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

Yes I did. It gives two sides to it, those that thibnk you can and
those that can't see why you can't use PWM.

That is so, so true.

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.


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.

it doesn't need a magical property any more than a light dimmer
does.


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?

yes I want a limk that explain why PWM can't be used.


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.

there was NO explanation shown that made sense.

It would to someone versed in basic electronics.