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

[Alan Bloom]

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.

Another way is to use a thermistor and amplifier to gradually turn up
the fan voltage as things warm up.

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.

Al N1AL


On Mon, 2008-08-04 at 16:43, Nick-WA5BDU wrote:
> That's a pretty good solution.  When I was making measurements I noted 
> that when I turned the supply voltage down to the 10 to 11 volt range 
> the fan got very quiet.  In fact, I was going to forget about the 
> thermostatic control solution.  But when I put the cover on, the noise 
> worsened quite a bit at the same voltage.  Pulling air through those 
> case perforations seems to do it.
> 
> Since the K3 is spec'd for 11 to 15 volts, I wanted to run at a little 
> over 14 V or so.  The fan really gets noisier as voltage climbs, so I 
> definitely needed either the resistor solution or fan control.
> 
> 73-
> 
> Nick, WA5BDU
> 
> 
> NZ0T wrote:
> > As I'm not a very technical person I just used a couple of resistors in
> > parallel to slow the fan down in my 4225.  I can't remember the values this
> > early in the morning but it seems to be working just fine.  The supply does
> > run a little warmer but not hot and the fan is no longer heard.
> >
> > Bill NZ0T
> >
> >   
> 
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