Message 24359 in TECH.WW
From: G8MNY
Date: Thu, 18 Jun 26 08:49:00 Z
Newsgroups: TECH.WW
Subject: Variable Speed Thermal Fan
Message-ID: <62739_GB7CIP>
Path: N2NOV|NS2B|GB7BED|EI2GYB|GB7CIP
R:260618/0853z @:N2NOV.#RICH.NY.USA.NOAM $:62739_GB7CIP
R:260618/0852Z 53698@NS2B.#WNY.NY.USA.NOAM BPQ6.0.25
R:260618/0851Z 13054@GB7BED.#21.GBR.EU LinBPQ6.0.25
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R:260618/0849Z @:GB7CIP.#32.GBR.EURO #:62739 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Jul 15)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
I have often been annoyed by fan noise from over powerful fans in gear. Here is
a solution I adopted for a 12V PSUs & 400W HF PAs. Small 12V fans can be found
in a scrap PCs etc. and draw about 70-100mA depending on speed & size.
2x PNP CIRCUIT (Germanium NPN can be used E-C reversed)
use idiot diode & fuse if fan manually wired up.
It uses a high gain (x100) tab silicon NPN or PNP controlled by a leaky
Germanium PNP or NPN placed between the hot heatsink fins (test a germanium
with a soldering iron for resistance change and Fans on/off). I used an all
plasic Tab silicon cable tied to the fans, with the insulated geramanium
transistor E & C leads twisted (make sure it's case is isolated or insulate)
and exposed connections in heat shrink etc.
cool!
The fan can be in the earth path or +12V side...
Silicon NPN & Germanium PNP CIRCUIT
/ + \ For a quieter fan,
\FAN/ or use a 24V one!
RESULT
In high use (waffle mode with processing on or a pile up) the fan starts up and
runs very quietly from about 5V across it, and gently runs faster if the
heatsink gets hotter.
See TECH bul "PA & PSU Fan Noise"
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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