SCR's... silicon controlled rectifiers.. UPDATE.1/5. Works awesome.. controls the element temp with

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daveomak

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Nov 12, 2010
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I have an electric skillet, (1500 W) griddle that is thermostatically controlled...  The heat is too much...  I want to reduce the heat in the element to improve the temperature fluctuations to a more "constant on" type condition...

I'm looking at this SCR...   and I don't know squat...  but you knew that...   My idea of a dimmer switch was first then I saw the SCR...  the 2000 watt dimmer is ~$85.....


My plan is to put a 15 or 20 amp. female and male 110V plugs on this to control any resistive piece I have and make it portable......

What else do you need to know... 
 
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A couple of thoughts.  

1) A SCR control is going to limit the on time for the element going to the skillet. In essence you run the skillet on "high" and throttle back the heat by reducing the power to the element via the SCR control setting (it pulses the power instead of it being on 100% of the time).  This also limits the ability of a skillet to recover heat between batches of food.  You are basically setting a governor on the the heating element.  You could manually turn up the SCR between batches to recover the heat level and then turn it back to the desired setting when you add food if recovery time is a a problem.

Is there any heat level control on the skillet now or is it just on/off?  I presume from your description it's on/off only.  If it has an analog dial heat setting, you may can replace the control module at a reasonable cost. Typically these look something like this and the heat sensor is in the center prong.  I've never modded one of these, but there is probably a way to modify the heat band with more precise components.


If you have this sort of controller, the ultimate solution would be to modify the housing so you can put a PID temp sensor in the center prong to read the heat level and use a PID to regulate the heating element.  Yeah, it's a little more involved, but it's the ultimate solution (and it will cost more than just a SCR).  Basically you would make (or buy) a PID module that had a 110v outlet, and using the shell of the above controller just to provide power to the element and house your temp sensor, plug that into the PID box.

But, back to the inexpensive SCR option....

I would consider using a different module and making a plug and play type of box for portability (and to be a little more kitchen safe).  Instead of something on Amazon of unknown reliability (ie, made in China), I would look at some of the products Auber Instruments offers. 

You have several inexpensive options here.  Analog SSVR (solid State Voltage Regulator) dial models run  in the mid $20 range and just need the addition of a box, heat sink, power cord, and outlet to make the unit.  A SSVR is basically the cousin of the SSR's we see all the time in smoker controls.  The SSVR acts like that expensive analog dimmer you found, it's just a more modern product and uses a triac instead of a SCR to control the heating element.  It regulates the voltage output just like a SCR module based on the analog dial feedback loop created on one side of the SSVR.They also have digital display models that come in the standard DIN sizes, where you have a percentage display instead of the analog dial.

Here are the options Auber has:

http://www.auberins.com/index.php?main_page=index&cPath=53

This is their least expensive option at $29.50 with the rheostat for 110v control, model SSVR25A.  You just need to add a proper heat sink, cabinet, and the power cord and outlet to the cabinet to complete the project.  It's rated to 25amps at 110v AC (with proper heat sinking just like a SSR).

http://www.auberins.com/index.php?main_page=product_info&cPath=53&products_id=332


Add a heat sink for $12.50

http://www.auberins.com/index.php?main_page=product_info&cPath=2_48&products_id=244


Add a cabinet of your choice (Auber also sells some of these), a power cord to provide power from the wall to your cabinet with the SSVR and then an outlet on the back of your cabinet to plug your skillet in and you are done.

Or you can hardwire the box with the VSSR in the middle of your power cord for the skillet if it's long enough and you don't care about using the VSSR with anything else.
 
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I looked at the description, and it should work.

Dimmers that use SCRs (Silicon Controlled Rectifiers) work just fine for things that heat. The only time you have to worry about using them is if you are trying to control a motor. The badly translated Chinese instructions on that site make it sound like it might work for that, but I'd be cautious using it.

Finally, even though the SCR electronic control is far more efficient than the traditional rheostat, don't be surprised it it gets pretty hot. If you think that is a problem, just set up a small fan and have it blow across the metal frame to cool it down.
 
So are you saying that, even if you turn down the temperature on this controller, that the temperature on the skillet is full-on maximum? If so, then you could try eBay for a replacement controller, rather than try to make it work with a light dimmer.

To that point, I totally agree with everything in dWard51's most excellent post. In particular, the controller (whether SCR- or Triac-controlled doesn't matter) is "open loop" which means that it has no facility to measure the temperature of the skillet and then turn the element on or off to maintain that temperature. That is most definitely what you want. It is what that probe sticking out of the end of your existing controller does.

What is the exact brand and model of this skillet? If you have that, you may be able to find an exact, new replacement at the half dozen appliance repair sites on the web. Also, if you have a local appliance repair store (we even have one in our little back-water community), they can order it for you. The price will be about the same as that light dimmer you were thinking of, but you'll get the unit repaired completely, and it will function like it should.
 
Another suggestion is if you have a local goodwill or other similar store, see if they have a used unit that uses a similar controller.  As long as it fit (I would take your current one with you) and is a 110v device (pretty much bet it will be), it should work and you can pick up the appliance it's attached to for probably $5 or so.

Also check out this generic replacement unit on Amazon.  The distance between the contacts is 1 9/16" and it is for "many brands of fry pans, griddles, etc..." and the temp range is what your current unit has marked.  Listed for $14.99


They also have this one, it has the contacts closer together (1 3/8")

https://www.amazon.com/Univen-Standard-Thermostat-Skillets-Griddles/dp/B00068KZ10

And there is this Presto replacement model.  A lot of brands come off the same assembly line as Presto.

 
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I had something typed up ON SCR's, really not applicable for  your use without a specialized controller to trigger the gate after I realized I had seen one of your posts before and though I would revise it to fit what I was thinking about what you posted about using a hot plate and a refrigerator back then.

I came out of the process instrumentation and control industry, so have a little background in what you are looking to try to do and have thoughts on why it might or might not work.  If your application were holding temp on a small one inch fast flowing pipe line or a vat of 400,000 lbs of lead to make glass smooth on one side, you have to have different equipment.  Different situations require different approaches.  Always, a bigger mass is easier to control IF you have the resources to keep it constant along with the ambient heat loss.

For instance, take a look at your smoker with a 600 degree soldering iron laying in the bottom.  At a point will read a 225 temp a certain distance off the tip of the iron, but not throughout the box.  Trying to hold 80 degrees to smoke cheese on a 60 degree day, different needs also.  Different extremes need different control, A box as large as you are trying to use needs some depth in stability.  -- mass.of box, resources of enough heat..

My advice is to first fill your hot plate as full as you can with clean sand for some heater stability and see if that might be enough help to make the temperature stable after a period of time.

You need to stabilize the temperature your controller is seeing.from its sensing point in the skillet to hold your sand temp stable.  Then next question, do you have enough air flow over your sand to heat the air in the box to a relatively consistent level?  Similar to someone trying to light a cigarette in the wind.  It did not light, is the flame not hot enough, don't stick your finger in it to ck it.  No, it has to average out over the entire box, not in the right spot ,but  in this case the entire box.. 

Then see how much differential you have to the meat heating point.  Right now your hot plate is free air, flowing this way and that with swirling air flow.  What you are looking for is an average temp to hold in your smoker box, not dependent on swirls of air current inside your smoker box.

Then similar screwball example, I can sit in my driveway and make my tachometer to go to 6000 rpm, OK,lets go out on the highway and put it in high gear and show me that 6000 rpm again  Similar here, your box heat leakage will have to be overcome by the amount of heat your heat source can produce in its environment..  I think it will take quite a while for your large smoker to come up to a stabilized temp.  I hope your heat source controller can handle that operating temp if it is mounted inside.

Now,. SCR's

SCR's are like a solenoid valve in a water line.  On or off.  When the small amperage signal exceeds the trigger voltage point needed, it turns ON allowing a higher current to be turned on.  When the sensor sends a trigger voltage below the trigger voltage, it turns off the SCR, hundreds or sometimes thousands of times a second if needed.   Yes you can design or purchase a controller that you can make one pinpoint hold a certain temperature.  I would think you are looking at keeping most of your smoker a relatively constant temperature like a kitchen oven.

My electric smoker is very similar to a kitchen stove.  ON if the temp is below 220, OFF if the temp is above 230.  Meets my criteria to made great smokes set at 225 average.  Works for me.  Simple controller, On or Off.  Yep, my smoker manufacturer will sell me a controller package to keep it between 224 and 226. Over $300, so what will it do better than I am doing or my Grandma did with her on/off controlled oven baking a Christmas turkey?  Not enough for me to spend $300..

All this is just my opinion.

Keep smoking, if it works out I will definitely envy your larger smoker, keep us posted..
 
I think I got stuff confused....   What I'm attempting to do is effectively reduce the wattage of the heating element...  I would like to be able to adjust the heat output of the element from 1500 watts, when in the on position, to say about 3-500 watts or something like that...   I want the pan to get warm and stay warm...  that will allow for the heat to radiate to the outer edges and not "burn" stuff where the element is located...

It is beyond me, why manufacturers put a "427 big block" in a Volkswagen, when you only drive to the grocery store...

Do I make any sense ????
 
Two quick responses. The first is not important, but for the sake of accuracy, SCRs when used in a typical light dimmer application do not turn on and off thousands of times per second. Instead, they turn on partway through each positive (or negative) cycle of the 60 cycle-per-second (60 Hz) voltage that comes from the wall outlet. The later the SCR turns on in each cycle, the less power gets transferred to the load (the griddle in this case). Triacs to the same thing, but do it during both the positive and negative halves of each voltage cycle. Once the SCR is triggered on, it is actually quite difficult to turn it back off until the current through it goes to zero. At that point it actually turns itself off and will not go back on again until it receives a pulse at its gate lead.

As for the basic idea that having less power delivered to the heating element will make the heat more uniform, it might help, but I am not sure. Heat distribution is a function of the metal used in the construction of the cooking surface. Some metals distribute heat more readily than others (copper and aluminum are better, cast iron and stainless steel are much worse). To get the best of both worlds requires a very expensive process which builds the cookware using multiple metals, like the old copper-clad Revereware, and the more current -- and incredibly expensive -- All-Clad pans.

So, if your electric griddle is not clad (and I've never seen one that has this feature), it is going to have hot spots.

All that said, your idea of reducing the power may have some merit. I have seen recommendations in the "Cook's Illustrated" newsletter for pre-heating omlette pans on relatively low heat in order to get the entire pan up a uniform temperature. Since most cooktops (i.e., your normal cooking range/stove/cooktop) do not have any sort of temperature sensor that regulates the amount of heat delivered to the pan, what you are thinking of doing is to turn the electric skillet into a normal cooktop where you'll have to regulate the temperature yourself. Actually, because the temperature controller will still be active, it can act as a anti-burn switch to keep the griddle from getting too hot once you turn up the power on your light dimmer. After pre-heating is over you'll have to turn up the heat because once you put food on the griddle, that will decrease the griddle temperature and now that you're modifying energy with your dimmer, you'll need to compensate for that drop in temperature manually. If you don't, and you continue to apply a significantly reduced amount of power to the griddle, it will take way too long to get back up to a decent 350-375 (for pancakes) and your food will not get brown and will probably stick (paradoxically, lower temperatures lead to food sticking).
 
OK, you are now entering my secret laboratory where I conduct my experiments.....

..The SCR hooked up to an appliance extension cord..   says it will handle 1800 watts or something like that... 

....

The 2 settings I tested to determine "simmering" values...    The bubbles just "SAT" there at the 170 ish setting...

I dumped the water and the skillet surface temp went up to 300+...   The water acted as a heat sink and evaporative

cooling kept the temp constant....  PERFECT for simmering clam chowder, chili, sauces etc....    The thermostat is still functional

with the SCR...  The skillet will rise in temperature slowly for simmering or frying... 

.. ....
I am  pleased...  this unit does everything I wanted at a fair price.....  $15.49...

EDIT.. when the controller is turned fully CCW, it "appears" it cuts all voltage "down stream"..  I will have to check it with my DVM...
 
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It looks like your skillet has a black surface. Given that, an instant read point-and-shoot infrared thermometer should be able to give you a very, very accurate reading of instantaneous temperature. What's more, you can point it at various places on the surface, and you will be able to "see" the hot spots.

These gadgets are pretty cheap (about $30, if I remember correctly). I use one almost every day to get the temperature of my cast iron skillets to exactly the right searing temperature. I think you might find that using one of these will make it much easier to fine-tune your invention.
 
I have 2 IR therms....  the pan has 3/4" water in it...    IR doesn't work on water...
 
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