[Elecraft] Battery Charging with DC Power Supply

[Wes Stewart]

Since Astron has been mentioned in this thread, I'll use that as an example.

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

--- On Mon, 6/8/09, Ron D'Eau Claire <ron at cobi.biz> wrote:

From: Ron D'Eau Claire <ron at cobi.biz>
Subject: Re: [Elecraft] Battery Charging with DC Power Supply
To: "'Bill Miner'" <wg6h at yahoo.com>, Elecraft at mailman.qth.net
Date: Monday, June 8, 2009, 8:15 AM

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.


Ron AC7AC

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