Laryn, If the power supply were a switching design, current foldback would occur. But, in the typical Astron RS-series linear supply, the firing of the SCR puts a bolted short on the output. As soon as the large capacitors on the output start to lose their charge, the regulator tries to maintain the output voltage by turning on the pass transistors to full conduction, quickly exceeding the current ratings of the transformer and rectifier diodes and blowing the fuse. Every time this has happened to an Astron RS supply (that I have personal knowledge of), it has blown the fuse. Every time. Odd that your experience is different.
Because of their (RS-series) relative instability in high-RF environments, I now install only Duracomm, Samlex, and Astron switching power supplies. Lightweight, very efficient, and very reliable. Nuff said. 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Laryn Lohman Sent: Tuesday, December 23, 2008 9:33 AM To: [email protected] Subject: [Repeater-Builder] Re: Astron P/S question --- In [email protected] <mailto:Repeater-Builder%40yahoogroups.com> , "Bob M." <msf5kg...@...> wrote: Whether it's the SCR itself, or the sense circuit driving it, something is causing it to fire and blow the fuse. You'd need to measure the actual output voltage of the supply to see if it's going that high or if the SCR is being falsely triggered. Of course, you only get one shot at trying it before the fuse blows. Why is the fuse blowing? Shouldn't the crowbar firing cause simple current foldback? All of my Astrons do, and never blow fuses. My apoligies if this has been brought up before... Laryn K8TVZ
