On 18/12/2015 12:45, whisky-dave wrote:
On Thursday, 17 December 2015 18:06:41 UTC, Syd Rumpo wrote:

Your own link says,
"Peltier devices are one of the few things you do not want to run with
pulses, particularly in cooling applications...", and then goes on to
explain why.

But doesn;t explain it.

There are two scenarios when driving the Peltier at say 1/4 max power.

The device has to pump both the heat from the cold side kI and any
resistive losses generated inside the device I^2R to the hot side.

So if you want to run it at I for 1/4 of the time and 0 for 3/4

Heat output = kI/4 + I^2R/4

But if you run it at I/4 continuously (ie filter the PWM drive to DC)

Heat output = kI/4 + (I/4)^2R = kI/4 + I^2R/16

In other words the pulse mode driven PEC is more inefficient turning a
greater proportion of the higher drive current into waste heat.

Driving it with DC you can either get the cold side colder for the same
input power or use less input power to obtain the same cooling.

--
Regards,
Martin Brown