Feasible electric fence

Hi all

After messing about for the last week or so, going back and fourth between Google and people's suggestions I managed to get an energizer working with components found in an old inverter.

Bought an ignition coil, had an arduino lying around, found two capacitors and a N channel mosfet controlled with the arduino using blink :o, a couple diodes and a transformer and boom put my father on his ass... Completely by accident mind you but anyway it works none the less

My next step would be to try hook up an alarm so that if it shorts to ground or someone cuts the fence the alarm will sound. Thought of using a toroidal transformer and measuring the magnetism with a hall effect sensor but not sure how to go about it.

If anyone would like a rough sketch of the circuit I would be happy to help. No one should have to struggle like I did... Also if anyone thinks of a good idea to measure the voltage drop or current drop or a way to detect the line has been compromised please let me know, would appreciate it...

I think if you are in the United States, you need to review the local laws relating to electric fences. They are there for a reason.

Paul

Where (why) does the Arduino fit in?

Ah, in the UK you can zap 'em as hard as you want as long as they can still be identified from dental records.

We Brits specialise in sarcasm and black humor, you may gather.

Hi, In Australia there are design rules for electric fence output, and an ignition coil does not feature. The output has to be controlled, voltage and current wise.

Your ignition coil fencer is regarded as "lethal" as it is capable of delivering an uncontrolled repetitive heart stopping shock.

My advice before you get a manslaughter case on your hand, and junk it and buy a decent fencer.

Tom.... :)

PaulRB:
Ah, in the UK you can zap 'em as hard as you want as long as they can still be identified from dental records.

Used to be that way here, also. But many years ago, a young girl was crossing a field with a rain swollen drainage ditch. She tried to wade across the ditch and grabbed a wire to steady herself. Searchers found her hours later dead, but still grasping the wire.

After that a law was passed requiring pulsing electric charges with a considerable time between pulses. My fence charger allows more than a second between pulses.

Paul

Paul_KD7HB: After that a law was passed requiring pulsing electric charges with a considerable time between pulses. My fence charger allows more than a second between pulses.

Paul

AFAIK this has always been th e case in the UK the fence should not be capable of delivering a lethal current. Just a deterrent shock. Using an ignition coil could easily defeat that. It is not a job particularly for an arduino , just a very competent electronic engineer.

Boardburner2:
AFAIK this has always been th e case in the UK the fence should not be capable of delivering a lethal current. Just a deterrent shock.
Using an ignition coil could easily defeat that.
It is not a job particularly for an arduino , just a very competent electronic engineer.

Not even an engineering problem. We had a fence charger on the dairy farm that was controlled by a clock motor tilting a mercury switch back and forth to close and open the circuit. Could not be more simple than that!

Paul

Paul_KD7HB: Not even an engineering problem. We had a fence charger on the dairy farm that was controlled by a clock motor tilting a mercury switch back and forth to close and open the circuit. Could not be more simple than that!

Paul

That only controls the timing.

An ignition coil could easily deliver a fatal current. I have had one of these apart while they look simple i suspect a lot of thought gets given to the electrical design to control the current.

Look in any farming magazine for suitable approved devices.

The main components are the specialist transformer and high-quality capacitor.

Here in the UK 'Electric Shepherd' are a well-known make. There are many others.

I've repaired them, mostly when the capacitor fails.

Allan

So thought someone would come up with a solution not babble on about law and all the rest. The fact remains, anyone that ignors the warning signs posted every 15 meters, as per regulations deserves to be shocked... It's too high for children and animals and the shock is everything but lethal. The coil pulses 15ms every second, more than enough time to let go, just saying. As it is someone tried to het over last night and between the dogs and the fence couldn't get it right. If anyone has anything valuable to post please do so, if not don't waste your breath...

Also if anyone thinks of a good idea to measure the voltage drop or current drop or a way to detect the line has been compromised please let me know, would appreciate it...

Make it in a loop and make sure voltage is getting to the end of the wire.

With no load, there's no voltage drop and no current (Ohm's Law).

Hi'

GMTjason: The coil pulses 15ms every second, more than enough time to let go, just saying. As it is someone tried to het over last night and between the dogs and the fence couldn't get it right. If anyone has anything valuable to post please do so, if not don't waste your breath...

GMTjason: Bought an ignition coil, had an arduino lying around, found two capacitors and a N channel mosfet controlled with the arduino using blink :o, a couple diodes and a transformer and boom put my father on his ass... Completely by accident mind you but anyway it works none the less

Have you measured the output. Not by how far it booted your father. Tom... Bye PS 15mS = 66Hz....

GMTjason: The fact remains, anyone that ignors the warning signs posted every 15 meters, as per regulations deserves to be shocked... It's too high for children and animals and the shock is everything but lethal. The coil pulses 15ms every second, more than enough time to let go,

Wrong.

In the UK this would be called murder if death occours.

Also 15 mS is too short , i think something like 500 mS is the norm.

EDIT , i misread that i think as the interval 15 mS per second sounds as though it is in the ballpark but probably a bit long.

GMTjason: the shock is everything but lethal

VERY VERY wrong. They are designed to give a sting, if it throws you on your ass it is designed wrong.i

A typical ‘fencer’ has its voltage limited to 9kV to meet specs. It can have an output of up to 12 joules/ pulse in units I’ve seen . The output has a string of MOV’s to limit the voltage.

This is obtained by charging a high quality capacitor of 50uF or more to about 350 volts , either by rectifying ac mains or by means of an invertor from a 12v supply. These capacitors are designed to withstand a very fast discharge. Shorting out such a 50uF capacitor at 350 volts with a screwdriver ( I’ve done it) gives a blinding flash and a loud crack, and eats significant bits of screwdriver. That’s only about 3 joules. They are expensive. eg EPCOS and Dubilier make them.

Their eventual failure is the commonest fault in fencers.

This capacitor is discharged at intervals of about one second by means of a SCR into the primary of a step-up transformer. Judging by the thickness of the tracks on the pcb of a fencer a large current flows. I’ve measured the primary resistance and inductance of such a transformer at about 0.1 ohms and 4mH.
These transformers are usually sealed in opaque epoxy, so I’m not sure of their internal structure. They seldom fail.

For comparison a car ignition coil has an output of typically <0.1J per spark at voltages of >>20kV.

Both will hurt and can (sometimes) kill.

regards

Allan

allanhurst:
Both will hurt and can (sometimes) kill.

regards

Allan

Biggest perceived risk is knocking someone on their back and hitting their head on something hard.
Stock have 4 legs and much less likely to fall over.

allanhurst:
A typical ‘fencer’ has its voltage limited to 9kV to meet specs. It can have an output of up to 12 joules/ pulse in units I’ve seen .

regards

Allan

Seems a bit high , that is the same energy you get from a shrike blasting box and they can be fatal although they work around 300V rather than 9 KV.

Thanks for all the useful information... Think threw my dad on his ass is used as an expression. Many times have I been hit with the spark of a spark plug pulsing at idle. Although a little brain dead never was it more than an ouch and a cuss or two. The spark created when shorted to ground is about 6mm long giving me the idea I'm working with about 20kv. On the DC supply side I draw max 40ma yes 40. Earth leakage protection trips at my mains at 300ma... Sure I'm not going to kill a healthy unwanted criminal. And any criminal that does have a heart condition shouldn't be jumping over my fence... Just saying. Besides all of peoples warnings to me about I might kill someone, which I appreciate, these thieves come into our homes with bush knives and kill our wives... Something to bare in mind. I will head everyone's warnings once I have an alarm circuit hooked up and if I could get the answer or suggestion from someone that would be great

Jasib

As far as the alarm goes it is rather difficult to detect a short occurring.

Be aware that an ignition coil has the primary and secondary connected , it is not isolated, hence not safe for this application.

While the spark energy is very low under some circumstances very high currents can flow.

Deriving an alarm signal i suspect would be easier with a fully isolated transformer.

9kV is the spec in England.

By the way, what’s a ‘shrike blasting box’?

Allan…