Ask The Mechanic – Cool air for hot heads

Cool air for hot heads

Camping is great in the summer; that cool rain swept evenings huddling under the duvet listening to the “pitter patter” of the rain and comforting howl of the wind. Quote from Val!!! This is of course what we all enjoy? But camping in France yields a different problem too much heat night and day.

Connie is equipped with insulation double glazing and a heater but no cooling so it’s open the roof vent and side window and spend sweaty night on the duvet. Also cooking causes heat to build up and if it is raining then hot heads result! I decided an extractor fan would help, but how to do this?

The obvious suspect was the roof vent pix 1. I obtained a piece of 3mm polycarbonate sheet, 2 of 100mm cooling fans 12 volt with grills, a double throw double contact centre off switch and a 2000 microfarad 63 volt capacitor (actually from my stores but easily purchased).

The polycarbonate sheet was chosen as it does not crack like acrylic and transparency was not a prime criterion. This was cut to fit the aperture under the roof vent it presses against the seal on the inside of the van. In Pix4 you can see that one edge is supported by 2 aluminium brackets fixed to the hinge bolts and the other edge is held by the raise lower mechanism cover. The edge strips add rigidity and stop rattles.

The parts were then positioned and the holes cut, the fans and switch project upwards under the roof vent. The switch is wired to put the fans in parallel for maximum speed (and noise) or series for virtually silent running at night. The power for this is by means of a cable fixed to the roof and lifting frame and connected to the over door light.

An important part is the switch wiring and the use of the capacitor. The fans are “brushless” so use an internal inverter to drive the rotor when used in series one can react with the other and so a capacitor wired across one fan will smooth out the supply and prevent “hunting”  pix 5,6

The results were very satisfactory, with the vent open, roof up and all doors and windows closed full power pulled in the roof “tent” so opening a cab window produced a strong draft. At slow speed the noise was very much less but a useful draft could still be felt.

As each fan can move 90 cu ft min so 180 cu ft min at full speed the air in the van could theoretically be changed every 3 minutes and this can banish the heat and smell build up during cooking.