Yeah, Bill brought that up too.
On reflection, it makes sense to keep some current flowing through the SCR. That would keep the system from oscillating. If the current through the SCR dropped to zero, it would stop conducting, allowing full voltage to appear at the supply output again which, if the excessive load was still present, would trip the crowbar again in a cycle that would go on indefinitely. In decades I've never had an Astron fail, so I never studied the schematic. I see at least some Ten-Tec supplies work the same way (I have one here). Tnx guys, it's been an instructive exchange. 73, Ron AC7AC From: Wes Stewart [mailto:[email protected]] Sent: Monday, June 08, 2009 11:54 AM To: 'Bill Miner'; [email protected]; Ron D'Eau Claire Subject: RE: [Elecraft] Battery Charging with DC Power Supply If still functional, the power supply regulator isn't "turned off", it still tries to supply some current* into the (nearly) short circuit SCR. At the same time the battery supplies current limited only by its internal impedance and the resistance of the interconnect. * If I'm not mistaken (always a good possibility) the Astrons use foldback current limiting to limit the dissipation of the pass transistors. The SCR that is part of the crowbar is connected directly across the output terminals of the supply. When used normally, the firing of the SCR shorts the output and the supply goes into current limit, if still functional, or hopefully blows the primary fuse if not. With a battery across the output, if the SCR fires, something is going to fuse. It will be either a user-installed external fuse or something else. It would probably not be a good idea to rely on the something else. Wes N7WS ______________________________________________________________ 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
