Oven Mod - Resister Method/Turbo Switch

[Lespaul20]

This oven mod was inspired by this post: http://www.pizzamaking.com/forum/index.php/topic,8730.0.html
 
Thanks dimarem!

Disclaimer: Like all oven mods do not try this at home. There are obvious risks modifying your oven including and most significantly fire. I have a fairly good understanding of electronics and soldering. Mod at your own risk 

My oven is an older Magic Chief electric oven which I acquired when purchasing our house. It's still in good shape and works perfectly. The stock max temp is 550 degrees F. This is probably fine for most of the recipes I currently use but I'm looking to expand so I want access to higher oven temps.

As written in the post I referenced, my oven, and I presume all ovens, uses a temp probe that changes resistance values as it heats. Augmenting this value with another resistor will cause the oven to think the oven is cooler than it really is. I my case I installed a 12K 1/4 watt resister in parallel. I actually have a compete set of 1/4 watt resistor that I used while in school. I deviated from 10K that dimarem used for no reason other than I could.

The resistor use can't be permanent since my wife and I use the oven for more things than pizza. So taking from dimarem's post I deiced to use a rocker switch I had and make it the Turbo Switch(term taken from Tannerwooden). I soldered the resistor on one leg of the switch and a wire on the other(see Pic1). The temp sensor connected to the oven control PCB with pin and socket connector. That helped because there was enough room on top of the connector to insert the wire leads from the switch without having to modify the connector.

I decided to make the Turbo Switch permanent instead of having it dangling outside of the oven. This required me to cut a hold in the top of the back panel. This was the most difficult part of the mod since the metal was much thicker than I thought and I didn't have a good way to cut it. I ended up drilling holes in a circle and using a dermal to smooth it. This wasn't problem free. The first hole was harder than I expected and when the bit made it through I still had my weight in it and managed to drive the bit into the PCB. I did damage a component but as with the resistor had several suitable replacements from my electronics kit. 

The switch looks good mounted and works great. The only down side to this mod is once you get above 550 degrees with the Turbo Switch on you cannot switch back as the oven will assume there is a problem. My oven gives the the fault code of F2 which means the oven is too hot. The solution is to wait until it cools and the Turbo Switch can be deactivated.

I've only run in Turbo Mode a few times and have yet to try a pizza . Of the few times I have run I guesstimate that I've reached at least 700 degrees at the bottom(I believe my oven thermometer was pegged). My oven is self-cleaning so I'm not worried about damage from the higher heat. I would not have modified the oven if this was not the case.

I'll try to post pizza results as I get around to it. Thanks again to dimarem for the inspiration.

Pic1 - Soldered Turbo Switch.
Pic2 - Oven Control PCB. The screws are from a previous fix I had to do about a year ago. The clip that holds the PCB in place broke making the buttons on the front unable. They are totally unrelated to this mod. The burn marked on the heat shrink are from me applying heat to the heat shrink not from components over heating.
Pic3 - Rocker switch in place and wired.

[Tannerwooden]

Hey Lespaul20.  Thanks for the nod to my joke trademark.   

Does the name Lespaul20 mean you love guitars as well as pizza?  If so, hi brother!  I have a beautiful piece of Myrtlewood in my garage waiting to be the top of a '69 replica whenever I get around to it.

I love that you mounted your switch.  In my ideal world, I would have done that too.  (ok, so actually, in my ideal world, I'd have an awesome WFO on the back deck)  But, in the interest of full disclosure, I want to explain why I didn't. 

1.  If I ever sell the house, I want to return the oven to the condition I found it in.
2.  I mounted the switch a little low on the back of the oven because I didn't want anyone who didn't know what they were doing to mess with it.  Standing in front of the oven, you hardly notice the switch.  I used double sided foam tape to attach switch to oven, and covered the whole thing with electrical taped for stability.  (pic below)  Going on one year now, I've had no problems.  I'm always pretty gentle with the switch though.  I do wish that I could have mounted mine as yours is.

I also get the F2 error.  I make a point of flipping the switch when I take the stone out after things have cooled.  A lot of people cook in my kitchen, and I always worry that I'll forget one day and someone will have a problem.  This leads to my big:

*******************WARNING!!! WARNING!!!  WARNING!!!*********************

So a month or so after putting the switch in, I wanted to make some pizza on Tuesday.  So Monday, I make the dough and stick it in the refrigerator.  Then I set the delay bake for 4pm the next day, and I flip the switch.  My mom was watching the kids on Tuesday, so I planned to tell her to pull the dough out at 3pm.  The idea is for the oven to be hot and the dough to be ready at 5 when I get home from work.  I timed the oven because I didn't want to give my mom more to deal with then the dough (watching my two boys is PLENTY to deal with). 

You may have already guessed the fatal error here.  My oven doesn't know am from pm.  You just hit an up arrow until you get to the time you want.  I didn't realize that even though I had bypassed 4 and gone on to the next 4, my oven would just turn on as soon as it hit any 4 o'clock, in this case, 4 am.  Thank God in heaven that my baby son, Quinn, woke up at 5 that morning.  When I got up to get him, I noticed that smell a pizza stone gets when it is truly hot.  Had Quinn not started crying, we probably would have woken to smoke or fire engine wails.

I freely admit that I'm an idiot.  Wild horses couldn't have dragged me to the keyboard for this story save the chance that someone else learn from my mistake.  Needless to say, I NEVER turn the TURBO SWITCH on anymore unless I or someone who fully understands the nature of the oven is around.

Happy baking!

PS  The other pic is of the back of my oven probe.  It is the small rectangle of sheet metal above and to the right of the white, round thing at the center of the pic.  I need to take more pictures and draw a couple of simple diagrams.  Someday, if dimarem or Lespaul20 don't, I'll post them all as a sort of instructional.  Only, I'll title it something like, "NOT A how to modify your oven"  just so i don't have lawyers banging on my door when you all burn down your houses.

[Lespaul20]

Thanks for the reply Tannerwooden and thanks for the trademark, I like it. I do love guitars but as with pizza making it's just a hobby.

I should say I did not mount the switch without thought. Even though the oven is still in good condition and still works great we have planned on eventually replacing our appliances since we moved in. So I didn't feel too bad about cutting a hole. If we don't end up replacing the appliances then I will figure out a way to make a plug to cover the hole and the wiring is not permanent.

Right now it's just my wife and I who use the oven and she is aware of the switch. However, it's not out of the question that either one of us would forget to check it and it would be my responsibly to make sure it's off after making pizza. 

LP

[oceanwanderlust]

Thankyou Lespaul20 and Dimarem! I built my turbo last week which has gotten me into sub-4-minute territory with noticably better pies!

I used a 11k resistor which should top out somewhere around a reasonably safe 720'. Instead of cutting any wiring on my new oven, I built a harness which simply plugs in!

My oven is a self cleaning gas Kenmore 790. After digging around Marvac Electronics for an hour, I found that the temperature probe uses:
Molex 39-01-2020
Molex 39-01-2021

The harness is simple and cheap enough that I'm looking forward to building another one with an 11-dial or big hyperjets toggle.

[benji99]

So I just attempted this mod on my self clean oven and keep getting an error f30 when using the resistor side of the switch. The oven is a self clean model and works good otherwise, just not with a 10k ohm 1/2 watt resistor in place.

Anyone have any ideas? Do I need a 1/4 watt? Lower resistance? What should my ohm readings be with the resistor in place at room temp?

[Tannerwooden]

What should my ohm readings be with the resistor in place at room temp?

I used a multimeter to determine the level of resistance on my oven probe at room temperature. Then I used a resistor which had a very similar resistance.  You are probably getting the error because you have picked a resistor which is outside of what the oven circuit thinks is an acceptable range.

[benji99]

I used a multimeter to determine the level of resistance on my oven probe at room temperature. Then I used a resistor which had a very similar resistance.  You are probably getting the error because you have picked a resistor which is outside of what the oven circuit thinks is an acceptable range.

Thanks for the response. I remember my readings being around around 1100 ohms at room temperature. This is similar to what others have experienced so I went with a 10k ohm resistor as others have had success with it. Any thoughts about what resistor I should try next?

Thanks again!

[apizza]

I am not familier with this mod, but I will say the watt rating of the resistor is not a factor. It is possible that lowering the watt rating may make the resistor overheat, depending on the current through it. The watt rating is more of a safty feature for the resistor. I believe the function of the mod is all about proper resistance

[Tannerwooden]

I believe the function of the mod is all about proper resistance

Exactly. All you are doing is attempting to duplicate the resistance your oven probe generates at room temperature.  This tricks the oven circuit into thinking nothing is getting hot.

benji99: Resistance increases with temperature. It may be that by going with a resistor that is 100 ohms less than your oven probe, you have gone outside your oven's circuit range. I would try something that is at least 11K. Honestly though, I don't really know what I'm talking about. I'm just guessing about how the oven's circuit works.

[benji99]

So I messed with my oven for just over 4 hours tonight and discovered the following, which compared to everyone's results here is the exact opposite!

My temp probe at room temp measured right at 1050 ohms. Good so far. I then started to add various resistors to one of the leads which lead to the ohm output increasing (not decreasing as I was expecting). With a 100ohm resistor, the oven was now tricked into thinking it was hotter than it actually was.

Does make sense? Also tried this with a 200ohm and 470ohm resistor. The 470ohm caused an error, the 200ohm resistor resulted in even cooler oven temps at the same setting.

I remember seeing that the room temp ohm reading of 1050 or so increased to almost 1500 ohms with the 470 ohm resistor. Shouldn't this decrease?

Help

[TXCraig1]

So I messed with my oven for just over 4 hours tonight and discovered the following, which compared to everyone's results here is the exact opposite!

My temp probe at room temp measured right at 1050 ohms. Good so far. I then started to add various resistors to one of the leads which lead to the ohm output increasing (not decreasing as I was expecting). With a 100ohm resistor, the oven was now tricked into thinking it was hotter than it actually was.

Does make sense? Also tried this with a 200ohm and 470ohm resistor. The 470ohm caused an error, the 200ohm resistor resulted in even cooler oven temps at the same setting.

I remember seeing that the room temp ohm reading of 1050 or so increased to almost 1500 ohms with the 470 ohm resistor. Shouldn't this decrease?

Help

Let me start by saying that doing this to your oven is completely irresponsible particularly if you don’t know what you are doing.

ohm is a measure of resistance. Resistors in a series are additive (i.e. R_total = R1 + R2 + …). When you added the 470 ohm resistor in a SERIES  with the probe measuring 1050 ohm, you should expect something near 1500 ohms (470+1050=1520). On the other hand, you calculate the resistance of a circuit with resistors in parallel as R_total = 1/(1/R1 + 1/R2 + …) As you can see, adding resistors in a series increases the circuit resistance while adding them in parallel decreases the resistance or leaves it unchanged. And with only two resistors in parallel, your maximum resistance is that of the lowest ohm value resistor. It doesn’t matter how high the other is. This is important as you will see below.

There are a couple different things happening in the posts above. Lespaul20 tricked the oven by adding a resistor in PARALLEL.  When he did this, the resistance of the circuit was lower than the oven expected at any given temperature, so the oven will always get hotter than it thinks it is (it has to get hotten than it expects to hit a certain resistance because the resistor added in parallel is artificially lowering the resistance of the circuit). In his case, the lower the ohm value of the resistor added, the hotter the oven is going to get at any given temperature setting. Using dimarem’s temperature/resistance data in the link at the top of Lespaul20’s post above, his oven expects 2516 ohms at 800F. However, when a 10K ohm resister is added in parallel, the resistance drops to 2010 ohm, and the oven only thinks it’s about 535F. If you know the resistance profile of your oven probe, you can match it with an appropriate resistor and calculate the oven temp based on the temperature setting.

What Tannerwooden did may have been very different.

I used a multimeter to determine the level of resistance on my oven probe at room temperature. Then I used a resistor which had a very similar resistance. 

In his mod, it sounds like he is bypassing the probe and instead using a resistor with a resistance similar to the probe to make the oven think that nothing is happening. Since resistance will not increase with temperature, he is tricking the oven into thinking it is at room temperature no matter how hot it gets. This is INCREDIBLY DANGEROUS and I can’t believe anyone would even consider doing it. The oven will never shut off no matter how hot it gets – at least not until it has a meltdown.

Even if I misinterpreted what he wrote and what he actually did was add a resistor of similar resistance to the probe in parallel, you get to the exact same place, and it is a perfect example of why you should not do these things especially if you don’t know what you are doing. Say your room temperature probe resistance is 1050 ohm at room temperature and you add a 1000 ohm resistor in parallel, as I noted above, that’s the highest resistance the circuit will ever be no matter how high the resistance on the probe gets (remember, the oven thinks resistance goes up as it gets hotter). Like bypassing the probe, the oven will never shut down no matter how hot it gets. Had his son not woken up, his house very well may have burned down.

Back to your last issue, as you added resistors in series, your oven sensed ever higher resistance and thought it was hotter than it actually was resulting in the lower temps at the same setting as you increased added resistance. The higher the ohm value of the resistor you added in series, the hotter the oven thought it was and the cooler is shut down at.

Don’t do this. It’s not smart.

[Tannerwooden]

So I messed with my oven for just over 4 hours tonight and discovered the following, which compared to everyone's results here is the exact opposite!

My temp probe at room temp measured right at 1050 ohms. Good so far. I then started to add various resistors to one of the leads which lead to the ohm output increasing (not decreasing as I was expecting). With a 100ohm resistor, the oven was now tricked into thinking it was hotter than it actually was.

Does make sense? Also tried this with a 200ohm and 470ohm resistor. The 470ohm caused an error, the 200ohm resistor resulted in even cooler oven temps at the same setting.

I remember seeing that the room temp ohm reading of 1050 or so increased to almost 1500 ohms with the 470 ohm resistor. Shouldn't this decrease?

Help

I may be misunderstanding what you are doing Benji99, and if so I apologize. It sounds as if you are adding a resistor in line with your oven probe. Is that correct?  I believe that is what oceanwanderlust did with his oven. It is not, however, what I did with mine.

My purpose in adding the "turbo switch" was to cause my oven to think it was at room temperature when in fact, it was at 700 degrees, or 800 or 1000. The oven's brain just keeps the burner on indefinitely as it continues to register normal temperatures.  To do this, I used a bypass switch. I cut into the wire leading to my oven probe and added the bypass switch there. When I flip the switch, the circuit bypasses the oven probe and instead runs through a resistor with a similar ohm value to my oven probe at room temperature. Again, if you already knew this, I apologize.

While the idea of being able to set my oven at 450 and have it heat to 750 is nice, I don't think it would be all that practical. Once you put your first pie in, you lose so much heat, you pretty much need the element on nonstop. I posted about the problem of keeping a kitchen oven hot for several pies in the "New York Style" section under, "5 Brick Baking."  Also, the oven temp isn't as important as the temperature of the stone. This is why a laser thermometer is pretty much necessary when you get into temps above 650. I tried it with one of those cheapo, hang on the wire rack thermometers. They don't really go any higher than 600. It's guesswork after that.

Again, if I am way off base here, let me know.   

[Tannerwooden]

This is INCREDIBLY DANGEROUS and I can’t believe anyone would even consider doing it. The oven will never shut off no matter how hot it gets – at least not until it has a meltdown.

I couldn't agree more, TXCraig1.  Please, Please, PLEASE! don't do this unless you really, really know what you are doing.  Look at my reply near the top of this post. I understood what I was doing and STILL nearly burned my house down. Any of these kinds of oven mods are really only for the pizza insane.

[Jackitup]

Let me start by saying that doing this to your oven is completely irresponsible particularly if you don’t know what you are doing.

ohm is a measure of resistance. Resistors in a series are additive (i.e. R_total = R1 + R2 + …). When you added the 470 ohm resistor in a SERIES  with the probe measuring 1050 ohm, you should expect something near 1500 ohms (470+1050=1520). On the other hand, you calculate the resistance of a circuit with resistors in parallel as R_total = 1/(1/R1 + 1/R2 + …) As you can see, adding resistors in a series increases the circuit resistance while adding them in parallel decreases the resistance or leaves it unchanged. And with only two resistors in parallel, your maximum resistance is that of the lowest ohm value resistor. It doesn’t matter how high the other is. This is important as you will see below.

There are a couple different things happening in the posts above. Lespaul20 tricked the oven by adding a resistor in PARALLEL.  When he did this, the resistance of the circuit was lower than the oven expected at any given temperature, so the oven will always get hotter than it thinks it is (it has to get hotten than it expects to hit a certain resistance because the resistor added in parallel is artificially lowering the resistance of the circuit). In his case, the lower the ohm value of the resistor added, the hotter the oven is going to get at any given temperature setting. Using dimarem’s temperature/resistance data in the link at the top of Lespaul20’s post above, his oven expects 2516 ohms at 800F. However, when a 10K ohm resister is added in parallel, the resistance drops to 2010 ohm, and the oven only thinks it’s about 535F. If you know the resistance profile of your oven probe, you can match it with an appropriate resistor and calculate the oven temp based on the temperature setting.

What Tannerwooden did may have been very different.

In his mod, it sounds like he is bypassing the probe and instead using a resistor with a resistance similar to the probe to make the oven think that nothing is happening. Since resistance will not increase with temperature, he is tricking the oven into thinking it is at room temperature no matter how hot it gets. This is INCREDIBLY DANGEROUS and I can’t believe anyone would even consider doing it. The oven will never shut off no matter how hot it gets – at least not until it has a meltdown.

Even if I misinterpreted what he wrote and what he actually did was add a resistor of similar resistance to the probe in parallel, you get to the exact same place, and it is a perfect example of why you should not do these things especially if you don’t know what you are doing. Say your room temperature probe resistance is 1050 ohm at room temperature and you add a 1000 ohm resistor in parallel, as I noted above, that’s the highest resistance the circuit will ever be no matter how high the resistance on the probe gets (remember, the oven thinks resistance goes up as it gets hotter). Like bypassing the probe, the oven will never shut down no matter how hot it gets. Had his son not woken up, his house very well may have burned down.

Back to your last issue, as you added resistors in series, your oven sensed ever higher resistance and thought it was hotter than it actually was resulting in the lower temps at the same setting as you increased added resistance. The higher the ohm value of the resistor you added in series, the hotter the oven thought it was and the cooler is shut down at.

Don’t do this. It’s not smart.

I coundn't agree more, I spent my time working in burn units. There's a reason why commercial equipment is made the way it is requiring spacing from wooden cabinets/walls, stronger, bigger exhaust fans, insulation etc. etc..........a few beers, full tummy, nod off and forget to turn the oven off. I put it on the level of using a turkey fryer in the garage or basement, happens all the time and poof. Even knowing what your doing electronically, this is still a coin toss in my opinion. No insult at anyone, just not a good idea.

jon

[benji99]

I really appreciate all of your input. I feel comfortable enough continue to attempt this. What I guess I don't understand is adding the resistor in parallel vs series. What I did was obviously in series and I need to add in parallel.

I've attached a diagram of what I essentially did. Could someone simply explain where the resistor needs to be added to be in parallel?

Thanks again. I understand the risks and again, feel comfortable doing this project.

[Tannerwooden]

There's a reason why commercial equipment is made the way it is requiring spacing from wooden cabinets/walls, stronger, bigger exhaust fans, insulation etc. etc.........

This raises a good point. My oven is a "self cleaning" unit.  This means that in the short term (3-4 hours, used rarely) it is designed to achieve temperatures of around 1000 degrees. I don't know how it differs from a regular oven, maybe more insulation or better materials. Modifying your oven is a terrible idea in the first place, but even worse if you don't have an oven designed for high temps.

Benji99:  I don't know exactly how the other guys did it, but wiring your resistor in parallel is pretty simple. Look at the picture.  Good luck!

[apizza]

Here's a parallel resistor calculator.
http://www.1728.org/resistrs.htm

You know one resistor is 1050, so try other values to get to a value you want test at.
Example. 1050 in parallel with 30000 will give a total resistance of about 1014 ohms.

Read TXCraig1 's post again to understand more.
Marty

[benji99]

Thanks again guys ... so is below what I am essentially needing to do?

[TXCraig1]

I really appreciate all of your input. I feel comfortable enough continue to attempt this. What I guess I don't understand is adding the resistor in parallel vs series. What I did was obviously in series and I need to add in parallel.

I've attached a diagram of what I essentially did. Could someone simply explain where the resistor needs to be added to be in parallel?

Thanks again. I understand the risks and again, feel comfortable doing this project.

I urge you again not to do this. No pizza is worth burning your house down and possibly killing you and your family. Anything I post is for educational and discussion purposes only. It is purely hypothetical and cannot be relied on for practical purposes.

Here is the difference between a resistor in series and parallel.

[TXCraig1]

Using the data from dimarem’s oven (http://www.pizzamaking.com/forum/index.php/topic,8730.msg75606.html#msg75606), you can run a regression and estimate the resistance of the probe in a reasonable range of temperatures. I calculated this to be:

Resistance (ohm) = 1.943 * oven temp (F) + 969.      [1]

Using formula 1, you can predict the resistance of the oven probe at any temperature reasonably close to the range of oven data. Using what you know about the probe resistance at temperature you can calculate the circuit resistance with a resistor in parallel at different oven temperatures using the parallel resistor formula in the picture above. Once we know the circuit resistance, we can feed that into a formula derived from a regression of the inverted oven data to predict what temperature the oven thinks it is at. I calculate this formula to be:

Oven thinks (F) = 0.515 * circuit resistance (ohm) – 498.5      [2]

NOTE: these formulae are based on data someone else gave for their oven and is generally consistent with the results Tannerwoden shared. Notwithstanding, it is critical that you collect data from your oven and make your own calculations. Understanding the how and why of these calculations is a bare minimum safety factor.

Here are examples of actual oven temperature vs. the temperature the oven thinks it is at with 10K and 12K resistors in parallel with the probe. “Max” assumes the oven will not continue heating once the oven passes what it believes to be 550F.