Stovetop Temperature Controller Hack





Introduction: Stovetop Temperature Controller Hack

This is a Zero Delta T cooking breakthrough. You've seen other Sous Vide stories, but you've never seen anything like this. Because there is so very little to see: Almost all of the gadgetry is eliminated.

To do this yourself, you will need a love of fine food and a sound understanding of electrical wiring. Materials needed are an old-fashioned non-computerized electric range, a temperature controller, a scrap electric cord with plug, and household electrical kit. 

Step 1: De-energize the Stove

Seems too obvious to mention, but I'm going to make this Step #1 anyway. Flip the breaker off, test to verify the stove is dead, pull the plug, do the job like a pro, and live happily ever after.

Step 2: Identify the Right Wires

It would probably be best to continue by cleaning the stovetop. You know it needs it. Your mother will be proud of you. And you certainly don't want to look like a slob taking pictures of this hack.

Now, lift the stove deck and identify the unique color of the wires feeding the target burner. These happen to be blue. That's it: Close it up, you're done here. The burner should not be modified in any way.

Step 3: Access the Infinity Switch

The burner controls can usually be accessed by disconnecting the panel they are mounted on. Mine was held with 5 screws. Infinity switches do fail on occasion. They are standardized and designed to be easily replaced. Wiring diagrams and diagnostic guides are available online if your stove documentation is missing.

My object was not to replace the switch, but completely disconnect it from the stove power supply. I also disconnected the switch from the indicator light, which was tied to the adjacent switch. The blue wire electrical connections between the burner and switch stay put.

Step 4: A Kinder Gentler Source of Power

Instead of 240 volts from the stove, I want this switch to operate with 120 volts from a wall outlet. So I attached a heavy-duty plug and cord. The circuit was completed the same way as the original.

This switch works correctly with half the original voltage, but now delivers half the current to the burner at any particular setting. Which is better for low-temp cooking.

Everything I'm doing here is reversible in minutes.

Step 5: Temperature Control

The new 120 volt stove line is plugged into the temperature controller outlet.

At HIGH, the burner will now draw about 300 watts of electricity. But only when the controller calls for heat. At the cooking temperatures I need to maintain, this happens 6 to 12 seconds per minute. So the burner is delivering the equivalent of continuous 30 to 60 watts of heat to the pot. That's what I use for all the LED kitchen lighting. It's fantastically efficient.

When the new stove line is unplugged, this switch and burner is completely de-energized. The rest of the stove behaves normally.

Update: Jah3 spotted an error. With half the voltage and half the current, the burner will deliver a quarter of the watts. Originally delivering a maximum of 1200 watts, the burner is now limited to 300 watts. Correction: On MEDIUM, it will give me about 150 watts, or the controlled equivalent of continuous 15 - 30 watts. Which is enough to maintain the cooking temperatures I need.

Step 6: Why? Why? Why?

I was driven to this by the need for a bigger culinary water bath. Low temp cooking has proven to be so superior, I want to use it all the time and on bigger chunks of food. Whole fish and birds for example. I looked at hot plates, countertop oven roasters, immersion heaters, deep fat friers, rice cookers, and everything betwixt. My stove is safer, and that's a comfort for multi-day sous vide recipes. My stove is also more efficient, more durable, more convenient, and far more flexible than all that junk. Plus I already own it, together with various sizes of cookware. 

See that back burner? I never even used it. I only have 2 hands, and 4 burners is functional overload for me. This burner will precisely heat various water bath vessels (formerly known as pots) from 1 quart to 5 gallons. No turkey can stop me now. Plus there is no gadgetry to clutter my precious little counter space. 

Goodbye crockpot? No, since the stove simply unplugs from the temperature controller, I can still Dork it and any other switchable countertop appliance. 

Step 7: Results

Tender, juicy, pasteurized, perfectly cooked end-to-end proteins with no bother or kitchen heat up. Slice immediately for service. You can rest, because with Zero Delta T cooking, the meat doesn't need to.

Bon appetit from Sarasota

Step 8: A Few Words on Safety

Food Safety

The simple USDA guides for safe food temperatures are based on high delta T cooking. That is to say, the temperature of the cooking medium is much higher than the target internal food temperature. For example, if you cook pork in 350F air, you must limit the cooking time to get an internal meat temperature of 145F. This results in temperature/texture/visual/flavor gradients in the food. 

With Zero Delta T cooking methods, there is no temperature difference between the cooking medium and the cooked food. Meat can and must be cooked longer at lower temperaturesfor pasteurization. However, longer cooking times generally lower the internal temperatures needed for pasteurization. This often improves flavor and texture. Whenever you cook to lower internal temperatures than USDA recommended, use the more complicated time/temp tables available online to be safe.

If you experience a power failure of unknown length during unattended cooking, you really can't tell if the resulting food will be safe to eat. So it should be tossed. It is foolish to tempt food poisoning. Many people get sick and die from this every year. If you are uncertain about any of this, call the USDA Meat and Poultry Hotline at (888) MPHotline. They have the last word on food safety.

Electrical Safety

Cody pointed out in comments that a displaced temperature probe could cause runaway heating. I completely agree and should have addressed this possibility. 

If the probe falls out of the pot, the controller may deliver continuous heat which could boil the pot dry. That could lead to smoking food and a pot meltdown and stove damage or worse. While this is unlikely, we should actively prevent the problem with unattended cooking. First, secure the probe in open water inside the pot with a bend or loose knot or something. Then turn down the burner switch to the lowest setting that will maintain cooking temperature. Longer heating cycles with less current creates a more stable water bath and is better for the controller anyway. 



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    You could have easily gotten 120 volts from the stove's existing supply. All you'd have to do is switch one of the power leads on the original control to neutral. If you choose the right one you might also be able to retain indicator lite function Just sayin

    how do you make yogurt with it? I have tried once to make yogurt and failed.

    With a bit more effort, you could add a switch and a socket to the stove and be able to use the burner in either mode whenever you wanted.

    Yes! I could have added an iPod jack, sound sound speakers, a flat panel TV, and wifi to be able to use my stove in entertainment mode too. With a bit more effort. But trying to switch circuits with different voltages on a burner sounds difficult, costly, dangerous, irreversible, and unnecessary.

    None the less, you may have a great idea. I will keep an open mind until you publish an Instructable that shows how you did it.

    I may well be doing something like this as part of another project once the budget allows me to continue working on it. I'll be sure to take plenty of pictures for you.

    The 240 volts used by the stove burner is made up of two 120 volt feeds. How safe and easy a switch would be depends on whether the stove has any 120 volt components. If it does, then you find a 3 pole switch capable of running the burner and set it to swap one of those feeds for the neutral wire used by the 120 volt stuff. Presto, your burner is switchable and it's only one switch so you won't short anything. You'll even be able to change it while the burner is running if you like. Use the high voltage to get your stuff up to temperature and then turn it down to let is simmer. If your stove doesn't have 120 volt components then you might need to hunt around a bit to find the neutral wire (if there even is one.)

    The connection for the external thermostat uses another 3-pole switch and an electrical socket (I recommend getting one of the varieties that doesn't match common appliances so nobody has any accidents.) Switch one way goes straight to the burner, switch the other way goes to the socket where you can attach whatever kind of switching mechanism you like from a thermostat to a push-button. The advantage here is that you can easily disconnect all the trailing wires when you're not using it so nobody accidentally turns on the wrong burner and melts anything (and, if they do, you don't have to take the stove apart again to replace it.) And, again, you can switch between the two at will, while it's running.

    I wouldn't recommend turning your stove into an entertainment center. Distractions while cooking usually have bad results in my experience. ;)

    1. I'm not sure what I'm looking at. Is the heating element and the temp sensor both inserted into the water bath? Could the temp sensor fall out or conk out and cause runaway heating of the water?
    2. I agree with you about the temperature consistency of the water. As we all know, heat rises, so there will automatically be circulation from the heated water to the unheated water, which will rapidly equalize and maintain the temperature.

    "I'm not sure what I'm looking at."

    That's a key problem with this Instructable: There isn't much to see. It is a method for converting a stove back burner to a builtin hot plate. Now we can have the control options that are commonly available for 120v countertop appliances, plus the safety, convenience, durability, and efficiency of a stovetop platform.

    "Is the heating element and the temp sensor both inserted into the water bath?"

    No, but I can see how the 1st image may be misleading. That was my trial run, and does not represent typical operation with a closed pot. Heat come only from the stove burner beneath the pot. One temperature probe from the controller goes into the water bath. Sometimes I put another directly into the food -- a jug of milk for example.

    "Could the temp sensor fall out or conk out and cause runaway heating of the water? "

    Since this is an unattended heating process, it's good to look at every failure mode with can find. The worst case scenario is an overnight run where the failure occurs right after bedtime. The range infinity switch and the temperature controller are both designed to fail safely.

    - If there is a blackout, or the range fails, or the controller fails, I wake up to a cold water bath and throw out the food.

    - If the power blinks, the controls keep their original setting. The process continues as though it were never interrupted.

    - If the power fails before the food is pasteurized, and lasts long enough to grow dangerous amounts of pathogens, and then comes back on for less time than needed to pasteurize the food again, there could be trouble. So it may be prudent to plug a timer into the same outlet as the controller to measure the actual processing time. Or just toss any food that has been subjected to a power failure during an overnight process.

    It is also possible for the temperature probe to fall out of the pot. Since the wire is stiff and the hole is small and there is no movement, this is very unlikely. But it certainly could cause runaway heating. This is why I incorporated the stove infinity switch into the circuit. By using 120v power and dialing down the current into the burner for long controlled heating cycles, the pot can not boil dry with continuous uncontrolled 30 watt heating overnight .

    I'm going to amend the Instructable to highlight your point about runaway heating. Thank you.

    While this is an elegant solution, it won't produce true sous vide cooking control because it still relies purely on convection to move the heat from the bottom of the pot to the top. That means considerable differences in heat and cooking in different parts of the pot.

    Temperature control is only part of the sous vide. The other part is pumped circulation that makes the temperature near perfectly even in all parts of the cooking vessel. This in turn means fewer temperature gradients inside the food.

    Thank you very much for a thought provoking comment. Let's look at your complaint about "true sous vide" from several perspectives.

    1) Zero Delta T cooking is the cornerstone of Modernist Cuisine. Widely heralded as a great break with culinary tradition, I am amused to view the sanctification Moderist dogma. As The Who taught us with We Won't Be Fooled Again, hypocrisy is baked into all revolutions.

    2) There is no mention of vacuum in this Instructable. The only place I used the phrase "sous vide" is in the very 1st paragraph. This was to highlight my process as something different from sous vide.

    I wrote: "This is a Zero Delta T cooking breakthrough." So you are objecting to a literary object that only occurred in your mind.

    3) "... it still relies purely on convection to move the heat from the bottom of the pot to the top. That means considerable differences in heat and cooking in different parts of the pot."

    This is false in every way. At cooking temperature. 99% of the heat flux occurs with *conduction* through the sides of the pot to the surrounding air. As the water bath approaches the target temperature, the pot behaves as an insulator and stops heating the water. Then the food is put into the bath. Virtually no convection can develop by applying 25 watts of heat to 20 pounds of water at that point, because there is a vanishing temperature gradient in the water. Conduction through the water takes care of the rest.

    The proof is in the illustrated results: There is no visual or tactile gradient in the protein until the surface is torch seared.

    4) "Temperature control is only part of the sous vide."

    Herein lies the fundamental problem with "sous vide." Cooking cannot occur "under vacuum." This process generates between 1000 to 2000 pascals of cooking pressure on the food. Whatever you decree in your kingdom to be an essential part of Sous Vide, time and temperature control are the *only* elements that matter to real food. Any vacuum that can be created in the cooking bag is instantly negated by evaporating water, which actually cools the food. So what you think is vacuum cooking is really vacuum cooling followed by pressure cooking from the weight of the water bath.

    5) I think it is distracting from the topic of this Instructable, but water bath circulation is interesting to me. I used circulators in the chemistry lab to regulate reactions within 0.1ºC. Circulators are also useful in commercial kitchens where large amounts of heat need to be transfered, in order to serve large amounts of protein in a hurry. Contrarily, circulators have no place in the home kitchen, which is clearly the topic at hand. In this setting, circulators serve no purpose other than creating a barrier to this otherwise very practical cooking method.

    6) Unattended electric cords and water hoses running across energized stovetops are failure points and serious safety hazards. We want simpler, cheaper, more reliable, more effective processes. Therefore, I strong recommend against using circulators with my design.