Hello - I don't have much experience with electronic components. What experience I do have, is with low voltage (12VDC) type operations.

The project I would like to build involves heating an aluminum plate (0.5" x 1.75" x 4.25") up to 350° F. I do not need a particularly fast startup, it's fine if it takes 5-10 minutes to reach this temperature. I'm planning on using a IR thermometer gun to check temperatures.

Conceptually, I was thinking of drilling and reaming an appropriately sized hole in the plate to accept a cartridge heater, similar to this: McMaster 120VAC cartridge heater. I'll need some way to control the temperature and voltage, perhaps a lamp dimmer? And an on/off switch. I think grounding the aluminum plate might also be a good idea, as I will be touching a steel rod that is bolted to the aluminum plate being heated.

Honestly, I'd love to find a similar cartridge heater that runs off 12V, as I'm a bit leery of of playing with 110VAC out of the wall outlet. But I haven't had much luck finding a comparable DC equivalent (5/16" diameter x 1.5" length @ 100 watts).

Anyways, I've attached a diagrammatic sketch, and am looking for some input on feasibility and the best way to approach this.

Cheers!

 

The project I would like to build involves heating an aluminum plate (0.5" x 1.75" x 4.25") up to 350° F.

May I ask why? There are commercial hot plates that I think would be very close to what you want, with all the design issues solved, a UL rating and all that sort of stuff that make a DIY project a bigger pain than you think.

 

May I ask why? There are commercial hot plates that I think would be very close to what you want, with all the design issues solved, a UL rating and all that sort of stuff that make a DIY project a bigger pain than you think.

Sure thing! The heated aluminum plate is that last component in a hot press stamping machine that I'm working on. My version is similar to this one:

This machine is used to create a heated emboss of metal type in various materials (paper, wood, leather, etc.). I believe that's a cartridge heater sticking out of the aluminum block.

This is my setup so far. The heated aluminum plate will mount to the underside of the middle steel plate. When hot enough, I'll pull the lever to stamp the material resting on the bottom steel plate.

 

These are 12 volt:See Diesel glow plug
https://www.google.com/search?q=Die...j69i57j0l4.18231j1j7&sourceid=chrome&ie=UTF-8

You would want the heating element in contact with your aluminum block to dissipate the heat.

 

Have you considered using heatsink resistors such as these screwed to the aluminium plate ? They are rated for use up to 250 Deg. C (483 F)

Les.

 

Do you want the temperature to be automatically controlled?

 

I may have found a 12V cartridge heater that is comparable in size and wattage to the 120VAC. I've repositioned the location of the cartridge in the aluminum heating block to match this 12V one, it appears everything will fit. Check out the attached PDF for some updated drawings.

Controlling the temperature automatically would be great, but it's not a critical feature. As long as I can regulate the voltage manually, I am ok with checking the temperature with the IR thermometer. Perhaps a cheap thermocouple + LCD display will sneak in somewhere.

Heatsink resistors are an interesting idea! Vertical space is at a premium, since the arbor press throat is so shallow, but I might be able to find a location to put them in if I can't get the cartridge heater idea to work.

 

One problem I can see is that your plate is 0.5 inch (12.5mm) thick, and the cartridge heaters 8mm in diameter. Even if you are able to precisely drill the holes to accommodate the cartridge heaters – the integrity of the plate may be compromised such that it cannot withstand the applied forces in use.

I would recommend you source smaller diameter heater cartridges or make the heat plate thicker.

Heating the plate to 350F (180C) probably could be achieved using 200W, I would recommend you use a pid temperature controller such as this to set the desired temperature. If the plate were to be made thicker (say 15mm) you might need more power.

https://www.ebay.co.uk/itm/Alarm-11...f0d8fc8d7:m:mmYNXiA_k_hRfBUic8tNmFg:rk:4:pf:0

 

I can increase the thickness of the heater plate to 5/8" (15.9 mm) if the 1/2" (12.5 mm) material doesn't work out. I should be able to accurately drill the 1/2" material, as I'm using a vertical mill. I'll give it a test with the 1/2" aluminum, as I have some spare material on hand.

A 200W 12V cartridge heater is hard to find. The few I've found are on Alibaba, and come with a long shipping time. If you feel a 100W cartridge heater is under powered, is there any merit to running two?

It looks like a 1/2" plate will heat up to 350F in a little over 7 minutes at 100W. At least that's what this online calculator indicated.

http://www.cartridge-heaters-metric...lator-for-heating-solids-fluids-and-gases.asp



That's a cool little unit. I'm not familiar with PID temperature controllers, similar to cruise control for a car? But it looks like I would need to input 120VAC and then it outputs 12-24VDC. Is there a common power supply used with these units?

Thank you for all the input so far! It's been very helpful to talk this build out.

 

You can use this with a relay for temperature control.

High Temperature Thermostat -30 to 999Deg.
Item #: 34687 MP
Sale: $12.95

 

A further consideration you should not forget, is what happens when your temperature control circuit fails and power is continually fed to the cartridge heaters? If no excessive temperatures/fire results, then all well and good – but you would be well advised to have some form of thermal cut-out wired directly in line with the heaters to prevent this fault condition resulting in a hazard.


PID temperature controllers are available operating on a 12 – 24Vdc supply.

These controllers work, obtaining the set temperature optimally by initially applying maximum power to the heater, as the temperature approaches the set point, the controller switches off the power (for a short while) to observe behaviour of the temperature – then switches the power on/off as required to obtain and maintain the set temperature.

 

I can increase the thickness of the heater plate to 5/8" (15.9 mm) if the 1/2" (12.5 mm) material doesn't work out. I should be able to accurately drill the 1/2" material, as I'm using a vertical mill. I'll give it a test with the 1/2" aluminum, as I have some spare material on hand.

You will not have a problem with the 1/2 " plate. your not able to put enough pressure on the plate with that arbor press, unless you use a pointed part on the ram and put the point over the hole that the heater is in. Even then you would just dent the plate.

As someone who has used cartridge heaters for many, many years in plastic and rubber molds, your fear of using mains to power them is not warranted. When they fail they fail open. There is a ceramic core in them between the heating element and the outside case, so no possibility of getting shocked by them. Unless this will be used where no mains electricity is available just do yourself a favor and use them. https://www.omega.com/prodinfo/cartridgeheaters.html

 

As someone who has used cartridge heaters for many, many years in plastic and rubber molds, your fear of using mains to power them is not warranted. When they fail they fail open. There is a ceramic core in them between the heating element and the outside case, so no possibility of getting shocked by them.

Good to know! I do have mains power available. AC cartridge heaters seem to be much easier to source than DC equivalents. So in your experience, when a cartridge heater fails, the circuit is open, so it stops generating heat? That would eliminate the need for a thermal cut-out.

A further consideration you should not forget, is what happens when your temperature control circuit fails and power is continually fed to the cartridge heaters? If no excessive temperatures/fire results, then all well and good – but you would be well advised to have some form of thermal cut-out wired directly in line with the heaters to prevent this fault condition resulting in a hazard.

After some initial thermal cutout education, they appear to come as a single use fuse, or as a reusable switch. I am leaning towards finding a switch. Would you try and position the cutout as close to the heated aluminum block as is reasonable, so that it cuts out at the correct temperature?

PID temperature controllers are available operating on a 12 – 24Vdc supply.

These controllers work, obtaining the set temperature optimally by initially applying maximum power to the heater, as the temperature approaches the set point, the controller switches off the power (for a short while) to observe behaviour of the temperature – then switches the power on/off as required to obtain and maintain the set temperature.

Thank you for the succinct explanation. It seems like a PID may be a little overkill, but when adjusted correctly, it will really dial in the temperature. Starting my PID research, RKC-REX C100 looks like the original, with several knockoffs from there. I'm not looking to invest $200 USD on an RKC, any recommendations on a more affordable one? There are a variety of units. Inkbird? Berme? Mypin?

Here's my first crack at workflows with the components.

1. Is there an AC to AC PID and SSR? The cartridge heater needs to receive AC power to work, most of the outputs on SSR's that I've seen are DC.
2. AC to PID to DC might be the most straightforward.
3. For AC to DC, I'd throw in a computer power supply for the 12VDC connection. And use DNA Robotics suggested thermostat. Not sure where the relay would go?

 

I would just use a cartridge heater rated for 120 VAC. - use multiple smaller ones if you can- more even heat.
Use a simple temperature controller that also runs on 120VAC

These will be the cheapest and easiest to find.
Heating with DC is not done too often, converting power to DC costs money, both in terms of extra hardware and losses during operation.

 

I did the cartridge heater/Aluminum thing. The Aluminum melted. it was about 4 of them in probably a 4x4" plate.
The blob was a good conversation piece.

PID is Proportional/Integral/Derivative control, There are controllers that have auto-tuning. Remember that a setpoint step has to be used to tune.
It's base on the error and terms proportional to the error, the integral of the error and the derivative of the error. the I constant basically makes the setpoint and measured value agree, The proportional constant is a mix of reductions of oscillations and closer control the D constant helps eliminate overshoot.

The grainyness of the control has some effect on stability and RFI interference. Phase Angle fired is the best you can do with AC. DC is rare, but I've done that too including making PID controller.

There are two general ways control operates. The controller can create a process signal of say 0-10 V or 4-20 mA. That is sent to a device that can say adjust the phase angle that's proportional to V^2, power or a "tungsten" load.

The # of cycles of the AC power can be used as well as time on/time off.

I wanted to give a "quick overview". Lots of details are missing.

 

So in your experience, when a cartridge heater fails, the circuit is open, so it stops generating heat?

Yes they fail open, the only way they can fail, due to the way they are made.

After some initial thermal cutout education, they appear to come as a single use fuse, or as a reusable switch. I am leaning towards finding a switch. Would you try and position the cutout as close to the heated aluminum block as is reasonable, so that it cuts out at the correct temperature?

If you don't need to adjust the temperature and know what you need for that temp, why not use a "Klixon" temp switch? They are used in furnaces, electric ovens, electric dryers, and many industrial applications to cut off or turn on heaters that only need to be at one set temp, or as a fail safe for things that are adjustable. Just one of what they sell to show what I mean.
https://www.sensata.com/products/temperature/11041-thermostat

 

Here are the components for an AC to AC build. Let me know if you see any issues!

1. 2 prong power cord
2. Rocker switch
3. 5 Amp fuse and fuse holder
4. Auber PID
5. K type thermocouple
6. Heater cartridge
7. Thermostatic control switch - hard to source
8. Ceramic cable sleeving, just in case

That particular PID says a heating element can be directly wired into it, as long as it is >3A.

 

Thermostatic control switch - hard to source

Don't understand why you call them "hard to source"? Most places like Digikey sell them. If you use that why do you need the PID and thermocouple?

 

I only say hard to source, because most of the manufacturer's websites I looked at did not do direct sales, provide pricing, or list a reseller. So I was having a hard time finding a temperature sensor that met the specs I was looking for. I haven't ordered from Mouser or Digikey, but it appears they are the electrical equivalent of McMaster.

I believe this is a comparable Digikey switch.

I don't know the exact temperature at which I need the aluminum block to heat to, so I thought using a PID and thermocouple would allow me to increase or decrease it with a good amount of control. The thermal switch in this scenario, is just a safety device, to avoid making molten aluminum.

 

Amazon sells them too. I only go to McMaster to look for things, and then buy them somewhere else. No sense paying McMaster's premium price, a lot of times double what others sell the same thing for.