[AMRadio] HV Wire - electric fence

Jim candela jcandela at prodigy.net
Sun Dec 24 16:37:22 EST 2006


   I ran across the following link that describes a home made fence charger.
The author also talks a bit about grounding. After thinking about Peter's
situation I bet he floated the coax shield, or had a poor ground return to
the earth. Then again lets suppose he had both a good earth ground at the
fence feed point (multiple ground rods bonded together), and the coax shield
was grounded at the same end. Would the fast pulses result in ringing of the
unterminated 75 ohm transmission line that might be several wavelengths long
at the pulse decay frequency? I bet that coax would take it for a while
before arcing internally, and maybe be pretty nasty to be around. Then
again, maybe my Egg-Nog has been spiked! ;=)

scroll down to pages 3, 4, 5 at the following link:



-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net]On Behalf Of KA5MIR
Sent: Sunday, December 24, 2006 9:12 AM
To: amradio at mailman.qth.net
Subject: Re: [AMRadio] HV Wire

Haven't messed with them in a long time, but the few I've worked with used
autotransformer or coil where a battery or low voltage was connected across
the primary and the fence and a ground were connected across the secondary.
A relay supplied power to the coil until it was charged, (usually about a
second) and when the relay interrupted the primary, the collapsing field put
a big pulse of energy on the wire.  Same principle as the ignition system of
a vehicle ...and DC powered relay kickback.


On Saturday 23 December 2006 20:12, Jim Candela wrote:
> Peter,
>     I am wondering how electric fence chargers work. I once heard that
> they pulse the HV on and off. I assume you grounded the coax shield near
> your home or barn yet the coax was still hot anywhere it touched the
> earth?? I don't see how that could be unless the coax braid was floating,
> and the HV pulsing was coupled to the shield from the cable capacitance
> per foot (~ 20pf/'). If the shield was grounded that capacitance would
> also charge to the peak value of the pulsed DC, and might end up changing
> the whole situation should a cow brush up against the wire. The 'danger'
> factor of the fence might  go up a notch or two this way.
>    I'd like to hear more of your electric fence story.
> Regards,
> Jim
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