fan controller for larder

[ericw]

Klaus

The temperature difference controller was easy to build, and works well. The output (as switched by a MOSFET) could change states it bit faster, at the moment the fan sort of is speed controlled in the switch-over area.
Klaus

The 1M resistor should give positive feedback forcing the fast switch over and some hysteresis - is it connected correctly?

[KLD]

Jack, back to square 1 then. This is exactly the controller idea I proposed in the beginning. Say square two, since it's built up already 
Can you propose any particular centrifugal fan?


Eric,

Yes. the hysteresis works OK, about 2C if I remember correctly. Yet, the switchover is not steep enough. I might try and put a couple of NANDs between the LM393 output and the MOSFET, so that there are defined logical values (voltages) driving the FET. In order to be able to drive a 240V fan, I'll change over from the FET to a transistor plus relay (and diode).

Klaus

[johnrae]

It all depends on the depth of your pocket and your ability to make do.

Ideally you want something slow running - to minimise noise - but powerful enough to get air actually moving.

In the past I have used a manrose 5" cetrifugal model to push bathroom air along  a very long duct with excellent results.  But it might be too noisy for continuopus running.  I think you should try and find an old (small) industrial vent fan and change its pulleys to run at slower speed.  This is a compromise between cost, speed (noise) and volume.

Alternatively see if you can find a bog standard (pun intended) bathroom or kitchen fan in a builder's skip and try that.  The cheap axial fans sold for bathroom fitting by the likes of DIY stores are about as much use as chocolate fire guards but if you can pick one up for nothing it'd be worth a try.

Bear in mind that if you over-pressurise the pantry you might not be able to get the door open to get at the food - an added bonus ??

jack

[rogeriko]

Instead of installing electric fans how about an electric door that opens to the outside at night. About one meter square should cool everything down nicely. Installed at the top I would presume.