In that old post they say that it cannot be controlled with PWM. My question is:
What if the peltier cell is 5 amps and I give it only 2? Will the power be less?
What I am looking for is some way to control my peltier cell in percentages, as dimmer modules are used to increase or decrease the intensity of the light. Because I don't want my peltier cell to turn on and off just to set the ideal temperature.
I plan to use relays to turn the peltier cells on and off, my question is: how do I control the power percentage?
Relays sounds like a poor way to go. If You can low side switch the peltier and You find a logic level N channel MOSFET that handles the current that solution lasts a lot longer.
What I have planned so far is:
A 14v battery, I reduce it to 12v with a step down voltage. I connect it to the relay and the peltier.
With this I will make a point H:
My experience in electronics is a bit basic. The relays are easy to use. What do you recommend me?
But, my main problem is the control of the power, that is, I want to decrease and increase the maximum temperature allowed by the peltier cell without having to constantly switch it off and on.
The easiest is to switch off and on until the X temperature is regulated, but, if there is a possibility that the peltier cell is regulated between 0% to 100% then it would be the best, it would be more elegant.
14 volt battery is odd but maybe exist.
Drop the idea about Hbridge. They are used for motors in order to change the polarity, being able to run both fwd and bwd. You have no use for that.
Use the MOSFET I suggested and a decent temperature sensor. Switch power on when it is too high and switch off at a desired point, maybe a little earlier then the target temperature. Then turn on at a desired warmer temperature.
This way You don't use PWM.
Trying to give the peltier less than full current, 5 Amps will result in a lower voltage across the element. I don't know what the result would be. Such a solution will create lots of heat in the powering unit, what ever that would look like.
I would look into an adjustable buck converter. They usually use a variable resistor but with a little creativity you might be able to figure how to control it with an Arduino.
I want to change the polarity, because I am not only going to cool, I am also going to heat a certain moment (not always). So I can't leave the ideal of the H bridge. The problem with the MOSFET is that I don't want to use the direct component, I want to use ready-made modules.
I really appreciate your help, but we are straying from the main topic. My problem is in relation to power. I want to know how to change the temperature without turning the peltier cell off and on.
A quick look through eBay I found a buck converter based on the XL4015 IC that has a feed back circuit one could replace a resistor (R1) from the divider with a controllable resistor (digipot??)
The Peltier would be fine but a "regular" 2 Amp power supply will burn-up if you connect a 5A load.
If you run it at a constant percentage the heating (or cooling) will be constant but not the temperature... If the temperature in the room goes up by 2 degrees the Peltier will also go up by 2 degrees.
Heat can't change instantly and almost every heating or cooling system works by power cycling and feedback. If the temperature in your home gets too low, the heat comes on until it reaches the target temperature, then it turns off. Your oven, your water heater, your refrigerator, air conditioning, ALL work like this.
There is usually some hysteresis (or "swing") so it doesn't turn on & off several times in a second.
If you try to use PWM (or any percentage control) it can be very tricky and the unavoidable delay can cause instability where it's constantly overshooting and undershooting and "hunting" for the right temperature and/or it can end-up responding too slowly.
That battery surely exist and it will give You 4 hours of running using one of them assuming You manage to draw only 2 Amps. Else, at 5 Amp, less than 2 hours of peltier powering.
They are 2 batteries of 9000 mAh at 14v (18,000 at 14v).
If it is at 12v it would be about 20,000 mAh. If the peltier draws 5 amp. it would last about 4 hours of uninterrupted use. Turning off and on about 6 hours, with a single cell.
I agree to that. Parallelling batteries is another discussion not asked for here. I don't know the LiPo technology enough to tell.
However, the same principle as in reply #6 can be used, even with a H bridge, heating or cooling.
