Friday 2 June 2017

A fan on Maplins
June 2017

You will remember that at the heart of the galley / saloon rebuild was a small 12 volt chest freezer?

Well, whilst it has been working for the six weeks we have been away, it hasn't been operating as efficiently or effectively as I had anticipated. Sure it has been freezing the contents but the cold was not evenly distributed and as the temperature outside rose the level of frost reduced (if you know what I mean).

I knew from the day I installed it that I could be designing in a weakness. Whilst the compressor is remote from the freezer box, it is housed under a seat where the ventilation isn't great. As a result the ambient air around the compressor fan has been rising and it has been struggling to dump the heat. I have increased the openings into the compressor box but there are limited options and whilst things improved a bit, the cooling fan kept droning away most of the time, wasting power.

I recall Halfie having this problem with his fridge a couple of years ago and decided to use his approach to my problem. 

Whilst we were moored in Jericho (Oxford) we took a walk to Maplins and bought a computer fan plus a switch and wiring. Then it was off to Wickes to get some six inch ducting which would fit over the square fan (echoes of Apollo 13 came to mind).

Bones paid us a visit as I was assembling the various components and offered some interesting, if slightly over complicated suggestions including thermal switches. I am a bit of a "keep it simple at all  costs" sort of boy and decided a basic on / off switch would be fine. This switch was a bit swanky because it had an option to have a light on when running so in the absence of an instruction card I asked Bones which of the three terminals I should avoid. She studied them carefully and sagely advised that I avoid the gold one at all costs. Why, what does that one do? I asked. I dunno came the reply - I just don't like the colour.

So, ignoring this patently girlie advice I wired in the said gold terminal and the light duly illuminated when the fan was on. The trouble was that the resistance of the led bulb reduced the power available for the fan which then turned at about 1/3 of its previous speed. Grr - she was right even if the logic was a bit iffy!

So the wiring was altered to avoid the gold terminal and the fan started to suck the warm air out of the cupboard and up and away behind the fridge.

So, did it work? You bet it did. The locker is cool, the compressor cooling fan hardly runs at all and the freezer freezes the whole box. And as an added bonus the through draft is helping disperse the heat produced by the fridge and that now cycles much less frequently.

You may be concerned that I cant see when the fan is on, but given its miniscule battery draw and long fife expectancy it can run 24/7, and I can check its still running by sticking a finger over the duct outlet, a DIY thermal switch!

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