View Full Version : Diodes for welder

Herb W
10-15-2003, 11:38 PM
I'd like to add dc capability to my ac welder as others have done / are doing.

I came across some diodes in the surplus section at Princess Auto today and am hoping that someone can tell me if they're suitable for the job.

There are two sizes and the store has them labelled only as "large h/d diodes with gate.

The larger size (only 3 of these) are GE and each has a different No.

GE 8493623 U505
********* U610
********* U523

The smaller ones - several of these:

GE 8493622 U529
********* U434
(didn't record the second series of numbers on all of the smaller ones bur most seemed to be one or the other of the above)

Compared to the ones I've seen in the pictures here on the board, these look similar except that they have two small wires along with the heavy cable. Is this to do with the 'gate' and what's the significance?

Can anyone ID these or point me to a site with information on them?

[This message has been edited by Herb W (edited 10-15-2003).]

10-15-2003, 11:47 PM
With the small wires.. I'd say you got SCR's or Silicon controlled rectifiers..

Diodes just have a in and out.. usually a stud mount on one end and a terminal on the other for the large ones.

I got a question, a couple of the dc welders I have junked has had a capacitor, how much does this help? Not all of them, just some of the welders. I remember a old craftsman welder that tig'ed really good, it had one.

I have one more set of diodes, but money is in transit for them. The good thing about getting these outa these welders was that they had the heat sink already on them.


10-15-2003, 11:56 PM
Those are General Electric thyristors. They are what is also known as a "solid state relay" used for full phase control of ac loads. The GE 8493623 is rated at 250 amps, 1200 volts.

I couldn't find the spec for the smaller unit but is surely less. Trying to find stuff at GE's web site is hopeless.

Not suitable for DC rectification of a welder.

10-15-2003, 11:58 PM

GAEwen posted a week or so back.. they had some cheap diodes listed with a supplier. I think about 30 a piece.. you need 4 to make a bridge.

retrieved it for you..

posted 10-09-2003 11:15 AM Click Here to See the Profile for Evan Click Here to Email Evan Edit/Delete Message Reply w/Quote If you can avoid do not send stuff to Canada via a courier service. It will have to be cleared by a customs broker with attendant expensive charges. The best is to send parcel post via US Postal Service.

As for the diodes see here for $31.38US


[This message has been edited by ibewgypsie (edited 10-16-2003).]

10-16-2003, 12:00 AM

I put a capacitor in my DC converter. Under no load it charges up to the full wave voltage provide much higher voltage for striking the arc and a momentary extra current surge to initiate it. Unless the sucker is honking huge it isn't going to make much difference when actually welding. Makes the welder more dangerous, DC kills much better, especially filtered DC.

Herb W
10-16-2003, 12:03 AM
Thanks guys!

I'll go back and read that thread.

That was fast...thanks again David

[This message has been edited by Herb W (edited 10-16-2003).]

10-16-2003, 12:08 AM

Actually, before I'd put another hundred into the welder you have... I'd look for a square wave machine. We bought several at auction recently for less then 50 each.

I do not have any for sale at the moment. Sorry friend.. But I will keep my eyes open for more.. MUCH smoother burning rods.. Smooth sounds, steady beads..

We bought two plasma cutters for 60 each. After I had bought the 3 phase one for 250..

If you give me a week, I can probably find you some diodes much cheaper then the ad I posted before.. I was selling them to "US" HSM'ers for 35 plus postage.. what we had in the HUGE 3 phase welders each. I sold the welders then bought the diodes back. If I had of had the time to remove them myself, I could have shipped them for postage only.

Evan is pretty sharp on these things, and I am up to my hips in work at the moment.

Herb W
10-16-2003, 12:40 AM
Very kind of you David...no hurry though, I won't have time to work on this for a while anyway.

10-17-2003, 10:57 PM
Hey, I'm new to the board.
I have some experience with electricity and welders. It just so happend that when I was rummaging around today I found several diodes that would work for adding dc capebility to your welder. Contact me off list and I will see if i can send you some.
contact me at cinexero@yahoo.com

Herb W
10-18-2003, 12:10 AM
Hi Xero, welcome to the board!

You have mail...and thank you very much!

Herb W
10-18-2003, 01:36 AM
Ibe mentioned square wave welders, which got me to thinking...I've seen that term many times but I don't have a clue what it means.

So, a quick google search and...

A simple, basic explanation of square wave. (though it is in reference to a pipe welder)

Next, I went to the lincoln site to see which of the welders have sq wave. In single phase, looks like it's the stick/tig units.

Question: For stick welding just how much difference in performance & capability would there be between an ac/dc 'buzz box' and a sq wave stick/tig of comparable output?

10-18-2003, 02:35 AM

The link you provided really doesn't have any relation to small shop use. In the illustrated application the main reason for the system used is to minimise losses in transmission over long cable lengths. By rectifying to high voltage DC and then using a full wave chopper mechanism (mechanical rotating) near the work the losses are minimised and the chopper frequency can be whatever you want. This is a way to provide high frequency AC and reduce losses. They note that with 60 cycle it is not recommended to weld over 90 feet per minute. Never been able to exceed that, myself.

Seriously, by rectifying to DC and then using a high frequency chopper before the transformer, then rectifying again, you have high frequency pulsating DC. It greatly reduces transformer size and weight and produces a much smoother weld with stick. I was looking at a suitcase welder the other day at the local supplier. The thing fits in a small carry case. It is about 12x5x8. It runs from 110 or 220 and will run up to 200 amps on 220. This is basically the same principle as a switching power supply. Small, light and efficient.

10-18-2003, 04:22 AM
Lunch box sized welders that outperform large 100 pound welders.

Really, Hot start blows the melted glass off a 7018 rod. Has a adjustment for it.

Right now the lil bitty welders I used at Sequoah were about 750$.. The ones we bought were the previous generationa and larger. but work equally well. Really consistient sound coming off a square wave welder. Really consistient beads being laid.

THE best ones say, "CC CV" constant current, constant voltage. have a actual current regulator that takes over once the arc is started. Neat new stuff that helps the OLD MAN In me weld as well as I used to..

NOW, if the new welders would just stop this old man from welding right next to the crack. Beautiful beads, in the wrong place.. HA..


10-18-2003, 08:48 AM

ain't it a bitch?

i welded pipe for a lot of years. used to be i could hit the groove pretty easy. can't see good enough any more.

also don't drag leads around near as easy as i used to. oh well.

hope the new shop is coming along well. i spent too many years being self employed ot want to do it again. retirement is where it's at. contrary to popular belief, you don't get to do what you want to do, but you aren't wading around in knee deep mud either. life has some compensations.

if you run across some more diodes, i would be interested in them. i kind of dropped the ball last time around. i do that more and more as time passes.

you talking about that big building has got me thinking about a new shop again. anther problem with retirement is lack of $$$$.

i have some motor control questions if you have the time to mess with it. email me [billr@tvec.net] if you think you do. be warned i am ignorant about this and need pictures and lots of guidance. i will understand if your time is too limited. got to make a living first.

good luck with shop, etc. wish i had your energy.

happy weekend.

10-18-2003, 09:46 AM

Carrying the 20 pound square wave welder and a 110 drop cord you only have about 6 feet of lead. they auto switch voltages. Plug it into whatever and it is happy.

It will burn 1/8" rods max thou on 220. Usually around the shop I use that or less...

Send me your question, expect me to be honest thou. If it is something best left to expert help, or something I think might hurt
you I'll tell you in so many words.


Herb W
10-18-2003, 09:22 PM
When I did the google search, I was just looking for a basic explanation of what square wave is. The site that I linked to was the first that came up and did provide what I was looking for. I wasn't particularly concerned with the pipe welding stuff...just skimmed through that and read the parts pertaining to sq. wave theory. I posted the link thinking that others would do the same...or not http://bbs.homeshopmachinist.net//wink.gif

Ibe, when you start to run beads in the wrong place, that's when you know you can't put off cleaning that lens any longer - been there...

10-19-2003, 12:17 AM
Yeah Herb,

That is what I figured. The modern square wave units are called that because square wave switching has minimal losses. For welding it also has the advantage of creating a bunch of higher harmonics since a square wave is composed of an infinte series of higher order even harmonics. With a high frequency transformer this helps with arc starting and holding. Current may be controlled by modifying the duty cycle of the square wave.

10-19-2003, 09:24 AM

You sure use a lot of large words sometimes to say.. "It works better"

Ha.. Ha..

Actually smoother and easier starting is the words I like to describe the new welders. Watching someone try to start a damp and cold 7018 is a trip. Stick, cuss,, stick... cuss.. splatter, cuss, hiss.. cuss.. stick... when the rod finally dries out it'll go..

I used to watch the pro's break all the flux off a rod and weld with it as well as I can with a dry and warm rod. I watched one guy bend his rods around in a loop to weld behind a pipe. I guess all that comes with experience.. years of it everyday welding.

This one is pricy, got descriptions thou..

Less at the moment..

Actually, neither of these are like the one I used at Sequoah nuclear plant. They were cheaper and smaller..

I got 3 more in the shop, got to check them out, probably "480 only" volt single phase thou.. OLD..


[This message has been edited by ibewgypsie (edited 10-19-2003).]

10-19-2003, 10:47 AM

I store my rod by the furnace downstairs. 7018 lo hi has a flux coating that is especially low in water content, water being the source of hydrogen. Get it wet and yep, stick, yank, stick... etc.

BTW, I don't know where I picked up the habit, but when I stick weld I always put a bend in the rod right at the top where it is clamped in the holder. Bend it down. Anyone else do this?

10-19-2003, 07:24 PM

Yep, it puts your hands in a different spot away from the heat.. seen it done by hundreds of millwrights around Chattanooga.