Heating Element Control

[Igor_From_Jdessa]

New to this site. Real new like 5 minutes ago. maybe this isn't the place for this question............ Why wouldn't it be possible to control a heating element with a Variable Frequency Control?

Variable Frequency Control is a system for controlling the rotational speed of an AC electric motor by controlling the frequency. You need system for controlling the power of a heating element.
Heating element is a resistive circuit. Power of a resistive circuit depends on the potential difference and resistance of heating element and does not depend on frequency. The change of frequency will not change power of heating.

How to change a power?
In resistive circuits , electrical power is calculated using Joule's law:
P = V x I, where
P is the electric power,
V the potential difference,
and I the electric current.

We can combine Joule's law with Ohm's law (V = RхI) to produce alternative expressions for the dissipated power:
P = V^2/R,
where R = constant - it is the electrical resistance of our heating element.
The change of potential difference will change power of heating.

Otherwise, P = I^2 x R
The change of current will change power of heating.

But the change of frequency will not change power of heating.

[rad14701]

The short answer is that you need to change the phase angle of the AC waveform in order to control power input... For our purpose this is generally done using one of the members of the thyristor family and most commonly by a Triac based controller... The information is here in the forums...

[AJ Cotton]

I'm assembling the parts to build pintoshine's 120v controller but not sure I understand his diagram, does this really un-technical drawing look right?



I'm using the LittelFuse Q6040J7 alternistor (TO-218X package) and saw several pages upthread that some triacs don't have insulated mounting tabs and will short when mounted to a grounded project box or heat sink, anybody know if that's a problem with this triac?

[rad14701]

AJ Cotton, the wiring diagram appears to be correct... That triac is isolated so mounting should not be an issue... Just make sure it is mounted to a good heat sink...

[grizzlypee]

Great info.
I'm new to the forum but been reading here for a few years. I'm running a reflux on a sankey keg. I'm in the US and would like to go from flames to electric. What are the differences in running 120v and 240v? kw usage? heat up time? I want to build a controller system but dont know which to go with and the different benefits. Also, does a 240v system run dual elements?

[rad14701]

Great info.
I'm new to the forum but been reading here for a few years. I'm running a reflux on a sankey keg. I'm in the US and would like to go from flames to electric. What are the differences in running 120v and 240v? kw usage? heat up time? I want to build a controller system but dont know which to go with and the different benefits. Also, does a 240v system run dual elements?

Theoretically, 240V is somewhat more efficient, but only marginally for occasional distillation purposes... The biggest issue is whether or not you have 240V access where you are running your still... For example, I'm stuck with 120V unless I pull out my electric stove and use that 240V outlet... My other option would be to run off two separate 120V circuits running two elements... Until my new boiler is completed I simply run off my stove top with a steel plate to reduce heat input fluctuations caused by cycling...

Overall, it's more of an issue of wattage and convenience than cost difference...

[new guy]

I just tried to put together a pinto controller, I added a voltmeter, it appears that I have no control of the voltage with the dimmer switch. Being electronically challenged, I dont have a clue what to look for. The voltmeter reads a constant 120 when I spin the dial on the dimmer switch. Any help would be appreciated.

[rad14701]

I just tried to put together a pinto controller, I added a voltmeter, it appears that I have no control of the voltage with the dimmer switch. Being electronically challenged, I dont have a clue what to look for. The voltmeter reads a constant 120 when I spin the dial on the dimmer switch. Any help would be appreciated.

The controller probably also needs a load in order to function properly... Do not attempt to crank the controller up without a load as you can cook the various components...

[new guy]

i did have a light plugged into the socket, the dimmer had no effect on the light or the voltmeter. help!

[rad14701]

i did have a light plugged into the socket, the dimmer had no effect on the light or the voltmeter. help!

You may need more load on the circuit, like a heating element... Do you have a picture of the wiring...???

[new guy]

sorry no pictures but I followed pint's wiring directions from page 2 on this thread, and then attached the voltmeter to the hot and nuetral screws of the outlet.

[rad14701]

This circuit works fine... I have one of these made with different components but the same layout... Mine uses a 600W dimmer, a 75 ohm 25 watt ceramic resistor block, and a 400V 40A non-isolated (only one available locally) triac...

120V 40A Controller

Edited to include triac pin-outs...

[new guy]

hey Rad, I am not real sure about reading the schematic since I am electronically challenged, but I tried to put more load on the circuit with my heat stick, the results were the same as before, no control of thr heat element, voltmeter read a constant 120 volts. I dont know what to look for? Can anyone help?

[HookLine]

If you are not up to speed with electronics and electrical stuff, I suggest you take it to somebody who is. Can get dangerous if you do not know what you are doing.

[rad14701]

As stated previously, your problem is that you're measuring voltage, which will always be 120V... The question is, does the element get hotter and cooler when submerged in water...??? Testing an element that is not submerged will cause it to fail...

If you can post or PM me a photo of the assembly I might be able to help you out more...

[Barney Fife]

I'm not very knowledgable in electronics, but, what -does- the dimmer raise or lower for control? I thought it was voltage, also. So, if frequency isn't it, and voltage isn't it, what is it? Amperage? But isn't amperage a function of voltage(lower the volts to a motor and it'll pull more amps to make up for it, for example).

I don't use a controller, yet, but I'd like to understand it more, now, in case.

[new guy]

Should i submerge my heating element in my BOP with a thermometer and then engage the dimmer to see if there is a deviation in the temperature?

[squidd]

I'm not very knowledgable in electronics, but, what -does- the dimmer raise or lower for control? I thought it was voltage, also. So, if frequency isn't it, and voltage isn't it, what is it? Amperage? But isn't amperage a function of voltage(lower the volts to a motor and it'll pull more amps to make up for it, for example).

I don't use a controller, yet, but I'd like to understand it more, now, in case.

Barney,

These devices control "power", the product of voltage and current. Yes, varying the voltage would by definition also vary the power, but that's not how these devices work. (That can be achieved by using a variable transformer or "variac").
And they don't vary the frequency either.

So, how do they work?

Think of a sine wave. In 1 second, there are 50 or 60 of them (depending where you live) in your electrical system.
So, if we were to cancel part of each of these 50 or 60 waves in each second, then we effectively reduce the power available to the load.

Another way is to have complete waves, but reduce their number in 1 second. If we reduced them to 25 or 30, then we would have reduced the power by half.

By the way, you are correct that reducing the voltage to an AC induction motor will cause the current to increase. But that is a special case. Otherwise, when a load voltage is reduced, so will its current draw.

HTH
squidd

[squidd]

Should i submerge my heating element in my BOP with a thermometer and then engage the dimmer to see if there is a deviation in the temperature?

That will work.

You are working with 240 volts, correct?
Are you comfortable with this stuff?

Be safe.

squidd

[Barney Fife]

Think of a sine wave. In 1 second, there are 50 or 60 of them (depending where you live) in your electrical system.
So, if we were to cancel part of each of these 50 or 60 waves in each second, then we effectively reduce the power available to the load.

Another way is to have complete waves, but reduce their number in 1 second. If we reduced them to 25 or 30, then we would have reduced the power by hal

Interesting! But, isn't this a frequency control? Regular frequency is 50 or 60hz, as you say, so varying that means varying the frequency, no? Not arguing, just trying to make light of something I thought I understood....

[Dnderhead]

My understanding is most of these controlers "chop" the wave.
they shut off part of the wave. how much depends on the velue you set it at,
there are others that "clip" thus limiting the peeks (cutting off the tops)thus votage. but that is more complacated used more in radio etc.
where as friquncy control whould be the same peaks but less of them in a given time. real complacated. specil aplacations.
(if I remember right ,converted to DC then back to AC at given fricency) (been a long time sense I played with any of these)
so if it chops (as most do) you still have all the peaks, and that is what you are measuring with a volt meter.(you need a oscillosope)


(how I do?)

[MuleKicker]

Here is a picture of how a dimmer switch works. Yes it does cut the waves, and what portion of the wave determines the power output. rather than the old less efficient way of resistors. I am working on building a controller that duty cycles a solid state relay to provide varying amounts of power. So here is how it works. In the states, we have 60hz current, or 1 cycle every 36 milliseconds. So most solid state relays when "turned on" stay on for 1 complete cycle or fininsh the cycle ending at the 0 point. every 36 milliseconds.....thats fast. But what if you built a micro controller and programmed it to turn on that solid state relay in varying multiples of 36? so if i turn on the relay for 144ms and off for 432ms, that would give me 4 waves on and 12 waves off, or 25% power. or 288ms on and 288ms off would give me 8 on and 8 off, or 50% power.. That is what i am in the process of building, total cost will be around $50us.

[rad14701]

The most common mistake with dimmer + resistor + triac controllers is improper triac pin identification and connection... Another common mistake is attempting to power up the controller either without an adequate heat sink on the triac... And yet another is attempting to run the controller without a proper load...

I took some pictures of my version of this controller yesterday but they weren't at angles that conveyed a clear understanding of what wires go where so I'm going to try to replace several wires with color coded wires for more clarity... My intention has been to do a photo tutorial but cash has been too tight to even purchase the few cheap parts needed to do so... In fact, I haven't even been able to make washes recently so my experimenting has temporarily come to a halt...

[Barney Fife]

What you guys are describing is precisely what the router speed controller is. You can't control the speed of an AC motor by lowering voltage, because it will try to make it up in amps and burn up, so they control them with frequency controls, which they describe exactly as y'all just did. Some quick Google work shows that many people use them(router speed controllers; henceforth known as RSC) for controlling heating apparatuses! Has anyone here actually tried a RSC? It would a nice, safe(for those without good electronics chops) and affordable control. Of course, it would have to be sized large enough for the element used, but there are some seriously powerful routers out there used in CNC applications, so they(large enough controllers) might exist.

[squidd]

Think of a sine wave. In 1 second, there are 50 or 60 of them (depending where you live) in your electrical system.
So, if we were to cancel part of each of these 50 or 60 waves in each second, then we effectively reduce the power available to the load.

Another way is to have complete waves, but reduce their number in 1 second. If we reduced them to 25 or 30, then we would have reduced the power by hal

Interesting! But, isn't this a frequency control? Regular frequency is 50 or 60hz, as you say, so varying that means varying the frequency, no? Not arguing, just trying to make light of something I thought I understood....

Barney,

In the first instance, even though the AC waves are "altered", their number remains the same in a given cycle, so there is no appearance of a frequency change.

In the second instance, it may appear that the frequency has changed, but it hasn't.

Look at it this way. For a frequency of 60 Hz, each wave lasts 1/60 = 16.666 milliseconds. That frequency/time relationship is cast in stone. It can't change. So for the portion of the cycle that the waves are ON, each one will still last 16.66 millisecond. Therefore, by definition, the frequency has not changed.

What does change, when you vary the power control, is the ratio of ON to OFF times that the power is applied to the load.

Still not sure?

Okay. Try this experiment. The speed of an AC induction motor (the kind that has the speed, either 1725 or 3450 RPM indicated on the nameplate) is fixed by two things:

1. The voltage frequency.
2. The number of pairs of poles.

So if you want to vary the speed of one of those, you have no choice but to vary the frequency.
Therefore, try it with one of those router controls if you believe that these units do in fact vary the frequency.

Let us know if it works.

HTH
squidd

[Barney Fife]

What does change, when you vary the power control, is the ratio of ON to OFF times that the power is applied to the load.


Right, and from what I'm reading, that is how the variable speed router controllers work; they just happen to call it frequency control. And again, doing some google footwork this morning reveals lots of folks using them to control heating devices. 15 amp units are under $20...!

[Dnderhead]

verying the friquency does not very the power,the same elament will work in US at 60cy or NZ with 50cy or some remote island with 40cy
and yes even on DC. (witch will lock a AC motor) .
""the ratio of ON to OFF times that the power is applied to the load.""
(no ,,the lenght of time)
the conteroler should 2x the power load . so a 15a x120=1800w .so to be safe use a 1000w (or less)elament.

[squidd]

What does change, when you vary the power control, is the ratio of ON to OFF times that the power is applied to the load.


Right, and from what I'm reading, that is how the variable speed router controllers work; they just happen to call it frequency control. And again, doing some google footwork this morning reveals lots of folks using them to control heating devices. 15 amp units are under $20...!

Barney,

Yes, these will work well. But you should allow for a bit of head room, say at least 20%. So, do not draw more than about 12 amps for a 15 amp unit. At 120 volts, this would translate to about 1440 watts - say 1500.

The problem arises when you wish to control a 240 volt 4800 watt element. That will require a substantially different unit than the one described above. They are available commercially, but are more expensive than the ones built by hobbyists out of discrete components.

HTH
squidd

[rad14701]

I think we're getting a bit off topic here as far as different theory goes... This topic was originally intended to cover Phase Angle controllers using a simple triac based circuit - nothing more... This theory is discussed, at length, early on in this topic... I think we have at least one other such topic, that I started, and perhaps more... And then we also have some Pulse Width Modulator topics and probably even a couple other methods of power control...

Dndrhead is correct in that from a reliability standpoint all components in a power circuit should be as close to double rated for their intended use... This allows components to run cooler, thus extending their service life...

Perhaps I can draw up an easier to follow schematic than the simple one I posted from earlier in this topic... They really aren't hard to build at all for 120V use... I built far more complex circuits as a pre-teen than these controllers...

EDIT: See my previous post to which I have edited for triac pin-outs...

[Barney Fife]

Harbor Freight has 20 amp controls for $34 right now. That'd be enough for a 1500 watt, 110 volt element. I'm aware that 220 would require a whole other setup, but it's the 1500w/110v I think I'd want to lower a bit when pulling heads. These days I only use my 3000 watt, 220 element for boilup, and switch to the 1500/110 when I feel the column is hot, to halfway up.

Rad, thanks for the efforts, and sorry for the hijack. We appreciate the effort to enlighten us! Part of the problem for folks like me is that I can't "read" a schematic; any way you could draw it out in layman's terms?