From: "Roger Hamlett"
Subject: Re: Pelitier Device? (cooling an IC)
X-Newsreader: Microsoft Outlook Express 5.50.4807.1700
Date: Fri, 20 Dec 2002 12:12:13 -0000
NNTP-Posting-Date: Fri, 20 Dec 2002 12:14:41 GMT
Organization: ntl Cablemodem News Service
"Rileyesi" wrote in message
> I am looking for information on a device that uses electricty
> to cool an IC. The device is called a Pelitier junction, if
> memory serves. I've tried various spellings on a google.com
> search without finding any specific technical
> information. Maybe my spelling is THAT bad! (Wouldn't be
> the first time...won't be the last!)
> I need to find out if they work in a hot environment. I have
> an application where a microcontroller will need to operate in
> a 150 degree C environment. I need to find out if a Pelitier
> device will cool below ambient (which I doubt).
> If not, I think I need to put the micro into an enclosure and
> add cooling.
> Shy of these, any other ideas???
> Any leads/tips/help would be appreciated.
A Peltier device, _will_ cool below ambient, but you have a series of
The first is the temperature involved. A Peltier stage, typically gives a
maximum of about 65C useable 'drop' (some versions go to 72C, but work much
better if not asked to do so much - as you increase the power to get a
higher drop, the dissipation in the Peltier junction also increases). At the
'hot' end', you have to get rid of the heat moved (the device is a 'heat
pump', moving heat from one location to another), as well as the heat
generated by the module itself. The modules use a relatively high current (a
120W module will require typically 14A), so any inefficiency in the supply,
will add significantly to the cooling required. The biggest problem with
your application, is that the temperature you are talking about for the
enviroment, is above the maximum rating for the modules (normally 80C, but
versions are available rated to 115C). If it wasn't for this, you could
cascade multiple modules, to get the drop required. The problem here is that
the 'bottom' module, has to remove the heat generated by the top module as
well, reducing the effective wattage that can be removed from the target.
Now you are in a very awkward situation, since there is no magic 'heat
remover'. Any solution is going to need somewhere to get rid of the heat,
implying that the 'hot side', is probably going to have to run several
degrees above this ambient temperature. Any cooling system designed to run
with the hot side at perhaps 160C, is going to be a very specialist item!.
If your actual power dissipation is quite low (a few watts), and there is
somewhere nearby that the heat can be dissipated, things are not so bad (for
instance, if there is water nearby, a heat-pipe, could be used to keep the
hot end of a Peltier device below 100C. The cold end of the junction, could
then be held below 50C, and the whole system will work fine.