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G8MNY > TECH 16.11.25 10:45l 116 Lines 5946 Bytes #999 (0) @ WW
BID : 45168_GB7CIP
Subj: 12V Cow Fence for /P
Path: IZ3LSV<ED1ZAC<LU4ECL<VK2RZ<VE3CGR<VE2PKT<GB7BBS<GB7JD<GB7JED<GB7CIP
Sent: 251116/0850Z @:GB7CIP.#32.GBR.EURO #:45168 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (New Dec 03)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
This is an active cow fence, ideal for those /P contests. It is quite safe for
cows, but may not be suitable for smaller animals, or shy ones unless they are
used to electric fences!
Although a car ignition coil can put out 30kV (3cm spark) when there is no
load, a 100m or so of electric fence wire 1m high has quite high capacitance to
ground and in practice fence voltages around 1kV (1-3mm spark) is more normal.
FEATURES
It has 3 modes:-
PULSE mode gives a steady pulse every 2-5 seconds. Ideal when you are first
in the field and the cows are very interested in what is going on.
However BOTH mode may be more appropriate if there is too much interest.
SENSE mode, sends no regular pulse, but monitors the insulation resistance of
the fence and fires pulses when the insulation changes. On a permanent
low fence resistance it gives up and the sense LED stays on. This mode
saves power and QRM.
BOTH mode, gives the advantage of pulse mode in case of insulation fault, as
well as much higher animal intrusion protection (e.g. fence being knocked
down between pulses) without the power drain of a much faster pulse rate.
A Neon gives output pulse and connection indication. It glows dimly on pulses
and brightly on heavy loads!
ÚÄÄÄÄÄÂÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÂÄÄoÄoÄÄ< +12V
³ ³ ³ SENSE ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ)ÄÄÄÄ¿ ³ ³ 3A
³ ³ ÀÄoÄÄ>oÄÁÄ´<ÃÄ¿ ³ e\³T1 ³ _³_
³ ³ ge ³ ³ PNP ÃÄÄ¿ ³ \_/
³ ÚÄÄÄÁÄÄÄ¿ BOTH oÄÄÄÄÄÄÄ´ ³ /³ ³ ³ _³_ 2x
³ ³ RELAY ³ ³ T2 \³ ³ ³ _³_ \_/ 10A
³ ÀÄÄÄÂÄÄÄÙ PULSE oÄÂÄ´<ÃÄÙ NPN ÃÄÄÙ ³ /_\ ³ diodes
³ ³ ³ e/³ ³ ³ ³
³ ³ OFF o ³ ³ 3n3 ³ ³ ³
+³ ÃÄÄÄ¿ NPN ³ ÃÄÄÄÄÄ´ÃÄÄÁÄÄ22KÄÄÁÄÄÄ´
=== ³ \³ T3 ³ 10u+ ³ ³ CAR
³220u ³ ÃÄÄÂÄÄÄÂÄÄÄ)ÄÄÄÄÂÄ´ÃÄÄÄ390RÄÄ´ ÚÄÄÄÄÂÄÄ´ IGN
³16V ³ e/³ ³ ³ ³ ³ ³ 2u2 ³ )||( COIL
³ ³ ³ ³ ³ 47K _³_ ³ 300v === P )||( S
³ ³ ³ ³ ³ ³ \ /6V2 1K poly ³ )||(
³ _³_ ³ 390K ³ ³ ÀÄÂÄ ³ ÃÄÄÄÄÙ ÃÄÄÄ¿
³ /_\ ³ ³ _³_ ³ ÃÄÄÄ´>ÃÄÄÄÄÄÄ)ÄÄÄÄÄ56RÄÄÄÄÄ´ 10K NEON
³ ³ ³ ³ /_\ ÀÄÄÄÄ´ hi piv ÃÄÄÄ¿ ³ ÃÄÄÄÙ
³ ³ ³ ³ ³ +³ _³_ ³ > / \³/
³ ³ ³ ³ ³ 220u === SENSE<- \ / 39K relay o/ FENCE
³ ³ ³ ³ ³ 10V ³ LED<- ÄÂÄ ³ ³ /³\
ÀÄÄÄÄÄÁÄÄÄÁÄÄÄÄÁÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÁÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÂÄÄ< -ve
_³_ GND
////
CIRCUIT
The 12V relay with a heavy duty make contact (several contacts paralleled!),
this momentarily powers the ignition coil's primary. On relay release the coil
resonates with the 2u2 cap. The cap must be connected directly across the coil
terminals. This provides the high AC energy to make the secondary voltage.
Having a small neon bulb in series with the fence wire confirms the output
power is there. The relay is driven by T3 (200mA device).
In PULSE mode, T3 turns on when the 220uF has charged up through the 47k, and
is over the 6.2V zener voltage. The 220uF is quickly discharged through the
high voltage diode and 56R to the high current contact, ensuring only a
momentary on time for high current to flow through the coil, keeping power
needs down. This forms the repeating pulse mode timer.
In SENSE mode, any DC load on the fence under 20M will cause a voltage drop
across the 2 power diodes and turn on T1. This turns on T2 with some filtering
to stop mistriggers from RF etc. T2 on in turn will pulse T3 base on. T2
turning on also lights the SENSE LED. If there is permanent low resistance
being sensed, then the 10uF will get charged up and T3 will no longer be
turned on.
The mode selection has been done with a simple single pole 4 way switch, but
this has meant a germanium diode must be used to maintain the sense circuit
sensitivity when BOTH are selected.
INSTALLING
Keeping the cows away, set up the insulated fence wire (orange nylon with 2
stainless steel strands in it), I use 1.2m tall GRP rods pushed into the ground
@ about 20m spacing or if tough ground I use a steel rod to make the hole or
with 10cm of garden hose as a top insulator.
Clove Hitch Clove Hitch
Insulator º- - - - - - - - - -º- - - - - - - - -º- - - - - - - - º
À´ up to 20m apart ºFibre º Spare wire @À´
Steel rod ³ ºGlass º ignÚÙ ³
³ ºRods º ÚÄÄÂÄÄÄÂÄÁÂÄÄ´Earth
³ º º ÀÄÄÙ ÀÄÄÙ ³ Rod
Battery Unit
To attach the fence wire I use a clove hitch as it is easy to adjust and does
not damage the wire. I suspend the end ball of wire and connect it to the
ignition unit with tinned copper wire. Also using this wire to a good earth
stake. Then connect the car battery.
WHAT A LAUGH
When the cows approach make sure the fence is in PULSE or BOTH mode. I normally
spend the next 30 mins or so falling about laughing at all the cow as they must
all have a lick and jump away in turn. Once this has happened the cows normally
give you a wide birth, and the fence can be safely put into SENSE mode.
Why don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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