Whole half-cycle variable heater controller

Would this draw current with big even harmonics (especially 2nd) and a dc component? The utility may not like that.

And, no, I might have seen that in a text way back dut I don't recall any details. I believe the control was referred to there as 'integral cycle control' if that leads you to anything useful.

| A few years ago I came across a triac controller design that gave from 0 | in 20 to 20 in 20 "on" half-cycles. It only used a few standard | components. "Really ingenious", I thought at the time.."Wish I had | thought of that"..

Don't worry. Lots of people have. It's not "ingenious" at all. It's just a basic concept. IMHO, it's not even patentable based on the real principles of patents (although it probably was granted a patent in the US model of every idea has to be owned by a corporation). OTOH, a clever way to _accomplish_ this might have been patentable in past decades. I knew in the late 1960's of this concept, but I could not envision an easy to build circuit to accomplish it.

| Now, of course, I need one. I can design a bog-standard one but would | love to find that circuit again..

A basic counter ought to do it today. One issue you might need to consider is if you have an even number of half cycles in a period, or skip an odd number of non-conducted half cycles, you'll be doing effectively a DC current. This could impact things like transformers if such a thing is involved. One way around this is a full-wave bridge and just reverse the direction of the current on those half cycles that are the same polarity as the previous. Doing that means there is no true neutral on the output.

The load better not depend on the frequency in any way.

| Anyone remember it/ know of it? | | It was, IIRC, a 110v design but would fairly easily mod to a 240v one | (which is what I need).

Just control both conductors. The full-wave method to ensure reversing polarity won't have a neutral issue since an American 240 volt load is not expecting a neutral.

If you can find a circuit to do this, go buy a Variac transformer.

Theis was already being done in the '60s. Thyristors have been around a *long* time.

...or make sure the positive and negative cycles cancel out over a small number of cycles. Such things are easy today.

Nor the eyeballs.

Or simply PWM the triacs and try to filter the EMI.

It was that really ingenious way of doing it that I couldn't remember and wish that I had thought of. As you say, there is nothing special in the idea of whole cycle controllers.

It's a heater - as in the subject line.

Variacs are way too big, expensive and have moving parts carrying load current. But thanks for the suggestion.

-- Sue

Thanks for the suggestion. I'll have a go looking for "integral". However, lots of small mains heaters now have a "half power" switch which simply puts a rectifier in series with the load and thus then only draws power from alternate hlf cycles.

I built one ~20 years ago using a TDA1024 zero-crossing triac controller. Still got it and use if for controlling the power to an electric frying pan. It is a good quality frying pan, but came with a crap power controller. It also got used for flashing lights on and off in a Christmas display many years years ago.

If you dig out the data sheet for the TDA1024 (or one for a more recent zero-crossing controller -- don't know if TDA1024 is still a current part), there are sample circuits you can use.