[Elecraft] Battery Charging with DC Power Supply

[Ron D'Eau Claire]

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:n7ws at yahoo.com] 
Sent: Monday, June 08, 2009 11:54 AM
To: 'Bill Miner'; Elecraft at mailman.qth.net; 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