eBay has a number of thermostatic controller boards for 12V
computer-type fans using a thermistor sensor and pulse width modulation
to vary the fan speed. Details vary, but typically the fan starts at low
speed when the sensor reaches about 30degC and ramps up to full speed at
75degC or above.
Search ebay.com for PWM fan controller. Typical price is under $10
with free shipping from you-know-where.
The available designs vary as time goes by, and I've had good success
with two different boards over the past year. One of the boards is used
inside a transceiver covering 1.8-146MHz with no trace of RFI problems
from the pulsed 12V supply to the fan.
73 from Ian GM3SEK
>-----Original Message-----
>From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Gary
>Smith
>Sent: 14 September 2016 15:19
>To: amps@contesting.com
>Subject: [Amps] Fan control
>
>I still haven't gotten round to putting in
>a fan control into my old Alpha. There is
>a wire resistor with slider that allows
>changing the fan speed and I have it on
>maximum RPM right now and the blower noise
>is excessive when un-needed.
>
>I think if I had a thermostat with the
>probe in the hot air duct and a 2nd slider
>on the resistor, the fan could be set low
>for normal resting & brief transmissions &
>when the temp goes up, the fan could kick
>in all the way.
>
>Has anyone done this and if so, is there
>an inexpensive small thermostat you can
>suggest which I can install inside the
>control section of the amp to do this? I'd
>be fine with running the cabling out the
>back & into the duct, I'm running my
>thermometer into the duct and it works
>perfectly.
>
>Seems like a small digital/mechanical unit
>with outputs to fire a SS relay would be
>ideal. I've looked at what I could find at
>the last two hamfests but no cigar. Yet.
>
>73,
>
>Gary
>KA1J
>
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