DC Welding

[John McGlynn]

I like the idea of adding a DC output to my stick welder, but the diodes cost $210 each here in Australia.

Does anyone have an address or even better a web page for the surplus diodes ($25ish) that were mentioned in the article?



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[John Stevenson]

Scrounge a couple of big truck alternators.
Get the diodes out the back and pair them up. Make sure you get each pair the same polarity then make a bridge rectifier out of the 8 you have.
Mount on two bloody great heat sinks and tap the DC power from the heat sinks.

Most of the truck diodes I have come across are rated at 70 odd amps each.

I did this a few years ago with an Oxford 140 amp oil filled welder.
I also fitted a small TiG torch and with argon and scratch starting it made a nice job on stainless and steel.

John S.

[ibewgypsie]

The inrush is what blows them, I was using 100 amp diodes and had to keep replacing them, If there is a northern tool store local. I priced a welder like my new one for less then 350.oo.. I got a hobart stickmate.
I used to however tig with the Dc supply from my lincoln mig welder. When I hooked the hi freqency box up I had to invert the leads thou. I opened up the side case and just made the connections, turned the gas and wire off and tied the trigger down, I was welding stainless less than 1/4 thou.
I got spoiled at work, I want a square wave machine now. With pedal..

[Randy]

These folks are worth a try:
http://www.cascadesurplus.com/
I got diodes for my welder from them quite cheaply several years ago.

[Ian B]

All of the stick welding that I've done has been AC (I have a 350 amp Lincoln box). Could some kind soul tell me the advantages of DC over AC (most of my welding involves 1" to 4" angle, 1/2" plate and the like, all mild steel).

Should I be sneaking up on unsuspecting trucks with a screwdriver to swipe their diodes?

Many thanks,

Ian

[Thrud]

Ian

Straight and reverse polarity DC have their place and is critcal in some applications. There are so many new rod types out there that employ one or more of the three (DC+, DC-, AC) for different applications.

AC for instance, breaks up the oxide layer on Aluminum and allows for a smoother weld. DC can be used to control the arc to concentrate the heat or spread it out.

I would suggest that you check out the local library and start reading some welding books. Unless you have a journeyman to teach you the fine points, you will have to learn them the hard way - reading & test welding pieces.

[mikem]

The Surplus Center in lincoln, nebraska has diodes. Sorry, but I can't find my catalog right now to give the phone #. Can look it up if you can't find the number. thanks--Mike.

[mikem]

The Surplus Center's phone is 800-488-3407. We are on US central daylight standard time. At this moment it is about 2:20pm. They also have a website "surpluscenter.com" My friend bought a set of 4 diodes for a total of around $125 US. Thanks--Mike.

[docsteve66]

when you buy those big diodes (for single phase you need four) try to get two straingt and two reverse. That way you can screw mount both sets on two heat sinks. Insulae both heat sinks and be sure they do not touch. Make a bridge configuration hook the welding leads ot the heat sinks.

The diodes run much cooler mounted that way. Add a jack for the ground wire so you can reverse polarity at will. And you need both reverse and straight polarity, especially for overhead welding. Rod's carton will give reccommended polarity for each rod.

I tried 65 amp auto alternator diodes in a home made high amperage battery charger. the diodes were mounted in the heat sink used in the alternator. The fan was unablew to keep the doides cool. so RR is right, use a massive heat sink, with a fan if possible. My charger was builtfrom a microwave transformer rewound with # 8 wire i think. 1500 watts at 12 volts is about 120 amps. If you use automobile diodes, you will have (on USAcars) 6 diodes (the alternators are 3 phase) two of them do you no good on single phase and since they are actually in series on each halfcycle you should keep the current below theraed out put, The alternator spins fast and has a large an sucking ait over the diodes- andthey need the cooling.

[wierdscience]

You could also look for a discarded electric lift truck charger lots of diodes and other goodies.