Arduino Uno temp monitoring & TEC Control

Hello,

I'm looking to do something incredibly simple with my Arduino UNO that I have laying around.

I want to do something that sounds incredible basic.

Monitor 2 different temps and control a TEC to switch ON/OFF when the desired temps has been reached at set parameters in the Arduino app.

The TEC's are these modules that are being purchased from eBay and enough for my project.

https://www.ebay.com/itm/382589937297

Also can you use a wire sensor such as this?

http://www.amazon.com/gp/product/B00CMR38LC/ref=ox_sc_act_title_1?smid=AELLOY6K8XB8X&psc=1

Display thru a display would be nice, or to send the data wirelessly to my device.

I understand that makes it a little bit more complicated, so let's start with sending the temps to a simple dual temp display.

P.S. Just to be clear, I am not monitoring the temp of the Arduino board. I'm monitoring something else that the temp sensors will be attached to.

Thanks in advance!

You do know this is a cooling plate? If you want it to be a heating plate you have to reverse the polarity using a H-bridge circuit like a motor. These plates draw on hell of a lot of current.

What is worse there is a temperature differential limit. That means if the temperature between the top and the bottom of the plate exceeds a certain limit the whole thing breaks down and becomes a heater despite the polarity applied to it.

That sensor wire looks just like thermistor, if so you will need some conditioning of the signal in order to read it.

But it is not.

Hi,
You will also need to fit heatsinks and fan to get the expelled heat away from the TEC if it is cooling or heating at full power.
Monitoring both surface temperature.
Monitoring TEC current.
Fan control.
15.4 V x 15A = 231W when at full power.

So basic it sounds, but all the extras to make it perform, add up as shown further down in the Amazon link.

Tom... :smiley: :+1: :coffee: :australia:

Hello Mike,

Thanks for your reply! I'm not looking to cool or even use the device to max temp. I'm just trying to maintain about 60 degrees F or so.

So luckily we won't be dealing with any conditions that are outside the TEC's operating limit and well within it.

My apologies for not including this important piece of info. Basically doing the same exact thing as any TEC based fridge does, except I'm using it for heating and not cooling. So no cooling fins or apparatus needed.

Thanks once again!

Hello Tom,

Thanks for your reply! Heating will be kept about 60 degrees F so no cooling necessary. Once the temp is maintained, the TEC can be turned off until it falls below a certain threshold.

Hope this info helps!

Thank you again,

Jimmy

My personal experience in doing the same thing is you must wait 15 minutes or MORE with NO voltage applied when switching from heating to cooling. Otherwise you destroy the diodes in the TEC.
Paul

Hello Paul,

There will be no "cooling" at all. Voltage will be applied only for heating purposes only.

Will there be any issues of having the TEC cycled on/off at shorter intervals?

Thanks so much for your input again.

Please study how Peltier devices work. there is ALWAYS heating and cooling taking place. You can only switch which side is doing the heating or cooling.
Paul

Think of "heat transfer".

From my understanding of how Peltier devices work and from all the stuff I've read about it, you are the only person who has ever mentioned the fact that TECs need to be "cycled" from heat to cool, or vice versa.

Doesn't that defeat the whole purpose of having it work with no moving parts, so it can be cycled on/off rapidly as needed?

Hi,

Same thing, you will need fins to gather the heat energy you need, just relying on that small exposed surface of the TEC will not be enough, it will possibly freeze unless you increase this area with fins.
You need to look at it also as ENERGY flow not just temperature.

What is the mass you are aiming to keep at 60F, that has a great influence on the amount of energy you will need to transfer.

Tom... :smiley: :+1: :coffee: :australia:

The surface area will be LARGE that it's attached to and made out of aluminum. So fins won't be a requirement either. There's at least 5x more surface area that it will be mounted to than the 40MM square size it comes in.

Also I'm just heating up water in an aluminum container. Basic, distilled water.
Just in case, the container holds up to 1L of water.

Thank you!

All true, but if you CANNOT remove the heat fast enough, then the diodes will eventually overheat and when ONE opens, the whole device is dead.
Paul

Then why use a Peltier device at all? They are expensive and bring complications. If you only want heating then why not just use a heating element?

Hi,

BUT if you use a TEC mounted to a flat sheet, the heat energy can only move towards or away from TEC via the thickness of the flat plate and the contact area of the TEC.

If you use fins mounted to the plate OVER the TEC, you have a greater area to transfer the energy from the TEC to the environment, this is through the fins thicknesses contacting the plate over the TEC.
That is why they have cooling/heating fins on heatsinks and not flat plates.

Tom... :smiley: :+1: :coffee: :australia:

Very good point. It would thus decrease the price of the overall unit if the Arduino is doing all the "thinking" part of the whole contraption.

Would something like this work?

https://www.amazon.com/12v-flexible-polyimide-heater-plate/dp/b07p2rjdpl/ref=ice_ac_b_dpb?tag=ditching9to0f-20

Also in that case, then how do I control the heating element and is there one made specifically for Arduinos or can I just use something that would be normally compatible for other items?

Thanks once again!

Thanks for the input and you guys make excellent points. I will decide to just go with heating elements then!

Yes if a 7W heater is enough. That would take 600mA at 12V.

Just like you would control a motor or other high current mode. That is using a transistor or FET to turn it on and PWM to control how much it heats.

Noting that if the system has any significant thermal mass as it seems in this case, "PWM" will generally occur over several seconds and be performed in software as easily as using PWM-enabled pins of a microcontroller.

No PWM will control the amount of heat generated by the heater no matter what the thermal mass. With a high thermal mass you can have a lower PWM frequency but you don’t have to.

Makes the control circuit simpler - don't have to worry about driving FETs gate capacitance.