A little lightweight MFJ-4225MV power supply. It puts out about 25 A, maybe 20 continuous, which is enough for my IC-706GII or my new K3. I also liked the fact that the fan was fairly quiet. But that was in comparison with myFT-1000 with its fairly noisy fan and my hamshack computer with two or more attention getting fans. After upgradingto a new laptop and the quietly cooled K3, the MFJ P/S became the
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distracting source of white noise in the ham shack. Actually, this project ought to be applicable to any P/S that can run with the fan off in low load conditions. I don`t like noisy fans. I also don`t like noisy fans that start, run for a few seconds, and stop again. If the unit is hot enough to require a fan, I want it to run long enough to cool the sink down a little. I don`t think the fan is too critical in this P/S, so I decided to go with a temperature reached after 5 minutes at 20 amps load. In this way, it might never come on during light duty operation and just listening. If it does come on, I want a deadband of about 10 degrees at the heat sink before it goes off. If the 20 A load continues, the fan might never go off, which would be OK. First I made some temperature measurements. The P/S has two heat sinks, one with two devices mounted to it and one with just one. Using a LM34Z sensor glued to the heat sink with two devices, I measured the temperature at 20 A load for 10 minutes. It went from 74. 5 F to 115 F at 5 minutes and 132 F at 10 minutes. But then I realized the sink toward the middle of the unit was getting hotter. So I moved the sensor there and did the test again. Ambient was 79F. In 5 minutes T was 134 F, in 10 it was 138 F. I also experimented with running the fan at lower voltage. It got very quiet at less than 11 volts, but with the cover back on, it was not so quiet. Pulling air through the...
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