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G8MNY  > TECH     26.11.23 10:00z 111 Lines 5913 Bytes #23 (0) @ WW
BID : 61078_GB7CIP
Subj: 12V Cow Fence for /P
Sent: 231126/0919Z @:GB7CIP.#32.GBR.EURO #:61078 [Caterham Surrey GBR]

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 & in practice fence voltages around 1kV (1-3mm spark) is more normal.

It has 3 modes:-

PULSE mode gives a steady pulse every 2-5 seconds. Ideal when you are first
      in the field & 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 & fires pulses when the insulation changes. On a permanent low
      fence resistance it gives up & the sense LED stays on. This mode saves
      power & 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 & connection indication. It glows dimly on pulses &
brightly on heavy loads!

 旼컴컴쩡컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컫컴컴컴컴컴컴컴컴컫컴컫컴o훟컴< +12V
               SENSE 旼컴컴컴컴컴컴컴컴)컴컴                  3A
              읕o컴>o컨캑<쳐               e\쿟1          __
                        ge               PNP 쳐커         \_/
  旼컴좔컴     BOTH o컴컴컴캑                /           __ 2x
   RELAY                           T2  \            __ \_/ 10A
  읕컴쩡컴    PULSE o컫캑<쳐        NPN  쳐켸          /_\   diodes
                OFF o                      3n3            
+     쳐컴  NPN                        쳐컴컴늘컴좔22k컴좔컴
===        \ T3            10u+                               CAR
 220u      쳐컫컴컫컴)컴컴쩡늘컴390鴛캑             旼컴컫컴  IGN
 16V     e/                                2u2      )||(  COIL
                  47k  __                  300v === P )||( S
                      \ /6V2       1k      poly      )||(
     __    390k       읕쩡                        쳐컴켸  쳐컴
     /_\        __      쳐컴>쳐컴컴)컴컴56鴛컴컴      10k NEON
               /_\  읕컴캑 hi piv     쳐컴                쳐컴
                       +           __            > /   \/
                  220u ===  SENSE<- \ / 39k   relay o/   FENCE
                   10V       LED<- 컫                 /\
 읕컴컴좔컴좔컴컨컴컨컴컴컴컴좔컴컴컴컴컴컨컴컨컴컴컴컴컴좔컴컴컨컴쩡< -ve
                                                                  __ GND
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, & is
over the 6.2V zener voltage. The 220uF is quickly discharged through the high
voltage diode & 56 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 & 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 & 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.

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 - - - - - - - - - -- - - - - - - - -- - - - - - - - 쨘
          윱  up to 20m apart 튔ibre                 Spare wire @윱
Steel rod                    튖lass                       ign粕  
                             튣ods                  旼컫컴컫컨쩡캑Earth
                                                   읕켸   읕켸   Rod
                                                    Battery  Unit

To attach the fence wire I use a clove hitch as it is easy to adjust & does not
damage the wire. I suspend the end ball of wire & connect it to the ignition
unit with tinned copper wire. Also using this wire to a good earth stake. Then
connect the car battery.

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 & jump away in turn. Once this has happened the cows normally
give you a wide birth, & 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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