I need an electric fence to enclose my garden. The perimeter of the fence will be approximately 160 feet. There is no mains supply nearby, so I plan to use a 12V battery that is recharged with a solar panel that produces 18V at a maximum of 111mA (2W.) I would like to build as much of this system as possible.

I want to start with the fence charger, and have found this project on the web. http://www.pocketmagic.net/2011/09/electric-fence-20kv/ I have all the parts (except the ignition coil) and have built several 555 circuits, and don't see any insurmountable problems building this charger. Using an automotive ignition coil to build a fence charger seems to be rather common.

What are your opinions about the project in general, and about the circuit linked above?

Thanks.

 

The unknown is how much current the circuit will draw so you can determine if the solar cell is adequate to keep the battery charged, especially on cloudy winter days.

Certainly you could reduce the coil pulse width and use a long duration between pulses to minimize current draw. The fence chargers I'm familiar with from my farm days operated perhaps once per second and put out a spark of no more than perhaps a quarter inch which is sufficient to deter even large animals.


Also CMOS versions of the 555 will draw less current.

 

The unknown for me is just how large an output will this have? How likely is it to kill someone?

With it's amateur heritage and lack of any posted test data I would hesitate to recommend using this.

 

The unknown for me is just how large an output will this have? How likely is it to kill someone?

With it's amateur heritage and lack of any posted test data I would hesitate to recommend using this.

Good question. It seems that it couldn't be any more dangerous as an electric fence than it is as an ignition coil in a car. But, I don't really know that. I suppose it depends upon the absolute maximum current it could deliver; I'll look into it.

I have redrawn the schematic in order to add some component numbers. It is attached for comments and corrections.

Thanks.

ETA: I also put a bypass cap (C7) on U2 that is not on the original schematic.

 

I built one similliar to this several years ago. Worked fine , except it was a power hog. I do not remember all the specs, but it seems like the circuit board with coil attached drew something like 4 amps.
I guess the point I'm trying to make is measure the current before purchasing solar panel/battery.

This may be the circuit I used?
http://chemelec.com/Projects/Fencer-1/Fencer-1.htm

 

One 555 should be suficient, independently control hi & lo with two diodes. Keep hi to around 20 μs, just long enough for 1/4 in spark.

 

One 555 should be suficient, independently control hi & lo with two diodes. Keep hi to around 20 μs, just long enough for 1/4 in spark.

I just completed breadboarding the portion of the circuit in the attachment. But I am interested in reducing the part count. Can you provide some additional explanation of how to control the pulse rate and duration with one 555? Thanks.

 

I just completed breadboarding the portion of the circuit in the attachment. But I am interested in reducing the part count. Can you provide some additional explanation of how to control the pulse rate and duration with one 555? Thanks.

You would build the 555 as an astable oscillator with a small duty-cycle (or large duty-cycle if you invert the output) as shown here.

 

You would build the 555 as an astable oscillator with a small duty-cycle (or large duty-cycle if you invert the output) as shown here.

And would it be possible to have both the pulse rate and duration to be independently adjustable via potentiometer(s)?

Thanks.

 

The thread for this EXTREMELY dangerous project should be closed.

People are different.
Some people will be killed if they simply get near it. Other people will hold the wires and laugh.

 

The thread for this EXTREMELY dangerous project should be closed.

People are different.
Some people will be killed if they simply get near it. Other people will hold the wires and laugh.

Click the little red and white triangle in the upper right corner and report it.

 

Click the little red and white triangle in the upper right corner and report it.

I did doo dat.

 

Click the little red and white triangle in the upper right corner and report it.

I did doo dat.
Can you imagine reading a dangerous thread, not reporting it then finding out that somebody was killed by it??

 

I did doo dat.
Can you imagine reading a dangerous thread, not reporting it then finding out that somebody was killed by it??

I have lived in the rural south for a lot of years. There are thousands of electric fences in use here in West Tennessee. I have crossed many, many such fences that are used to confine livestock and to keep wildlife out of crop fields and gardens. I have never been killed by an electric fence and have never been even semi-seriously hurt by one, nor have I ever heard of even one person hurt or killed by one.

I have also worked on a lot of internal combustion engines that had ignition coils or magnetos, and have never been killed or even semi-seriously hurt by one, nor have I ever heard of even one person hurt or killed by one.

But maybe you have documented cases that you can cite of people who were killed by the electricity supplied by a 12V battery and transformed by an automotive ignition coil. I would be very interested in any such data.

 

The thread for this EXTREMELY dangerous project should be closed.

People are different.
Some people will be killed if they simply get near it. Other people will hold the wires and laugh.

The project uses low voltage DC and an ignition coil. I've never heard of anyone being killed by the output of an ignition coil (although it sure hurts like heck).

 

What if the intruder carries a pacemaker?

 

When considering a device that by design is to produce pain I would ask the designer to prove it is safe, rather then ask another to prove it is dangerous.

While I do not doubt such devices can be designed to be completely safe and effective while delivering a non lethal jolt every time I see no such safety features in this device.

Looking at the schematic I do see several areas where the work is quite basic, and at least one out and out mistake.

 

What if the intruder carries a pacemaker?

That guy is in the wrong line of work, I'd say.