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Reverse engineering: car cooler

What

A car portable cooler was obtained to modify. It is a Gio'Style brand, type "Fiesta 25", rated at 12V/4A. It uses thermoelectric cooling and has 25 liters of volume.


Box outside

Box outside

Box label

Label detail

Lid inside

Sticker detail

Box inside

Connector detail

Inside

The cooler consists of a top lid on a pair of hinges, and a bottom vessel.

The vessel is a "dumb" plastic moulding, with two spaced layers insulated with presumably air, maybe with some fibrous filler to mitigate convection heat transfer.

The top and bottom half of the lid are snapped together and held with six wood screws.

The lid contains a styrofoam spacer, separating the hot and cold side. The spacer has a hole, with a Peltier element sandwiched between a pair of finned heatsinks, which facilitate an efficient heat transfer between the metal and air.

The styrofoam spacer is freely laid in the hollow lid, held in place with the fan chassis. The fan itself is attached to the bottom lid half with a pair of wood screws, the same size as the lid ones.


Lid inside, top side

Styrofoam spacer, top side

Lid inside, bottom side

Lid top and separated spacer, hot side

Lid top and separated spacer, cold side

Fan side detail

Fan mount, fan and lid screws

The electrical connection is very simple - the connector is directly wired to the Peltier element, and a fan connected in parallel.


Power connector detail

Wiring panel

Wiring panel

The air is forced through the heatsinks with a pair of fans on a common shaft, sharing a motor. The fan on the hot side sucks air through a grille, forces it through a heatsink, and exhausts the warmed air through another grille. The fan on the cold side is circulating air through the closed cooler space, and over the cold heatsink.

The Peltier element is sandwiched between a pair of heatsinks. The bottom (cold) heatsink is attached to the element with a heat-transfer spacer, a block of aluminium. All thermal interfaces are coated with a white-crap thermal grease. The heatsinks are screwed together; the top heatsink has just holes, the bottom one has threaded holes. The screws have plastic spacers, probably to mitigate heat transfer from hot to cold side.


Bottom heatsink

Bottom heatsink

Top heatsink, screws removed

Top heatsink, screw detail

Heat transfer block and bottom heatsink

Heat transfer block and bottom heatsink

Heat transfer block and bottom heatsink

The cooling device is a Peltier element, a 40x40 mm square, 4mm thick, with sides sealed with silicone; its type is TEC1-12705. It is rated at 43 to 49 watts (at 25/50°C hot side), delta temp 66/75 °C, max. current of 5.3 amps and voltage at 14.2/16.2 volts, resistance 2.40/2.75 ohm.


Top heatsink removed, Peltier top

Peltier top detail

Peltier and bottom heat transfer block

Peltier side detail

Peltier detail

Peltier size

Peltier and top heatsink with new heat transfer paste

Performance

The cooler is fairly underpowered for its size. The temperature difference achieved is less than desired (todo: measure). This is however expected, given the low power and nature of the device.

The fan is slightly noisy.


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