[Elecraft] OT: fan control in MFJ-4225MV switching P/S

[Ian White GM3SEK]

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