[Elecraft] KX3 Battery Holder and Batter Removal

[Ron D'Eau Claire]

I can say from experience that the heads can be screwed down into the
holders so that the edge of the screw cannot touch the battery cell. Since
the screws are not directly under the cells, they can't touch the cell when
fully inserted. 

There are two ways that you can have battery short trouble:

1) A mounting screw digs into the side of a battery, penetrating the thin
insulating cover, grounding the cell's container or "can". That shorts out
the cells between that point and the negative terminal end of the battery
pack. This can happen with either rechargeable NiMH cells or with Alkaline
cells. 

2) The spring on the base contact shorts out an Alkaline cell. This is not a
problem with NiMH cells since they have a "can" covering the bottom and
sides that is all part of the negative terminal, just like old carbon-zinc
"dry" cells. But Alkaline cell chemistry reverses the terminals so the "can"
is the positive terminal and the negative terminal is the insulated center
electrode. To keep Alkaline cells looking and installing just like the older
cells, manufacturers physically turn them upside down. What was the smooth
bottom of the can on a dry cell they now stamp to look like the top of the
battery, with a button for the positive terminal molded into the "can".
Close inspection will reveal that there's no insulator separating that
positive button from the rest of the "can". At what is now the bottom there
is an insulated electrode that covers the negative end of the cell. The
insulated electrode is attached to a disk that covers what appears to be the
bottom of the "can" but which as actually insulated from it. 

Some manufacturers have an insulator around the edge of this disk just under
the plastic sheath where it wraps around the bottom of the cell that
separates it from the positive "can". If that sheath is broken, the spring
in the battery holder can easily bridge the insulator and short the cell.
One manufacturer moves the insulator up onto the side if the battery which
eliminates that problem, but most of the cells that I've unwrapped show the
insulator just under the edge of the sheath on the bottom of the cell where
the spring will cause a short if the insulating sheath is damaged. 

(There are pictures of this in the KX3 Kit Assembly manual on the web site:
http://www.elecraft.com/manual/KX3%20Kit%20Assembly%20Manual%20Rev%20F%20WEB
.pdf
 
See page 35, Figure 54)

Obviously failure of the sheath at the bottom of alkaline cells is rare,
since virtually all cell holders use a spring to contact the negative
terminal, but it has happened. 

73, Ron AC7AC



-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Gary Marklund
Sent: Saturday, January 19, 2013 2:48 PM
To: Phil Hystad
Cc: elecraft at mailman.qth.net
Subject: Re: [Elecraft] KX3 Battery Holder and Batter Removal

I took this opportunity to install ribbons on mine, too. Was certain it was
only a matter of time until I gouged a battery case. I'm also convinced the
problem is more that the screw holes are not countersunk than screw length.