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'[EE]: Electric fence energy safety level'
2002\08\03@175500 by Morgan Olsson

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Me again trying to repair this electric fence unit...
Seem no problem redesigning the charge cap charger, and fire cirquit.

But...

I have earlier repaired an electric fence unit in which a microcontroller adjusted the charge according to the load.  (Trial-measure-increase/decrease style)  That one was a whopping 9 Joule per pulse unit.  (If anyone wants to know, it was only the FET switch that was blown in that one.  They had stupidly used a 600 V part, operating at about 620V peak @ full load and 230V supply.  Replaced with it´s 800V rated sister.)

Most units i have seen is 1.5 to 4 Joule.

The one i repair i calculated to 6 Joule capacitor stored energy.
Scaring, it has room for another equally large capacitor, yeilding 12J!

It is possible this IC incorporate some clever function for load adaption, but it seem that would be an add-on ckt to connect to 3 unused pin connectors.  Maybe only used with the larger capacitor bank.

Now, is it recommended to just shoot 6J in every shot...?  I mean personal safety.
I know for sure i will keep my hand at safe distance, as the 9J machine blew 2W carbon film resistors like New year bombs when i tried to test it, and wire wound types arched...

BTW it is a TORO model 6000 made by IAAB
I searched but could not find the manufacturer on the web.

/Morgan
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2002\08\04@080529 by Olin Lathrop

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> Now, is it recommended to just shoot 6J in every shot...?

I don't know anything about electric fences or sheep, but this doesn't make
sense to me.  I thought the point was to make touching the fence
uncomfortable enough so that the sheep will eventually learn not to do it,
without creating well done lamb chops on the spot (Baah, Bzzzzz, Pfft,
sheep--).

I would think the two relevant parameters are the spike voltage and
duration.  The fence leakage resistance and capacitance to ground can vary
due to environmental conditions and from installation to installation, so
the manufacturer may have added a circuit to adjust the strength of the
pulse automatically.  So far OK, but why doesn't the circuit try to hold the
spike amplitude (or some measure of "feelability") constant instead of its
power into the fence?  Why isn't the power per pulse only whatever is
required to overcome the leakage?  For the same effect per pulse, wouldn't a
long fence on a damp day require more power than a short one on a dry day?
What am I missing here?


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2002\08\04@132551 by Morgan Olsson

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Olin Lathrop wrote:
>So far OK, but why doesn't the circuit try to hold the
>spike amplitude (or some measure of "feelability") constant instead of its
>power into the fence?  Why isn't the power per pulse only whatever is
>required to overcome the leakage?  For the same effect per pulse, wouldn't a
>long fence on a damp day require more power than a short one on a dry day?
>What am I missing here?

Nothing! :)  
Well, cost issues as usual...
There are cheap units that pulse about 1J (if not open cirquit, then an internal spike gap fires) every shot, then there are those advanced units that senses the result and adopt, sending up to 20J in each pulse!  And everything in between.  There are also those nasty continuous AC types...

This 6J charge unit seem to be the largest nonadopting electric fence drive i´ve seen.
In the 9 Joule adopting unit i repaired earlier i could se cirquitry for the controller to measure utput spike level.  On this unit i can´t indentify such cirquit, but some componets in th etransformer drive stage that only connect to 3 auxillary pins not used in this unit, but maybe get used in an advanced sister unit.

Some info: http://www.electric-fence.com/gloss2.html

/Morgan

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2002\08\04@135039 by Peter L. Peres

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On Sat, 3 Aug 2002, Morgan Olsson wrote:

>Me again trying to repair this electric fence unit...
>Seem no problem redesigning the charge cap charger, and fire cirquit.
>
>But...
>
>I have earlier repaired an electric fence unit in which a microcontroller
>adjusted the charge according to the load.
>(Trial-measure-increase/decrease style)  That one was a whopping 9 Joule
>per pulse unit.  (If anyone wants to know, it was only the FET switch

Ahh. You do direct shawarma from the sheep, right ?

>Most units i have seen is 1.5 to 4 Joule.

I don't know about sheep but people (like me) tend to react very badly
from 20mJ up.

{Quote hidden}

Imho you need to know the capacitance of the wire to know this. Is there
some kind of voltage or current feedback from the output ? (look carefully
it may be a current transformer implemented as PCB traces).

I'm no expert on fence zappers but usually when you have an
inductive/capacitive load like several hundred feet of fence wire then you
treat it as a RLC resonant circuit and either tune it into the generator
or excite it by pulse. For example by placing a spark gap in series with
the generator secondary feeding it. The goal is to up the voltage on the
fence RLC to something that will go through wool. This may or may not take
6J but you will never know until you know the fence impedance. Do you have
a RLC bridge to measure the fence ?

One method I've seen used to test a fence (for cows) was to make a string
of 12 neon bulbs and connect it to the fence through a 100R resistor and
to GND. If they flash there is enough energy (12 neons fire at about 1kV).
Then you would turn down the converter until they stop flashing, then turn
it up until it starts flashing again. An active feedback would be good
because in bad weather there will be more leakage.

The only fence generator I've ever seen used two valves (!), one as a slow
oscillator the second as self oscillator exciting the fence through a
spark gap (no capacitor, no rectifier). It worked forever, you just had to
change valves and and electrolytic filter capacitor every ten years or so
(or so I was told - I only changed them once for the owner). I heard that
pure neon bulb based designs existed once upon a time. They may have been
thyratrons but who knows.

Peter

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2002\08\04@153626 by M. Adam Davis

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face
Olin Lathrop wrote:

>>Now, is it recommended to just shoot 6J in every shot...?
>>
>>
>
>I don't know anything about electric fences or sheep, but this doesn't make
>sense to me.  I thought the point was to make touching the fence
>uncomfortable enough so that the sheep will eventually learn not to do it,
>without creating well done lamb chops on the spot (Baah, Bzzzzz, Pfft,
>sheep--).
>
That is exactly the point.  But there's a gotcha - weeds.  Most zappers
now are 'weed cutters', and will zap plants that get close enough.
Obviously a lower power fence won't damage the weeds faster than they
can grow, and will quickly be dampened by them necessitating a manual
weed whacking job around the fence line - not fun for even small pastures.

Sheep, IIRC, need rather large pastures since a lot more of their food
comes from the grass rather than normal feeding.

Therefore a good fencer will have to remove several /miles/ of actively
growing weeds in order to stay in good shape.  Each zap is going to not
only zap any sheep that is close, but 300-3000 or more weed leaves that
are also in contact with the fence.  The sheep will get only a very
small current, and during the active growing season will get much less
unless the fencer can tell how much of its previous zap was actually
consumed.

I'm curious what the speed of adaptation is though - I hope it on the
order of minutes or hours.  A small child who grabs on to the fence may
not have the reflexes or ability to unlatch their hand in he 1-2 seconds
between zaps.  If the current gets stronger each zap it would be a Bad
Thing (TM).

As an aside, horses like to touch things they plan on jumping with their
noses before they do so.  The nose is one of the most sensitive parts of
a horse...  Cows, on the other hand, won't jump a fence so much as run
it over (or get tangled in it).  They are affected very little by
fencers and thus barb wire is still preferred to a fencer.  I don't know
about sheep, though.  I suspect that they are more like cows, but you
don't want to damage the skin/fur with barb wire (if it reaches all the
way through the fur - curious thought).

-Adam

{Quote hidden}

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2002\08\04@185857 by Morgan Olsson

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Peter L. Peres. wrote:

>Ahh. You do direct shawarma from the sheep, right ?

Yes http://130.225.180.126/JohannesHolmertz/shawarma
Actually that article forgot to mention this new hunting+cooking technique

>I don't know about sheep but people (like me) tend to react very badly
>from 20mJ up.

Then i wont investigate my reaction to 6000mJ...

How theese units are leagal i don´t understand...

Problem is only a fraction goes through an eventual sheep touching the wire somewhere in this landscape...
Most energy go eaten by weeds, bushes, bad/moistcovered/missing insulators, wire loose and dropped on ground, ...
And thick fat water repelling fluffy fur is good insulator!
Combine that with rain wetting all weeds that hang over kilometers of wire and wet insulators... You really need to bash in quite some electrons if you want a fraction of them to say hello to the sheep instead of taking a nice swim in the rain...

>Is there
>some kind of voltage or current feedback from the output ? (look carefully
>it may be a current transformer implemented as PCB traces).

Not in this one, but i believe a sister model do:

High voltage part analysis:

##### = windings :
A = charge transformer secondary (Flyback)
B = Open air power inductor
C = Fence transformer primary
D = Fence transformer secondary

D1 = fast 1 amp (actually 2 in series)
D2 = small switch diode
D3 = 6 amp 700V rectifier
SCR = 800V 300A pulse rated
C3 = 3 in series of 100n 660VAC rated.  Across C3 there is also 5 sereis connected 10k 12W R and a small SCR with gate resistors triggering a Neon lamp just for indicating operation OK

   D1    ,-[2M2]-[2M2]--Charge voltage sense to firing controller
,--->|---+-----+--------+----+--O NC1
|        |     |        |    |  ,------+--------+-O FENCE
|      C1|     |      C2|    |  |      |        |
#  600V ---    |   630V---   #  #      |C3      |   #  32µF ---    |   1µF ---   #  #     ---     Open Spark Gap
#        |     |        |    #  #     ---     about 6mm
# A      +-->|-'        |  C #  # D    |        |
|   D2   |  D3          |    |  |      |        |
+---|<---+              |    |  '------+--------+-O GROUND ROD
|        |  SCR    B    |    |
+--[10R]-+--|<---#####--+----+-[180k]-[180k]-[Trimmer]-O NC2
|        |   '-[33R]---firing from controller |       GND on controller
'-[3k3]-Sense to charging switcher controller (charge current)


Basically: C1 is charged by D1 and then dumped to fence by SCR.
Now, i think the capacitors C2 & C3 on both sides of the Fence transformer, (plus fence capacitance) toghether with the B inductor would make the voltage "overshoot" to much higher voltage than possible without B.  This inductance also would make it shoot back and the 32µF charge cap go negative if it was not for D3.  Thus C! always get fully discharged, and tha tis the only feedback voltage for the output.

The only way i can think of that the controiller can evaluate the result is by measuring time from firing until voltage hit zero.  But i think that would be very not exact as components tolerance is pretty high, and the behaviour is complex.

But the two unconnected pin s NC1 and NC2 is across fence transformer, and could provide a measurment of the result by i.e integrating the voltage during the pulse.  However, thees pins seem intended for a doughter board controller.

My analysis is that his unit is simply sending full charge pulses without regulation.  (Before it broke...)
And that a regulator board was at least planned, maybe used in a sister model.

(BTW the owner have now got anoter unit running, borreowe this weekend, and it seem too expensive to rebuild this if i charge by the hour anyway... Have to reverse design as i can´t find a new controller IC.  So i put it on hold for an unspecified while.)
/Morgan

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2002\08\04@192850 by Michael Simpson

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Most of the electric fence chargers on the market are leagal only because
they dont put out a constant voltage.  They pulse the full charge for a very
short time every 1-2 seconds.  Most states have outlawed the use of constant
fence chargers.  Also another thing you have to watch out for is fires.
The largers ones can start fires when weeds touch the lines.

I live on a large piece of property in N. VA and have been using electic
fence chargers for a while now to protect my gardens from deer, coons an
rabits.

{Original Message removed}

2002\08\05@100354 by Alan B. Pearce

face picon face
>> Now, is it recommended to just shoot 6J in every shot...?
>
>I don't know anything about electric fences or sheep, but this doesn't make
>sense to me.  I thought the point was to make touching the fence
>uncomfortable enough so that the sheep will eventually learn not to do it,
>without creating well done lamb chops on the spot (Baah, Bzzzzz, Pfft,
>sheep--).

One of the problems with using an electric fence on sheep is they have this
long greasy wool covering which stops moisture penetration. This requires a
reasonable energy pulse to get a large enough tickle into the sheep itself
to make it notice the shock, even in wet weather.

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2002\08\05@101353 by Alan B. Pearce

face picon face
>As an aside, horses like to touch things they plan on jumping with their
>noses before they do so.  The nose is one of the most sensitive parts of
>a horse...

Once a horse is aware of an electric fence, it will not go near it. One of
the products around for setting up electric fence lines, on a temporary
basis, consists of an orange plastic strip (a bit like the plastic banding
strip for parcels) with a single strand of wire through it. This sort of
stuff is often used for partitioning up a field where it is desirable to
restrict the quantity of feed an animal can access (can be important for
horses as they get colic if they over eat, and they tend too when there is
plenty of feed). One person I knew found that once the horses were used to
the idea of the orange strip being an electric fence, then sometimes they
could put it up without the shock unit turned on, and the horses still would
not come near it.

>Cows, on the other hand, won't jump a fence so much as run
>it over (or get tangled in it).  They are affected very little by
>fencers and thus barb wire is still preferred to a fencer.  I don't know
>about sheep, though.  I suspect that they are more like cows, but you
>don't want to damage the skin/fur with barb wire (if it reaches all the
>way through the fur - curious thought).

Another scheme has used poles stuck in the ground, with the shock unit
connected between poles. This creates a potential across the ground, and
with the distance between front and rear legs on a cow, could give them
sufficient shock to discourage them from coming that way. Other animals such
as horses tend to jump such "obstacles". :)

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2002\08\05@103711 by Eoin Ross

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face
From my experience with these units (ones made by Gallagher in Hamilton NZ) in the field (literally) it doesn't appear that there is compensation for line conditions - the voltage of the pulses would vary depending on a whole range of things. Anything from 8 kV to 3 kV

The amount of grass on the fence, whether or not it was dry, the moisture in the soil (to make these systems more efficient you need to run an earth out as well as the hot wire, using each y-standard as a ground spike)

The one the family farm used (and was bitten by a few times) ran maybe 10 - 20 km of wire?


>>> KILLspamolin_piclistKILLspamspamEMBEDINC.COM 08/04/02 08:04AM >>>
<snip>

I would think the two relevant parameters are the spike voltage and
duration.  The fence leakage resistance and capacitance to ground can vary
due to environmental conditions and from installation to installation, so
the manufacturer may have added a circuit to adjust the strength of the
pulse automatically.  <snip>
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(978) 742-9014, http://www.embedinc.com
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2002\08\05@113307 by Russell McMahon

face
flavicon
face
From my experience with these units (ones made by Gallagher in Hamilton NZ)
in the field (literally) it doesn't appear that there is compensation for
line conditions - the voltage of the pulses would vary depending on a whole
range of things. Anything from 8 kV to 3 kV

The amount of grass on the fence, whether or not it was dry, the moisture in
the soil (to make these systems more efficient you need to run an earth out
as well as the hot wire, using each y-standard as a ground spike)

The one the family farm used (and was bitten by a few times) ran maybe 10 -
20 km of wire?



ALL modern NZ electric fences, and also ones made "long tme since", have to
comply to a strict standard. This specifies, amongst other things,  peak
voltage deliverable and probably also peak energy deliverable. Regulation is
(or was) achieved by two (maybe 3?) parallel banks of VDRs which allow a
flat topped response as load varies. Your Gallagher should have this inside
if made in the last 20 years plus. The reason for the multiple banks of VDR
in parallel is that in testing they can open or short circuit various
components and the device must fail safe or keep working OK. .

Bill Gallagher allegedly invented the electric fence in the 1930s to keep
his horse from scratching his car but no doubt it was a case of "steam
engine time". Regardless - it made him and his descendants rich.



       RM

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