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Re: [Phys-l] Chimp unsuccessfully hangs from high voltage line



At 07:45 AM 8/26/2006, Joe, you wrote:
Some years ago, I had a crazyish uncle who had a small resort in the
Catskills, and decided it would be fun to have a chimp to entertain
the guests. While as it happened, one day the chimp got away. Now
this "resort" was in the middle of cow pasture country, a very lovely
setting with pastures separated by electric fences...a single wire
with some high voltage on it. There was enough internal resistance
in the power supply so that animals got shocked by not killed.
///
Joseph J. Bellina, Jr. Ph.D.


I have lately developed a personal interest in electric fences.
During a hot Summer, when grass easily burns out, horses are tempted
to reach through wire to the greener grass on the other side.
If that wire is barbed, they cut ears, shoulders, legs etc., in reaching
through. Unlike cattle, they are said to be slow to learn from their cuts.

Horse owners like to place an offset electric wire, to keep them back.
The ordinary sort of fence charger resembles an induction coil, which
pulses the fence wire with a high voltage pulse.
(Some are apparently configured like a transformer, instead)

The source impedance is high enough to avoid permanent injury to
animals. But this leads to a problem. The grass that is no longer
nibbled, grows to touch the wire, and this can easily emasculate
the pulse.

A recent approach to fence charging takes a different tack: a high
voltage pulse is still generated, but now, its output is lower impedance.
Instead, its duration is limited in order to avoid injuring the
quadrupeds. These are billed as "Low impedance" in that they are
not disabled by moderate grass/weed loading.
Chargers are also rated by pulse energy:
0.1 J to 1.5 J are to be seen in the feed store.



Brian Whatcott Altus OK Eureka!