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From: John De Armond
Newsgroups: rec.outdoors.camping
Subject: Re: Peltier cooler
Date: Tue, 12 Jun 2001 19:12:54 -0400

Giacomo Ciani wrote:
> Hello, I'm thinking to buy a Peltier coller, because using the freeze packs
> is often impossible!! There are camping in which people are not very kind
> and the stole your pack... so the food in the WARM coller goes away!!
> I would like to know if someone tried theese peltier coolers and can tell me
> something about them!

You'll be greatly disappointed, I'm afraid.  The problems with
peltier coolers are many.

First, the coefficient of performance is only about 1.  That is, it
will pump 1 watt of heat for each watt used.  A conventional
refrigerator has a COP around 3 for standard efficiency units.  It
follows that one either consumes a lot of power or makes do with a
lot less cooling.  The latter is the case.  I've had several of
these and have found that while they will keep stuff cool if the box
is inside, they lack the cooling capacity to chill stuff over any
reasonable period of time.

Even with feeble cooling, these things typically draw 8-10 amps.
That will flatten a 100 amp-hour deep discharge battery in about 10
hours.  It will do actual damage to a regular car battery in much
less time.

A single junction stack can only pump across about a 40 deg F
differential.  That's fine with the box in a 70 degree room but it
really sucks in a 110 degree car.

The peltier junction makes a dandy Seebeck junction.  That means
that when you turn the unit off, it will merrily generate power,
enough to drive the cooling fan, while pumping heat back in the box
even faster than it pumped it out.  therefore you either leave it on
or allow it to warm up fast.  Modifying the circuitry to disconnect
the fan and power LEDs help but not much.  I've ended up
disassembling the peltier coolers I've bought to get the junctions
out and discarding the rest.

The only satisfactory use of a peltier cooler is how my parents use
it.  They put it in the car with the air conditioning on.  They'll
only make short stops on the way to the destination, whereupon they
yank it out, take it to the motel room and run it on a portable 12
volt adapter.

There is a solution, though it is a bit more expensive.  Dometic and
a couple of the other major manufacturers make portable absorption
refrigerator/freezers that will run on either line current, 12 volts
or propane.  Here's a typical one.

I have camped next to some people who had one of those and I was
quite impressed.  About the only negative is the relatively small
refrigerated space.

Stepping up in price and refrigerated space a bit is the 12 volt
operated conventional refrigeration unit.

In truck stops I have also seen dormatory-style mini-refrigerators
that run on 12 volts, designed to be carried in the sleeper on semi
trucks.  Seems like the price was in the $300 range.


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