I want to control it from my arduino, either with a MOSFET or something else. My question is, how to control the power? Just as the intensity of a light bulb is controlled, because I don't want to consume the maximum of my peltier cell, maybe half, maybe 20% or even 100%, but I want to be able to choose.
I want everything to be digital, that is, controlled from Arduino and not with a mechanical potentiometer, for example.
Hello
Post your current sketch, well formated, with comments and in so called code tags "</>" and a schematic, not a Fritzy diagram, to see how we can help.
How do you will take control the Peltier element?
Have a nice day and enjoy coding in C++.
Дайте миру шанс
Do you really use it for cooling? If so provide a big heat sink and fan to distribute the heat taken and also added by the Peltier itself. For heating better use ordinary heating foil or the like.
Some people warn from using PWM on a Peltier element, for possible damage by thermal cycles, but I think that usual PWM frequency of 500-1000 Hz will do well.
More critical is a PID controller due to large time lags between energy invested and temperature change of the object. This may lead to temperature cycles of the Peltier element which should be avoided.
But, I think I did not explain my problem well. I want to control my peltier cell to change polarity (so one side heats up and cools down and the opposite when changing polarity), turn on and off.
For that I can use an H bridge like the L298N (or another better one that you recommend)?
Yes, I plan to cool with the peltier cell. I'll put a big heatsink on it and another one for cooling, both with small fans.
Abstract: This project is designed to build a controller to control the bath temperature of a petri dish. The device will be used by student lab of neurobiology to conducting experiments on fruit flies’ thermo channels. An ideal device should have the following feature: easy to use, small development budget (less than $100) and satisfying the performance requirement for conducting experiments. The project is based on an atmega-1284 microcontroller as the main control unit
with a PID control algorithm running inside. The petri dish’s bath temperature is heated or cooled by a Peltier Plate. A Thermistor is used as the temperature detection device and sent feedback to the microcontroller regarding to current bath temperature of the petri dish. All components are connected with analog circuits to form a close loop feedback controller in order to dynamically control the petri dish’s bath temperature. Graphic user interface is built with
MATLAB to provide easy user access and monitoring.
Be sure to but several as they will quickly destroy them selves. You need at least 5 minutes of quiet time between polarity changes. Likely a lot more, depending on your heat sinks. It's the INTERNAL heat that kills the diodes.
Unless you give the time to dissipate the stored internal heat that is in the diodes, they will be destroyed if you reverse the current to reverse the hot/cold sides. Read the on-line documentation ion on Peltier devices.
If you have one for hot and one for cold, then you are not changing the current polarity and you do not have the build up of internal heat.
That's what I say, have two, one for hot and one for cold when. Instead of changing the polarity I just turn one on and off the other. It will be more expensive, but I will save time.
This way is safe, right?
That's one option, the other option to make it safe is to have just one board, but, as you say... wait for it to sit at room temperature with a fan and heatsink, say after 10 or 15 minutes. After that time, I just change the polarity, right?
PWM = analogWrite() will "pass through" a MOSFET (or transistor) and it's "easy". Linear/analog control is inefficient and your MOSFET would heat-up and maybe burn-up.
BUT... Virtually all heating & cooling works by cycling on & off. The temperature can't change instantly and I'm sure you've noticed that's how your home heater works (and your air conditioning if you have it) and you can probably hear your refrigerator cycling and although you may not notice it, the oven in your kitchen cycles on & off too.
And if you are tying to maintain a target temperature by measuring it in a feedback loop (like a thermostat) It's actually easier to precisely-control by cycling than by trying to feed it the "right" amount of power moment-to-moment.
Hmm, how can a Peltier device become cold? AFAIK it always heats up by applied power. Only if the hot side can be kept at low temperature the other side can become cooler than the ambient.
That's for the moment, but then the heat of the hot side will affect the temperature of the cold side. The temperature difference can be kept only by continued current that continuously increases the temperature of the device. That's why both the resistively generated heat as well as the heat sucked out of the cold ambient must be removed effectively from the hot side.
