Olin, Michael, and others experienced in this, could I press you a little
further on this issue ?

As Michael pointed out, an LC filter on the PWM output to the Peltier
smooths the current and improves efficiency.  As I said before, I have
achieved minus 30 degrees in a test box using this exact setup.  Probably
should have mentioned an LC filter, thanks for pointing that out.  If I
recall, you pointed this out to me quite a long time ago when I first
started controlling Peltier's with the PIC16F877 PWM module & FET switching.

However, when efficiency is not so much an issue, could an LC actually
create more problems than it solves ?  An example would be ringing, which
can be a real problem in a PIC environment.  What is the trade off here
between efficiency and noise ?  I have used a simple LC.  I cannot recall
right now what values I used for L and C, but I do remember just wrapping
thick magnet wire around a small ferrite toroid and using a simple mono cap,
but maybe you could suggest a better LC configuration with ideal values to
drive a 12V/8A Peltier at 5kHz ?  I have found that this is not the easiest
thing to simulate with Spice.

Rgs
Ian

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Olin Lathrop
> Sent: Monday, 19 January 2004 3:17 am
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE:] About test boxes (hot and cold)
>
>
> Ian McLean wrote:
> > I have brought this topic up before and generating a lot of
> criticism
> > and alternatives for driving TEC's.  Some will say that PWM is also
> > not the best way to control them.
>
> It isn't, unless the individual pulses are filtered so that
> the Peltier
> device sees a constant current.  This is again due to their
> inefficiency at
> high drive current.  This means you will get more cooling at
> a constant half
> current than alternating between off and full on half the time.
>
>
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