Alan Bloom wrote:
The cool (pun intended) way to do it is to use a thermostat wired in
parallel with a resistor in series with the fan. The fan only runs at
full voltage when the heat sink gets hot.
The Astron SS-30 has a very noisy fan that is controlled by a thermal
switch on the heatsink. But there isn't sufficient cooling when the fan
is off, so every few minutes brings another blast of fan noise.
A 100-ohm 3W resistor in parallel with the thermal switch will keep the
fan running slowly and quietly, all the time. With a typical load from a
"100W" transceiver, I've never heard it switch to full speed again.
The main concern is to be sure that the fan still turns on reliably
with the resistor in series. I would test to find the largest
resistance that allows the fan to start and use no more than half that
value, to allow for changes in fan characteristics as it ages.
Agreed. 100 ohms gives brisk and reliable starting for that particular
12V fan, but other fans will vary.
--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek
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