Let's talk about fence Chargers.

Thread Starter

Wendy

Joined Mar 24, 2008
21,914
This is part of a series I am making that is indexed at Wendy's Index. It is meant to stimulate conversation and possibly teach new things. I am a firm believer In the maxim, if you want to learn, teach.

Fence Charger are a borderline project on AAC. Our TOS (Terms of Service) strictly forbids circuits designed to shock a person. The only reason AAC allows fence chargers to be discussed is they are meant strictly for animals and are very useful besides. So I will go over them with that understanding. This was discussed at length by the previous moderating staff(we have had some turnover since then. So the subject may be revisited and a new interpretation of the TOS may be implemented. If that happens this and possible other threads may be closed. Because it is inevitable humans will be shocked by these circuits if only by accident a strong emphasis on safety will be in place .I plan on showing designs and discussion of pros and cons. feel free to jump into fray This is my thread and I will be moderating it.

Posted somewhere on every page ofAAC. Terms and Rules.
 
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#12

Joined Nov 30, 2010
18,167
I saw a fence charger about 55 years ago. It had a mechanical pendulum firing a car ignition coil from a 12V battery charger at a frequency of less than 1Hz. Obviously antique technology, but it was pretty smart for 55 years ago.:cool: The only think custom about it was the pendulum.

Being about 10 years old, I just had to test it by using a piece of grass as a resistor. It worked!:D
 

Thread Starter

Wendy

Joined Mar 24, 2008
21,914
Peeing on a charged wire was some thing my FFA class(Future Farmers of Ameria) class would try to get freshmen in high school to do. I declined, having more sense than that, There were always a few idiots that would do it. and would try to talk folks into it the next year. Teen peer pressure is strange. FFA is a common class for rural schools like mine. It is also why safety on these circuits is so important.
 
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cmartinez

Joined Jan 17, 2007
6,647
I saw a fence charger about 55 years ago. It had a mechanical pendulum firing a car ignition coil from a 12V battery charger at a frequency of less than 1Hz. Obviously antique technology, but it was pretty smart for 55 years ago.:cool: The only think custom about it was the pendulum.

Being about 10 years old, I just had to test it by using a piece of grass as a resistor. It worked!:D
So you only felt a mild shock? What do you think was the potential generated with such device? About 20kV?
 

Thread Starter

Wendy

Joined Mar 24, 2008
21,914
Safety
In many ways a fence charger(hereafter refereed to as a FC) resembles an inverter A120vac inverter produces continuous power. It is the duration of exposure that is deadly. AnFC tries to produce a short pulse that stings,but is not dangerous Some times duration is used to increase the pain of the shock. I have done this on older designs, and have concluded it is a really bad idea because of the potential danger.Earth conductivity is a major variable. Some places get very little rain. which means the ground may be a good insulator. In those cases it may be necessary to up the voltage or duration if the shock to get the unwanted animals attentions increase the pain level of the shock, duration is my last choice but I will show examples in later designs.
 

#12

Joined Nov 30, 2010
18,167
Peeing on a charged wire was some thing my FFA class(Future Farmers of Ameria) class would try to get freshmen in high school to do. I declined, having more sense than that,
Yeah, that's not my favorite part to check for electricity with.:eek:
 

crutschow

Joined Mar 14, 2008
23,816
The fence chargers we had on my home farm when I was a kid put out perhaps only a few hundred volts, as the maximum spark length was only a tenth of an inch or so.
One particularly nasty fencer we had was called a "weed burner" to burn off the leaves of weeds that would touch the fence and short out a normal fencer, allowing the cattle to go through the single wire fence, once they realized it was dead.
It had about a second duration and a second off. It didn't have a particularly high voltage but generated sufficient current to burn off any weed leaves.
I remember seeing weeds next to the fence with leaves that had brown burn marks on their cut off edge.
They gave a nasty shock because of the long duration.
I think they fell out of favor because they could cause grass fires in dry conditions.

A number of years ago I built a charger for a friend who wanted to keep critters off his backyard wall.
I built it using a 115V isolation transformer, rectified to charge a ≈1μF capacitor to about 150V.
This was discharged once a second into the primary of a car ignition coil by an SCR, triggered by a unijunction oscillator (remember them?).
Generated about 10-15kv at the secondary and worked well to keep the critters away.
 

Thread Starter

Wendy

Joined Mar 24, 2008
21,914
Transformers

I wiil assume a standard transformer the 120vac:6.3vac transforner dating back nto the days of tube circuits. They used to be readily available from radio shack. witch is defunct It is standardized and cheap. I have to admit a certain fondness for ig nition coil circuits,as yhey will provide a kick that can not be ignored. I have jury rigged electric fences using flasher modules for a car an and ignition coil .We put it in a make shift kennel for a particularly destructive dog who was an escape artist. He tried to ignore the fence got stuck ib a way the wire was touching bare skin under the energized wire, and was yelping in perfect unison with the flasher click. I was a teen acting under my Dad's orders, I don't think I would do that again, When I was a teen my Dad was always yelling to me from the living room to turn it off whatever it was,because we lived in the country and TV reception was weak. Usually worked too. Amazing how many oscillator are also jammers. Square waves and all that. I was always making things.
I once made a FC designI found using is the 120vac:6.3vac transformer, just for the fun of it . The one I built sent a single pulse down the line and was very simple. wish I still had that design. We had a cow when I was a teen that was a fence jumper she knew she could tear up fences to go through them. Eventually we ate her.I had just finished this simple project when she tore up our fence next to the drive way Dad let me try it out with a spare car battery .The cow couldn't believe we replaced the damage with a single wire shoulder high.Every time she tried to go under she would gt shocked and back off to look at that single wire, We got tired of watching her and started to work on the garden.We heard a loud woof and came back to find her sitting on her haunches like a dog, something cows never do.I figure she licked the wire, she left it alone after that. good thing because she burned my crude project out.

About Ignition coils, they are not used on cars anymore though junkyards should have lots.Solid state ignitions have replaced them I am hoping the members will clear up any errors I make in the drawing I am about to provide.


A typical ignition coil,,,
Ignition coil.png
 
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cmartinez

Joined Jan 17, 2007
6,647
About Ignition coils, they are not used on cars anymore though junkyards should have lots.Solid state ignitions have replaced them
Solid state ignitions have replaced motor distributors (breaker arm, rotor and capacitor) but not ignition coils, to my knowledge.
 

Blank_Stare

Joined Jul 29, 2017
44
If I understand correctly, new autos use what is called a "coil pack", that includes solid state electronics to replace the old mechanical distributor. I think I am correct in calling the new coil packs a hybrid of the coil and distributor. Too bad they are so large, or I could try to use one in my current project.
 

crutschow

Joined Mar 14, 2008
23,816
If I understand correctly, new autos use what is called a "coil pack", that includes solid state electronics to replace the old mechanical distributor. I think I am correct in calling the new coil packs a hybrid of the coil and distributor. Too bad they are so large, or I could try to use one in my current project.
For cars with an even number of cylinders, each coil typically has a dual output (one from each end of the secondary winding) that goes to two sparkplugs in a wasted-spark configuration [1 plug is firing at the top of the exhaust stroke (wasted) while the other is simultaneously firing at the top of the compression stroke].
So there is one coil/electronic assembly for each pair of cylinders.

There is no distributor since there is no spark that needs to be distributed.
 

Blank_Stare

Joined Jul 29, 2017
44
For cars with an even number of cylinders, each coil typically has a dual output (one from each end of the secondary winding) that goes to two sparkplugs in a wasted-spark configuration [1 plug is firing at the top of the exhaust stroke (wasted) while the other is simultaneously firing at the top of the compression stroke].
What? That is unacceptable!
Someone call the Efficiency Police! - Sparks are being wasted!
 

bwilliams60

Joined Nov 18, 2012
1,233
Coil on plug is the new norm now. Each cylinder has its own coil placed directly above the spark plug opening and connected with a short section of high tension wiring encased in a rubber type boot for sealing and insulation. Very effective and low breakdown. Waste spark is old school now for the most part.
 
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