How to make an Electric Fence

ronsimpson

Joined Oct 7, 2019
2,404
And, since he hasn't replied to any of our posts recently, ...............
Braking news, Man found dead on his electric fence.

Seriously, I got on a unmarked fence when I was about 7. He just plugged the fence into a outlet. It was real bad.
I looked at a number of "internet circuits". They are not like the commercial unites.
 

crutschow

Joined Mar 14, 2008
30,821
I love that it was purely electromechanical.
We also had some other fencers before that, which used a sort of spring loaded oscillating wheel to momentary close mechanical contacts and generate the spark.
Problem was the contacts would wear out, causing a failure of the fencer.
The Surge mercury switch solved that problem.
 

Ya’akov

Joined Jan 27, 2019
6,616
We also had some other fencers before that, which used a sort of spring loaded oscillating wheel to momentary close mechanical contacts and generate the spark.
Problem was the contacts would wear out, causing a failure of the fencer.
The Surge mercury switch solved that problem.
Mercury switches and reed relays have a special place in my heart.
 

BobaMosfet

Joined Jul 1, 2009
2,029
Hello guys, I need to make an electric fence for my goat. Can you please help me and give me an easy method to make it?
You can, but it must be AC, not DC. All electric fences for animals are essentially AC (or should be). Some 'cheat' with oscillating DC. Never use constant DC. DC will burn, can cause fires, etc. AC will 'buzz' and startle. Use a transformer to drop 120VAC to 12VAC, and then keep the current to an acceptable (very low) level. Use appropriate fusing, etc- Be smart about it.
 

crutschow

Joined Mar 14, 2008
30,821
Use a transformer to drop 120VAC to 12VAC,
Certainly you don't mean to connect the 12Vac directly to the fence, since 12Vac cannot cause a shock.

The TS stated he wants to have a battery powered fencer.
The fencer electronics turns that into a high voltage, periodic pulse to the fence.
 

BobaMosfet

Joined Jul 1, 2009
2,029
Certainly you don't mean to connect the 12Vac directly to the fence, since 12Vac cannot cause a shock.

The TS stated he wants to have a battery powered fencer.
The fencer electronics turns that into a high voltage, periodic pulse to the fence.
You don't feel 12VAC low-current as a shock, but instead as a buzz. I know, because I've gotten across such electric fencing before. However, having said that, a little extra digging shows that today's electric fences may simply store a charge, waiting for it to be grounded, and dumped that. Other designs exist:

https://en.wikipedia.org/wiki/Electric_fence
 
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MisterBill2

Joined Jan 23, 2018
13,176
The fence chargers that I have worked with all deliver a single spike pulse, although it may actually be a few cycles of the transformer ringing, since it is a capacitor discharging into the transformer primary. Thus a constant shock is not possible. One interesting option would be a version of a capacitor discharge ignition system, but with a much lower powered inverter to charge up the capacitor every two seconds, instead of in just ten milliseconds.

The only constant voltage systems are those designed to keep humans from attacking bases in other parts of the world.
 

MisterBill2

Joined Jan 23, 2018
13,176
Unless he stuck his tongue on it.
From a correctly functioning "cow" typefence the spark will jump about a quarter inch to a well grounded wire. Just one pop and then a second later another pop. Cows get a few shocks because it takes them a while to figure it out. A"horse" type charger makes a half inch spark that is a bit louder, because a horse needs more convincing tha a domestic cow.
 

MisterBill2

Joined Jan 23, 2018
13,176
I have used the "Mark 10" CD ignition system on a number of cars, back in the day. And it DID have a warning about shocks from the high voltage spark.
That spark would jump about 3/4 inch to almost anything, even from a less than perfect cable from the distributor to a spark plug. So if it was possible to add a gate to the inverter of an older Mark Ten, so that it would activate once every two seconds and then fire, that could certainly be a very effective package. Probably it would only take about 8 milliseconds to charge the cap, and then fire the charge into the coil. A similar design should be available someplace, since probably dragsters still use CD ignition because those plugs foul quickly. The beauty of the Mark Ten is that it would fire fouled spark plugs. IT certainly did deliver a bit of power.
 

MaxHeadRoom

Joined Jul 18, 2013
26,000
I am looking to put one together for a short fence for deer.
I intend using an older AC Delco coil, from some out there on other sites, a 0.1sec pulse every sec appears popular.
20VDC and a Mosfet switch
 

MisterBill2

Joined Jan 23, 2018
13,176
Actually, Max, an interesting pulser can be made from an old flash unit, suc as one in a timing light. Just put the coil primary in series with the flash tube and then use a neon relaxation oscillator to deliver the trigger pulses. Or even simpler, get one of those strobe lights with the variable flash rate and put the ignition coil primary in series with the flash tube. It might also work using a horizontal output transformer. But there might not be enough power to charge a very long wire.
 
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