"regular" dimmer switches and transformers

Some dimmers are rheostats, which should not pose a problem, the others are thyristors (triacs) which generally do not have much in the way to suppress the collapse at unexpected events. Of course there are the auto transformers but I don't think you're referring to those.

All I can say is, yes, it'll work because we have some applications like that however, the secondary side gets rectified to a DC buss. Other than that, it produces a rather saw tooth type of wave, more or less, depending where the phase angle is.

You do need to add some snubbers for the unexpected collapse of mag field out of control.

I wouldn't be using it for mission critical systems!

Jamie

It works for me. I use a regular dimmer on my hot wire cutter. The dimmer feeds a MOT on which I have replaced the secondary with about 10T of 12ga. That goes to a piece of piano wire which does the cutting. Been using it for over 10 years with no problems. Art

By coincidence, the application I'm asking about is a hot wire cutter. Whadaya know.

Some thyristor dimmers are built to drive transformers, some are not. The issue is maintaining DC balance in the transformer, to avoid saturating the transformer core.

Lutron has a number of models that are intended to dim low-voltage light strings (like under-cabinet lights) through a step-down transformer.

If you are interested in the technical details, look up the patents listed on the box or the instructions, or do a patent search for patents assigned to Lutron.

Joe Gwinn

yes!

get one that's designed for inductive loads.

Or roll your own. I found, back in my discotheque days, that I could dim neon displays via the transformer, by feeding the transformer integer cycles of AC... used a TRIAC, feed a few full cycles, dead-time, feed a few full cycles. ...Jim Thompson

I was hoping to find out if a dimmer switch from Home Depot and a transformer from Radio Shack would fulfill the need.

I'm gonna try it, and see if anything gets hot or lets out magic smoke.

As long as the ultimate load is resistive and the dimmer generates a symmetric waveform it should work. For my neon situation, that didn't work, because the neon tube didn't always strike, and I smoked more than few transformers before I caught on >:-}

My discotheque days were fun, but probably why I now need to wear hearing aids :-( I still like the music from the disco era... my wife hates it ;-) ...Jim Thompson

Once upon a time, I was stuck on a holiday weekend trying to patch together some assembly line equipment. One problem was a small AC spot welder, that I had fabricated from a disemboweled Weller soldering gun. It worked too well and would blast holes instead of welding. I needed a way to reduce the voltage. I had an auto transformer, which worked, but I didn't want to leave it on the production line. So, I "borrowed" a handy light dimmer from someone's office wall, and wired it to the spot welder. Much to my amazement, it worked. Well, it worked for about 5 minutes or about 30 welds, when the dimmer overheated and exploded (no fuse). I don't recall the brand or type. I temporarily wired some random resistors to a switch in series with the xformer on the 117VAC side. Temporarily lasted about 6 years.

Lessons learned:

1. If the transformer load is resistive, a dimmer should work.
2. Ignore the maximum rated load, and it will not work for very long.
3. Nothing useful can be accomplished on a holiday weekend.
4. If it works, it's permanent.

My understanding is that it depends on the length of wire, the width of the styrofoam you're going to cut, and the speed that you draw the wire through the foam.

But -- I haven't actually cut any foam that's made its way into a model, so I'm hardly an expert. I'm just regurgitating things I've read.

The length and guage of the wire determine it's resistance. The forcing voltage gives you watts/unit length so the thickness of the foam isn't a big factor for that. Thickness will effect the force you need to feed the foam for a fixed cutting speed. Faster cutting speeds need higher watts input. Don't forget the cutting wire's length will change as it's temp varies from no cutting to cutting. Art

Well, I've never had a building board yet that, sooner or later, wasn't too small for the next project. I'm sure that wing cutting bows are the same.

Foam comes in different densities, and as you get better you'll cut faster (or smoother, or both). So even if you never changed bows, you'd still need to change the setting at some point.

I cut styrofoam and foam rubber. The rubber requires a higher setting for the same cutting speed. It's pretty much set and forget but it's much nicer to twist a knob to get the initial setting than to fiddle with adjusting cutting wire length. Art length

When I last built such a creature, used for Plexiglass bending, I used NiCr in a slotted Bakelite fixture, spring-loaded to keep it taut as it heated. ...Jim Thompson

ve

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remember I guy I worked with he had an old car, Opel I think, the ground strap to engine block would corrode and break eventually melting the clutch cable that became the only ground for the starter

the quick fix was ten alligator test leads, worked for many years an never fixed

-Lasse

That's a different lesson:

1. Never sell a used car to a friend. I've made this mistake twice and had to endure endless complaints, denunciations as me being a crook, and pleas for repair advice. If my present vehicle ever needs to be sold, I'll break it down to parts before I sell it to anyone whom I value as a friend.

cutting

My cutter uses salvaged nichrome wire (from a 5A heating coil) to adjust the heat I just change taps on the replacement secondary of the repurposed MOT i use to run it

Maybe 50 year old theatrical dimmers, but some of those were banks of Variacs to reduce the waste heat & fire hazard.

The issue, being that inductors for AC input will burn up if fed DC.

USE A FUSE.

The dimmer switch uses a Quadrac (a triac with an integral trigger diode). The trigger is NOT accurately symmetric.

If you omit the fuse, it's a race to see if the dimmer switch burns, or if the transformer gets carbonized. A short circuit related to transformer saturation is nearly certain.