Electronics > Beginners
Building a PWM filter for a Peltier
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wraper:

--- Quote from: chemelec on November 17, 2018, 03:47:25 pm ---I have built many Peltier coolers and I find the best option is to monitor both the Hot and Cold side temperatures, using a comparator circuit to turn the peltier on and off. Set correctly you can get better efficiency.

--- End quote ---
It's better to not keep it on/off at all but running constantly at minimum current required.

--- Quote ---Set correctly you can get better efficiency.
--- End quote ---
It's a way to greatly compromise efficiency to begin with. And it does not make much sense financially too. You need to use larger heatsink, higher power PSU, control additional temperature sensor.
Kleinstein:

--- Quote from: Hero999 on November 16, 2018, 06:43:44 pm ---....
Let's put some more figures into the equation.

Suppose the resistance, i.e. the part of the load which doesn't do any useful work, is 3Ohm and the full power current consumption at 12V is 2A.

Full power consumption:
P = I2R = 22×8 = 12W

50% power consumption, using PWM.
P = 12*0.5 = 6W

50% power consumption, using half the DC current.
P = I2R = 12×8 = 3W

Conclusion: reducing the current by half uses a half of the power of PWM at the full current.

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PWM is even worse than that: the additional 3 W are dissipated in the Peltier element and this way effectively to half the amount at the cold side. So 50% PWM is not only using twice the power, but also has less cooling effect. It is especially bad if the current is high, near the maximum current.  As an extra point the added power makes the hot side a little warmer and this way reduces the a bit more.

It is allready more efficient to use a simple linear regulator or series resistor to reduce the current than to use PWM. It takes the same power, but at least that extra power is lost in the regulator or resistor and not in the Peltier element.

Slow PWM can be bad for the reliability as it causes a superimposed temperature cycling. Faster PWM at least reduces the temperature swing. So it is slightly better, but not much.
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