman grade welder for just over $100. When I constructed this monster an entry level welder cost about $600.

But does it work ?  YES!

actual artifacts manufactured with the welder o' doom

The transformer is mounted on heavy duty 100kg rated castors. The transformer weighs about 100kg. Notice the bare tap terminals, they are at mains potential. Not recommended for children under three! Fully approved by not one single electrical authority..anywhere!

I can select from one of two chokes.  The GPO outlet on the top is to allow me to plug in a spot light to facilitate the work.

Extra primary and secondary turns were wound on to drop the secondary voltage to 50 volts

Homemade electrode holder

Standing next to a meter stick


please dont try this at home!

imgp4675-drillshaft.jpgA method for the repair of a fractured high valued drill bit without the use of precision tools.

mod record  Wed May 27 18:58:32 EST 2009 added email sig
Mon Nov 23 18:55:25 EST 2009 added linkto drillbit article