Adjustable inductor

[HughF]

Does anyone have any idea whether an adjustable inductor is best built with taps, or an adjustable iron core? Shenion would know, if he's still active on here...

Adjustable iron core could be simply bodged together from an old buzz box...

 

[Cobbler]

Last on here in March, strange really, unless somethings happened as he was always posting & answering questions.

 

[rtbcomp]

Tappings would be simpler, moveable core would give finer adjustment.

With moveable core the resistance (as opposed to impedance) would remain constant if that matters.

 

[HughF]

finer adjustment would be a benefit for what I want to achieve. Another thought, all the literature about saturable (saturatable?) reactors talks about their use in AC welding sets. Will they work on a DC output machine as well? A saturable reactor would allow me a remote 'fine' inductance/arc force adjustment..

 

[gordon stephenson]

Try sending Shenion a P.M

 

[HughF]

he's active on facebook... I'll pm him.

 

[rtbcomp]

An inductor doesn't have an effect on DC, but the DC from a rectifier in a welder has ripples superimposed on it, ie it's not smooth. The inductor smooths out the ripples and gives a cleaner DC.

It also resists a change in current, so the startup surge will be reduced when you strike the arc.

 

[HughF]

But by varying this inductance (through more or less wraps of wire or magnetic saturation of the core) I can control the smoothness of the DC and also the voltage surge (essentially arc force) when the arc length changes, no?


The lincoln sae300 and 400 dc engine drives (they are dynamos) use an adjustable reactor for the course current control iirc.

 

[rtbcomp]

Yes - the current surge is when you initially strike the arc, once the arc is stable the inductor will help maintain a smooth arc.

Not sure about the dynamo coarse adjustment, if they do use an inductor I'd be very interested to know how it works.

 

[HughF]

A quick google of sae300 inductor seems to reveal a tapped inductor with a wiper instead of fixed taps, like a variac but without a second set of windings.

 

[rtbcomp]

A variac only has one winding, like an auto-transformer, but with continuously variable output.

 

[HughF]

Behold, the inductor/reactor fitted to sae300 and sae400 lincolns... sa200 has a 4 position switch in place of this. Basically, on the sae300 & 400, this adjusts the 'process selection', overhead, flat/horizontal, special electrodes, large electrodes. It basically adjusts the slope of the v/a curve. The current and voltage control is done on the 'fine adjustment' that is a field excitation reostat.

 

[rtbcomp]

That makes sense. I'm surprised at the small number of windings, that said, I'm sure I read somewhere that somebody made an inductor by wrapping the earth return round a lump of iron.

 

[HughF]

From looking at the wiring diagram, it looks like this inductor is just in series with the output, which makes sense.

Where I'm going with this crazy idea is, I have an engine drive that I'm very happy with, but it doesn't like running 6010. A quick google shows that the mosa magicweld (also a high frequency rectified PMG based design) has an optional output inductor for running 6010 rods. This got me thinking, perhaps I should add an output inductor to my machine.

My machine is by default AC output at 475Hz, I've added a full wave bridge so now have dc output as well. As you would imagine, the DC arc is very smooth (so is the AC arc actually)... I wonder if I could use a saturable reactor with the AC output to give me stepless, remote current control. I have 110v dc available on a seperate winding that I could use to power the DC side of the saturable inductor.

I will dig through some old transformers and have a play.

 

[rtbcomp]

Interesting idea - keep us informed!

 

[HughF]

I will do... first step is to wrap the earth lead 20 times round a lump of iron bar and see if that makes a difference!

 

[HughF]

SAE300, 400, 500 wiring... the one with the reactor. SA200 (shorthood, transition model, or redface) and SA250 don't have this.

 

[HughF]

Bingo, saturable reactor (magnetic amplifier) before the diode bridge will give me variable current control, tapped inductor after the diode bridge should give arc force/slope adjustment...

http://www4.hcmut.edu.vn/~dantn/CNH/cnh_figures/Hb2-c01.pdf

 

[rtbcomp]

Sounds good, the variable inductor will limit the AC current into the bridge without dissipating any heat*

*If it was 100% efficient that is. In real life it has resistance and eddy currents in the core will dissipate heat.

 

[HughF]

Make a welcome change from hand assembling surface mount digital electronics