I need a circuit schematic of 2 KW light dimmer...

[Cyrano]

Hi People...
I need to control the temperature of an oven heating element.For that purpose I have found this kit: http://fadisel.com/cebek-electronic/dim ... 3_290.aspx ,but the price is exaggerated to me,considering that the pieces costs less 5 bucks...Has anyone here avaiable a circuit schematic to build a similar dimmer?
I THANK YOU in advance...

[reloadron]

Hi Ya

If you want to control a temperature within an oven using a 2 KW heating element using a 2 KW dimmer circuit may not be the best way to approach this. Other than manually turning a pot, you really won't have any control. You don't mention the allowable error or temperature region you want to maintain. For example a home electric stove the oven temperature can vary as much as 10 to 25 degrees from set point drifting above and below the desired temperature. That is fine if you want to place a 6 pound roast in the oven and cook to medium but isn't as fine for some applications. Using a 2 KW dimmer circuit will require constant monitoring and tweaking to maintain any real control. Additionally if a "load" is moved in and out of the oven getting stable control can become more of a problem.

I would look towards a SSR and control the SSR from a temperature controller. Much of how this should be done really is a function of the application. A simple Triac circuit isn't all that difficult but may not give you the results you want.

Ron

[Cyrano]

Hi Ron
Thank you for your time.I dont need a precise temperature control, so a triac circuit is good...
I have to seal thermocapslues on wine bottles; I dont need a precise temperature control, so I think that a triac circuit is good...
Cyrano

[reloadron]

Hi Ya

The linked drawing is a triac circuit I found. Now if you aren't heating over 250 or so degrees F. it would offer some basic control. It uses a handful of parts from Digi Key or just about any supplier. It doesn't use a digital indicator or anything fancy but should work. The C1 cap is a 33 nF cap.

This is also my first attempt at posting a linked thumbnail image so I hope that works.



<Edit> Oh well the thumbnail didn't work so just Click Here.

I would guess once you find a sweet spot for R1 it should control the oven. Some of the other members may have some better ideas.

Ron

[Cyrano]

Great, Ron!
I Hope It Works!

[reloadron]

Just remember the thermistor is your temperature sensor and goes in the oven so watch what you use for leads. Most thermistors like this are good for about 250 degrees F. You may want to also wait and see if the others have any thoughts.

Ron

[dacflyer]

why not just get the mechanical thermostat control off of a junk oven somewhere ?
that has the temp markings on the knob and it has the thermal probe already on it as well.

you can find them all day long for almost free at any appliance repair.
might be a few bucks if that even that..

[Cyrano]

Ron..
Thermistors works at maximum 125C...
To work on thermoscapsules, I need at least a temp of 300C...

[Bob Scott]

All of the TV studio lighting controls I worked on used solid state relays for their output into high power bulbs in the Kilowatt range.

[Robert Reed]

Ron
Am I missing something here. When Q3 is in its turn on state, won't that completely kill power to the control circuitry?


EDIT:
Oh, I think I see what I overlooked- the 32 volt Diac which allows control circuit to power up on each half cycle before the diac fires.

[reloadron]

Hi Robert

Works a little like this:

Let's suppose that a positive half-cycle starts. As the voltage rises, the 22k resistor will feed the circuit. The upper Zener diode will clamp the voltage at 42V, with the lower one just conducting. The 100k pot is adjusted in such a way that the base-emitter voltage is just enough to make the PNP transistor conduct. The capacitor will slowly charge up, reaching 32V sometime within the half cycle. The DIAC will then fire, dumping the capacitor's charge into the TRIAC, which will also fire, and conduct for the rest of the half cycle, keeping the control circuit powered down.
For the negative half cycle, everything will be the same, except that the Zeners reverse roles, and the NPN transistor conducts. The unused transistor in any case stays off, with 0.6V inverse voltage across the base-emitter junction, and its collector insulated by the diode.

So yep, you guessed it as to how things work with respect to the Zeners. The transistors take turns on alternating half cycles.

My first choice for something like this would have been as was mentioned, cannibalize a thermostat using a capillary tube switch from an old electric oven. What I wasn't sure of till now was the temperature operating range. Since the load in the oven needs to soak at 300 degrees F. the thermistor is sort of out of the question. I still feel that a dimmer concept won't work simply because it lacks control in any way. I just tend to think the temperature will creep up. That was why I mentioned conventional home ovens and the temperature spans they have from a set point.

I charted a home electric oven once to settle an argument with a woman who claimed her oven temperatures were way, way off because her food didn't cook right. New digital electric oven and it held +/- 10 degrees of set point at 250, 300, 350 and 400 degrees F. Temperatures measured at the center of the working zone. Then she questioned my data which led to an argument much like a fight with a porcupine as even if you win you lose.

Anyway, I figure a home oven bulb and capillary tube controller or something using a thermocouple to replace the thermistor and the thermocouple feeding an op amp with some form of compensation?

Ron

[cindyjolly]

As Dac said, a mechanical thermostat can help you out controlling the temperature of your oven. Have you tried that one. This idea is looking logical to me. Give it a try.

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[cindyjolly]

Have you given a try to the mechanical thermostat. I was willing to try also. Please inform me when you tr this one. I will start my work then only. Thanks !!!!

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Thermostat