PID Toaster - Preliminary Questions

J. Keeton

J. Keeton

Joined
Nov 15, 2005
Messages
1,213
So I'm doing preliminary research for putting a PID controller on my toaster oven for tempering. I've read Stacy's sticky from 2008 and casually clicked though other threads on the topic. This is out of my current wheelhouse so I have some questions! Closest thing I've done to this is build Chris Crawford's DIY etcher.


  1. I have recently installed kaowool in the air jacket around my toaster oven for insulation. Am I good to leave it there? Any danger? (I will not have it in contact with the electronics)
  2. Where will be the best place to locate the thermocouple?
    1. I was thinking of building a steel structure (cage) for the blade so that it won't see direct heat from the heating elements on top or from the bottom.
    2. Would it be best for the blade to be suspended in air by means of clamping the tang to a piece of angle iron as a stand? Or sandwiched between 2 plates... with the thermocouple in contact with the blade? I could see the suspended method having higher temp swings.
    3. Could I build a "thermocouple carrier" that the thermocouple screws into... that could be attached some how to the blade surface? Anyone try that?
  3. Will a cheap ebay controller like the one below work? (Looks like it has the whole package heat sink and all... I have a spare computer fan to put on it too.)
    1. Would it need an upgraded thermocouple? (The one listed claims it's good to 400C) .... it's just short.
    2. I have a light switch that I can use as the power switch and I guess I'll have to buy a 15A fuse.

https://www.ebay.com/itm/Digital-PI...1&hash=item3d3e0daadc:g:PgEAAOSw6YtZPtYJ#rwid




The planned wiring I'm shooting for based off jtdesigns' diagram:




Am I missing anything? Any tips? I'm trying to get this done on the cheap, but I want it to work!

Edit: Any pictures of your PID toaster set-up would be greatly appreciated!

Thanks,
JK
 
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I do remember the insulation job you did on the toaster oven - good job.

While I can't comment on the actual terminals to the PID for each item, the overall wiring scheme looks good. Since you show the neutral wire as the broken line, why did you show it as a red line from the neutral buss (labeled power buss) to the PID and fan? Perhaps for clarity it would be good to label the terminal strip with the broken line as "neutral" rather than "power" since the solid line is black or power wiring?

With the heat sink that 40 amp SSR should hold up and do good. Be sure to have the heat sink in open air for cooling.
 
Don't bother with computer fan unless you plan on your electronics being tightly on the side of the oven. If you mount the electronice in a box about an inch away from the oven, they will be safe without a fan. Also, there is high temp wiring inside the oven and so long as you stay 450 F or less it should be within safety rating.

I say all that because wiring a 12v fan is kind of a pita unless the toaster already has a 12v lead you can repurpose.
 
Good points Randy - but since the fan shown in schematic is 120 vac I "assumed" it was the fan for circulating air inside oven.
 
He mentioned a computer fan in point #3.

In regards to #2.3, i believe that thermocouple has 1/4 npt thread, so you can tap your blade holder with whatever thread the thermocouple is. That kind of thermocouple will move around everytime you move the oven unless you secure it somehow. I actually carefully cut the threaded sleeve off of mine and just binder clip the probe to a blade.
 
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I apologize on the lack of clarity on the fan. I did mean a computer fan to cool the electronics. Not a circulating fan like outlined on the diagram. I stole that diagram from an old thread created by jtdesins and am looking at it as a rough guide.

My toaster oven does have a fan in it for convention, so I could attempt to incorporate that into the wiring.

R Randy3000 Good. Tips on the probe! I guess for a tempering operation it doesn’t matter if the braided wire is exposed to the oven heat? Since it’s only getting to ~475 max temp. I like the idea of building a “blade carrier” and tapping the thermocouple into the body of it. A binder clip sounds like a good idea too although I could see it being a little hairy on tempering cycle #2 while everything is still hot!:eek:
 
Build the controller in a separate box/cabinet that can site near the toaster oven. Put a 120V socket on the back of the box that is hooked to the SSR output. The toaster oven ( or any heating/controlled device) plugs in to this. Put a TC socket on the back, too. The TC should have a proper type wire with the proper plug/socket type to match the TC ( type J or K) … they are not universal, and you should not use regular coper wire.
By having the controller box separate, the controller is an independent device that can be used to control any 120VAC electric heating device ( quench tank with a heating rod, water heater, fish tank, etc.).

Here is a chap who makes the same type setup. He has them from this simple one to ones with ramp/soak capacity for kilns. This simple one would run a toaster tempering oven.
https://www.ebay.com/itm/Plug-Play-...024470?hash=item1c72422f96:g:gLUAAOSwDkVaIbOL


As to the TC placement - The TC should be in the oven in the same area that the blades will sit. The best way to insert it is from the side so it lays in the direction of the blade. You want it to not be directly exposed to the heating elements if possible. The easiest way to do that is to place a 1/8" sheet of steel on the two shelves and position the TC just below the top shelf, or set the TC on the lower shelf. The steel sheets should leave about 1" of open space on all sides for air circulation.
 
Randy3000 said:
He mentioned a computer fan in point #3.
Click to expand...

OOops, Randy, you are correct. I got wrapped up looking at schematic and forgot to read the rest of post. Again, it's a faceslap for me to slow down and read before posting :oops:
 
Here's one I built with a fan for cooling the internals.

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Stromberg Knives Stromberg Knives wow that looks great. I love it. I will do something similar to this! Pictures always help. I’m excited for this project... maybe it will a stepping stone for a DIY HT oven, who knows.
 
So I’m reading though the details on the eBay link I posted above. Relay Output contact capacity is 250V AC 3A. Power: AC 100-240V 50/60HZ. Says Output Voltage is 24-380V AC.

Does this mean it could be used for a 110 and 220 application? I just want to make sure it’s not 220V only... Is there a such thing?
 
J. Keeton said:
Stromberg Knives Stromberg Knives wow that looks great. I love it. I will do something similar to this! Pictures always help. I’m excited for this project... maybe it will a stepping stone for a DIY HT oven, who knows.
Click to expand...

I agree, pictures are always nice. By the way, I also made one with a heatsink instead of a fan. Works just as great, but it's quieter.

VmR12Ba.jpg
 
On a small amperage like a toaster oven, the SSR will be fine with just a heat sink, or with just a fan. On bigger draw loads, the extra cooling is a good thing to have. I always use a heat sink, and usually add the fan.

BTW, you need to put heat sink compound (AKA - thermal grease) between the heat sink and the SSR. Buy it on ebay for about $3 with free shipping.
 
It is quite important that the thermocouple be positioned where it is the most sensitive thing in the oven to temperature changes. It is also important that it have low thermal mass, so that it is the most sensitive thing to temperature changes and "sees" any change before the blade does. I would not use the thermocouple that comes with the controller (it looks like it is intended to fit into a large thermal mass heatsink).

I'd want an exposed-junction thermocouple made from thin wire.

TBH, I'd probably buy a TM902C handheld pyrometer off ebay for $5 delivered and use the 3'-long glass-fibre-insulated bead probe that comes with it. It seems to be good to about 400 degC, 750 degF.
 
It says pretty clear the power is "AC 100 to 220, 50 or 60 cycles" Per the specs above it'll run on anything from 100 vac to 220 vac.
 
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