Arduino Uno PID Control and Kapton Heater

Hi Everyone

I'm new to Arduino, but have some experience with C++.

Project Goal: Heat up a 1/2x3x4" aluminum platform anywhere from room temperature to 150F using a 1x2.5" Kapton heater and an Arduino Uno with PID control . Let the user set the temperature within this given range. Use a thermocouple to read the temperature of the platform and have the temperature displayed on an LCD monitor.

I would like to use K-Type thermocouples as my temperature sensor. Therefore I believe I will need either a MAX31855 or AD595 - anyone have a preference?

With the Kapton heater I have (model: HK5369R101L20A), the resistance is 101 ohm and yields 1.43W at 12V (current = 0.12A). This gives about 0.55W/in^2. If I use epoxy to mount the Kapton heater to my platform, it can crank up to ~240F! However, I think I need a lot more than 12V input to achieve a high temperature. Hoping to use about 50V (24.75W, 0.5A) to heat up the platform in a reasonable time.

Seems like I need some sort of amplifier to increase the power signal from the Arduino . What is the best way to get a high voltage to power this Kapton heater without frying the Arduino Uno? Any idea if I need a solid state relay and if so, what kind? Do I need a shield? Budget is not a concern - more focused on a simple solution.

Really appreciate your help!! Thank you.

How about the DS1820 One Wire temp sensor ( around $2.00 ea. on ebay). There are libraries to support it. And no cold junction compensation and amplification to deal with. Data sheet says its good up the 257 degrees F.

At 24V, your 101 ohm heater will draw about 240mA. You can switch that amount of current using an NPN transistor such as BC337 or ZTX851, if the 24V supply has a common ground with the Arduino.

I agree with groundfungus, there is no need to use a thermocouple for measuring such modest temperatures.

Hi, have you got a link to the specs for the kapton heater. It will tell you the optimum power requirements to get the most out of your heater. I tried to look for the model number you have but could not find it.

Tom.. :)

TomGeorge: Hi, have you got a link to the specs for the kapton heater. It will tell you the optimum power requirements to get the most out of your heater. I tried to look for the model number you have but could not find it.

Tom.. :)

I'm working with alexjhanan on this project

TomGeorge, the specs for our foil heater can be found at the following: http://www.minco.com/~/media/WWW/Resource%20Library/Heaters/Polyimide%20Thermofoil%20Heater%20Tech%20Spec.ashx Our model number is 5369 with dimensions of X=1.23" and Y=2.48"

Thank you TomGeorge and dc42 for your help!!

We are going to go with the K-type thermocouple because we cannot have the breadboard in the same room as the platform. Therefore the thermocouple will be great to get a temperature reading from a distance.

It seems like we can use an NPN transistor (BC337 or ZTX851) with 24V, but I don't believe we can get up to 150F with only 24V. Therefore, it seems like we'll need 2 power sources. One for the arduino (possibly a wall adapter or 12V battery), and a much larger one to power the Kapton heater (perhaps with 50 or 60V capacity). If so, could we still use an NPN transistor and perhaps specifically those models above? Will we also need a Solid-state or non solid state relay? Also, do you see us needing anymore components? Thanks!!

alexjhanan:
We are going to go with the K-type thermocouple because we cannot have the breadboard in the same room as the platform. Therefore the thermocouple will be great to get a temperature reading from a distance.

Almost any temperature sensor can be read from a distance, including semiconductor sensors such as DS18B20 and LM34. If you use a thermocouple, then you must make sure that the thermocouple itself has long enough wires to reach the breadboard, because you cannot extend the thermocouple wires without messing up the cold junction compensation.

alexjhanan:
It seems like we can use an NPN transistor (BC337 or ZTX851) with 24V, but I don’t believe we can get up to 150F with only 24V. Therefore, it seems like we’ll need 2 power sources. One for the arduino (possibly a wall adapter or 12V battery), and a much larger one to power the Kapton heater (perhaps with 50 or 60V capacity). If so, could we still use an NPN transistor and perhaps specifically those models above? Will we also need a Solid-state or non solid state relay? Also, do you see us needing anymore components? Thanks!!

The current would be about 500mA @ 50V or 600mA @ 60V. I wouldn’t use a BC337 to switch these currents from an Arduino, but the ZTX851 would be OK if you limited the voltage to 50-55V (its Vceo rating is 60V). Alternatively, use an N-channel logic-level mosfet - there are many suitable ones, including STP40NF10L.

PS - what is it that you will be heating? Are you sure that you need as much as 50-60V (that’s about 25 to 36W of power)?

Thanks for the feedback. I think I'll go with the ZTX851 and STP40NF10L. I calculated that much power needed from the equation below: P=[m*Cp*(Tf-Ti)]/t Where P is in watts, m is grams, Cp is specific heat J/gC, Tf and Ti in Celcius, t in seconds.

Therefore if P= 24.75W @ 50V, 500mA m=1lb ~453.592g Cp=.89JgC (Aluminum) Tf=65.55C (150F) Ti=21.1C (room temp)

It would take about 12 minutes to heat up to temperature. I don't think I want any less power - then the time to heat up becomes too long. I think it's common to give these Kapton heaters about 100V Minco's heater catalog is below: http://www.minco.com/~/media/WWW/Resource%20Library/Minco_HeaterDesignGuide.ashx

And any thoughts on an appropriate diode for this project? thanks.

Where are you intending to use a diode?