Controlling a Peltier

Danko

Joined Nov 22, 2017
1,361
I want to control a peltier (tec1-12706) using arduino uno pwm pins. The voltage across its terminals is 12v when pwm is 255 and it is 0 when pwm is 0. What circuit can be used to do so?
"Using PWM without smoothing causes increased I2R losses in the Peltier element that reduces the available cooling and efficiency."
https://electronics.stackexchange.com/questions/515425/optimise-peltier-cooling-system-pwm-or-not

It should be minimum ripple, no phase control, no PWM:
https://www.meerstetter.ch/customer-center/compendium/71-peltier-element-efficiency

Recommendations of the manufacturers
Manufacturers of Peltier elements suggest using direct current and limiting current ripple for the regulation of the output current. They explicitly advise against the usage of direct PWM control of Peltier elements:
  • Ferrotec: "However we recommend limiting power supply ripple to a maximum of 10 percent with a preferred value being <5%."
  • RMT: "TEC [Peltier elements] controlled by PWM operates less effectively than at DC current. The PWM control is always less effective than TEC operation at the same average DC current and power consumption."
  • Marlow: "Thermoelectric coolers require smooth DC current for optimum operation. A ripple factor of less than 10% will result in less than 1% degradation in ∆T. [...] Marlow does not recommend an ON/OFF control."
 

crutschow

Joined Mar 14, 2008
30,102
As noted from Danko's comment, to use PWM control of the Peltier current with maximum efficiency, you will need a smoothing inductor in series with the Peltier.

The PWM signal could control a power MOSFET in series with the inductor/Peltier to regulate the Peltier current.

As an alternate, If you average the PWM signal to give linear control, the MOSFET will dissipate up to 18W (at 1/2 power of 6V, 3A to the Peltier).
 

crutschow

Joined Mar 14, 2008
30,102
Does the circuit shown is going to work?
Not sure since it doesn't show a schematic, and I don't work from a picture of a breadboard.
But it apparently uses just a MOSFET with the PWM input to control the Peltier current, and that will be less efficient than what I proposed using an inductor.
Depends upon how much you are concerned about efficiency.
 

crutschow

Joined Mar 14, 2008
30,102
I have tested the circuit practically, I got a maximum voltage of 8v instead of 12v as I want. What could be the issue?
Can't tell without a schematic, and I'm not clairvoyant, so please post one of what you did.
I do not have any kind of inductors, but I can make a RC filter instead, I am just worried about impedance I don't want to use many resistors and capacitors
No, you can't use resistors and capacitors in place of an inductor for that purpose here.
Does averaging the PWM signal = passing it through a low pass filter?
Yes, but that will give high dissipation in the MOSFET as I noted.
 

Danko

Joined Nov 22, 2017
1,361
Could you please explain in brief the role of each component, i.e. why did you use zener dioded? Why this MOSFET specifically, can I replace it with IRF540N, because I don't have this one? What happens when using the PWM frequency of arduino which is much less than the used frequency here.
Diodes are not Zener, but Schottky. Two diodes in one package. Low V forward, low dissipation. They provide continuous current through Peltier between PWM pulses.
IRF540 has R_ds_ON = 0.04 Ω, dissipates max 545 mW in this circuit. AON6560 has R_ds_ON = 0.00068 Ω, dissipates max 210 mW.
Low frequency PWM required coil with bigger inductance, which is more expensive and has higher resistance, so it dissipates more energy.

Question:
Could you please explain in brief the role of each component on Arduino board? ;)
 

crutschow

Joined Mar 14, 2008
30,102
I just need to mention that this design is not my own one, I have just used the design I mentioned before. This desgin uses pwm of arduino directly, which has an amplitude of 5v.
As I stated, that MOSFET needs a 10V gate voltage to fully turn on.
Using 5V may be the reason the measured voltage across the Peltier was only 7.85V.

You either need to increase the gate voltage, or use a logic-level type MOSFET (max Vgs(th) <2V) which will be fully turned on with a 5V gate voltage.
 

Danko

Joined Nov 22, 2017
1,361
For your design, as you said using a coil of bigger inductance will have a higher resistance, and dissipates more energy. This was expected, but I am mentioning at the beginning that I want to control it with arduino, and it cannot output a frequency of 31k!
For the transistor, unfortunately I don't have the AON65650 one so I have replace it with IRF540 while the energy dissipation will be greater, but think about compensating this energy dissipation.
Did you saw this link in my post #13, about Arduino"s PWM frequency changes?
Or see here: https://www.electronicwings.com/use...frequency-changing-of-pwm-pins-of-arduino-uno
 
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