Controlling immersion heating element

Hello all!

First of all, I apologise for any spelling mistakes or unclearness as English is not my native language.

I am trying find a way to (semi-)automatically control an 2000W immersion heating element for distillation purposes. As I am more of a mechanical person, I don't have a lot of experience with electronics. I have been playing with my Arduino for some time now but this will be the first serious project. I've done some reading and found a few options but I am not sure if they are suitable for me. Oh, and I'd like to, if at all possible, avoid burning my house down :D

I am not really interested in temperature based control as my liquid will be heated to and remaining at its boiling point. So adding more power will not raise the temp, but it will influence the rate of evaporation. And that, I am interested in. 2kW is nice to get to boiling temp fairly quickly but after that it will have to be lowered.

  • Option 1: I've found some people use this Solid State Relay with a potentiometer as a manual power controller.

  • Option 2: Some other people use another kind of SSR, like this one with a fancy PID controller which can give the 4-20mA output. (something called a current loop, I believe?)

  • Option 3: And lastly there is the option of using a simple on-off SSR and varying the time it is on. ( 250ms on+750ms off = 25% power, 500 + 500 = 50%, etc)

Option 1 is simple and self-contained, but it requires an operator to turn the pot to adjust power. All I've been able to find on that is: 'attach a servo'-solutions. Seems not very efficient to me.

Option 2 would require getting the Arduino to output in the 4-20mA range or use some voltage-to-current converter. I've been unable to find any (simple enough) solutions.

To me, Option 3 seems appealing as it looks quit a simple solution an I feel I could write the code for it without too much trouble. But will it control the power the same way the other options do?

I am also concerned about causing electrical interference at such a high load, which I'd like to avoid as much as possible. Is this a problem with any of the options?

So basically the summary of my questions are: - What would be the best option for my applications? Have I missed other suitable options or solutions for the problems mentioned above?

Hope it makes sense :confused: Thanks in advance!

P.s.: don't know if it matters but I'm in Europe, my mains are 230V@50Hz

That is an interesting problem since the temperature can't go above boiling... It makes it hard to build a feedback-system.

I don't see any advantage to using 4-20mA control. It would require additional circuitry.

Almost all heating/cooling systems cycle on & off rather than being continuously-variable (like a light dimmer or motor speed controller). The temperature doesn't change instantly so on/off cycling is usually adequate.

I'd go with Option 3. You could add a pot to adjust the duty cycle, but once you find the duty cycle or (average power) required to sustain a boil you wouldn't need the pot.

The amount of energy required will vary with room temperature, so you might need the pot to make small adjustments.

Hi, Does this application have to operate long periods of time unattended? What temperature will you be working at?

Option 1 and 3 are basically the same, like an electric cooker control. There is no feedback so constant monitoring by the operator will be needed, not all distillation runs will be the same because of ambient temperature, air humidity and power supply level.

Option 2 is just a power controller, it uses phase control so you will have switching noise.

It makes it hard to build a feedback-system.

It makes a feedback system just about essential and easy.

From what I gather you need to get the mash up to [u]just below boiling[/u] as quick as possible, then keep it at just [u]below boiling[/u].

No brainer. Tempsensor. Arduino UNO, Opto isolated zero crossing triac driver, or SSR Potentiometer or press buttons to set required temp (just below boiling)

Use PID programming if you like, but not needed. 5DegC hysteresis. (adjustable) With slow ON-OFF control, 30Sec sampling.

Tom.... :)

EDIT PS, SORRY see post #12, my mistake "just below boiling" should be "at boiling"

Yulaw: Hello all!

First of all, I apologise for any spelling mistakes or unclearness as English is not my native language.

I am trying find a way to (semi-)automatically control an 2000W immersion heating element for distillation purposes. As I am more of a mechanical person, I don't have a lot of experience with electronics. I have been playing with my Arduino for some time now but this will be the first serious project. I've done some reading and found a few options but I am not sure if they are suitable for me. Oh, and I'd like to, if at all possible, avoid burning my house down :D

I am not really interested in temperature based control as my liquid will be heated to and remaining at its boiling point. So adding more power will not raise the temp, but it will influence the rate of evaporation. And that, I am interested in. 2kW is nice to get to boiling temp fairly quickly but after that it will have to be lowered.

I would set up your system with 4 major components.

  • Thermal Cutoff (Thermal Fuse) mounted on vessel (NTE8115) inline with Heating Element
  • Solid State Relay with HeatSink (controlling Heating Element)
  • immersive Temperature Probe (monitoring solution temp)
  • Arduino running a two stage closed loop sequence: Stage one: turn on element until, temperature is above preset (95C) and temperature no longer rising. Stage two: start a PWM cycle from 100% working down until temperature reduction is detect.

If the heating vessel drys out the Thermal Cutoff should blow disabling the heating element.

Chuck.

So you wanna build a distillation (purposes) device/container that will heat up the liquid and reaching the
boiling point to lower down the heat and get a stable temp under boiling point but max temp so in that
way the liquid will not be evaporated.

If you will use water as I understand for distillation purposes you can use this:

Using a liquid temperature sensor connected to arduino/chip and getting the temp.C` you like
you will be able to turn Off/On the water heater or the voltage/current down to make the water at
stable under boil but max temp in the way the water will not start evaporate.

D.60

Given your post count, and unless you’re really interested in learning microcontrollers, you’d be better off buying prebuilt PID controllers (example). This particular model has a 3A/220V rated relay built in so it can control a 600W heating element (at 220V) directly, or you can use that relay as a switch to control a larger SSR or relay if you need more amperage. I’d also suggest you ensure that you buy a controller that accepts a K-type thermocouple (not just an RTD); the cheaper, RTD-only models tend to be much less precise in their temperature measurement.

You can certainly build these controllers using an Arduino, but once you add on all the parts like the display, wires, thermocouple amps, etc. you’re not really saving yourself much money (if at all). There is an economy of scale with the Arduino though; if you needed to control ~five or more heating elements each with different temperature probes then the Arduino would start to make economic sense.

Chagrin: Given your post count, and unless you're really interested in learning microcontrollers, you'd be better off buying prebuilt PID controllers (example).

+1

this is the way I would do it.

I don't understand the suggestions for using a PID in order to keep the temperature just under the boiling point. He posted that he wants it to boil. If the liquid is below the boiling point the vaporization rate will be greatly reduced as compared to boiling, even a low boil.

I really don't know how you'd monitor the rate of vaporization. There must be some way to do it. Maybe boiler pressure is one way? Alternatively, I wonder if you could determine the correct heating rate experimentally and then, once boiling is achieved, have the controller apply that much power to the heating element.

How about a microphone..

If im steaming something i know enough from the sound to stitch the kettle on and off to keep it boiling.

I wonder how well that would work. To what degree could you discriminate the rate of boiling with your ears?

Some sort of gas flow meter would probably be the best way, or so I imagine. If you could somehow weigh the liquid you might be able to measure the boiling rate that way. Maybe. The electric kettle in my kitchen senses boiling via pressure, but it only cares that it is boiling, not how violently.

Another problem with using temperature is that the b.p. is variable in a still.

I would think weighing the remaining liquid is one of the easiest way to approximate rate, and give feedback to that parameter, as mass of the remaining liquid is directly related to the mass being vaporized. I've seen papers using lasers to measure liquid levels via taking the difference in frequency but they were performed on non super heated vapor so there wasn't any risk of damaging instruments.

ApexM0Eng: as mass of the remaining liquid is directly related to the mass being vaporized.

Same holds true for the mass of the product, only a little later.

Wouldn't it be simpler to weigh the distillation product?

Hi,

Sorry my mistake, it is at boiling point, but still the control will need feedback.

Tom… :slight_smile:

jboyton: I don't understand the suggestions for using a PID in order to keep the temperature just under the boiling point. He posted that he wants it to boil. If the liquid is below the boiling point the vaporization rate will be greatly reduced as compared to boiling, even a low boil.

I really don't know how you'd monitor the rate of vaporization. There must be some way to do it. Maybe boiler pressure is one way? Alternatively, I wonder if you could determine the correct heating rate experimentally and then, once boiling is achieved, have the controller apply that much power to the heating element.

what we are talking about is a phase change. you are correct that getting enough temperature to change phase from liquid to gas is alll you need. for water, you only need to add enough calories to the remaining fluid to continue boiling.if you kept the total energy the same as when you started, the fluid would over heat and boil much faster. look at all the mis-information about Global warming. it takes the same amount of energy to turn 32 ice into 32deg water AND that same amount of energy will turn that 32 water into 175 deg water. the total amount of energy hitting the planet that melted the glaciers 20,000 years ago, and raised sea level over 300 feet, that same energy is hitting us. the NORMAL and EXPECTED result if MAN was not here is that the Earth should achieve about 175 degrees. not sure how any mathematician could come up with any other answer. so with putting a constant amount of energy into the sauce, and the volume reducing, the heat remaining constant the temperature will rise. seemingly uncontrollable. but just like the Earth, calculable. the feed-back loop would allow the operator to achieve the desired rate and then keep it there. if distillation is desired, you do not want to overheat or you will get other things in the result. and if you splatter with boiling, you can toss particulate out of the soup.

dave-in-nj: the total amount of energy hitting the planet that melted the glaciers 20,000 years ago, and raised sea level over 300 feet, that same energy is hitting us. the NORMAL and EXPECTED result if MAN was not here is that the Earth should achieve about 175 degrees. not sure how any mathematician could come up with any other answer.

I think the accepted theory is that an increase of CO2 caused more of the energy to be retained instead of re radiated.

Later increase in water vapour reversed the effect.

There are conflicting theories as to where the CO2 came from but personally i think it was all the exhaust gas when the ailens left. :o

In would be useful to know the application.

If it is indeed a still and its for hooch the traditional way is to monitor temperature of the reflux column.
The column itself regulates in such a way that means the control system does not need to be fancy.
Bloke closing dampers.

If its a steam boiler thats different.

Wow, thanks a lot for your replies! They’ve been helpful in one way or another.

Now I fear I’ve perhaps given you a bit too little information to go on, I apologize. I tried not to go too deep into distilling theory but that might not have been the best idea.

For you who are interested:
I am, as I think some of you have guessed correctly, building a system to destill a mash/wash after fermentation. It’s goal ultimately is to separate ethanol from the water and from all other nasties (a bit oversimplified but hey you get the point). So it is true my ‘liquid’ does not have a single boiling point as its composition changes over time.

To complicate things even further, I’m not building a simple pot still but a still with a fractionating column. I’ve attached a picture of a still which represents my own design quit well.
The goal of the fractionating column is to make the separation of the ethanol and all other compounds easier. This is basically done by letting the liquid evaporate out of the boiler, up through the column, condensing it with the cooler at the top and then re-evaporating it while it falls back down. Without going too much into the theory behind it, what happens after a while is that the compound with the lowest boiling point is concentrated at the top and the one with the lowest is at the bottom. By slowly removing the top one, making sure not to disturb the equilibrium too much, this still is capable of ultimately collecting nearly all ethanol at azeotropic level of 95%. By measuring the temperature of this top compound, it becomes possible to determine where the process is at.

So that means I do not want to control this temperature but, on the contrary, I monitor it (sort of as a variable) as it tells me what compound is at the top (the ethanol I’m looking for, some nasty stuff or just mostly water vapor).

By the way, the still will NEVER run unsupervised. Creating very hot and extremely flammable ethanol vapor is not something I am comfortable letting a machine do while I’m not around. Thanks for the tip about a thermal fuse, had not thought of that!

To answer the question of why not just use a PID instead of an Arduino: apart from the fact that I’m not directly controlling temperature, I looking to (semi-)automate the entire still. I already have a steppermotor and an encoder hooked up to the needle valve to control the output and some solenoids for various other things. Seems useful to me that the Arduino should handle the power as well. Cost-effectiveness is not really an important factor, its all a hobby anyway.

Now I’ve done some more reading and thinking and from the heating element’s point of view I think the process would be as follows:

  • Turn on, heat the solution to a boil, as fast as possible, max power (waiting is boring, right?)
  • Reduce power somewhat to be able to remove nasty stuff with boiling points lower than ethanol.
  • Set power so that the evaporation rate is matched to the condensing rate of the cooler and create the equilibrium with ethanol at the top.
  • Increase power slightly (when I’ve got nearly all ethanol) to collect some stuff with boiling points higher than ethanol but lower than water.
  • turn off, job done!

I think that these power settings can indeed just be a few fixed values and I’m thinking of just doing some trial-and-error to find the right ones (and using the SSR from Option 3). I might have been over-complifying things in my OP.

Just one question: if I for example want 25% power, does it matter if the element turns on-off for 250ms-750-ms or 1s-3s or 20s-60s or whatever? Is one better than the other?

P.s.: wow, one post and I already have a thread mentioning lasers and aliens, awesome! :smiley:

Fractionating Column.jpg

Boardburner2: I think the accepted theory is that an increase of CO2 caused more of the energy to be retained instead of re radiated.

Later increase in water vapour reversed the effect.

There are conflicting theories as to where the CO2 came from but personally i think it was all the exhaust gas when the ailens left. :o

and you know they left..... How?

Yulaw: P.s.: wow, one post and I already have a thread mentioning lasers and aliens, awesome! :D

it is fitting as we arre using technology that was taken from our off-world friends.

Yulaw: I've attached a picture of a still which represents my own design quit well.

no you have not.

Would be good to see.

True fractionating columns are difficult, from your description however it appears not to be the case. Water or air cooled ?

Yulaw: I might have been over-complifying things in my OP.

Just one question: if I for example want 25% power, does it matter if the element turns on-off for 250ms-750-ms or 1s-3s or 20s-60s or whatever? Is one better than the other?

Complicifcations,- more information the better.

Length of time, just make sure you switch at zero crossing, that increments of 10 milliseconds in europe