On Thursday, 17 December 2015 19:36:16 UTC, Fredxxx wrote:
On 17/12/2015 16:55, whisky-dave wrote:

In any case, PWM is utterly safe for controlling a peltier.

It is utterly safe. However it's not a smart way to run a peltier as
already explained to you.

it was explained that it was not as efficinet where they advertised their controllers, yes, which are also way outside the student budget.



First hit will assist you:
http://lmgtfy.com/?q=peltier+pwm+vs+constant+current

Constant current is best. It you really need to drive it from a PWM,
make the frequency as high as you can and stick a big inductor in series
to make the current as constant as possible.

http://tetech.com/faqs/#19

The "ON" and "OFF" pulses occur so rapidly that the module does not have enough time to change temperature in response to each electrical pulse. Instead, the module assumes a temperature difference relative to Vaverage. When the controller is properly tuned thermal cycling is eliminated. Thus, these controllers do not degrade the reliability of a module from thermal cycling in the same way that a thermostatic or slow "ON-OFF" controller would.

as said the diferce is in teh speedd of switching.

One thing our students get confused by is that a square wave pulse that goes from 0V to a higher voltage is NOT AC. it's still DC as current only flows in one direction.


If you don't understand the different between average current and rms
current in terms of resistive heating may I suggest you go away and find
out. There is a very big difference.

0.707 compared to 0.636 isn't it for PWM square wave it would vary.

The RMS voltage is the voltage that would give the same heating effect as AC in a resistive load.
That's basiclly where RMS comes in as meaingful in power.





There's sources that say don;t run it in the 10s of Hz .

Cheers -- Syd