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post #1 of (permalink) Old 06-02-2001, 09:54 PM Thread Starter
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On board welder instructions

I found a link to instructions for converting an alternator to a welder. I did a cut and paste below. I don't think the ASCII art will cut and paste correctly, so if you are interested, you will have to use the link to get the art work.This sounds like a good way to go about building an on board welder. It is a cut and paste from
http://reality.sgi.com/rogerb/Welding/alternator.txt No WWW is in the address.


Some years ago my economic status was on the tight side and I had need
of the use of an arc welder. A friend of mine had a portable DC welder
manufactured by the Scott company, which he loaned to me. It was very
interesting, as it was quite small and looked like a portable standby
generator minus the roll cradle.

It certainly wasn't the gas driven Lincoln arc welders that were common
to contractors in that day (late 70s). Those monstrosities took up the
better part of the bed of a full size pick-up truck The unit was
advertised at 125 amps DC, and it was powered by an 8 horsepower Briggs
and Stratton engine. It weighed less than 100 lbs, and it could be
carried by one person, though it was it bit on the awkward side.
Mounted on the engine was a small box about 10 inches on a side with a
potentiometer and Miller brand type welding lead connectors. What was
in that small box that changed 8 Briggs and Stratton horsepower into
120 amps of DC welding power? I really wanted to know that secret.

Despite its diminutive stature I knew that you could actually weld with
it as a contractor at work had one and I had personally observed it

During the course of my using it, naturally, the belt broke. Of course
this was no ordinary belt, it was only about 1/4 inch wide instead of
the 1/2 inch or more of a typical "v" belt. I finally tracked down the
Scott dealer, as this happened to be a quasi holiday, (Christmas eve
day and Christmas was on a Saturday). The manager just happened to be
working at his store/shop and while he was no longer the Scott welder
dealer, he did have some parts, ie,. the belt.

I drove over to this place and found a small assembly shop, that was
making, you guessed it, portable DC welders of the Scott Welder type.
Being the curious type I not only purchased a belt, but got a tour of
the factory and found out what was in that box. Would you believe a
Delco alternator, some diodes, heat sinks, and a small controller
circuit. The owner explained how after he lost the Scott dealership,
how he decided to make his own. He did some reverse engineering and a
lot of messing around in his garage and brewed up his design which was
called an APACHE welder.

Anyway he bought Delco Alternators from GM with the stators not wound.
He had worked out the appropriate windings and hired people to wind
them for his operation. He explained the control circuit and even how
he used the magneto of the engine to help the self-excitation process
get started.

Hot dog, I now knew how to build a welder. I had the engine and Chief
auto parts had lots of Delco alternators. I bought a rebuilt 60 amp
model, no built in regulator, and took it home. After tearing it apart,
expecting to find fairly small wire in the stator, I was surprised to
find that it looked like the same size wire the SCOTT guy was winding
into his alternators. Great, I won't bother ripping that stuff out,
I'll just slide some 32 gauge stuff in between for my field windings,
throw in a bunch of rectifiers, pots, capacitors, and wahhla! I will
have a welder.

Well the long and short of it is, that you can make a welder this way.
It wasn't quite as easy as I thought it would be, but I learned a lot
about 3 phase power, Y connected and Delta connected, transformer
effects, and bunch of other stuff. It wasn't entirely cheap either
although my home brew machine was less than 1/2 of a new one, even if I
had went out and purchased a new engine which I didn't. A real good
scrounger could probably do this for less than $200 engine included.
The engine is the single most expensive item.

Delco alternators from the 60s and 70s without the built in regulator
are the most suitable. It needs to be at least the 60 amp size or
larger. You could use one of the newer integral mounted regulators,
but in the past they were more expensive. That may no longer be true.
I don't think Chrysler alternators will work as they are already delta
connected where as the Delco ones are "Y" connected. You need the Delta

A 60 amp Delco alternator is capable of 110-120 amps if it is
reconnected in a Delta configuration. They come "Y" connected.
Basically you buy the alternator, take it apart, throw out the diodes
and the regulator if it has one. Then find where the 3 phases of the
stator are tied together and undo that connection. In a "Y"
connection, one end of each of the 3 phases is connected together. In
a "Delta" connection, the 2 ends of 2 phases are tied together. If
the windings are drawn as a series of loops along a straight line, the
3 windings form the sides of a triangle, which is the symbol for the
Greek letter delta. The "Y" connection schematically looks like a

Changing this configuration will lower the output voltage and raise the
current by a factor of 1.732 (square root of 3). This will give you an
open circuit voltage of about 50-60 volts and about 20 volts when you
are welding and maximum continuous output of 104 amps (60 x 1.732).
The math and theory behind the actions of a 3 phase circuit can be
rather daunting. If the reader is so inclined there are numerous books
around that will explain far better than I ever could. Suffice to say
it works and certainly isn't new. Almost all of the power grid in the
US uses 3 phase circuitry. Your house typically has only one phase
hooked up to it.

You can safely overdrive the system to 125 amps if you keep the duty
cycle down. I have never have had to stop and let the unit cool down
in my use of it. The time required to change rods and restart would
probably be sufficient to prevent melt down of the windings at 125

The alternator has to spin a bunch to do this. You need about a 3 to 1
increase in speed to do this. This means at 3600 rpm engine speed, the
alternator is doing about 11,000 rpm. Not to worry. Check out a small
block Chevy. It depends on the gear ratio, but if you were blasting
down the freeway in the old days (75 mph) the Chevy motor was doing
2500-3000 rpm. The crankshaft pulley is about the size that you are
looking for, which means that the alternator is buzzing along at 9000
or so rpm. Stomp on it and passing gear will get you well above the
11,000 that your welder is running at. So the engineers at GM have
already considered this form of abuse for you.

The existing diodes are too small, so they get canned. You need at
least 25 amp 200 volt PIV diodes. Get 3, stud-to-anode and 3
stud-to-cathode. Fortunately these are fairly cheap, few bucks, bigger
is better, but anything over 50 amps is overkill.

You need 2 heat sinks with plenty of fins like you see in large audio
amplifiers. You mount 3 of the diodes of one polarity on one of the
heat sinks and the other 3 on the other heat sink. If you don't
insulate the diodes from the heat sinks then the heat sinks become a
common conductor for the 3 diodes and one is ( ) and the other (-).
This assumes that the two heat sinks are electrically insulated from
each other. If you follow this suggestion then you must follow the
suggestion to buy the diodes as cathode to stud and anode to stud
types. You can do it with all one type but it is more difficult and
messier as a connection must now be made to the stud portions of the
diodes and you need to electrically isolate the diodes from the heat

Electrically isolate the heat sinks from the cabinet by mounting them
on isolation shock mounts. These typically come either with threaded
studs, or threaded inserts. I used ones that were about an inch in
diameter and had 1/4-20 threaded studs on them. Connect your welding
leads to the heat sinks. One is positive, the other negative. I
bought some female connectors at a welding shop. They sometimes
referred to as Miller style. They are a tapered brass rods that mate
with a tapered sockets. I mounted these sockets on the side so that my
welding cables were not permanent with the welder. The sockets come
and red and black so that you can keep the polarity correct.

You can get the shock mounts from Grangers. The diodes form factor is a
D0-5 shape and most electrical/electronic supply houses carry them. A
1N1186 or 1N1188 should work fine.

For excitation I found that the self excitation route was a pain, so I
obtained a small permanent magnet motor. You need 3 amps at 16 volts.
Burdens surplus catalog has bunches of them. I used a vacuum cleaner
belts to drive the motor and made pulleys to give about a 2 to 1
increase in the crankshaft speed. This ratio will vary depending on
what kind of motor you end up buying, but the permanent magnet motor
will have to be driven at least the rated nameplate speed to get
anywhere near the maximum nameplate current rating.

A simple power rheostat will suffice to control the field although a
simple power transistor circuit out of a Radio Shack book is a nice
touch and it is what I evolved the circuit to.

I made a small box about 12 inches on a side and 6 inches deep. On one
of the 12x12 sides I cut a hole to match the shape of the alternator.
Make the other 12x12 a removable door. The older GM alternators have 4
screws to hold them together. I removed the screws and made the hole in
the box to fit over the end of the alternator with appropriate bumps to
match the casing. I bored holes in the bumps to match where the screws
went. Then I put the screws back in and now I had an alternator with a
box on its back side. I mounted the heat sinks on rubber shock mounts
which are electrical insulators and help protect the diodes from all
the engine vibrations. If you drill some holes in the cover and on the
bottom under the heat sinks, the fan on the alternator will now draw
air over the heat sinks and keep the whole thing cool.

I constructed a mounting bracket that bolted to the gasoline engine.
The alternator sits above the crankshaft, although it could be mounted
on the side. Alternators are not direction sensitive when it comes to
generating electricity. However, the cooling fan may not be as
efficient when operated in a reverse direction but the effect would
probably not be harmful. Also the brushed are mounted off to one side
for the direction of rotation. There are many approaches to mounting
the alternator and it is a matter of preference and what kind of engine
you mount it on.

The welder will run 3/32 rod quite nicely and if you push it, 1/8". It
is a little hard to get the arc started and an arc stabilizer from
Burdens would probably help.

I still have mine and I made a second one for my brother. I went so
far as to make a foot control for it and used it with a tig torch.
Works pretty good. I haven't fried any diodes yet.

1015 West "O" Street
P.O. Box 82209
Lincoln, Ne 68501-2209

"Honestly, I didn't lift the Jeep.
I,um..ah..lowered the axles"
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