Simmerstats: The genius old tech that controls your stovetop
Summary
TLDRThe video script offers an in-depth exploration of the simmerstat, a device found in glass-top radiant electric stoves that controls the power output of heating elements through a pulsing mechanism. The simmerstat, also known as an infinite switch, achieves this by repeatedly switching the heating element on and off for varying periods of time, a method known as duty-cycle control. The script explains how the simmerstat operates, its historical roots dating back to the 1920s, and its advantages over traditional resistors or variable transformers in terms of energy efficiency and cost. It also delves into the technology's limitations, such as its compatibility with certain heating element sizes and the potential for arcing. The video concludes with a discussion on the potential for modern solid-state switching components to replace the simmerstat for more precise control, while also acknowledging the simplicity and effectiveness of the simmerstat's crude technology.
Takeaways
- š„ The glass-top radiant electric stove uses a component called a Simmerstat, which is responsible for the pulsing behavior of the heating elements.
- š”ļø The Simmerstat, also known as an infinite switch, modulates the power output of the heating elements by using duty-cycle control, which is the method of switching the load on and off for varying periods of time.
- āļø The heating elements in a conventional electric stove are large resistors capable of high wattage outputs, making them unsuitable for gentle cooking tasks like simmering without a device like the Simmerstat to control their power.
- š” The technology behind the Simmerstat is quite old, with its origins dating back to a 1924 patent by Chester I Hall for General Electric, and it was used in coil-top stoves to modulate power output.
- š The control knob of the Simmerstat adjusts the duty cycle, which is the percentage of time the heating element spends powered over an average period, allowing for fine control over the heat output.
- š© The Simmerstat is essentially a double-pole single-throw switch with a bimetallic strip that deforms with heat, causing the switch to open and close, thus controlling the power to the heating element.
- š The bimetallic strip in the Simmerstat bends as the copper bar heats up due to the electrical current flowing through it, and this deformation causes the switch to open and interrupt the power flow.
- š§ The cam mechanism attached to the control knob presses down on the switch contacts, and its profile determines how far the contacts are pushed down, which in turn determines the temperature at which the switch will open.
- š°ļø The Simmerstat has a memory effect that helps with the reaction time of the cooktop; when the power level is changed, the Simmerstat produces a long pulse of output to help the burner reach the new target temperature quickly.
- š ļø The simplicity of the Simmerstat makes it cost-effective, but it does have limitations, such as not working correctly with loads outside of its rated current range and potential arcing issues due to the lack of snap-action in the switch.
- š Modern solid-state switching components could potentially replace the Simmerstat for more precise control, although this would likely increase the cost and might introduce new challenges such as increased noise from the switching frequency.
Q & A
What is the primary function of a simmerstat in an electric stove?
-The primary function of a simmerstat is to modulate the power output of the heating elements by using duty-cycle control, allowing for fine control over the heat without significant energy losses or high component costs.
How does the pulsing behavior of a radiant electric stove's heating element work?
-The pulsing behavior is due to the operation of the simmerstat, which periodically interrupts the power to the heating element. As the control knob is turned away from the highest power setting, the length of each power interruption increases, creating a pulsing effect that repeats indefinitely.
What is the technical term for the component that enables the pulsing behavior of a stove's heating element?
-The technical term for the component is an 'infinite switch,' which is also known as a 'simmerstat.'
Why are conventional electric stove heating elements not suited for gentle cooking tasks like simmering?
-Conventional electric stove heating elements are large resistors capable of outputting a high amount of power (e.g., 1,200 watts or more), which is suitable for boiling but too intense for gentle cooking tasks like simmering.
How does a simmerstat achieve control over the power output of a heating element?
-A simmerstat achieves control over the power output by repeatedly switching the heating element on and off for varying periods of time, based on the temperature of its internal bimetallic strip and the position of the control knob.
What is the difference between a simmerstat and a variable transformer in terms of controlling power output?
-A variable transformer, such as a variac, can produce a range of voltages to lower the power consumed by heating elements. In contrast, a simmerstat controls power output by using duty-cycle control, which involves switching the load on and off for varying periods of time to achieve the desired average power level.
Why are glass-top radiant electric stoves able to produce near-instant heat output from cold?
-Glass-top radiant electric stoves can produce near-instant heat output because their heating elements, made of nichrome wire, heat up very quickly when voltage is applied across them, glowing brightly and transferring heat rapidly.
How does the special ceramic material in the glass of a radiant electric stove affect the heat transfer?
-The special ceramic material in the glass is poor at conducting heat energy through itself, keeping the stovetop cool to the touch, but it allows infrared radiation to pass through almost completely unimpeded, enabling the radiant heat to reach the cookware efficiently.
What is the purpose of the sensing probe in the heating element assembly of a glass-top stove?
-The sensing probe serves two purposes: it activates the hot surface indicator to warn users that the cooktop is still hot, and it is connected to a safety switch that cuts power to the heating element if the temperature under the glass gets too high, protecting the glass from damage.
Why is the switching frequency of a simmerstat potentially too slow for glass-top stoves?
-The switching frequency of a simmerstat might be too slow for glass-top stoves because the radiant heat is transmitted immediately through the glass, and the pulsing behavior of the heating element may be noticeable during cooking, which could affect the evenness of the heat distribution.
How does the control knob of a simmerstat influence its operation?
-The control knob of a simmerstat is attached to a cam that presses on the switch contacts, closing them to allow current to flow. The cam has a ramp profile that determines how far the top switch contact is pressed down, which in turn determines the temperature at which the bimetallic strip will cause the switch to open, thus controlling the duty cycle and power output.
Outlines
š„ Understanding the Simmerstat in Electric Stoves
The first paragraph introduces the glass-top radiant electric stove and its unique pulsing behavior when the heating elements are adjusted to medium power. The explanation revolves around the 'infinite switch' or 'Simmerstat,' which is responsible for this pulsing action. The Simmerstat allows for fine control over the power output of the heating elements through a method known as duty-cycle control, which involves switching the load on and off for varying periods of time. The paragraph also touches on the history of this technology, dating back to the 1920s, and its cost-effectiveness over other methods like variable resistors or transformers.
š”ļø The Workings of the Simmerstat and Glass-top Stove Heating Elements
The second paragraph delves into the thermal dynamics of the heat distribution in coil-top stoves versus glass-top stoves. It explains how the heat is transferred through the sand-filled metal tube in coil-top stoves, which obscures the pulsing behavior due to the thermal mass. In contrast, glass-top stoves feature a heating element assembly with a nichrome wire that heats up quickly, providing instant heat output. The special ceramic glass of the glass-top stove allows infrared radiation to pass through, which is why the heat is felt immediately. The paragraph also discusses the sensing probe for the thermostatic switches and the safety measures in place to prevent the glass from overheating.
š ļø Dissecting the Simmerstat: Duty Cycle Control Explained
The third paragraph provides a technical explanation of how the Simmerstat functions as a duty-cycle controller. It describes the difference between duty cycle control and pulse-width modulation (PWM), noting that while both involve cycling a load on and off, PWM can serve other complex tasks beyond power modulation. The paragraph also explores the internal components of the Simmerstat, including its double-pole single-throw switch nature and the bimetallic strip that deforms with temperature changes, causing the switch to open and close periodically.
š© The Mechanical Operation of the Simmerstat
The fourth paragraph focuses on the mechanical operation of the Simmerstat, highlighting the role of the bimetallic strip and the copper bar's thermal behavior. It demonstrates how the switch contacts open and close based on the temperature of the copper bar, which is influenced by the current flowing through it. The cam mechanism attached to the control knob is shown to adjust the duty cycle by changing the resting position of the switch contacts, thereby controlling the temperature at which the switch opens.
š°ļø The Simmerstat as a Thermostat and Its Predictable Switching
The fifth paragraph explains the Simmerstat's core function as a thermostat, which is used to control the temperature of the copper bar before it switches off the cooktop burner. It describes how the cam profile determines the specific temperatures at which the switch opens and closes, creating a consistent duty cycle. The paragraph also discusses how the device uses the heat generated by the current passing through the copper bar to maintain a specific duty cycle, effectively acting as a heater and a thermostatic switch.
š© Adjusting the Simmerstat for Different Heat Settings
The sixth paragraph illustrates how the Simmerstat adjusts its operation based on the selected heat setting. It describes how a higher setting causes the switch to close for a longer duration until a higher temperature is reached, while a lower setting results in shorter and less frequent pulses. The paragraph also addresses the limitations of the Simmerstat when used with heating elements outside its rated current range and the potential issues with arcing due to the lack of snap-action in the switch.
š¤ Modern Alternatives to the Simmerstat
The seventh paragraph contemplates the relevance of the Simmerstat in modern times, comparing it to induction stoves which do not require such components. It suggests that while the Simmerstat is effective for coil-top stoves, it might not be ideal for glass-top stoves due to the slower switching frequency. The paragraph ends with a consideration of modern high-power solid-state switching components that could potentially offer more precise control over cooktop burners and a tease about a future project involving a simple recipe.
š¶ Wrapping Up with a Taste of November in April
The eighth and final paragraph humorously wraps up the video with a few light-hearted remarks and a pun about cooking. It includes some playful banter about the challenges of timing the operations of the Simmerstat and the host's intention to attempt a simple cooking project soon. The paragraph ends with a smooth jazz background, signaling the conclusion of the video.
Mindmap
Keywords
š”Glass-top radiant electric stove
š”Infinite switch
š”Duty-cycle control
š”Bimetallic strip
š”Thermostatic switches
š”Nichrome wire
š”Ceramic material
š”Pilot light
š”Cam mechanism
š”Arcing
š”Induction stove
Highlights
The glass-top radiant electric stove uses an infinite switch, also known as a Simmerstat, to control the pulsing behavior of the heating elements.
Simmerstats are wired to each heating element, modulating power output through periodic interruptions.
As the control knob is turned down from high, the heating element goes off and on, creating a pulsing effect that adjusts based on the knob's position.
The Simmerstat operates by using a bimetallic strip that bends with heat, controlling the flow of current to the heating element.
The heating elements in a conventional electric stove are large resistors capable of outputting significant power, which is not ideal for gentle cooking tasks.
The Simmerstat is a cost-effective solution to regulate the high power output of stove heating elements.
The technology behind the Simmerstat dates back to the 1920s, with its first description found in a 1924 patent by Chester I Hall.
Coil-top stoves also use Simmerstats to modulate their power output, although the pulsing behavior is not visible to the user.
Glass-top stove heating elements are made of a zig-zag piece of nichrome wire on a heat-resistant disc, providing instant heat output.
The special ceramic glass of the stovetop allows infrared radiation to pass through while remaining cool to the touch.
The Simmerstat functions as a thermostat, with the control knob adjusting the temperature at which the switch opens and closes.
The Simmerstat uses a cam mechanism to adjust the duty cycle, which is the percentage of time the heating element spends powered.
The Simmerstat's bimetallic strip has a memory effect, which helps the stovetop react quickly to changes in power level settings.
The Simmerstat can maintain full power when set to high by using a high point on the cam profile to keep the switch firmly closed.
Simmerstats are designed to work with specific heating element sizes and may not function correctly with loads outside of their rated current range.
Modern high-power solid-state switching components could potentially replace Simmerstats for more precise control, although at a higher cost.
The Simmerstat's switching action, while not ideal for modern standards, provides a simple and effective method for controlling the power output of stovetop burners.
Transcripts
This is my stovetop.
Itās a glass-top radiantĀ electric stove and if youāve ever used one of these,
you might have noticed somethingĀ interesting about its behavior.
The heating elements quickly begin to glow once switched onĀ and you can feel the intense heat coming from them right away.
but when you turn the control knobĀ down to, say, medium power -
the element simply goes out.
Itās not still running but at half-power,Ā itās just off.
But then, before too long, it comes back onā¦
then switches back off.
This pulsingĀ behavior endlessly repeats.
Whatās causing that?
The answer is this funky component calledĀ an infinite switch,
also known by the much, MUCH better name Simmerstat.
It may not look likeĀ much, but each heating element in the cooktop is wired to one of these things,
and the simmerstatsĀ are responsible for that pulsing.
Let me show you -
through the magic of buying two of them, andĀ some other stuff,
Iāve built this little box so I can control anything with a simmerstat.
IāllĀ plug in a lamp to make what itās doing obvious in addition to a mystery load on the other outlet
which isnāt important right now.
Let me just stick on a control knob.
Thatās better.
Set to high, theĀ simmerstat doesnāt interrupt power flowing through it at all,
but when you move it off of the highestĀ power setting, eventually power cuts out.
However, the interruption is pretty brief.
Eventually, power returns.
TheseĀ periodic interruptions will repeat indefinitely, but as you turn the control knob further clockwise,
eachĀ interruption increases in length.
Once you reach the medium setting, it will eventually settle into a point where it spends roughly equalĀ time on and off.
And then the trend will continue - if you go further, it only operates in brief pulsesĀ and those pulses get farther and farther apart.
The reason the simmerstat behaves likeĀ this is becauseā¦
This is kind of the only option.
Electrically, the heating elements in aĀ conventional electric stove are merely resistors,
a very simple component.
But those resistors are huge!
EachĀ one in this stovetop is capable of outputting at least 1,200 watts and the larger ones pump outĀ three kilowatts.
Thatās great for boiling water, but way too much power for more gentile cookingĀ tasks like, oh, whatās a good example,
Oh! A simmer.
To allow for that, we have to tame them and reduceĀ their power output.
But how would you do that?
You might think of adding a second resistorĀ in series with the cooktop element, maybe even a variable resistor.
but at these power levels, that theoreticalĀ resistor would have to be gigantic
and as it restricted current flow it would generate quite aĀ lot of heat of its own which is both wasteful energy-wise and would require cooling.
So instead you might wantĀ to use a variable transformer such as a variac to produce a range of voltages to choose from -
lower the voltage and you lower the power consumed by those heating elements.
But there we have aĀ similar problem:
to handle this much power, that variable transformer would have toĀ be quite large and thus quite expensive,
and remember youāll need four.
So,Ā to allow for fine control over the power output of the heating elements withĀ minimal energy losses and component costs,
the simmerstat was born.
This device producesĀ any arbitrary power level by repeatedly switching its load on and off for varying periods ofĀ time,
a method known as duty-cycle control.
Before I explain whatās going on inside here,Ā though, I want to point out that these things arenāt by any means a recent development.
In fact, the tech is quite old.
Coil-top stoves going back to the 1940ās use these sameĀ exact controls to modulate their power output.
As a matter of fact, the tech just had itsĀ 100th birthday.
The first place I found it described is in this 1924 patent for Chester IĀ Hallās invention assigned to General Electric.
Coil-style heating elements like this areĀ also just giant resistors,
so just as with the glass-top stoves which came later, theĀ simmerstat was the most cost-effective way to regulate their output.
That means coil-topĀ stoves are exhibiting this pulsing behavior, too.
However you generally arenāt aware of this happening with a coil-top stove because you canāt see it.
The heat produced by these coils is generatedĀ by a thin wire element embedded in the center of the hollow metal tube which actually forms the coil.
But the gap between the wire that produce heat and the walls of the tube is filled with a sand-like material.
The sand fills the tube so it can be bent into different shapes with the wire inside staying centered,
whichĀ keeps you from getting electric shocks.
Which is pretty nice.
But to get the heat produced by theĀ wire element out of the tube and into cookware,
it must make its way to the outer surface,Ā meaning it also has to warm up all the sand in the way which is a lot of thermal mass.
The upshot is that it takes a long time for these elements to get hot enough to visibly glow,
so the pulsingĀ behavior of the simmerstat is visibly obscured.
The elements below a glass-top stove are very,Ā very different though.
If I explained them would that be a tangent?
Well itās not directly related toĀ simmerstats so I suppose it would be,
but too bad - I bought this so we gotta discuss it
(I expensedĀ it).
This heating element assembly is whatās actually under the glass of many glass-top radiantĀ electric stoves.
Itās incredibly simple, just a flat disc of heat-resistant support materialĀ hosting a very long zig-zaggy piece of nichrome wire.
Actually, two - this is a selectable sizeĀ burner just like this one on my stove at home,
composed of a six-inch inner-section and anĀ outer ring to fill it out to the whole 9 inch diameter for larger cookware.
Theyāre not all madeĀ exactly like this, sometimes the heating elements are structured a little differently,
but they allĀ work the same way: when voltage is applied across the nichrome wires,
they get very hot very quicklyĀ to the point of glowing brightly.
That speed is the main functional advantage of a glass-topĀ stove: near instant heat output from cold.
But youāll notice that in open-air this looksĀ very bright and orangey like the heating elements of a toaster.
Thatās because, well, thatāsĀ pretty much what these are!
But, you say, under the glass of a stove these appear a deepĀ cherry red when operating.
Why is that?
Well, this glass is in fact a special ceramic materialĀ with some very peculiar characteristics.
Itās deliberately very bad at conducting heat energyĀ through itself
which keeps other areas of the stovetop cool to the touch even when parts rightĀ next to it are hot enough to melt lead.
But the glass lets infrared radiation pass right throughĀ it almost completely unimpeded.
Thatās what allows the radiant heat produced by the heating elementsĀ under the glass to make it into your cookware,
and why you can feel intense heat coming fromĀ them right away once they're switched on.
The deep red color seen through the glass is the resultĀ of filtering:
the glass is opaque to almost all wavelengths of visible light, making itĀ appear black to our eyes.
But since it passes infrared light just fine,
the near-infraredĀ frequencies at the very edge of the visible spectrum will escape that filtering andĀ you can see them.
Pretty wild, right?
And if youāve ever noticed the probe thing goingĀ across the center of one of these burners and wondered what itās for,
well two things,Ā actually:
this is a sensing probe for two thermostatic switches in this little remoteĀ enclosure.
The first of those switches is very sensitive and closes its contacts in theĀ presence of minimal heat
to illuminate the hot surface indicator (or indicators) to warn you thatĀ the cooktop is still hot.
Count your blessings if you get a separate light for each burner,
moreĀ often than not theyāre all wired in parallel so any one of them can light up just a singleĀ warning light.
Those cost-cutting cost-cutters.
But the other switch in here is wiredĀ in series with the heating element itself.
Remember that this flat discĀ of searing heat is trapped below glass,
and while that glass is transparent to infrared,Ā itās not perfectly transparent so it will absorb some heat energy and get quite hot.
Plus, evenĀ if it were perfectly transparent to infrared,
thereās gonna be a piece of cookwareĀ on top of the glass which reflects some of the heat energy right back down and into the element.
Therefore, tremendous heat builds up in the tiny littleĀ sliver of air space between the glass and the bottom of this infernal frisbee.
To protect theĀ glass from getting too hot,
the temperature probe will open a safety switch to remove power from theĀ heating element and keep things from getting all melty.
It usually resets in a matter of a fewĀ seconds,
but will kill power again if it needs to in order to enforce a high temperature safetyĀ limit.
This usually only occurs if the burner has been in continuous use at full power for severalĀ minutes,
such as when bringing water to a boil.
Anyway, this video is supposed to be about theĀ simmerstat.
But, before we talk ab - no Iām kidding.
Earlier I said that these modulate the powerĀ output of the cooktop burners using duty cycle control.
If that doesnāt mean anything to you,Ā thatās just a way to say āthe percentage of time spent powered over an average.ā
Imagine you haveĀ a 1,200 watt burner unit but you only need 600 watts of output for whatever particular cookingĀ task youāre doing.
Well, If you run that burner with a 50% duty cycle,
perhaps by running it forĀ 5 seconds of every 10 second period,
then although the actual heat output will be alternating betweenĀ zero and 1,200W,
over time the effective heat output is the full power multiplied by the dutyĀ cycle -
in this case, 1,200 X .5, or 600 watts.
Those of you who are more digitally minded mightĀ be thinking about pulse-width modulation just now.
Duty cycle control and PWM are quiteĀ similar when it comes to their net effect of producing a lower average power output by cycling aā¦
whatever on and off repeatedly,
but the two terms technically describeĀ different things.
Some might choose to argue with me on that, but PWM isnāt necessarilyĀ trying to modulate the power output of anything.
In fact it can be used as a signaling protocol forĀ fairly complex tasks.
Servo motors, for instance, are sometimes controlled through PWM signaling.
The length of the pulses they receive encodes a position for it to assume.
When you are using PWMĀ simply to modulate power output,
say when you use a PWM dimmer to reduce the intensity of DC-poweredĀ LEDs,
strictly speaking that is still duty cycle control:
the apparent brightness of the LEDsĀ is determined by what percentage of time they spend on vs. off,
which is literally just anotherĀ way to say their duty cycle.
Pulse width modulation in that context is simply a modern means toĀ the end of attaining duty cycle control,
with the added benefit of high switching frequenciesĀ providing it with some functional advantages.
But since the simmerstat is literally 100-year-oldĀ tech,
well there aināt anything modern in here.
Yet it absolutely is a fully-functional,Ā fully-capable duty-cycle controller.
How on Earth could that be?
Well, letās lookĀ inside the simmerstat to see whatās going on.
That, uh... that is less clear than youādĀ think.
So first, because weāre- I'm gonna turn this off now.
Because we're dealing with the US split-phase electrical system here,
inĀ the 240V circuit this is used to control there are two hot wires and no neutral.
The heatingĀ elements of a cooktop are wired across line one and line two just like any other 240V device.
You can learn more about that in this video if you'd like.
Because of this fact, this deviceĀ has two switch contacts in it,
here and here,
so that it can open both sides of the circuit whenĀ switched off and completely isolate the heating element from voltage.
That makes the simmerstatĀ at its core a double-pole single-throw switch.
Now the left side of the simmerstat doesnāt actually matter at all for its power modulation purpose.
Thatās reallyĀ just an extra isolation point breaking line 1,
and itās only ever open when the controlĀ knob is in the off position.
In all other positions itās closed.
Oh, and this extraĀ copper piece here is used to send power out to a pilot light to indicate that aĀ cooktop burner is switched on.
Thatās why the terminal on the back is labeled P and whyĀ they didnāt bother giving it a proper contact surface -
itās just sending a tiny little amountĀ of current to a neon indicator like this one.
Youāll notice, though, that the right side ofĀ the simmerstat features a much more robust pair of switch contacts,
one of which is attachedĀ to a wide copper bar.
This is the contact that regularly opens and closes to modulate powerĀ output.
Uh, to hopefully avoid confusion,
remember that you only have to break oneĀ side of a circuit to kill current flow.
When the other switch is closed but this one isĀ open the heating element will still have 120V potential on it from line 1
but there isn'tĀ a complete circuit to line 2 for any power to actually flow through it.
Except the pilot light - wellĀ the pilot light is only operating at 120V and the other side of it is connected to neutral
so thatĀ stays on no matter what cooktop burner is doing.
Iām very sorry our power system is weird.
Justā¦Ā ignore everything on the left. It doesnāt matter.
Moving on,
if we look at the backside of theĀ copper bar hosting our main switch contact
weāll see something that looks an awful lot likeĀ a bimetallic strip.
Because it is.
These little heroes show up in the darndest places.
Whyās itĀ in here?
Well, this copper bar carries the current flowing through to the cooktop heating elementĀ when the switch contact is closed and power is flowing.
And thereās a small amount of electricalĀ resistance across the copper bar -
itās too small to measure with a multimeter
but itās enough to produce a bit of heat when the 10 or 11 amps drawn by the cooktop burner flows through it.
BimetallicĀ strips deform when they change in temperature,
and since there's one attached to this copperĀ bar which weāve just established gets warm when current flows through it,
the bimetallicĀ strip will start to bend as that happens.
Now, unfortunately I canāt really demonstrateĀ this well in-circuit.
Youāll see why in just a moment.
What I can do, though, is useĀ this little heat gun and show you what happens when the support bar warms up.
ItāsĀ pretty subtle, so watch closely.
When hot, the copper bar bends such that the bottom switchĀ contact moves deeper into the simmerstat body
and farther away from its partner above.
Now, think about what that means.
If the copper bar warms up whenever the switch isĀ closed and power is flowing,
and that warmth causes the bar to bend such that the switch will open,
then the switch does not want to stay closed.
Any time it is closed, it heats upĀ and the bimetallic strip then tries to open it.
In practice, it looks like this.
From belowĀ we canāt see the switch contacts but we can see the copper bar moving back and forth everĀ so slightly.
Every time the switch is closed and power flows to the load, the copperĀ bar begins to warm up because of internalĀ resistance.
We can see this quite clearlyĀ with the thermal camera.
As that happens, the bimetallic strip bends the bar such thatĀ the lower contact begins moving closer to the camera and away from its partner.
EventuallyĀ the strip bends far enough to break the circuit, so current stops flowing.
Once it does,Ā though, the bar rapidly begins to cool down.
That causes it to reverse course and startĀ moving closer to the other switch contact,
then they actually touch, current can flow again,
the bar warms up, and the cycle repeats.
And now, letās see if you make a TechnologyĀ Connection.
I'm using a lamp right now plugged into the simmerstat.
And that lamp, because of the simmerstat, is flashing.
Iāve covered a certain other piece of tech which we use to make lamps flash in the past.
ThatĀ piece of tech is put in-series with the lamps itās meant to flash.
Current flowing through itĀ would cause a switch inside to briefly open then shut repeatedly.
Iām speaking, of course, aboutĀ the turn signal flasher.
These old-school thermal flashers also work thanks to a bimetallicĀ strip.
That strip will deform when heated and open or close a switch (depending on theĀ design particulars)
which repeatedly applies and removes power to the incandescent lamps which form the turn signals toĀ make them flash and thus more noticeable.
Now that behavior is certainly aĀ great deal faster than the pulsing the simmerstat is doing right now
but itās not reallyĀ any different, is it?
Itās the same thing, just sped up.
And at its core, this simmerstatĀ really is just an overgrown turn signal flasher capable of handling up to 11 amps of current atĀ 240V, or 2600W.
But the simmerstat is a flasher with a twist -
uh, literally.
The turn signalĀ flasher has a fixed duty cycle and behavior, at least when controlling the same loadĀ at the same voltage.
But the simmerstat can adjust its duty cycle based on the position of the control knob.
Why? And how?
Y'know, in Britain they call cooktop burnersĀ hobs.
Does that mean that this is a hob knob?
Anyway, when we were looking at this from above,
you mightĀ have noticed that the switch contacts were nowhere near each other.
Theyāre clearly sprung such thatĀ they default to the open position,
so what closes those switches in the first place?
To find out,Ā letās switch to the Cam Cam. ā« Offenbach plays out of nowhere ā«
Itās this cam!
I donāt know how I live with me either.
TheĀ control knob of the simmerstat is attached via a shaft to this plastic cam covered inĀ a copious amount of grease.
When assembled, the cam presses down on these protrusions onceĀ rotated out of the off position, and that is what closes the switch contacts.
Youāll notice theĀ cam has two sections with different profiles -
the inner section presses on and closes the switchĀ on the left of the simmerstat which remember, doesn't matter.
Itās just a safety switch.
But the outer section, which engages with bimetallic switch, has a very subtle rampĀ built into it.
Can you see that?
This is the off position which doesnāt press on the switchĀ at all.
But just to the left of that position, the cam profile gets very tall.
That meansĀ it presses the switch down quite far.
But then thereās a fairly steep dropoff before theĀ cam very subtly gets thinner and thinner all the way back to the off position.
Can you figureĀ out why that might be?
Vote now on your phones.
What that varying cam profile actually doesĀ as you turn the knob is change the resting position of the two switch contacts in the bimetallic switch.
You canĀ see from below that as I turn it, the copper bar and bimetallic strip are moving up and down veryĀ slightly.
This might seem pretty inconsequential,
but that right there is actually the key to thisĀ whole device.
But explaining why... is complicated.
Iāve been stuck on this script for a while becauseĀ although this component is incredibly simple,
there are three connected concepts allĀ working together here to make this what it is,Ā Ā
and that makes it hard to explain withoutĀ getting stuck in a loop.
But Iāll try.
Letās revisit that footage from earlier.
Here,Ā the simmerstat was set to medium and I let it stabilize.
In this condition, the switch isĀ closed for about 5 seconds before it opens,
and then it stays open for about 5 seconds, and thisĀ repeats.
Thatās how we get a 50% duty cycle.
But why precisely is the switch opening andĀ closing with such predictability?
To find out, letās look at the thermal camera again.
Youāll notice that at this setting, the contactās support bar seems toĀ peak right near 100 degrees Celsius,
then the temperature begins to fall.
We thenĀ see that it consistently bottoms out right near 78 degrees Celsius and it begins to riseĀ again.
This tells us that the switch is actually opening and closing based upon the temperatureĀ of the support bar and its bimetallic strip.
Simple enough, but why, though?
Why is theĀ circuit opening and closing at those specific temperatures?
Well, thatās because of this cam and how far itās pushing down on the top switch contact.
Remember that the bottom switch contactĀ retreats into the body of the simmerstat as it warms up.
How far that contact actually moves isĀ a function of the temperature of the bimetallic strip in the support bar.
And through the positionĀ of the cam and its profile,
we have chosen to place the top switch contact at some specific pointĀ along that deflection path.
In this position, the contacts are forced to stay together untilĀ the copper bar has reached 100 degrees Celsius.
At that precise temperature, the deflection of theĀ bar is sufficient to open the switch.
So really, the core function of this device... is a thermostat.
Through turning the knob,
weāre deciding how hot we want to allow that copper bar to get before it switches off the cooktop burner.
So, the last piece of the puzzle isĀ how that choice becomes a consistent duty cycle.
Because remember, the goal ofĀ this device is not to maintain a specific temperature like the thermostat in an oven,
butĀ to maintain a specific duty cycle and thus power output for the cooktop burners.
Yet somehow weāre doing that with whatĀ ostensibly is a thermostat.
Well, hereās where I hope it all comes together.
Remember thatĀ the copper bar inside here is both a thermostatic switch AND a heater.
Whenever the switch is closed, itĀ dissipates a consistent amount of power and that generates a consistent amount of heat withinĀ the bar.
And like all heat-producing things, with a consistent power output
howĀ hot it actually gets and thus how far the bar will deflect is a function of howĀ long that heater runs in a given period.
And now physics becomes our friend.
Letās say I changeĀ the knobās position to that of medium-high.
What that will actually do is press down farther onĀ the top switch contact
to force the two contacts to remain together until the lower support barĀ has reached 130 degrees.
So, letās do that.
The temperature of the bar, since power is now flowingĀ through it, is climbing.
But youāll notice that the rate of change in temperature is slowing down asĀ it continues to increase.
Whatās happening here is the result of the fact that the bar is approachingĀ the limit to how hot it can possibly become
before the heat it gains through its internal resistanceĀ matches the heat that leaves through radiation to the air surrounding it.
And as we approachĀ that limit, heat gain slows significantly.
This means that it will take longer to reach theĀ new target temperature of 130 degrees,
which in turn means that the switch contacts will stayĀ closed for a longer period of time before they open again.
And adding to that, the temperatureĀ differential between the bar and the air around it is greater when itās hotter
whichĀ means that once it stops being heated, itās going to lose heat energy faster than it didĀ before.
That shortens the time the switch spends open before it closes again,
though that effect isĀ minor compared to the stretching of the on-time.
But what about going in the other direction?
What happens when you turn the knob to, say, medium-low?
Well, with the knob at the nineĀ oāclock position, the cam is only very slightly pushing on the switch.
Itās pushing so gently thatĀ the bar only needs to hit about 60 degrees Celsius before it bends enough to open the switch.
SinceĀ thatās much closer to ambient temperature than 130 or even just 100 degrees,
it takes a veryĀ short time for it to reach that temperature when being heated by the current passing through.
And youāll notice that the switch only closes again when the bar drops to about 40 degreesĀ Celsius -
but it takes quite a while for the bar to cool to that temperature,
so the pulsesĀ it sends out are both short and infrequent.
Do you see how this all fits together?
We areĀ really controlling this circuit based on the temperature of the heater inside of it.
WhenĀ calibrated correctly, that can be used as a duty cycle controller.
Because to get that heaterĀ hotter, the heater itself must run with a longer duty cycle,
so its average temperature becomes anĀ effective proxy for the duty cycle necessary to attain that temperature.
And thatās incrediblyĀ fortuitous.
Just calibrate the bimetallic bar to dissipate the right amount of heat when theĀ circuit is passing current,
give the cam pressing on the switch a nice subtle ramp to allow you toĀ break the circuit at a specific temperature of that bar,
and you can produce any duty cycleĀ you need with incredibly crude technology.
But it gets even better!
Because the switchingĀ action occurs based on the temperature of the bimetallic strip,
thereās a really helpful memoryĀ effect happening here.
The main annoyance of using a conventional electric stove is the reactionĀ time.
The thermal mass of the materials involved retain heat for a while,
either the coil ofĀ a coil-top stove or the glass of a glass-top.
Thatās useful because it helps smooth out theĀ effect of the pulsing behavior
but it also means it takes a good while for the cooktop toĀ react to a change in power level.
The simmerstat canāt solve that problem, but consider whatĀ happens when you change the power level:
If, say, you were on a medium-low heatĀ but needed to move to a medium-high heat,Ā Ā
then your turning of the knob is simplyĀ changing how hot the internal heater needsĀ to get before it cuts power.
And if at theĀ medium-low setting the heater was maintaining, letās say, 80 degrees on average,
then when youĀ change the setting itās gotta get all the way up to 130 degrees before it switches the elementĀ off.
That means itās going to produce a very long pulse of output and help the burnerĀ get to your new target as quickly as possible.
The same goes when you lower the output - if itāsĀ already quite hot,
then turning the knob will open the switch and it wonāt close again untilĀ the heater has fallen down to the new target,Ā Ā
which is going to take a while.
I firstĀ noticed this behavior of my glass-top stove and assumed that this was being accomplishedĀ with logic but nope!
Thatās just how this works!
Now Iāve left something important out.
You mightĀ wonder how the simmerstat can keep the element on at full-power when it's set to high.
Well, thatāsĀ what that really high point on the cam profile was for.
That just really jams that switch down soĀ itāll never open no matter how hot the bar inside is getting.
Pretty crude, huh?
Exceptā¦ the crudeness doesnāt stop there.
This particular simmerstat only works correctly with fairly large heating elementsĀ that draw the 8.9 to 11 amps itās rated for.
Thatās because how quickly the copper bar heats upĀ depends on how much current passes through it.
If you try and control a load outside of that range,Ā things get out of whack.
Through sheer dumb luck, this 1,100 watt hot plate draws about 9 ampsĀ at 120V,
so this simmerstat works correctly with it.
The hotplate has been my mysteryĀ load throughout the video.
But if I plug in this smaller hotplate which only draws 900Ā watts,
the duty cycles this is meant to produce get all out of whack.
And with a load muchĀ smaller than that, it never interrupts power.
You also might have noticed that the way thisĀ switches the load is terrible!
Switches ideally should have a snap-action to reduce arcing when they break electrical loads.
This fella just doesnāt.
The contacts barely move despite switching 10 amps,
and so some fairly nasty arcing occasionally happens.
Itās notĀ too too bad because these are just used to switch resistive loads,
and the overextension ofĀ the switch as the cam presses down produces a wiping effect that helps to clean theĀ contacts of carbon buildup and debris.
Incidentally, that also happens inside the switches ofĀ an electromechanical pinball machine
and yes part three is coming I havenāt forgottenĀ about it hold your horses!
I just thought a script like this one would be faster.
Why didĀ I think that?
I donāt know. It never works!
Anyway, before I end this video I want to makeĀ sure I say that not all simmerstats are going to function exactly like these ones do.
For instance, theĀ simmerstats on my stove at home?
Three of the four canāt possibly use the current flowing throughĀ them to heat the bimetallic strip inside because they have selectable size elements.
One even hasĀ three sizes.
I suspect the core functionality of these simmerstats is exactly the same as this simple one,
but thereās probably a dedicatedĀ resistor with its own path back to neutral producing the heat for the bimetallic strip,
thatĀ way the duty cycles are consistent regardless of the load they're controlling at any particular time.
I also think it mightĀ be controlling a relay or, another possibility,
the knob could actually be controlling a variableĀ resistor producing differing amounts of heat to open a limit switch.
I kinda think that might be the case becauseĀ these have a definite click as they cycle on and off which this basic model doesnāt.
Thatās just a guess,Ā though - Iām not tearing this apart.
I need it.
And by the way, I built this box for this videoĀ but Iāve been wanting to build something like it for quite a while
specifically because of theseĀ cheap hotplates.
If youāve ever used one, you might have noticed that they are impossible to control!
Thatās because this knob is not controlling a simmerstat - itās just a plain olā thermostat.
NoticeĀ it only clicks on when youāre well away from the off position.
You can kind make this work forĀ what you need,
but itās incredibly hard because you donāt even know where itās measuring theĀ temperature and itās going to change based on whatever cookware you're using
Itās a bit easier to controlĀ this style of hotplate
where the heating element is embedded in a metal disc and its averageĀ temperature kind of means something,
but this coil style is flat-out impossible to control withĀ a thermostat.
Iām sure itās just a lot cheaper than a proper simmerstat - I mean, these thingsĀ are like $15.
But itās incredibly annoying and makes these pretty much only useful for boilingĀ water.
I thought I was going to end up building, like, an Arduino-based controller or something
but it turns out you can just stick a simmerstat in a handy box and be done!
I added the lights becauseĀ it pleases me.
The red one is the pilot light and the yellow one indicates power is flowing.
Uhā¦ I will not show you how I made that work.
And a final point: it could be argued thatĀ we really shouldnāt be using these anymore.
I mean, if you get an induction stove itās not goingĀ to have them, but donāt get me started on the touch controls those often have -
hey,Ā note to appliance designers, nobody wants that!
Just use knobs.
Touch controls on a stove would be like taking away a carās turn signal stalks and forcing people to adapt to weird buttons for noĀ good reason at all.
Anyway, what I mean by that is the simmerstat works great with coil-top stoves since these heating elements retain so much heat,
but with glass-tops, where radiant heat is transmittedĀ right through immediately, the switching frequency is arguably too slow.
I donāt often notice this,Ā and to be honest Iām not sure it actually matters,
but when Iām frying up some veggies in a thinnerĀ piece of cookware,
I can tell when the element is running and when itās not.
The sizzling gets aĀ little louder whenever itās on and if thereās any water in the bottom of the pan, it bubbles moreĀ vigorously.
Again, Iām honestly unsure of how much that actually matters,
but Iām not a goodĀ enough cook to pretend my opinion is any good.
Anyway, with modern high-power solid-stateĀ switching components,
cooktop burners could in theory be controlled with as much finesse asĀ a dimmer switch provides.
That would cost more, of course, but at this point Iām not sure howĀ much it would.
I mean, induction stoves have some wild power-switching circuitry in them and theyāre not very expensive anymore.
Now, the main thing Iād be worried about in this hypothetical is actually noise.
These fellas make a fairly noticeably humming when theyāre switched on,
and adding someĀ high-frequency switching to that mix could turn that hum into a weird ring.
But hey, evenĀ just, like, a 1 Hz switching frequency would be a huge improvement over the simmerstats inĀ my stove at home.
Something to think about.
OK. Well, thatās it!
I think.
Didnāt imagine thisĀ script would get so out of hand.
I mean itās literally just a bimetallic strip in a box with a knob.
But at this point,Ā I donāt know why Iām surprised.
Here - how ābout we gey a taste of November in April?
I think Iām gonnaĀ make something actually simple before the month is out.
Can I rise to the challenge?
Find out onĀ the nextā¦ whatever.
Whenever it happens.
Bye.
ā« dutifully smooth jazz ā«
Iāll plug in a lamp to make what itāsĀ doing obvious in addition to the
eahhhh
The ans- [strange noises]
However, the interruption is pretty brief.
Eventually, power returns.
[eventually stretches on]
[laughs]
This is gonna be harder to time thanĀ I thought it was going to be
Once you reach the medium setting, now -
oh right, thatās whatās supposed to happen
These periodic interruptions will repeatĀ indefinitely,
but as you continue to control the turn knob further clockwise [breaks into laughter]
Earlier I said these modulate the power output of the cooktop burners (loud thud)
that was loud!
But to maintain a specissssffsfsfsfssfs
You've heard of a flash in the pan,
what about a flash below the pan?
I think that joke needs a little more time in the oven, don't you?
Half-baked at best.
But hey, at least I made a meal out of it.
Soup's on!
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