Modify arc welding (AC in DC)

[Ivans]

English is my bad, but I hope that you will understand me. I have a welding machine 375A, which provides the AC current. I would like to modify it to provide DC current. I consolidated the four diodes and it works, but bad. Very difficult to use the DC electrodes. I learned that you need to make an electric choke. I do not know how to make it. What are the core to take, what kind of wire, how many turns ..

 

[shenion]

Mine was 25 to 30 turns of heavy wire around a cast iron pipe about 1.75" in diameter. Then a steel frame around it.

You can also add a motor run capacitor on the output terminals of the rectifier. It will smooth it out a bit more. Get as big as you can find, 100uF or more.

Mine I used a 4700uf/200V electrolytic (screw terminal type, computer grade.)

 

[mrcheese]

Does it make much of a difference? I have thought about doing this to my big old buzz box. 200A rectifier diodes are pretty cheap. Everything else can be found surplus.

A word of caution on the capacitor. The ripple current will be very high. You will need a high spec aluminium electrolytic or you risk it failing (splitting or exploding). A big film capacitor would be a better choice.

Would you then need to use dedicated DC rods or would I see an improvement with the 6013s I have.

 

[shenion]

The arc is more stable on DC and you will get less spatter.

You are right on the caps, I used computer grade low ESR caps.

Almost all rods that can run on AC will run on DC. Some better on DC+ or DC-.

Here is a thread on converting an old buzz box.

DC is easier on positional work

 

[mrcheese]

Thanks for the very interesting link. I'll keep an eye out for some suitable parts.
I would probably build it into a separate box.

From the link what is the purpose of the caps across the diodes; RFI suppression or do they improve the arc?

 

[shenion]

The small diodes across the caps help protect them. The main thing is they will reduce the noise radiated back up the power line.

You see cheap MIG and arc welders without them. That will drive some of your house electronics crazy and possibly damage them.

 

[mrcheese]

Many thanks. It is always good when you learn something new.

 

[Ivans]

Here's a picture
Diode for 300A. I agreed with an electrician to spoil another old welding machine, and make it a choke.
After I add a capacitor. After that, we will take an oscilloscope to see the form of electricity (apparently sinusoid)

 

[cuba]

Ivane imas PP.