Modifying a peltier device to heat/cool and show temperature

Projects General Guidance
1

Alright, so I have a wine cooler I want to turn into a sort of incubator for a university project to store cell cultures.

It needs to have relatively precise temperature control, but nothing too fancy, a resolution of +/- 1C is fine with me.

Anyways, the wine cooler I have has a display on the front that shows the temperature as well as two buttons to regulate it. (Up/Down)

I am wondering if I can use an arduino to control the peltier device for heating and cooling based on the input I give it with the controls.

For example, I am thinking of purchasing this:
http://www.dx.com/p/tec1-12706-semiconductor-thermoelectric-cooler-peltier-white-157283
for the peltier and using this:
http://www.dx.com/p/arduino-digital-temperature-humidity-sensor-module-121350
to sense temperature, and humidity.

To keep the temperature even, I plan on having a fan running. The peltier will heat up or cool down a heat sink, and the fan will blow hot/cold air into the wine cooler until the desired temperature is achieved, as set by the front buttons.

However, I am not sure what kind of screen to use.
I want something preferably that lights up with an LED in it for clarity.
My size constraints are really small. Essientially i need the smallest possible screen i can get for outputting the following:
[12/40 45%]
Where [ Current temperature / Set temperature / Relative humidity]

The fan will be a standard computer fan.

What would be the best arduino to use for this, and how should I proceed?

My biggest issue here seems to be the size constraint.

All I will be putting in this incubator is petri dishes of cell cultures. No need for sterility or anything, just relative cleanliness. (I will add a small filter to the air intake.)

Any ideas?

2

The DHT11 is not that accurate especially for humidity.

Check the waterproof DS18B20 for the temperature - Temperature Sensor - Waterproof (DS18B20) - SEN-11050 - SparkFun Electronics -

and the - SparkFun Humidity Sensor Breakout - HIH-4030 - SEN-09569 - SparkFun Electronics - would be a better humidity sensor.
(Sensirion has a few nice ones too)

An Arduino UNO would be good to run all of this, incl fan and peltier.
Note that the fan and peltier cannot be controlled directly from the Arduino.
(google images arduino fan for schema)

1 Like
3

Thanks for the reply!

I'm assuming I'll be able to use the arduino to control a relay that will control the peltier and the fan, correct? A 5v relay or w/e should work, no?

What about the screen? Any good screen recommendations?

4

Actually, forget the relay. I could just use a transistor for this, could I not?

5

Anyways, the wine cooler I have has a display on the front that shows the temperature as well as two buttons to regulate it. (Up/Down)

This statement suggests that the wine cooler already has some sort of cooling unit, so why are you buying a Peltier module?

You should realize that those Peltier modules are very inefficient. They normally run from 12 V at about 6 amps (for 72 watts) but move only a few watts of heat. Depending on the insulation of the wine cooler and the thermal mass of its contents, you may find that even running full time, that module is incapable of reducing the temperature to the intended value. You should conduct a few simple experiments before designing the entire system.

For those experiments, to run the module you will need a hefty 12 V power supply capable of providing at the very least 6 amperes. For Arduino control, you will need a relay, MOSFET or H-bridge also capable of handling at least 6 amperes.

6

jremington:
This statement suggests that the wine cooler already has some sort of cooling unit, so why are you buying a Peltier module?

You should realize that those Peltier modules are very inefficient. They normally run from 12 V at about 6 amps (for 72 watts) but move only a few watts of heat. Depending on the insulation of the wine cooler and the thermal mass of its contents, you may find that even running full time, that module is incapable of reducing the temperature to the intended value. You should conduct a few simple experiments before designing the entire system.

For those experiments, to run the module you will need a hefty 12 V power supply capable of providing at the very least 6 amperes. For Arduino control, you will need a relay, MOSFET or H-bridge also capable of handling at least 6 amperes.

Sweet! Thanks for the device.
As for why I need the peltier, it is because i broke the one that came with the cooler itself.

What would be a better way to heat/cool my area? The insulation is very good as far as I can tell. (I realize very good isn't specific, but eh).

Any recommendations?

7

You can usually replace the Peltier modules that came with the cooler with units of the same dimensions. The number of modules will provide a good hint about the cooling capacity. Usually, the modules are connected in series, with the total power supply voltage equal to 12V times the number of modules, but be sure to study the connections before dismantling.

The modules are almost always sandwiched between heat transfer plates connected by screw fasteners. Clean the plates and apply a VERY THIN layer of thermal transfer grease to both sides of the module before installation. Do not over tighten the screws.

Note that modules differ in the ability to withstand high temperatures. Some of the cheap ones cannot have any part exposed to temperatures above about 80 degrees Celsius, or the internal connections will melt. The more expensive ones can tolerate up to 250 C in some cases, but check the specifications. Here is a useful FAQ FAQ's & Technical Information - TE Technology

8

If you only need to heat the chamber, then a resistor will do the job very well. You can use a high power resistor, or several of them to act as a heater.

9

Perhaps I can add some information based on experience with my current Peltier project. I am using a common portable food/beverage cooler/warmer that is plugged into an automobile power jack.

I originally used a relay to reverse power from cool to heat and then after 15 minutes, go back to heat. I knew the device would eventually die from abuse and it did after about 3 weeks. It switched only on business working days. So 15 to 20 times. Proof of ruggedness done and I replaced the Peltier with one from EBAY.

Now adding Arduino control with two DPDT relays to give a 5 minutes for the device to stabilize before powering up again. Then when I applied 12 volts to the Arduino, it died and I discovered it was a Chinese knock-off. Real Arduino is on order.

What I learned that may help you is there is up to a minute lag between then you power up the Peltier and when you can feel the cold or heat inside the storage box. I discovered there are a couple of aluminum plates plus a stainless plate between the Peltier and the inside of the box. So, you will have to be very careful about designing your control circuit to allow for the time lag.

Also, on my unit, there is a thermal switch next to the Peltier that opens when the temperature gets to between 120 and 140 degrees F. This limits the heat of the box. PErhaps your unit has the same protection.

Good luck.

10

Thank you very much! I'll look into all the info provided.

Now, about that screen....