They were power hungry units that worked by passing a current through dissimilar metals and using a heat sink with a small fan. They did work but consumed lots of amps. They were ineffecient compared to todays units and imho not worth the money. You can still buy units using this system at outdoor stores for around $100 in portable coolers. They plug into a cigarette lighter.Except for day sails with already chilled food or drinks are not worth the effort.