Heating Element Control

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Heating Element Control

Postby cwood » Thu Oct 26, 2006 10:56 am

What about a Router Speed Controller....? I believe they are just HD rheostats, not the preferred variac.However, because they are designed to regulates the speed of a router motor, probably up to 3 HP at say 10-15 amps, wouldn't that do just as well...? Easy to plug into wall, and plug heating element into Speed controller....??? Not too pricey either..... Anybody ever done that??? Feed back............??

Thanks,

CW
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Postby masonjar » Fri Oct 27, 2006 7:22 am

What's an HD rheostat?

I can't say much without knowing more about the type of motor and speed controller the router uses. If the motor is an AC brushless, then the control would have no effect at all on the heat output. If it's a DC motor, then it might work great - or it might blow up the speed controller, depending on how it's designed. I'll spare you the details unless you really want an explanation.

Don't use a rheostat, they waste too much power. Variacs are too expensive and bulky. I would use a triac. I almost did this recently, but found a free electric stove that someone was throwing out, so there was no point anymore. But, if you're any good with a soldering iron, you can build a very cheap, very simple controller that would work great with a heating element. It's the same principle as a light dimmer switch. The triac connects and disconnects the element to the power source on and off at 60 times a second, and varies the amount of power by changing the ratio between time spent on and off. I think a lot of electric stove-top burners use this method. If you're interested, I can show you the plans that I was going to use. The parts were going to only cost a few bucks.
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Postby Tater » Fri Oct 27, 2006 8:09 am

No elect cook stoves dont use those type switches .Most use a switch called a infinite switch.That are a on and off type Hi being on all time med being on 50 percent of the times cycle they are set for.
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Show me the plan

Postby tonkyman » Fri Oct 27, 2006 12:20 pm

Hey Masonjar! I'd love to see your plan if its for a 115-120volt circuit. All I can find are for 220-240 volt circuits and it's been way to long since I had electronics in school. Most of the triac circuits look simple it's just knowing what part numbers to put together.

Thanks a bunch,
Tony T
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Postby masonjar » Sat Oct 28, 2006 9:03 am

Wow Tater, you're right. I thought infinite switches made a clicking noise when they cycled on and off and since my burners don't make any noises, I assumed they were triac controlled. But I just removed a heating element and connected the oscilloscope in its place and saw a plain 60 Hz, 165 volt sine wave no matter where the control was set, which means it isn't triac controlled. Interesting.

Tony, what are the power requirements for your switch?
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Postby tonkyman » Sat Oct 28, 2006 11:37 am

Hi Masonjar,
My heating element is a 120 volt 1500 watt element. My home power will vary from 115V to 125V or so.

If you can help me out can you also let me know where to find the parts. The last circuit I built I hunted IC's from about 5 different places and the good old Radio Shacks don't really carry "electronic parts" anymore.

Thanks for your help,
Tony T
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Postby cwood » Sat Oct 28, 2006 2:13 pm

So does this mean somebody is gonna post a schematic, etc. for a good temperature control circuit...? I have access to all the parts.....I wasn't really looking to do a PID controller or anything, just a turn-up..turn-down sort of item...but who knows...I build tube amps and they work great.....I mean really, all we need is a "variable voltage regulator"....

Seems to be an iatem a lot of home distillers would be interested in.

Thanks,

CW
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Postby Hackers » Sat Oct 28, 2006 3:58 pm

If you do a search around this site I posted schematics for both a Triac and a twin heat triac controller modification about a month ago. Only problem for you is it was 230V but you should be able to adapt the parts list if you know your stuff. 8)
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Postby masonjar » Sat Oct 28, 2006 6:22 pm

I need to find a web host before I can post a schematic.

Hackers, do have 50 Hz power where you're at?

I buy parts from www.digikey.com
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Postby Hackers » Sat Oct 28, 2006 9:12 pm

Yes here in New Zealand our voltage is 230V 50Hz (+/- 6%)
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I'll get it posted

Postby tonkyman » Sun Oct 29, 2006 6:10 am

Hey Masonjar,
Send it to me and I'll get it posted and then post a link to it here.

We have 60 hz power here in the land of the not so free, but I'm sure you know that.

Later,
Tony T
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Postby masonjar » Mon Oct 30, 2006 7:53 am

I still need to run some numbers to tweak the capacitor for 120 volts, but I haven't forgotten.

If you're in a hurry, you could use Hacker's circuit and reduce the values of C2 and C3 by about half. That should get it pretty close. There's also a trim pot in his circuit for tweaking. If you have tons of capacitors laying around, as I would expect for someone building tube amps, then you can find the proper values experimentally (but don't use polarized ones). The idea is that you slowly charge the capacitor through a potentiometer and when the voltage of the capacitor reaches the trigger voltage for the triac, it turns on and stays on until the next AC zero crossing. If the capacitor is too large, it will never charge up enough to trigger the triac, making the burner never turn on. If the capacitor is too small, it will charge up right away and turn the burner on prematurely. The perfectly sized capacitor is the one that turns the burner on immediately when the potentiometer is set to high and it never turns the burner on when the potentiometer is set to the lowest setting. You need an oscilloscope to really see that it's doing what you want.

The problems with this very simple circuit are that the control response is not linear (the control is the most sensitive in the middle range) and that it can generate some high frequency noise (possibly make some funny lines show up on your TV). Hacker's circuit may correct these problems some since it is a bit more complicated than just one resistor and one capacitor, but I can't tell just by looking at it.

A better way to do this would be to rectify the AC into DC and put that on a somewhat large storage capacitor, then a MOSFET could be used to switch the burner on and off. This would give a perfectly linear control. The next addition/complication would be to put a temperature sensor in your still head and read that with a microcontroller which controls the MOSFET and you could have a digitally tunable PID and regulate the still head temperature to exactly where you want it. Then you could get even more thorough and have the microcontroller also operate a servo on your reflux valve. But that would take all the fun out of it, wouldn't it?
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not in a hurry

Postby tonkyman » Mon Oct 30, 2006 8:58 am

Hi Masonjar,
I'm not in a hurry. I want whatever is the simplest. I live in the woods and don't care if I cause a little radio noise.

I only neeed to be able to cut the power back from 1500 to 1000-1100watts. My element is about the right size for my boiler but once it getsup to temp I could cut it back a little bit to save on energy and get a tiny bit better product. I have a rolling boil now but I would like to have a simmering low boil. Any energy above that is just wasted anyway.

Thanks for your help
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Postby cwood » Mon Oct 30, 2006 4:50 pm

Well stated. And since my company designs/builds Glycol Dehydration packages for the oil/gas industry, I could draw up a P&ID, runit through drafting, send it to purchasing...viola! All my parts come in and I only have to do some smuggling and a bit of fraud. Actually, i don't mind turning a valve now and then.I'd like to see the schematic and go from there.....

Thanks,

CW
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Postby pintoshine » Sat Nov 11, 2006 1:48 pm

I have a bit of experience building alternister triac controls capable of controlling 120vac or 240vac at up to 40 amps.

For the 120 volt ones, I use an off the shelf light dimmer, driving a Littelfuse alternistor rated at 600v and 40A. The part is available from Mouser for less than $8 USD. I put a 75 ohm 25 watt ballast resistor in series with the off the shelf light dimmer. The output of the light dimmer goes to the gate on the alternister.

For the 240v controls I use the triac chip from the light dimmer but I replace the pot with a 500k ohm and the capacitor with a .1 microfarad rated for 400v. I like the polyester film typ of capacitor. I used to use a lot of them in tube amps.

The alternistors put out about 20 watts of heat running on 240vac so a nice finned heat sink is required to keep it cool. I usually build the whole thing in a double sized outdoor outlet box and add stainless steel face plates. I have always bolted these on, over top the elements. This makes a neat setup.

The circuit, typical on most dimmer circuits requires the control to be turned up to about 1/3 power before it will come on but it can be turned way down after that.

I would be glad to provide part numbers and diagrams if anyone is interested.
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Love to see it

Postby tonkyman » Sat Nov 11, 2006 3:43 pm

Hi pintoshine,
I'd love the part numbers and drawings. I'm still looking for a way to control my 120V 1500w element.

Thanks for sharing with us.


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Postby pintoshine » Sat Nov 11, 2006 6:01 pm

I get my parts at Mouser.com

Image

Others have gotten this one to work also depending on the store bought dimmer.
Image

This one costs about $11.00 USD

For the power you are talking about, the aluminum sheet the store bought dimmer is on should be heavy enough to absorb the heat from the alteristor.
Last edited by pintoshine on Tue Dec 12, 2006 7:53 pm, edited 5 times in total.
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Postby pintoshine » Sat Nov 11, 2006 6:05 pm

I forgot to mention, I drill the rivets out of the dimmer to get mor area to mount parts. I drill a small hole and use a 6x32x0.5 inch bolt and nut to mount the alteristor onto the dimmer plate.
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Simple

Postby tonkyman » Sat Nov 11, 2006 9:24 pm

Dude! That looks simple. I Ordered the parts from Mouser so I should be able to knock one out next week --- Thanks a bunch.

Later,
Tony T
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Postby masonjar » Sun Nov 12, 2006 1:24 am

Looks like I dropped the ball on this one :-) I actually ordered the parts so I could personally test the controller before handing it out to anyone. This is a clever idea to use the commericially available, low-amperage dimmer switch to trigger the high-amperage triac, though.

I think there might be an error on the schematic though. Shouldn't the resistor connect to the other side of the plug?

The triac I ordered was the 30 amp Q6030LH5. You really don't need a 40 amp triac for this, but it won't hurt anything either - and might actually dissipate less heat. The peak current draw will be less than 20 amps for your 1.5 kilowatt burner.

The reason it doesn't start until you turn the knob past 1/3 of the way is due to the 75 ohm series resistor, which has to be there in order to not blast the gate of the triac with the full 120 volts.
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Edited to help future builders.

Postby pintoshine » Sun Nov 12, 2006 6:34 am

I'll double check the circuit. I drew this one up from memory. If it is wrong, it won't take long to fix it. :oops:

You are right, one small correcection. I forgot to tell you that the previous circuit diagram is now correct. I changed the image file.

Edit 2005:11:25 both diagrams are posted now.
Last edited by pintoshine on Fri Nov 24, 2006 11:37 pm, edited 2 times in total.
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Show us what you got

Postby tonkyman » Sun Nov 12, 2006 8:48 am

Hi MasonJar,
I'd love to see what you've come up with also. I love to build stuff like this and try it out. Once you get your parts and build one show us a diagram so we can build one.

Thanks a bunch,
Tony T
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Postby pintoshine » Sun Nov 12, 2006 9:23 am

These are the original diagrams that led me to think of such a circuit.
Typical dimmer circuit...
Image

How to use a sensitive triac to control a power triac...

Image

How to calculate the limiting resistor value...

Image

I could not resist the temptation to use the off the shelf dimmer.
I can buy the whole circuit for the control less than the parts. Its nice to have a mounting plate also. Whenever I build the 240 volt ones, I replace the pot and the cap. The off the shelf ones are not rated high enough on the capacitors. I tried it with disasterous results. The caps exploded and stank the place up really bad.
Last edited by pintoshine on Tue Dec 12, 2006 7:55 pm, edited 1 time in total.
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Postby masonjar » Sun Nov 12, 2006 9:51 am

In Pinto's most recent post, the first schematic is what I was going to give you except with a higher amperage triac. It should work with slightly less accuracy without the DIAC, so I was going to attempt that as well. My parts came a few days ago - I was waiting for some ambition to come my way. :-)
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Postby pintoshine » Wed Nov 15, 2006 5:38 pm

Have your parts come in yet?
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not yet

Postby tonkyman » Thu Nov 16, 2006 7:07 am

My parts have not come in yet but I did notice Mouser charged my Credit Card on Monday. Maybe they'll get her today or tomorrow.

Later,
Tony T
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They're here

Postby tonkyman » Fri Nov 17, 2006 5:18 am

Hi Pintoshine,
My parts were at my house when I got home from work yesterday. I can't wait to build this little thing over the weekend. Is the diagram with the light dimmer correct now? it looks like it is to me but what do I know :D

I do have a couple of questions on the other diagrams above though. The top one with the Diac and the Triac, can the Q2010l5 be replaced with a higher rated Triac? Also, the 100 ohm resistor and the .01 uf capacitor. is the cap there just for spike suppression and the resistor to bleed the charge once the power is removed from the circuit? I also assume that C1 is there for spike control. Please correct me if my theory is incorrect because it's been 25 years since I had any of this is school and I've not used it since.

You have another circuit that just has a resistor and switch across the gate of the triac, could the resister be a variable pot to control the gate and give a rough adjustment. I don't want to use it for still control but I've been working on a oxy/hydrogen generator that I think it would be useful on if that is the case. Right now I'm using 120v with a full wave bridge connected to several generator in series but it would be nice to be able to turn the voltage down a bit.

Anyway! thanks for the great info.

Tony T
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Postby pintoshine » Sat Nov 18, 2006 6:52 am

I understand your confusion. Let me explain each circuit in a little better detail.
--------------
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.
-----------------------
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.
------------------------
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.
------------------------
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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Postby pintoshine » Sat Nov 18, 2006 7:14 am

I hope this is enough information. I know it was a long explaination. By under standing the circuits and their relation ships allow for other modifications. One nice modification is to the third circuit and replace the reed switch with a ttl level, isolated photo diac. This allow switching from the parallel port on your computer. This is what I use. I wrote some nice c# software to allow me to turn the element on and off rapidly with a known pulse width. My computer also has k-type thermocouple interface to allow me to monitor and log vapor and distillate temperature.
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Thanks

Postby tonkyman » Sat Nov 18, 2006 9:28 am

Dude! That was great. I want to thank you for taking the time to explain how the stuff works. I have all my parts today and I intend to find time to build it.

I'd love to build the top circuit just to say I did. The parts are CHEAP on Mouser so I would want to buy enough to make several. Do you mind giving me the part replacements if I were to make circuit one in a 220-240 volt lets say 40 amp --- I'll order all the parts at one time to save on shipping. I love stuff like this, thank you so much.

Tony T
Last edited by tonkyman on Tue Mar 10, 2009 5:27 am, edited 1 time in total.
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