On 17/12/2015 16:55, whisky-dave wrote:



On Thursday, 17 December 2015 16:00:16 UTC, Syd Rumpo wrote:
On 17/12/2015 15:38, whisky-dave wrote:
On Thursday, 17 December 2015 14:22:54 UTC, Syd Rumpo wrote:
On 17/12/2015 12:58, whisky-dave wrote:

snipped

Yes I've messed with one of those, I used an arduino PWM output which runs at about 500HZ I changed the pulse width to change the amount of cooling or heating. Using a TP31 transitor.
I used a CPU cooler on the other side as I found that I couldn;t get much cooling or heating for any lengh of time without finding a way to 'disipated' the heat or cold from the other side of the device.

You shouldn't PWM a Peltier device directly, at least not if you're
using it for cooling. Cooling is proportional to current, but the
unwanted ohmic heating is in proportion to current squared (I*I*R).
Think about it - a 50% PWM at 1A peak in a 2ohm device will produce 1W
ohmic heating (I*I*R for half the time) whereas a continuous (100%) 0.5A
would produce 0.5W ohmic heating.

You can of course use PWM indirectly if you filter it to give a fairly
steady current.

Well I haven't seen any info that says I can't run it from PWM.

You just did, see above. Apart from that, you'd need to look. If only
there were some way of searching the Web for key phrases such "PWM Peltier".

I did I have done.

http://electronics.stackexchange.com...eltier-element

You do know that you're meant to read this stuff? 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.

Most of the microcontrollers I am familiar with do PWM in the hundreds of cycles per second range. No thermoelectric module is going to be able to distinguish that from a steady voltage.

Rubbish. What magical property does the Peltier module have which
allows it to integrate PWM? Peltier modules have no reactance other
than strays.

Also, (google it) there is a paper out there where they tested PWM cycling with rates of 1/10s all the way up to 1000/1s rates and the peltiers did not exhibit any decline in performance over thousands of hours. The one that cycled every 10 seconds did exhibit temperature fluctuation due to the slow response time.

Link?

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

It's safe, of course, but quite inefficient when cooling, for reasons
explained ad nauseum. Best stop digging.

Cheers
--
Syd