AC to DC welder??

[mudneck]

I've been asked by a friend if it would be possilbe to change an AC welder from and AC output to a DC output and i'm pretty sure it can be done, but my question is how exactly and how much is this going to cost my friend??

any info on this would help

mudneck

[GregH]

mudneck,

You sure can.
You will need a 150 amp selenium rectifier for the a/c to d/c conversion.
I believe modern dc welders use capacitors as well to smooth out the arc but I am not sure.
I remember years ago these rectifiers were available in surplus shops but I haven't seen them in quite awhile.

I've been kinda looking for one to try it myself.

[mudneck]

Thank you very much I'll search for ane and if i find them i'll let you know.

mudneck

[chuckinnc]

I tried this, bought 4 large surplus diodes, made a bridge rectifier for the old
ac welder but i couldnt see any difference. A welder repair tech told me you
had to have a inductor (coil) in line with one lead or the pulsating DC would
act as ac.
I found a old 480v 3 phase ac/dc welder in a junkyard, i took out a inductor
and installed it in mine, wow what a difference a coil can make.

[GWIZ]

I been planning to make a Converter for a long time but just cant find the time, now that I have a AC/DC welder I may not.
=========================================
This is what I came up with un-tested, rough plans.
If your not familiar with electrical Safety have someone with knowledge check your work for Safety before connecting it to your welder.
==========================================
Wow.
I haven't heard the word Selenium for 25 years.
The old selenium had a large voltage drop maybe 20 volts.
an other words if your welders output is 50 volts it would be reduced to 30 volts.
Selenium rectifiers are no longer the choice.

They use general purpose diodes or you can use the term rectifier diodes, power diodes.
The standard diodes range from 0.7 to 1.37 voltage drop.
The diodes must be rated above the amperage and voltage rating that you intend to run

You would use 4 diodes configured in what is called a full wave rectifier bridge.
that would get the raw DC output.
welding with just the 4 diodes.The arc maybe unstable,
The raw DC has a voltage ripple, they add a reactor on the output side of the diodes to lessen the ripple.
----------------------------
This reactor has an iron core and about 45 turns of copper wire wrapped around the iron (about 47 feet of #4 wire)

The iron core is about 2" square 6" long
The core is made up of laminate sheets of low grade iron/steel 1/32" thick x 2" x 6" long, 64 pieces should make a 2"sq core.

You would wrap the core with some heat proof tape maybe fiber glass tape, a 1/16" thick minimum layer over the core then say 24 turns of 4 gauge wire then 21 turns on top of the 24 continuing back to the start.
Use some string to secure the ends.

4 gauge magnetic wire, its solid copper wire coated with varnish used for winding coils.

I was thinking of using a 2" dia round bar of steel 6" long but I don't know how well it will work.
you may try 4 ga copper THHN insulated stranded house wire if you keep to a 20% duty cycle, I don't know if the insulation will burn off.
Just a note: do NOT use stainless steel for the core.
If you go 200 amps you may need # 2 copper wire and a longer iron core.
and a larger heat sink for the diodes.
-------------------------------------------------------
I have a 230ac/140dc century welder that uses two diodes and only has an reactor, No capacitor.
the transformer configuration on the century welder allows the use of only two diodes.
It appears the MIG welders have capacitors, but the home use stick welders don't.

I would not advise the use of a capacitor without a reactor, the capacitor may over heat.

--------------------------------
search the net for " full wave rectifier bridge"
Go to millers web site and down load the manual for the thunder bolt AC/DC stick welder you will see the diodes and reactor coil
I think miller calls it a stabilizer.
--------------------------------
Diodes rated at 150 amps 1200 volts go for about $10.00 each.
the diodes come in two different polarities
you would get two diodes the same polarity and two the opposite polarity.
Two diodes with the same polarity mounted on one large aluminum heat sink.
the second two mounted on the other heat sink
Two heat sinks minimum 1/4" x 6"x 6". you may need to add a fan.
Mount the diodes equally spaced, each one will get hot.

......... = Blank
--------- = wire


____________________________............................................_____________________________
HEAT SINK 1....................................................................................................HEAT SINK 2


................+diode---------------wire--------------AC from welder-----------------wire----------diode -

Plus side of diodes mounted on......................................................... minus side of diodes mount
this heat sink.....................................................................................on this heat sink.

................+diode----------------wire-------------AC from welder------------wire---------------diode -


wire from reactor screwed to.........................................................Output to minus welding cable
this heat sink.....................................................................................screwed to this heat sink
____________O______________].........................................[___________O________________
.........................]...............................................................................................[
.........................]...............................................................................................[
.........................]...............................................................................................[ minus CABLE
_____________]_____________...................................................................
line one screwed to heat sink above


REACTOR

...................Line 2 from reactor------------Cable------------------Output from reactor to PLUS CABLE for welding
___________________________]


**

[GregH]

GWIZ,

Thanks for the info.

Ya, the rectifiers I had seen awhile back were from a surplus place.
Makes sense they would be selling yesterday's technology.
I knew nothing more about it that their pitch to "convert your ac welder to dc with these selenium rectifiers".

Glad I waited untill they invented the internet before buying one! ;)
I think I'll just wait untill a deal on a ac/dc machine comes along.