Triac Based Controllers

[tonkyman]

--Mod Edit--
This topic has some schematics, builds, theory, and parts lists of different triac based controllers that different users have done. Please read and understand this topic before attempting to build a controller covered in this topic, or any electric topic for that matter. I cannot be over emphasized the importance of saftey when attempting to build. If you do not understand something, please ask. Or get someone qualified to do the build for you. Serious injury or death can result from improper assembly of electronic controllers.
Original Topic: http://homedistiller.org/forum/viewtopic.php?f=2&t=3342
Here are the parts



With the dimmer in place



Inside wiring. For this to be correct the white and the yellow wires should be switched on the Triac. Also, the extra wire hanging goes to the near side of the resistor (I didn't have it connected in this picture).



An earlier view of the inside wiring



Here is a picture showing the back. The screw on the lower left knock-out is the screw holding the triac down to the bottom of the box. There are better ways to do it and I will post them as I build them.



The finished unit





Anyway! There are much better ways to build this thing and I've been scrounging through my junk box to find what I need for an enclosure and heat sink. I'll let you guys know with a better step buy step when I put the new one together.

Later,
Tony T

[snuffy]

I made some modifications to the schematic: adding an outlet to plug the element into, meters to monitor the power, a switch to go to full power and changed the dropping resistor to a light bulb. The light bulb serves as a current limiting resistor, just like the power resistor in the original design. I was hoping I could choose a bulb wattage so it would glow dully, but more on that later.



The case was salvage from a computer power supply. The triac came from eBay, the meters from MPJA and the rest was in my junk collection.



First step is figuring out how and where the bulky stuff fits. The dimensions of the parts provide enough constraints that things converge pretty quickly. At this point I haven't found a space to cram the outlet. The paper templates for mounting the meters are CAD printed at 100%.





The dimmer was too big, so I cut off the mounting tabs. The heat sink interfered with the leads from the dimmer, so it got major violence inflicted on it with a hacksaw and file.



That left room for mounting the outlet.



The leads for the dimmer were to short, so I extended them with a black wire to the lamp socket and a black wire to the triac gate with a yellow lead to the switch.



Another black lead goes from the ammeter to the triac M2 and from there a red goes to the lamp socket.



Two orange wires (twisted together) will go from the voltmeter across the outlet terminals. The two yellow wires to the switch go out of the picture at the lower right.



Then the leads to the lamp socket are terminated. The wires go around the socket to prevent having a sharp bend right at the terminals. The switch wires go off to the left and the voltmeter leads go to the right.



The supply line is connected: green to outlet ground, black with spade terminal is the hot to ammeter, the neutral to triac M1. Because things were so tight in the case, I had to dismount the heat sink for the triac. The heat sink is a CPU cooler less the fan. I ground the heat sink and the triac against a flat surface to confirm I would have good thermal contact. The white ties the ammeter to the outlet. The orange voltmeter leads are terminated across the outlet. The yellow switch leads won't be connected to the switch until the case is assembled.



The heat sink is reinstalled and all the connections snugged down. The case is assembled (omitted to spare the squeamish - there was a lot of hacking, filing, drilling, grinding to get the case halves to go together. The switch mounts on the other half of the case, so it's leads run through the switch mounting hole and are soldered to the switch. Another brief but violent episode as the switch gets its little feet and locking tabs crammed back into the case. Finally, some new holes are drilled in the case to secure it -- the meters covered two of the original holes.



The moment of truth: will it work or will all the lights in the neighborhood go out?



IT'S ALIVE!!! (*deranged laughter that goes on for an unpleasantly long time*)



The dimmer won't bring it up to full power - there must be a tiny delay before the diac fires, possibly because the voltage has to reach some minimum value before it conducts. Sadly, the bulb doesn't glow - the gate current for switching the triac must be very low. I settled on 25W by experimenting with wattages from 7.5 to 200. With wattages over 40W, the controller won't go below about 35%. This requires more experimentation.



Secret Switch Saves the Day. By shorting directly across the dimmer, the switch clamps the triac into full conduction.



make an esthetically pleasing knob for that massive feel of raw power and exotic excitement. A friend pointed out that since my entire house has only two 15A circuits for lights and outlets, I should just wire the thing straight into the mains and dim the whole house at once.

[rad14701]

Yet another rough schematic in an effort to help with dimmer-controller assembly... The ground lead is not shown but should be run from the outlet ground to the lead on the dimmer as well as run to the boiler...

[Pamulli]

OK so as promised here is the documentation for my 240V switch. Thanks to Rad's suggestion, mine turned out to be different than anything else I've seen on here since I used an unmodified off the shelf dimmer rather than adding a new Pot and capacitor. I have no idea if this is going to have a shortened life span, I just know that it works at the moment with a 4500W element. I also haven't done a complete run with it yet, just heated water. I'm posting it now because I've gotten some IM's asking for more info. If I later see issues with this setup I'll come back and post.

Parts List
Dimmer: Lutron D-600PH-DK (It's important that you use this dimmer or one with similar circuitry. I got mine at Ace for less than $12)
Triac: LittleFuse Q6040J7 - Mouser PN 576-Q6040J7
Wirewound Resistor: Arcol HS25 75R 1% - Mouser PN 284-HS25-75F

Underside of Lutron Dimmer

Final Switch without cover plate

Resistor and Triac are mounted to an aluminum heatsinc

Switch Diagram

Parts in place without connections

I tried to make the diagram as simple as possible for those of us who find electrical diagrams confusing.
One thing to note is that all of the ground wires are connected, but not shown in the diagram.

Hopefully this will be of use to someone.

[Pamulli]

Here are a couple of low quality pictures showing the final product.

Element attached to keg

The keg is grounded back to the main electrical, you just can't see it in this picture.

[rad14701]

Here is a schematic straight out the the Teccor Thyristor Product Catalog... This is a single time constant circuit consisting of a minimum of parts... I'm guessing that the component ratings should be in the 1/2W to 1W range... This is not one of the schematics I mentioned that I was looking for in previous posts but I felt that it might be useful to anyone looking to experiment with a simple 120V controller for an element up to 1500W...

[Centar]

After reading here about how to make a high power controller from a common household dimmer, and seeing the MAJOR mistakes in the design I had to tell you all here the BEST and easiest way of doing it. (using my 30+ yrs electronics experience)

The basic idea and circuit is correct BUT the dropping resister is WRONG.
Most of you have noticed that it doesn't get hot or even warm and one guy (Snuffy) even hooked a light in series with it (great idea) but to no avail BECAUSE the amount of current going through it is about 10 ma. TRIACS need very little current to switch on, just check the data sheet for the TRIAC I used...a much larger resistance and smaller power rating is needed here....

The best TRIAC to use can easily and freely be scrapped from a larger type microwave oven (got half a dozen this way myself from discarded microwave ovens) or purchased for as little as $2 on ebay.
Mine was marked TG25C40.
This is a 25A unit rated at 400 volts good for up to 3000W at 120vac and should work for up to 6000w at 240 VAC.
It has a large 2 hole mounting for better heat transfer, spade/solder terminals, and an insulated mounting for simplicity of mounting/heatsinking.
I used one of these Triacs for a 1500w 120vac controller. So the design for double rule works good here.

As for the light inline/replacing with the dropping resister idea, this is perfect for many reasons BUT was flawed in that not enough current was present to light the bulb...To fix this I used 2 LEDS connected in parallel in reverse polarity. They do not shine as bright as they could so use bright white ones (got mine out of a dollar store light). The LEDS have to be of the same type and color to keep the switching of the TRIAC symmetrical. AND yes 2 are REQUIRED connected in PARALLEL and REVERSE polarity to each other as this is AC we are dealing with and LEDS are diodes after all...
This Light serves as a ON light, a indicator that the dimmer is working (as it gets a little dimmer on the highest setting), and as a load tester (will not light if there is no load connected, ie. if your boiler is not connected or burned out)

AS for the Dropping resister a 1K 1/4 watt proved to be the perfect value for 120 VAC. YES that's 1000 ohms at 0.25 watt
This can be scrapped out of most any piece of discarded electronic equipment (color code brown black red as the 1st 3 colors) or purchased very cheaply.

Any cheap dimmer (300 or 600watt) will work and connecting 1meg 1/4 watt resisters (color code brown black green) across it's pot until the dimmer just comes on at its lowest setting gets rid of the hysteresis of the dimmer and gives a expanded range to the dimmer control. (mine used 3 1meg resisters, so a 330k would have been good by itself)

Both the LEDS and the resister should be mounted on the dimmer (the LEDS connected in parallel but reverse polarity to each other and in series with the 1k dropping resister), the LEDS are easily mounted in holes drilled in the mounting plate and pushed through from behind and crazy glued in place. This keeps all the parts on the dimmer except for the TRIAC which of course should be mounted on a heatsink with thermal compound for good thermal transfer. (I saw alot of posts about a substitute for thermal compound, some crazy ideas, BUT the stuff is just ZINC OXIDE and silicon oil to keep it from drying out, You can find a substitute right in your medicine cabinet or drugstore as an ointment)

I have built and tested this under load and it works perfect so will house it all in a pretty box, etc and upload some pics here...

Hope this helps clarify and simplify this a little...
--Mod Edit--

[Centar]

Ok here are the circuits, I modified the schematic and included one for the optional mod to the dimmer.

I'll get some pics up soon showing how to mount it all on the dimmer plate.

[MuleKicker]

Let me explain each circuit in a little better detail.
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First Circuit
The first circuit is a typical light dimmer which we can buy for a small price. First allow me to point out the dashed components are there for florescent lamps and transformer operated lamps such as low voltage halogens. If you are building this type of circuit, leave out the optional components, because they have no effect.
The triac is a special type of switch, designed to operate on AC. If you put the power terminal in series with a load (heater element, light, etc.) it is effectively an open circuit. If you connect the gate terminal to the top lead of the triac (MT2), it will come on with full current flow. Of course this is not much use to us.
In the first circuit of the three, there is a capacitor connected to a diac. A diac works like a pair of diodes connected in parallel. These diodes are special though. Their turn on voltage is usually very high, in the range of 10 to 30 volts. If you connect the diac to the MT2 leg of the triac and the other side of the diac to the gate, the triac will turn on. This doesn't help much either.
Let’s return to the capacitor. If a capacitor and a resistor are connected in series, across a DC power source, the capacitor will slowly (compared to a short circuit) charge to the supply voltage. Changing the value of the resistor will change the speed the capacitor charges.
In the circuit for the light dimmer there is a special thing going on. Since we are dealing with an AC signal, we have to look at things from a starting point and I will start with the voltage at 0 and rising for the first half of the cycle.
If we watched the voltage across the capacitor, it will start climbing, following the rising voltage of the ac signal. When the voltage, across the capacitor, reaches the breakover voltage of the diac, the diac will trigger the triac. The triac will stay on, all by itself, for the rest of the positive part of the cycle. The voltage across the triac, and therefore the rest of the circuit drops to nearly zero volts with the voltage being dropped across the load instead. This discharges the capacitor. When the voltage on the circuit crosses zero, heading for the negative part of the cycle, the triac goes off.
The negative voltage starts charging the capacitor. When the capacitor voltage goes negative enough, it turns on the diac, triggering the triac, and again the capacitor gets discharged but the triac stays on until it crosses zero again.
Let’s consider the resistor part. The resistor controls how fast the capacitor voltage follows the line voltage. A large resistance, slow charging capacitor, will cause the turn on time of the diac to lag the supply voltage and only trigger the triac late in the cycle. Smaller resistances allow the trigger earlier in the cycle, larger resistances for later in the cycle.
We can adjust the turn-on time by varying the resistance from high to low. A large enough resistance keeps the device from coming on. A small enough resistance allows it to be on all the time. A resistance in between, allows the device to be on part of the time.
Since the loads we deal with are slow to react to voltage changes, they behave with parts of cycles as if it were a reduction in supply voltage.
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Second Circuit.
The second circuit is just a snippet of a circuit and shows that a sensitive triac, like the one in our light dimmer, can be used to trigger a power triac. The reason this is important is because of the more current a triac can handle, typically the more current it takes to turn it on. In the case of a 40 amp triac, it could take as much as 4 amps to trigger it. A variable resistor, capacitor combo can't deliver that kind of current. The other important part of that snippet is the note which explains that the resistor has to be calculated to make sure the gate current of the power triac is not exceeded.
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Third Circuit.
This is a simple switch circuit. Realizing that the resistor in this circuit is the same as the resistor in the second circuit is the important part of this diagram. The equation shows how to calculate the value for the current limiting resistor. The resistor in this circuit is the same as the resistor in the second circuit.
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The whole story, (the first diagram I posted)
1. Start by mounting a power triac and the big resistor on a heat sink.
2. Connect one side of the resistor to MT2 of the power triac.
3. Connect the other side of the resistor to a dimmer.
4. Connect the output of the dimmer to the gate of the power triac.
5. Connect the MT1 terminal of the triac to the neutral side of the line.
6. Connect MT2 to the heating element.
7. Connect the heating element to the line voltage.

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