1. Sep 21, 2004

### Evil Knievel

Hi. I have an arc (Stick) welder with a 1200 Watt output. In South Africa we run 220v single phase electricity. The current should not be above 20 Amps.

In order to weld thinner materials (and maybe even aluminum ) than possible with an AC welder, I am attaching a Wheatstone bridge (Each diode having a 10 Amp/1000 Volt capacity) to the output to obtain DC. How would you suggest that I control the output or is the different settings of the welder OK? I am not able to commercially find a reostat with a capacity of over 300 Watts. Excuse my ignorance, but where can I find (free) info on construction of a suitable reostat?

Knievel

2. Sep 21, 2004

### Cliff_J

A wheatstone bridge is used to find an unknown resistance (or impedance).

You're constructing a half-wave (2 diodes) or full-wave (4 diodes) rectifier.

Welding with DC helps but you have an simple problem with the large electrodes used in stick welding. You might adjust the amperage enough to weld 14 gauge steel but getting thinner than that and sticking the rod from too low a current or burning through from too much current are going to within a very narrow margin.

The small wire in a MIG wire-feed welder helps tremendously to get the heat very localized to the arc, this allows enough heat to get good penetration in the weld area but without so much total heat as to burn up the surrounding metal. Regardless, when you get to really thin sheet metal and butt joints, its tough. I haven't had a chance to use a TIG yet (prices are outrageous as I'm sure you know) but this is suppossed to be where they really shine is on thinner metals.

I could say that you would be better off constructing a resistor bank to drop the power delivered to the electrode, but anything with that kind of capacity would cost more than just purchasing a wire-feed welder. Some of the flux-core wire feeds are quite resonable in price here in the states, might be worth checking out.

Cliff

3. Sep 22, 2004

### Evil Knievel

Yeah, I hear you.

Cliff

Hi. Thanx for your reply. I was actually wondering about the rods but the copper wire seems like a good idea. Now for the next problem: Flux/atmosphere control. Building a wire feed with gas supply will most certainly be complicated and expensive. I will have a quick look at obtaining a secondhand unit. The other alternative is to simply build a full wave rectifier and see how far I get with off-the-shelf equipment, welding so as to reduce heat buildup. Hehe... As for the resistor bank, yes, that sounds like a good idea. I will post an article on this from a local magazine when I get permission.

Go well all
Evil

4. Sep 22, 2004

Evil Knievel,
Does your AC 'buzz box' have any adjustment for controlling output amperage?
I’ve worked with budget equipment before but my mind is not quick to recollect something like that.

5. Sep 23, 2004

### Evil Knievel

Boulder

Hi. Yes, it has different electrodes that you can attach the live (stick) cable to. Do you think that will be sufficient output control? Also, what thickness is 14 gauge mild steel? We do not use that measurement here.

Many thanx
Knievel

6. Sep 23, 2004

Hello Knievel,
Yes, I believe that will provide you with sufficient output control for most purposes, although I’m struggling to picture the integration of your diodes into this type of welding rig, but perhaps it will come to my later.

Here is a chart to help make sense of it;
http://www.coasteltools.com/tech_steel_gauge_chart.htm [Broken]

Last edited by a moderator: May 1, 2017
7. Sep 27, 2004

### Evil Knievel

Welder output connection

Boulder

Hi. Well, the way how I am going to do it is to build a separate box for the full wave rectifier with 2 buzz-box like input electrodes on the input and the same for the output of the rectifier. Then I simply make two short welder cables with eyelets on both ends that go from the output of the welder to the input of the rectifier and then my normal welding cables go from the output of the rectifier to th eworkpiece.

8. Sep 27, 2004

Ah, I was thinking along those terms myself because the multi-tapped transformer this model likely uses does not lend itself readily for convenient rectification the way a variable inductor type would. Well, be sure and let us know how it works!

Last edited by a moderator: Sep 27, 2004
9. Sep 27, 2004

### Gokul43201

Staff Emeritus
I didn't know that you could weld aluminum with DC. Would that require much higher currents than AC welding ?

10. Sep 27, 2004

I don't know (never tried it with AC, haha).

11. Sep 27, 2004

### Gokul43201

Staff Emeritus
You're kidding ?? You weld aluminum with DC ? Don't you simply make an oxide layer that just never, ever melts ?

12. Sep 28, 2004

### GENIERE

$105.00 will buy you a 90amp (DC) mig type welder that uses flux core wire from Ebay. The flux core prevents oxidizing. About$15.00 buys 2 lbs. of Aluminum wire with a flux core.

13. Sep 28, 2004

### Evil Knievel

Well, I don't know yet but will be sure to update you. It's been a few years since I've seen a textbook but the theory behind this whole concept is that with DC you can maintain a spark at a lower current because the current is not going through zero on every cycle. Lower current = lower temperature at the same resistance. There are 2 problems with welding Aluminum: 1: It oxidixes very, very quickly. 2: It melts at a much lower temperature than normal arc welding temperatures. I hope that, with the DC current, I am able to maintain the arc at aluminum melting point.

The second problem is the oxide layer. If one can find flux coated aluminum welding electrodes the problem is theoretically solved. Also see Cliff_J's reply to my original question. Basically, the thinner the better. This would probably be the better solution as I believe such electrodes are available.
Another way of solving this problem would be to weld using CO2 wire but because this is not flux coated one would have to augment the setup with a CO2 wire feeder and CO2 gas supply to maintain an inert atmosphere around the weld. I have not yet looked at the cost of such a setup but am sure that a secondhand one can be had.

Aha, here comes Geniere with a solution. I see the US is more friendly to it's consumers. In South Africa, an ARC welder costs around R 1000 whereas a MIG/TIG welder costs around R 20 000. The rectifier can be built for around R20, which is why I started looking at this option. At US prices, I would suggest simply buying a MIG welder. Maybe I should have a look at Ebay..

Last edited: Sep 28, 2004
14. Sep 28, 2004

### GENIERE

Also 2 or 3 automobile 12v batteries can work if you can come up with the flux core wire feed mechanism, maybe as a spare part.

15. Sep 28, 2004

### Cliff_J

If the current is required to flow-stop-jump the gap-flow-stop... like with AC then the problem can come from the jumping the gap part and it seems to dance around more, esp on low current where you're holding the electrode closer. My welds look awesome on DC and just above average on AC although its been years so I'd likely just use MIG to bolster my ego.

The aluminum needs to be super clean (sand it or steel wool surface) or don't bother and just braze the parts. Oh and the toughest part is the puddle is near impossible to see as it doesn't glow red like steel.

If you can weld aluminum with a stick welder, you will have developed some serious welding skills. Can you even get the electrodes for it?

And its pure argon for aluminum welding and no CO2 at all.

Cliff

16. Sep 28, 2004

I'll take that as a compliment !
Yes, you can definitely obtain the sticks. I had purchased a quantity through the [then] local Mennonite farm store but have since used them all up and forgotten the number for them in the process.

17. Sep 28, 2004

### Gokul43201

Staff Emeritus
I'll have to second that compliment. I think DC welding aluminum is crazy and stupid...but if that's your bread 'n' butter...

18. Sep 28, 2004

You do what must be done as dictated by circumstance. Not all welding options are available at any given time or place. I have, for instance, successfully performed more than a single welding operation using two 12V batteries wired in series. From my perspective, to limit oneself only to convention is absurd. This is no doubt because unlike so many, I have spent a great deal of my life in remote areas where you either get the job done yourself or it simply will never get done, often resulting in penalty. As may happen, one discovers new techniques which can be effective and refines them. I don’t really consider ability to stick-weld aluminum using DC much more than a useful [survival] skill. Try testing your hand at maintaining an arc by practicing with a coathanger, now that's an insane survival skill, haha!

19. Sep 29, 2004

### Evil Knievel

OK, I think we have a winner here... Coat hanger?! Hehe..

While it is not ideal, one could even build a generator using a normal DC engine/petrol engine and a car alternator to recharge your car batteries quickly. By the way, is an alternator DC or AC? And a generator?

I will build the rectifier this weekend and will hopefully have some feedback on Monday. Wish me luck.

20. Sep 29, 2004

### Cliff_J

A generator is effectively a permanent magnet DC motor being spun to generate DC using the brushes to keep it DC.

An alternator produces AC in 3 phases and the rectifier inside it converts it back to DC for output.

The generator varies in its output based on the speed. With the alternator the output is regulated by controlling the electromagnetic fields. Regulation is very nice to have to avoid overcharging the batteries and possibly ruining equipment.

Good luck Knievel, may your landing be soft and on the other side of those cars you're jumping.

Cliff