EEVblog #1277 - Electric Fence Controller Teardown

Random Bunker dumpster item teardown. A 20 year old Australian designed and made electric fence controller.

#Teardown

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[EEVblog]

UPDATE: Pakton have responded and unfortunately don't want to release the schematic for the MBT200. They are actually a bit embarrassed by this old unit and think "the plastic case was horrible".
They have offered a more modern JVA brand unit for a loan teardown and are happy to answer questions on operation etc.
The designer (Paul) has chimed in with a few comments:
"That unit was one of the first prototypes of that model, hence the "not for sale" on the back. I designed that unit. The PCB and firmware were all Pakton.
JVA is our in house brand. Pakton is an OEM designer and manufacturer, we make and badge product for a lot of the other brands in the industry. 90% of what we make is exported, we are one of the larger manufacturers in this niche in the world.
It was a very reliable model. The output transformer is our most reliable by far. It was designed by myself in conjunction with an incredibly talented engineer in NZ called Bob Smith of Marque Magnetics, since deceased.

One of the key new features in this energiser design (when it was released) was the moving of the filter capacitor (usually across the primary) to the output. I had a patent on that. This improved the pulse shape without increasing I^2R losses in the primary, it also allows the leakage inductance of the transformer to work with the filter capacitor (or more accurately it's reflection in the primary). The goal was to produce a soliton pulse shape when coupled to a real fence. We did a lot of testing on long fences in western Queensland. Real long fences are mostly capacitive in load. I.e. lots of reactive power flows. We have since patented methods of measuring the real versus reactive so we can isolate faults. Some of our monitors can pin point a fence fault to within 1/1000 on the fence. See the ZM20.


The move in electric fencing now is all towards monitoring, farmers do not have time to test their fences, and it's critically important to know if there is a fault on an electric fence if it is being relied on to keep stock in or bad guys out."

[kuhny]

Would love to see a reverse engineering of this thing.

[dglcomputers]

Bigclive would have seen for himself if the output worked, he's his own volt meter!

[suaspont]

When I was much younger, my buddy and I decided it would be a clever thing to run an insulated wire from the electric fence surrounding the pigsty over to the nearby metal clothesline as a "surprise" for my buddy's mom. We ran the hidden wire and the last step was to reach through the barb wire fence and hook a little loop onto the electric fence. I squatted down with my derriere a short distance from the ground. The moment the hook connected with the electric fence, there was a discharge between my butt region and the ground. I learned everything I needed to know about electric fences in a few milliseconds. I basically defibrillated my privates. I have always been careful around capacitors and anode terminals on CRTs ever since. Yowzer.

[DairyNZ]

Dairy Farmer here; livestock fence units are normally either 5kV (sheep/small lifestyle blocks) or 10kV (Cattle/large farms). Although voltage can increase as you move down the fence line, due to bounce effect, or decrease due to shorts.

[amiralozse]

I love Aussie caps!!
Its just: in the northern hemisphere you have to mount em upside down so no electrons gonna fall out!

[franciscandie]

I was holding onto a fence surrounding a horse field, I remember looking at the farmer hooking up the fence to close it behind him. It only took a little moment before I got zapped. Learned a valuable lesson that day.

[Mrjm]

When I was younger ;) we would test the fence charger by grabbing a long reed or length of grass (meter and a half or so) and then slowly walking it over and in contact with the fence wire until we just started to feel the tingle. From this we could gauge the charge in the 12V batteries used to power the devices.

[jimlagraff]

I never see those caps at the parts store, They must keep em Outback!

[feynthefallen]

Dave! Do you really have to ask whether or not we want a reverse engineering video?! How long have you known us?!

[vintagepc]

So the way these generally work is on magnetic impulse. The caps charge at and store a lower voltage charge on the order of a few hundred volts. Then at regular intervals a triac triggers and dumps this into the transformer, which has a HV secondary to the output terminals, boosting the voltage to the kilovolt output.


The ticking noise these boxes make is not a relay, it's the magnetostriction of the transformer core getting all that current dumped into it from the caps.
I repaired one myself previously with a failed triac (same symptoms, not ticking when switched on). It actually had a spade-mounted capacitor inside that could be changed to alter the amount of kick it gave (depending on your type of livestock, I assume)

[stclairstclair]

I grew up kind of poor and as a mechanic I cant help but repair anything like this I find, Resurrecting things is always satisfying .

[jamesgrimwood]

In the 80s I remember my grandad used to test his electric fences by touching them with a blade of grass held in his fingers. It still zapped you, but much less than touching the actual fence.

My dad touched an electric deer fence in the alps once with an aluminium walking pole. He said there was a large *crack* and then the pole shot out of his hand. Apparently he was pushing the fence down, ready to climb over it 🤦🏻‍♂️

[sympoz]

Hey Dave, bush electronics repairer here....the yellow lug is sense, its designed to go straight to a peg in the ground, or directly connected to the green lug to give feedback when it dumps its 3KV is a small unit, I have measured a 200KM unit at over 12kV, approx 2KM out.


The official bush test is holding a piece of green grass and holding it against the hot wire on the fence, if you can feel the zap then you are good. Gallagher had a unit on display at Ag-Quip a few years ago designed for 200KM+ runs and it was basically burning the grass with a 2M piece of 2.5mm fencing wire.


Edit: When they break it is usually the caps or transformer that goes, 50% of the time it is from corrosion, often just on the spade terminals you were praising, I have seen it a few times where farmers will keep the energizer in the same shed as bags of ferts/chemicals....ants are a good one too.

[dvlachy]

I made long time ago fence controller from ignition coils of Suzuki GSX-R motorbike. Two secondary winding of the coils in series (to make it adequately painfull) and an MCU with a switching transistor to repeatedly charge the primary winding of the coils. One can use even simplier NE555 for that. This is very easy and cheap way how to make it. I added some indicative diodes to show function and that was it. Worked from 12V so can run also from a car Pb acu. Any ignition coil you may have can be used. Mine model produced up to 40kV @ 2Hz frequency and about 0.6J max. energy. Was good enough for sheep I made it for. It hit several times my neighbor you know where and she told me it was not a pleasant experience. :)

[twoody]

was just wondering if it required on its "first startup" that it required that 16v AC to start the transistors or something along those lines, then 12v DC was "backup"

[Haarschmuckfachgeschafttadpole]

I touched an electric cow fence before. Doesn't feel like a shock at all, feels like someone kicking you in the arm and chest.

[ianwilliamtait]

Dave.
From 1969 to 1976, I worked for 7 years for an electric fence manufacturer in New Zealand,
From memory the max pulse rate was about 60 pulses per minute or PPM.
The max pulse length about 3ms
.
The voltage was about 3000v to 5000v for fences up to about 100 miles approx 160Km.
I believe this was increased to about 10000v for fences up to about 100 miles approx 160Km. Mainly for Australia's dry conditions,
I forget how many Joules but the figure of 150 meg nah!!!

You can't measure the output voltage with a ordinary volt meter. Analogue or digital
We used a transformer, full bridge rectifier, cap, resistor, preset pot and a 50ua meter scaled to read the voltage directly. The needle bounced about but gave a good indication of the fence performance that had to be checked at various places along the fence line,

One time I was testing some units and was distracted while about to disconnect the test leads.
I should have disconnected from the power source then disconnect the test leads.
What I did was forgot to disconnect the unit from the power. Disconnected the test wired from the test load and pulled the wires through my left hand. ZAPP.
My hand was white for several hours and had no feeling for about 24 hours.
Scared the bejibers out of me.

[garretthaynes]

14:03 I Calibrate 10Kv HeNe Laser power supplies for a living, and yes, I have been bitten from left hand to right hand. Painful is an understatement.

[tomhague]

Go for it. Reverse engineering any circuit is a challenge that everyone should attempt at least once. It can be frustrating but the satisfaction is worth it.