Cadco CSR-3T hotplate modification

[still_stirrin]

A few times I've been asked about my Cadco hotplate modifications to control heat input instead of temperature with the thermostatic control. So, I think I'll add a build thread with my hotplate mods.

Note, the hotplate is already built, so I'm showing what it looks like now assembled and functional. I'll also include the bill of materials for the modifications as well. This should give you innovative members a place to start.

modified hotplate

Here's a close up view of the controls. Notice, I reused the power switch that came on the Cadco 3T. But I did remove the thermostat control (look for it in a later photo).

power control knob

Next, turning the hotplate over, you'll see how to remove the bottom panel and expose the "goodies".

removal of bottom panel

So, with the bottom removed, this is what it looks like inside. Please note that this is after the modifications are done. You'll note the insulations that I put on the steel air channel that draws air from below the hotplate up through the element. I put the fiberglass insulation there to keep the heat from the element focused on the stock pot boiler and isolated from the circuitry I added inside the case.

bottom opened for viewing

Look it over...it looks complex, but is really quite simple. When you see the schematic, you'll understand better what the components are. This is the "high level view". More to come...
ss

[still_stirrin]

Continuing on, this slide shows how I mounted the internal equipment to the case...pretty simple really...just screws and nuts. Also, you'll see the reuse of the hotplate's lighted power switch for the same function...to power the hotplate on/off. Again, look to the schematic for the circuit logic.

Oh, and here's a photo of the thermostat element that I removed from the Cadco 3T. It was located where I've reinstalled the control potentiometer. I didn't even have to redrill the hole for it to fit.

old thermostatic control (removed)

This slide shows the potentiometer installed adjacent to the power switch. You'll see the wiring is quite crowded in the area. I used 10 gage wires for the power circuit and insulated them with fiberglass woven wire covering. I didn't want the PVC jackets on any of the wires to melt in the hot environment...thinking "safety" here.

controls and fan on front panel of case

Also, you'll get a glimpse of the cooling fan I installed to pull hot air out of the case. The Triac generates a lot of heat, so I wanted to duct it out, again for safety's sake.

cooling fan mount

And this is the power supply for the fan, since the fan is a 2" 12VDC 125mA (16.1CFM) fan, I had to convert some of the 120VAC source power to 12VDC. I could have built a power supply circuit, but instead I purchased a wall wart with the proper specs and removed the plastic case to mount inside the Cadco 3T. I mounted the power supply with wooden boards to insulate it from the rest of the case electrically.

fan power supply board

It works well. I have a switch (refer to schematic diagram) to turn the fan on/off. In addition, I wired in a lamp so I could see that it was switched on...although you certainly can hear the whine of the fan when it's spinning. The lamp is just a visual indicator in case the radio is blaring too loud.

More on the way....
ss

[still_stirrin]

This slide shows the triac mounted to the heat sink (you've gotta' use one of those). I use heat conducting paste between the heat sink and the triac case as required. I also attached the heat sink directly to the Cadco steel case to further act as a heat sink for the element. I have not had any overheating resulting from this installation, and I've run the hotplate a full power for an extended period of time.

triac mounting in case

This slide shows the wires routed inside of the fiberglass woven wire case (it's like your oven has on the wires as well, if it's electric). You'll notice the wire inside the jacket that routes out of the Cadco case to the small project box. That's for the ammeter. With all the equipment stuffed inside the case, I simply didn't have room to add the ammeter, so I added it externally. The project box is screwed to the Cadco case and houses the ammeter for convenience. Inccidently, I use the ammeter to set my power adjustments. It give a very good reading of the relative power input (approximation).

ammeter power input/output

This is the view from the "business end".

ammeter face

Next well get into the control circuit board. Hope you're following me so far.
ss

[still_stirrin]

OK, you've been waiting for the circuit board through the "boring stuff". Here it is.

circuit board view 1

And another view...

circuit board view 2

And finally, the schematic of the hotplate (with modifications).

schematic diagram

And last, but not least, the components bill of materials (BOM).

BOM

The triac I selected is a 40 amp 600 VAC rated triac. So, it has plenty of margin of safety for this measly 1500W element.

In fact, this circuit would work for any element up to approximately 20 amps. The limiting factor is not the electrical components. Rather, the limitation is the ammeter and the wiring for the power circuit. I've used 10 gage wires for the power circuits, so it should be good for 30 amps (it is copper wire).

This circuit would work 240VAC systems with slight corrections to the resistors, in particular the control potentiometer. The 250K ohm isn't enough "sweep" for a higher source voltage. Similarly, the trigger voltages would be different and so the divider circuit would need to be addressed.

I have two of the (same) power control circuits in my big keg boiler because it has two 4500W elements installed. However, I run those from separate 120VAC 20A circuits because I do not have 240VAC power in my still house. So, the tandem control circuits allows me a very fine degree of control for the boiler.

I hope those who've asked about my triac powered hotplate can make sense of this assembly. I do realize that there are SSR controls which can do the same type of controls. But for me, building the triac powered circuits was easy and fun. And it allowed me to creatively integrate the system inside the Cadco 3T hotplate.

It works great.
ss

[Yummyrum]

Quite possibly the best documented build for a long time
Well done still_stirrin

Your a man after my own heart . I used a BTA41/800 though . Best bit about rolling your own is you know whats in it . ....and how it works if you need to fix or mod it .

Thats a really nifty unit you have

[jonnys_spirit]

Thank you this is awesome!

Cheers,
-js

[still_stirrin]

...I was wondering what app/software you used for your schematic design in your Cadco mod...

Here, let me help you all; I used this design specification data sheet as my basic design:

http://m.littelfuse.com/~/media/electro ... og.pdf.pdf" onclick="window.open(this.href);return false;" rel="nofollow

Refer to page 33 of 442 for figure AN1003.15 Double Time Constant Circuit for Light Dimming, Heat Control, and Motor Speed Control

Notice that I have selected an upgraded power triac for the control of my heat input because of the current requirements...up to 40A, although the 1500W element will only draw 12.5A maximum. This affords me “future compatibility” if I upgrade the heat element to a higher wattage, say 2000W, if available. My power circuit will still work (16.7A max. draw).

I also refer you to the “epic thread” in the Related Electrical Accessories forum, pp 11-16: viewtopic.php?f=85&t=3342&start=450#p6841878 for an exhaustive discussion of the triac designed power circuit.

As for an “application” to calculate the values, I used pencil and paper and a calculator and the specification data sheets for the devices. Input biasing was first calculated and then "tried". Success led to implementation. No “black magic” involved, just good old fashion electrical engineering design. Sorry, no easy way out.

And I used Powerpoint to make the schematic drawing....no fancy CAD program...just plain old “time investment”. Again sorry, no “bells & whistles” program for you.
ss

[Fire3331]

Helll SS, I’ve been reading up quite a bit on hot plate modifications and ran across your build. I also have the csr-3t. There’s a couple difference on the internals, mine just had one big infinite controller, then the same power switch. I tried to use the plate to distill my 5gallon copper still. I added a 3lb aluminum heat sync which helped, but it still isn’t running well. By the time I get half way through hearts I’m at 212 and have to shut down. I purchased the MileHi 110v controller and bypassed the internals on the hot plate so hopefully this will make for a smoother run! Love your set up!

[still_stirrin]

I used this design specification data sheet as my basic design:

http://m.littelfuse.com/~/media/electro ... atalog.pdf <— Dead link.

Refer to: figure AN1003.15 Double Time Constant Circuit for Light Dimming, Heat Control, and Motor Speed Control

Notice that I have selected an upgraded power triac for the control of my heat input because of the current requirements...up to 40A, although the 1500W element will only draw 12.5A maximum. This affords me “future compatibility” if I upgrade the heat element to a higher wattage, say 2000W, if available. My power circuit will still work (16.7A max. draw).

I also refer you to the “epic thread” in the Related Electrical Accessories forum, pp 11-16: viewtopic.php?f=85&t=3342&start=450#p6841878 for an exhaustive discussion of the triac designed power circuit. <— This is a good read through for anyone who has an interest in electronics or an engineering background. It’s long and sometimes convoluted, but very educational.
ss

I’m updating this post with an attachment to the (now dead) littlefuse hotlink above.
Here’s the TECCOR document (pp 135-137) with the circuit design for the Triac power circuit: