> Finally, I went back to my Aston 35m which has no fan and helps hold down > the desk. Ahhh....No noise, No hash....Just nice clean DC.
I've been dealing with the same issues as I transitioned from a 20 year-old Astron RS-35 to an HP bench supply and an Astron switcher. In each case, both supplies use loud rotational fans. Recently, I've added fan speed control with a PWM controller. Instead of limiting the fan's speed through current alone, a pulse-width-modulator controls speed by producing short pulses of voltage. Speed is then controlled by the duty-cycle of the circuit's pulse train. After trying several attempts to smoothly control rotational speed with series resistors and voltage-dividers, I found several low-cost PWM kits (~ USD $20) available that accurately control speed down to slow levels without stalling. In the case of the SS-20, I created two threshold steps, one to engage when the heatsink temperature rises above a pre-determined amount. However, after adding the PWM controller and letting the idle speed rest where no noise is heard, enough air flows to keep the higher speed from kicking in, except when I key down into a load for more than a minute. Paul, W9AC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
