Electric Fencer

Hi all,

First time post, so please go easy!

I would like to make a very simple electric fence energizer for a poultry pen, that will only be on my land for about 8 weeks (which is why I don't want to spend £70 on one!).

I was thinking of using a car ignition coil and a 12V car battery as the source, but don't know how I can make it "pulse". I need the pulses approximately every second or so.

The pen will be extremely remote, so there is no fear of anyone being hurt by it, although I don't think car coils can produce the sort of current that will do any damage to humans(???)

The pen is pretty small (about 150 feet circumference) and I need a voltage of about 2500-5000V.

I've trawled the site but can't find anything useful for a newby.

Any advice much appreciated... including making one from a capacitor.

Kemist.

**broken link removed**

You'll need Acrobat Reader to open that file but the 4th page of that document has a good circuit, exactly what you are looking for. It was easy to find with my web browser and only the 3rd link on the page!

kemist said:

I don't think car coils can produce the sort of current that will do any damage to humans(???)

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It depends on the input driver pulse, the voltage, duty cyle and frequency if you get this wrong it can be leathal. Second from worrying about people what about your livestock? You don't want to end up with a load of dead chickens.

I also would suggest that you consider the device as having lethal potential. The commercial units available during the 1960s (when I was a kid on a farm) never seemed to hurt the cows. A bird landing with one foot on the wire and one foot on the nail holding the insulator to the wood post would be fried to a crisp.

Along with injury or death from electrical shock please also consider the risk of fire. Our "fencer" (that's what it was called) had the potential to burn weeds that would otherwise short the fence. That feature started several grass fires.

A friend and I gave some thought to constructing our own battery powered fence charger. Battery life was an issue so we thought we'd "scan" the wire at some proper rate then apply high voltage only when it seemed that an animal was in contact. That may be exactly how some commerical units work.

stevez said:

as a kid on a farm) never seemed to hurt the cows. A bird landing with one foot on the wire and one foot on the nail holding the insulator to the wood post would be fried to a crisp.

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Obviously it depends on the size of the animal, a human might hardly feel a piezo ignition from a cooker but it'll kill an insect (I've tried it before), a biger pulse might give you a nasty shock but kill a small bird or rodant so it wouldn't surprise me if your fence would leave you gasping for breath while a cow would feel a more gentle shock.

I would like to think that the commercial units are such that lethal potential for any human cannot be attained. With the home brew unit a reasonable approach would be to assume it's lethal if you aren't 100% sure it isn't or can't ever be in a mode of failure. I've never heard of someone dying from being sparked to death by an ignition coil in a car or in any home brew application but then the "death by home brew electric fencer" might never get noticed either. The approach is rather conservative but I'd prefer to encourage that behavior when death or serious injury can be a consequence.

I must say I'm horrified by the idea of an electric fence dangerous enough to 'cook' a bird!.

The electric fences I've come across over many decades have all worked the same, they provide brief pulses of current every couple of seconds, and are usually powered by an old car battery.

There was one serious exception! - back in my school days (late 60's) we used to go 'beating' for pheasants during the season, on a local land owners estates. This involves walking miles through soaking woodland and farm land chasing the pheasants out to be SHOT! - we got paid the princely sum of 15 shillings for this! (a friend of mine used to get £4 - 80 shillings - for the same job elsewhere).

One field we used to beat through was of 'kale' this is a foul smelling horrible plant used for feeding cows - and cows absolutely love the stuff. So the technique is to run an electic fence across it, a little way in, and allow the cows to only eat that far across - then move the fence gradually across the field.

Apparently the farmer found that the cows loved it so much the electric fence didnt stop them, and as it wasn't far from his farm he ran a mains wire directly to the fence wire - full 240V live mains (at 13A) directly to the fence wire!.

Us poor children had to repeatedly climb over this fence, in the pouring rain! - obviously never heard of 'health and safety' back then!.

I remember seeing one of those "stupidest videos', some rednecks were hanging out drinking beer... one of decided to go relieve himself over by the fence. He was jumping around and yelling, but don't think he was dying. Then again, who knows how real those home videos really are...

This wasn't Jackass by any chance was it?

I don't remember what show it was on, I was at a friend's house and it was on cable TV. Just thought it was kind of messed up. It was funny because it was something stupid a drunk man might do. But for me, I hate getting shocked, just seeing it creeps me out.

Sounds like a topic for Myth Busters to investigate. Adam is stupid enough to pee on an electrified wire but I'd like to see Jamie suffer the shock! You'd have to be very close to the fence to likely get shocked since the further back you stand, the pee stream would be of individual droplets with air as the insulator between them. No shock would occur.

Weeds growing up into the fence would reduce or eliminate the effectiveness of the fence. One manufacturer, at least, had a weed-chopper feature - it would burn the weeds as they grew up into the fence. It worked, I can tell you that. The on-off period was about 2 seconds on, 5 seconds off. How safe this was is unknown to me. I did convince my little brother to pee on the fence and the experience, as I recall was unpleasant. It didn't knock him to the ground.

The weeds that grow on the farms near me don't affect the fence's operation unless they are soaking wet from rain. Besides, it's typically the top most wire that's carrying the current, with the remaining lower wires acting as just a barrier.

For temporary pasturing of relatively calm cattle we'd run one wire about 36" from the ground - electrified. That worked most of the time.

For relatively aggressive cattle we'd have at least 5 strands of barbed wire on posts. Then we'd make standoffs from the post - about 12 inches inside and 36" from the ground - and would run an electrified wire with insulators on the standoffs.

There was a light on the fencer control that would light when the voltage on the line dropped - from short circuiting of weeds, insulator failure, birds, etc. We'd have to walk the fence line to remedy the problem or the fence was ineffective.

HiTech said:

**broken link removed**

You'll need Acrobat Reader to open that file but the 4th page of that document has a good circuit, exactly what you are looking for. It was easy to find with my web browser and only the 3rd link on the page!

Click to expand...

The link is broken

can you post a new or pdf?

Most good energisers have a 'weed burn' facility these days. A hundred meters or so of weed on your electric fence will cause problems, however you are correct in that when it rains this kind of overgrowth can actualy disable the fence.

Car ignition coil for fence

I have heard of people using a ignition coil for an electric fence, the usual standard coils put out around 14 to 15,000volts HT.

As a kid (in the early 1950s) I once saw a man open the bonnert of a WWII Jeep then he placed the whole length of his arm accross the sparkplugs and kill the 4cyl motor. His arm jumped around a bit doing this. Now that got my attention.

This circuit uses a Car Ignition coil and works quite good.

**broken link removed**

But Yes, You Need Good Insulators on the Wire and the wire needs to be in Free Air.
Rain and Plants touching the Wire can Short it out.

Gary