Variable AC control (low cost)

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You're correct. That's just you!

"An autotransformer (sometimes called autostep down transformer)[1] is an electrical transformer with only one winding. The auto prefix refers to the single coil acting on itself rather than any automatic mechanism. In an autotransformer portions of the same winding act as both the primary and secondary."

I was thinking of a relay controlled by thermostat or just controlled by a

Greg

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An efficient autotransformer will have fatter wire in the lower-voltage winding, where the higher current is. A literal single winding would usually be a huge waste of copper. So it's not really a single coil.

I think of a 4-wire transformer, connected in 3-wire mode, as an autotransformer.

No math? Where's the fun in that? ;)

Cheers

Phil Hobbs

If you're just pushing symbols around, math can be a way of proving stuff that you don't really understand. It's fun when someone does pages of math, makes a small mistake somewhere along the way, and arrives, unawares, at absurd conclusions.

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Oops, we all screw up, it's a learning opportunity in my opinion.

I see it in the time domain. Heater's on for 1/2 the time... it's 1/2 the power. (on average) George H.

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Done well, it's a very efficient way of learning to understand new things, both in physics and engineering. Some of my technical heroes produced a lot of great gizmos using a lot of great math. Oliver Heaviside, for one.

Cheers

Phil Hobbs

Oops, we all screw up, it's a learning opportunity in my opinion.

I see it in the time domain. Heater's on for 1/2 the time... it's 1/2 the power. (on average) George H. ______________________________________________

Right, I see it now. Just a brain fart.

How about using the electronics, sans the HV and RF, from an old microwave oven? Including the triac. That should control 1500 watts using duty cycle regulation.

restrictions prohibit wood fired BBQs) from a stove top. Problem is that sometimes, 1500W is too much and I need to throttle back the temp.

stove but can't find anything local. A new one is in the 70-bucks range and that can't happen.:)

opening and closing a vent to let heat escape as cooking times can often be in the ten to twelve hour range.

that with 1500W? I am using that in the smoker now, but it does not get quite hot enough so that control is always on max.

Use a light dimmer and swap out the triac with a bigger one on a heat sink.

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John Larkin doesn't understand how to use math. You've got to cross-check to find those "small mistakes" - a one-line formula in a paper can represent weeks of tinkering aimed at finding the right way to formulate a representation of what's going on.

Once you've found it, you can't imagine how you could have been so slow to see the obvious ...

see the pictures of my wood fired outdoor oven, in Walnut Creek, CA:

Jure Z.

Nice. A lot of people build these just for bragging rights and use them only once. But yours is obviously being used a lot:

Thanks guys,

The element is 110v even though the stoves are plugged into 220v/30A, The smaller elements generally use one leg of the 220 for 110. I guess they do the smaller elements that way so the controller can be smaller and save a few pennies. Just a guess.

Anyway, I will continue the search for an old electric stove to get an oven control as has been suggested.

Thanks to all.

Dave

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About 95% of my pcb and product designs work first try, without prototypes. That includes precision analog, GHz FPGAs, picosecond timing, trace impedances, thermals, firmware.

Last week I brought up a new NMR box, combo gradient driver and temperature controller, with new firmware, new thermal design, new packaging:

Plus, I had to hack the test software (the thing that plots the graphs) to run under XP... it was an old DOS thing. All that took three days from when manufacturing gave me the first unit, until it all worked. The design did involve some math.

We had some noise and pulse settling issues, straightforward stuff. The worst problem was that it was erratically throwing PFG loop errors at startup. Karla and I spent a lot of time scoping and thinking, and it really didn't makes sense. Turns out that one of the MeanWell supplies, the big +48 one, starts right up. The smaller -48 supply, loaded by the reservoir caps on the board, takes ** 15 seconds ** to get to -48. The output waveform is a very nice staircase, about 2 volts per step. Seems like the switcher dumps into the caps, current limits, shuts down, and retries roughly a second later.

I just hacked the uP firmware to add a 30 second delay before the PFG stuff is enabled. But there must be a more elegant way to do this.

You've got to

I don't "tinker" and I don't spend weeks on practically anything.

How's your oscillator coming along?

control as has been suggested.

OVEN control? A thermostat control will be rather expensive. Why not a continuous type electric rangetop burner control, instead?

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In other words you do lots of small incremental modifications/ =20

Not a lot of innovation then. =20

Not as fast as you'd like. I've just had a small insight involving putting = a little phase advance on the make-up current, which shrunk it from an absu= rd 75uA (compared with a circulating current of 150uA) to a very reasonable= 0.8uA - the Q of the inductor ought to be about 300 at 16kHz, and 0.8uA fi= ts with that.

It's all simulations still though there are a pair of professionally wound = inductors sitting on my desk. The latest simulation results mean that I'll = drive down to Horst on Monday to get the not-all-that-local transformer win= der to wind me the first three coils onto the definitive transformer.=20

There's a hand wound prototype transformer sitting on my desk as well, but = the pro will do a better job with the two 144-turn coils - I had to wind th= em bifilar, and that made for an uncomfortably low self-resonant frequency.

--=20 Bill Sloman, Nijmegen

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Sometimes things go wrong. A transistor may oscillate. The PCB layout may have problems. I had to hack one resistor into my recent picosecond pulse generator, to slow down the switching of a PHEMT and reduce some ringing. There's an optimum amount of engineering and checking; I could have analyzed it for another month, roughly tripling the design time, and possibly avoided that kluge. It wouldn't have been worth it. A design is, to me, optimum if we can ship the first one soonest. The cost of a parts value change, or a small kluge, is part of that calculation.

In design reviews, someone will sometimes bring up a possible, low probability, but hard to analyze, hazard. If the fix would be just a parts value change, or a simple kluge, we often just go with what we have, and fab the board. Sometimes we'll route traces, or add zero-ohm jumpers, to make sure a kluge will be possible. We bring out unused FPGA pins to test points, for klugability.

On the PFG gradient driver, we want 10 amp pulses to be flat to 10s of PPM. I included parts on the board to allow us to add two exponential overshoots and two undershoots, with parts-selectable amplitude and tau, just in case. At these levels, you can get thermal hooks, eddy currents, ground loops, all sorts of PPM ugly things. We wound up using one of the four RCs to pound the pulses really flat.

We manufacture, practically mass-produce, new electronic designs. That is a macro-process of its own, with its own sets of techniques, rules, ticks, optimizations. We have designed a system for designing systems. It's surprising how many companies have no such thing.

Look at my web site. I conceived and architected all of it, and designed most of it. I just didn't dawdle doing it. I sure wouldn't tinker with one LC oscillator for years. I did recently designed and breadboarded a zero-startup-time low-TC gated LC oscillator, at 50 MHz, but that took a day, mostly fiddling with NPO caps to get the TC down. Surface-mount NTC caps are really hard to get; we order them custom, big reels, long lead time. We only have a few values in stock, so I mostly have to work with what I have.

Anything having to do with temperature is a PITA.

Air-core inductors seem to have TCs in the +120 PPM range, and FR4 runs roughly -900. Ferrites, like pot cores, are sometimes available with TCs that compensate typical capacitors, but I use air or ceramic cores at my frequencies.

How about this - I have used this company before (crap name though)