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WA2ISE > TECH 06.12.20 03:53l 5 Lines 922 Bytes #999 (0) @ WW
BID : 358_WA2ISE
Read: GUEST
Subj: Samlex SEC1223 power supply fan mod
Path: IW8PGT<IZ3LSV<IR1UAW<I0OJJ<LU4ECL<ZL2BAU<F1OYP<KE0GB<GB7YEW<AL0Y
Sent: 201206/0152Z 10525@AL0Y.#NNJ.NJ.USA.NOAM BPQ6.0.20
The Samlex power supply has an internal fan that should turn on when the supply gets hot. But the thermostat must be set rather high, the supply gets warm. So I figured I'd make the fan be dual powered. Normally the fan is controlled by a transistor, Q5, a 2N2222. The fan positive lead goes to the 13.8V output, and the negative lead goes to this transistor's collector. If the thermostat goes open, the transistor turns on, turning the fan on. I added a 68 ohm power resistor from ground to this transistor's collector, to run the fan at a low power level, and low audio noise, when the supply isn't so hot that it triggers the thermostat. This will keep the supply cooler, and should help make the caps last longer. If the supply does get hot enough to trigger the thermostat, the transistor Q5 will still turn on hard, essentially shorting this new resistor, and the fan goes into high powered mode.
73 de WA2ISE
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