Number of Transformers for arc welder

[KCW]

Number of Transformers

Hello,

I just signed up, this looks like a great place. Anyway, I am a chemist so I'm a little out of my knowledge space but, I also dabble in electronics.

I am starting a project where I am going to build an arc welder. I am going to build the step down transformers from scrath. I have a bigger picture question that I can't seem to answer for myself.

Would four large transformers with a cross sectional area of approximately 2.5 square inches be better than around eight to ten smaller transformers with cross sectional areas of about one square inch each?

The input service would be 120vac @ 20 amps.

 

[WimRFP]

Number of Transformers

Hello,

The 4 transformer solution is better (efficiency point of view) as you have the largest core Area over Circumference ratio. So you need less copper to make your transformer.

There can be other reasons for sacrificing some efficiency and using 8 smaller units (space, cooling, power control, etc).

 

[KCW]

Number of Transformers

Thank you! Yes that makes sense. The larger design I have is about a 5" by 7" transformer, with each leg being 2.5 sq.in.

With the 120vac service, do you think the larger ones will offer a fair duty cycle? I worry about them getting hot too quick.

 

[WimRFP]

Hello,

Without any further details, this is impossible to say. In general, removing heat is more challenging in large transformers. You may incorporate a fan with temperature sensor.

Other thing with large transformers is that you should avoid too high switching frequency as RF propagation aspects within the ferrite may degrade performance. The reason for this is that ferrite materials have high permeability, but most power materials also have reasonable permittivity.

I would really recommend you to do such a project together with somebody who is into power electronics. You also have to design the circuitry to enable the correct current in the arc. Arcs have negative impedance mostly, so you need some form of passive or active control.

 

[KCW]

Would that be something like a pulse controller? I wonder how difficult that would be to set up.