filterless Peltier PWM

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no - in fact the filtering requirement may need to be much larger than you would like to get good heat pumping efficiency

any ac content will cause loss/heating in the Peltier element severely degrading its cooling performance, they really want very low ripple DC, don't skip the filter
 
Well I just remember reading it somewhere before,I do a search and found this :

It seems that not the DC itself that cause damage, but the cycling. and this only happen in temperature controlled operation, when the device must be turned ON / OFF

The problem in using DC to control peltier temperature is the thermal cycling, which lower the life expectancy of the device. DC control will do ON and OFF cycle causing thermal cycling.

PWM is also pulses of DC but the ON/ OFF cycle timing is controlled to minimize thermal cycling. the key is in the timing

http://www.tetech.com/techinfo/


Hartono.
 
jcx said:
no - in fact the filtering requirement may need to be much larger than you would like to get good heat pumping efficiency

any ac content will cause loss/heating in the Peltier element severely degrading its cooling performance, they really want very low ripple DC, don't skip the filter
http://www.maxim-ic.com/appnotes.cfm/an_pk/1757
The filter in the circuit is very simple.

I think I'll try powering a Peltier from a 3.3v power supply and from a 12v power supply PWMed at high frequency to have an effective voltage of 3.3v and compare. Then I'll add a simple filter and see what happens.
 
I was refering to the thermal efficency being reduced by pwm current in the Peltier

http://www.marlow.com/TechnicalInfo/frequently_asked_questions_faqs.htm

the COP, Qmax, Tmax will all be reduced for a given average current when that current is on/off PWM modulated instead of being steady DC, even if the PWM frequency is much higher than thermal time constants

this is a simple consequence of Ohm's law, higher peak current heats the resistance of the Peltier element by Ipeak^2

if 2 A @ 50% duty cycle gives the equivalent of 1 A steady state heat pumping then 50% * (2^2) gives twice the resistance heating over the low ripple 1 A DC current

there can be extra loss from eddy current/skin effect at high switching frequencies too
 
> think I'll try powering a Peltier from a 3.3v power supply and from a 12v power supply PWMed at high frequency to have an effective voltage of 3.3v and compare. Then I'll add a simple filter and see what happens.

Your probably better off using an open loop system, instead of a PWM instead of closed loop temperature regulation with Peltiers. An open loop system works like a heating system, that turns on until the desired temperature reached. This is because peltiers are a array of a large number of N-P junctions, and likely have large internal capacitance and slow recovery speeds. Every time you cycle that capacitance will probably rob you of efficiency. Running at lower voltage will probably also cost you because of the forward voltage drop across the junctions. Its probably better to run it at the voltage the manufacture spec'd since they probably designed to operate with the most efficiency at that voltage.
 
TechGuy said:
> Its probably better to run it at the voltage the manufacture spec'd since they probably designed to operate with the most efficiency at that voltage.

Nope, specified voltage is for biggest possible temperature difference between hot and cold side, assuming that hot side is cooled with infinite heatsink.

To get any reasonable "effiency" (COP) from peltiers they must be used with considerably lower voltage than specified, often less than 50% of spec.

And yes, filtering IS recommended, for reasons that jcx already explained. If supply voltage is lot higher than specsed max/"optimum" voltage then filtering is absolute necessity.
 
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