Zapper voltage source

[Robert Scott]

There have been several postings recently about using electric
current to heat up a center pin - the so-called zapper.  While I
cannot comment on the effectiveness of this technique in 
freeing up action centers, I would like to say something about
the methods being proposed to generate the electric current.

A center pin has extremely low resistance - on the order of
1/10 Ohm.  In order to generate any substantial heat by an 
electric current flowing in the center pin, quite a large current
must be used, yet the voltage required across the pin is tiny.

Several people have suggested using train transformers, or other such
sources of medium voltage.  These sources are very poorly matched for
the task at hand, which is to produce high current at very low
voltage.  While it may be possible to get the required current from 
a really heafty train transformer, you would be generating much more
heat in the transformer than in the center pin.  And as others have
mentioned, even medium voltage under the right conditions can be
hazardous.

Fortunately, there is an easily available source of very high 
current at very low voltage.  They are soldering guns.  They
use current through a copper tip to heat the tip.  By the way,
when your soldering gun tip wears through and breaks, you don't
have to buy a new tip.  If you have any 12-gauge house wiring
in your junk box, just form a small length of that wire into the 
shape of the broken tip.  I use my soldering gun a lot and I 
have not bought a new tip in 30 years.  Anyway, I disconnected 
the tip and measured the open circuit voltage produced by the 
gun.  It was .385 volts.  Then with the tip reconnected, I 
measured the loaded voltage at .290 volts.  So this voltage 
source is both safe and effective at heating up low-resistance 
objects.

Finally, I manufactured a zapper by cutting my wire tip 
in the middle, spreading it, and inserting a #21 center pin
between the cut ends of the wire.  When I clicked on the
soldering gun at full power, the center pin was hot enough
to melt solder in four seconds.  Apparently .385 volts is
still too high.  If I thought zappers were of any use (and so
far I don't), I would find just the right size and length of
wire to add to the circuit to give a more gentle heating.
But starting with an inherently low voltage source, this job
would be a lot easier than trying to use a medium voltage 
source.

Robert Scott
Ann Arbor, Michigan