AC to DC welder??

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  #1  
Old 07-24-05, 02:17 PM
mudneck
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Question AC to DC welder??

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
 
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Old 07-24-05, 04:42 PM
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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.
 
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Old 07-25-05, 05:58 PM
mudneck
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thanx

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

mudneck
 
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Old 07-26-05, 02:02 PM
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you will need a good inductor

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.
 
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Old 07-26-05, 02:40 PM
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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
___________________________]


**
 
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Old 07-26-05, 04:21 PM
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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.
 
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Old 04-10-10, 07:26 PM
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Where to get diode parts cheap for welder

Go to a junk yard that lets you rummage through the motor and welder section of the yard. I found a nice diode bridge unit with plate heat sinks and mount assembly for the diodes. They charged me $3.00. They charged about 15 cents a lb, no matter what street value is. I also got a polarity switch for a dollar. I plan on installing the bridge some day soon and also using the polarity switch so i can do dc reverse welding an not have to use plug in lead wires that have to be plug in and out every time you reverse polarity. Just flip the switch. I bought an old welder for 17 dollars , fixed it and sold it for what i paid to a friend. It just had a broken wire lead to a plug in. I also just acquired a Lincoln 225 for about the same price, but the welding leads where cut off and no 220 plug in connector. Bought all new ones and replaced it all and sanded and painted it red. Looks like new. Made a few welding passes and it welds nice. I still want to put a reactor coil and dc bridge and polarity switch on it.
 
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Old 04-19-10, 06:50 AM
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Yes, it can be done but in most cases as a practical matter its not worth it unless its a real hobby or one has the free parts and experience to do it. Ideally is to sell the existing welder and buy one set up to go. Even a new Hobart Stickmate XL can be had for a touch over 400$, see used DC machines in the 200 range.
These little machines are really good, great arc that nearly matches up with the best of them, great values.
 
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Old 04-28-10, 08:13 PM
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Originally Posted by popeyeus View Post
Go to a junk yard that lets you rummage through the motor and welder section of the yard. I found a nice diode bridge unit with plate heat sinks and mount assembly for the diodes. They charged me $3.00. They charged about 15 cents a lb, no matter what street value is. I also got a polarity switch for a dollar. I plan on installing the bridge some day soon and also using the polarity switch so i can do dc reverse welding an not have to use plug in lead wires that have to be plug in and out every time you reverse polarity. Just flip the switch. I bought an old welder for 17 dollars , fixed it and sold it for what i paid to a friend. It just had a broken wire lead to a plug in. I also just acquired a Lincoln 225 for about the same price, but the welding leads where cut off and no 220 plug in connector. Bought all new ones and replaced it all and sanded and painted it red. Looks like new. Made a few welding passes and it welds nice. I still want to put a reactor coil and dc bridge and polarity switch on it.
Here are pictures of a lincoln i am converting to dc.
Picasa Web Albums - 11161594099760881... - welder images
 
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Old 05-01-10, 08:06 PM
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dc mod to ac lincoln welder

Just completed today. Finally got around to connecting up all the parts for a dc conversion of a 225S lincoln ac welder. I welded with it, but am still testing it out. One issue I may have is that i put 3 capacitors in parrallel before the reactor coil or choke coil. I am worried about the peak voltage I am seeing. It is about 115 volts DC. It makes for easy starts, but is high enough to get a bad shock from I believe. I would like to know what commercial welders have for a op en voltage on dc for welding. I may have to just use the reactor coil by it self, so I get the rms voltage of about 80 volts dc. I also have a ac capacitor that I can put on the transformer primary to improve the power factor. I also installed a polarity switch in it.
Here are some of the picture before I started connecting. I will take more picture soon and post them. Diodes are running cool, even at 130 amps that i tested it at. I still have to make a screened enclosure for the diode assembly and put a fan on it. check out picture link below. popeyeus

Picasa Web Albums - 11161594099760881... - welder images
 
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Old 05-05-10, 07:08 PM
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Picasa Web Albums - 11161594099760881... - Lincoln 225S ...

Above is the link to the wired ac to dc conversion of the lincoln 225 S welder
 
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Old 07-09-10, 11:17 PM
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I'm about to do the same conversion.

I've recently found an eBay seller that has high amperage (250A & 300A) rectifier bridges w/ heatsink for about $80-$90

250A 1000V SQL250A 3 Phase Diode Bridge Rectifier - eBay
300A 1000V SQL300A 3 Phase Diode Bridge Rectifier - eBay

They're 3 phase, but all we would need to do is wire just two of the three legs available (and have an unused leg in case one ever blows out - bonus!!).

I think using one of these prebuilt units would be better for packing this mod into a smaller space (like the cubby hole in the top of the AC-225), as opposed to the gigantic DIY rectifier bridges I've seen bolted to the back of the machine. Just install a fan to this unit and we're good.

Don't get me wrong, I'm not dogging on the DIY version of the diode bridge. All I'm saying is that they are huge in comparison to newer prebuilt units.

========================

I'm still looking for info on building the "inductor" (which you guys are calling a "reactor".

I don't want to just go hap-hazardly wrapping some wire around a core without fully knowing it will end in the desired smoothing of the waveform (for 48V @ 30-225A).

Any solid info on inductor design would be a welcome addition to this topic.

Thanks.
 
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