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!
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!
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
