[Elecraft] Battery Charging with DC Power Supply

[Doug Faunt N6TQS +1-510-655-8604]

There was an article in QST a good while back about this.  Theer were
two things that needed to be done, one of which was a fuse between the
battery and the power supply so if the crowbar triggered, the PS
wouldn't burn up, and the other was a resistor added so the 723
regulator would be protected against the reverse voltage condition
when the AC power side is off.  I can't spot the article in the ARRL
QST index, but may be able to locate information later.

And the Astron supplies with the battery backup option will cheerfully
fry a battery in a pretty short time.

73, doug

   From: "Frank Ross W4NHJ" <w4nhj at comcast.net>
   Date: Mon, 8 Jun 2009 11:21:03 -0400

   I believe I read somwhere that you can do a mod to Astron power supplies to 
   make the float chargable.  They sell supplies that say they are for battery 
   back-up, I suspect they are already modified for float charge.

   Frank - W4NHJ

   ----- Original Message ----- 
   From: "Ron D'Eau Claire" <ron at cobi.biz>
   To: "'Bill Miner'" <wg6h at yahoo.com>; <Elecraft at mailman.qth.net>
   Sent: Monday, June 08, 2009 10:15 AM
   Subject: Re: [Elecraft] Battery Charging with DC Power Supply


   > Bill - K6WLM wrote:
   >
   > In the case of Astron supplies it can damage parts of the DC regulator. 
   > If
   > there is a "Crow Bar" circuit that operates with a battery connected to 
   > the
   > power supply output it will ruin your day or even burn your house down.
   >
   > ---------------------------
   >
   > How can that produce damage or a fire hazard?
   >
   > A "crowbar" shuts off the power supply so it produces no output if too 
   > much
   > current is drawn from it specifically to protect the regulator.
   >
   > That might happen if the power supply is turned on when the battery is
   > discharged enough it demands more than the crowbar current limit, but the
   > crowbar is designed to avoid any dangerous or damaging operation.
   >
   > Typically, the supply remains *off* until the power switch is operated
   > manually, off then on, so it won't keep trying to feed current into a 
   > short
   > circuit somewhere. I know that's how the Astrons I've used work.
   >
   > So, as far as I can see, the worse that could happen is you end up with a
   > dead battery if you have a discharge path with the supply off.
   >