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. http://www.campingworld.com/browse/skus/index.cfm?deptID=&subOf=40&skunum= 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. http://www.campingworld.com/browse/skus/index.cfm?deptID=&subOf=40&skunum= 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. John |