Poor mans electric fence

MY friend would like me to help him build a cheap electric fence. I found l ots of designs, and of course we could go solid state but the simplicity of this one really intrigues me. I showed him the schematic and he questioned if the repeated opening and cl osing of the flasher points used in this application would quickly burn the m out. I was thinking that in spite of the inductive component, the load of the coil would be much less than the load imposed by a lighting circuit. S o I thought that combined with the correct capacitor and perhaps the additi on of a small snubber circuit (a small resistor in series with the capacito r) would cut down on the sparking. Perhaps I'm way off base here. Does any one have any opinions on this or has anyone ever done this? This uses a sta ndard automotive ignition coil. Thanks, Lenny

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Reply to
captainvideo462009
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If you do you will be in violation of several laws regarding harmful interference.

Reply to
dave

Please make an effort to reduce the amount of EMI/RFI to tolerable limits.

I like the title "poor mans electric fence". Yeah, I suspect you'll probably become poor after the doctors treat you for electric shock. Please remember that you have but one life to give for your profession.

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Jeff Liebermann     jeffl@cruzio.com 
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Reply to
Jeff Liebermann

Indeed, the FCC (if in the USA) will pay you a surprise visit for broadcasting without a licence, along with your local HAM radio folks, Civil and Military Aviation folks, possibly National Guard and anyone else (neighbours with pitchforks and burning torches) who your broadband long wave RF noise generator annoys...

Look up "Spark Gap Transmitter Interference" on your favourite search engine.

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John ;-#)#

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Reply to
John Robertson

nd lots of designs, and of course we could go solid state but the simplicit y of this one really intrigues me.

d closing of the flasher points used in this application would quickly burn them out. I was thinking that in spite of the inductive component, the loa d of the coil would be much less than the load imposed by a lighting circui t. So I thought that combined with the correct capacitor and perhaps the ad dition of a small snubber circuit (a small resistor in series with the capa citor) would cut down on the sparking. Perhaps I'm way off base here. Does anyone have any opinions on this or has anyone ever done this? This uses a standard automotive ignition coil. Thanks, Lenny

http%253A%252F%252Fgardengalbevy.files.wordpress.com%252F2013%252F01%252Felectric-fence.jpg%3Bhttp%253A%252F%252Fgardengalbevy.com%252F2013%252F01%252F22%252Fbasics-of-electric-fencing-informed-farmers%252F%3B822%3B691

Well then I imagine that every rancher with an electric fence must be repea ting Marconi's experiment as well. And what about the computers in the area that break the squelch on my low band radio in my truck as I drive past th e same houses. And not to mention those infernal speed controlers and light dimmers that raise hell with AM radio. MJy friend is just trying to keep c oons out of his garden. How do these guys get away withit. Lenny

Reply to
captainvideo462009

They don't use a spark-based generator.

I looked at a few of the schematics out there on the net, and a lot of them seem to use a low-voltage astable multivibrator (e.g. a 555) to trigger a triac, which dumps a pulse of chrarge from a capacitor (e.g. a couple of hundred volts) into the primary of a step-up coil. The coil then drives the fence wire.

This approach would (I think) result in the rising and falling edges of the current pulse into the primary not being incredibly fast... the rising edge would be limited by the coil inductance, and the falling edge would result from the stored-up charge in the cap damping down - there's be some ringing to the latter, but not the sharp edges you'd see from a spark gap. Hence, a lower bandwidth and less (or no) RF interference.

Commercial cow fences usually seem to pulse once a second or so - it's not a constant buzz. It's enough to displease the cows (and probably deer as well), but it's not continuous enough to risk that somebody will grab the wire and find themselves unable to let go (which would be a real risk if you just let a vibrator drive a coil and keep the wire energized all of the time).

People *do* get in trouble with the FCC over electric-fence chargers, if the chargers are badly designed and do result in RFI. The fines for failing to correct such sources of interference can be quite stiff.

Reply to
David Platt

Harbor Freight will sell you a solar powered fence charger for $66 less 20 or 25% coupon. Older I get, the more I shy away from "helping" someone do something that may cause someone to "claim" they were harmed. Just not worth all the legal hassles you can get into.

Reply to
mike

I thought one of the HF chargers would be just the thing for a deer fence around the garden. Worked great till winter came. Then the amount of daylight was not enough to recharge the battery for all night use and eventually the whole thing became useless.

Just the solar charger and battery now work great to power the trail camera for long term use. Disconnected the charger portion.

Paul

Reply to
Paul Drahn

sparking. Perhaps I'm way off base here. Does anyone have any opinions on this or has anyone ever done this? This uses a standard automotive ignition coil. Thanks, Lenny

Make a capacitor discharge into a car coil via an scr.

Use a pulsed DC to charge the cap at a high rate so they'll be a gap in the supply to the cap. Use a timer to trigger the scr which shorts this cap to ground.

The pulse being in the DC to charge it up has a void of no current in the off duty part of the pulse (Diode) and allows the SCR to turn off so the cycle can repeat itself.

if you're doing all of this from low voltage you can use a 556 timer, this would be the DUAL version. One timer is used as a pulse generator to charge the cap while the other would be the long duration pulse to supply a very short duty pulse with long off time.

Some designs use the falling edge of the charging pulse to charge up a cap on for the trigger pulse to the scr so that it's asynchronous and that circuit will discharge that cap for the next whack on the cattle's body!

Have fun.

Jamie

Reply to
Maynard A. Philbrook Jr.

Here are links to a couple of electric fence projects, complete with PCB layouts:

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Dave M

Reply to
Dave M

Why not just use a flyback transformer? Do cars even have coils these days? There are tiny flybacks on each sparkplug wire. Run by computers, not distributors. More efficient. Babbling.

Reply to
dave

lots of designs, and of course we could go solid state but the simplicity of this one really intrigues me.

closing of the flasher points used in this application would quickly burn t hem out. I was thinking that in spite of the inductive component, the load of the coil would be much less than the load imposed by a lighting circuit. So I thought that combined with the correct capacitor and perhaps the addi tion of a small snubber circuit (a small resistor in series with the capaci tor) would cut down on the sparking. Perhaps I'm way off base here. Does a nyone have any opinions on this or has anyone ever done this? This uses a s tandard automotive ignition coil. Thanks, Lenny

http%253A%252F%252Fgardengalbevy.files.wordpress.com%252F2013%252F01%252Felectric-fence.jpg%3Bhttp%253A%252F%252Fgardengalbevy.com%252F2013%252F01%252F22%252Fbasics-of-electric-fencing-informed-farmers%252F%3B822%3B691

Well, I was trying to keep it simple. And that's where the spark gap gizmo came in. Lenny

Reply to
captainvideo462009

lots of designs, and of course we could go solid state but the simplicity of this one really intrigues me.

closing of the flasher points used in this application would quickly burn t hem out. I was thinking that in spite of the inductive component, the load of the coil would be much less than the load imposed by a lighting circuit. So I thought that combined with the correct capacitor and perhaps the addi tion of a small snubber circuit (a small resistor in series with the capaci tor) would cut down on the sparking. Perhaps I'm way off base here. Does a nyone have any opinions on this or has anyone ever done this? This uses a s tandard automotive ignition coil. Thanks, Lenny

http%253A%252F%252Fgardengalbevy.files.wordpress.com%252F2013%252F01%252Felectric-fence.jpg%3Bhttp%253A%252F%252Fgardengalbevy.com%252F2013%252F01%252F22%252Fbasics-of-electric-fencing-informed-farmers%252F%3B822%3B691

Aside from the interference factor as already mentioned I was wondering (ju st from a hypothetical point of view) if anyone would like to comment on my original Question about the flasher points and snubber circuit as stated b elow?

Lenny

"I showed him the schematic and he questioned if the repeated opening and c losing of the flasher points used in this application would quickly burn th em out. I was thinking that in spite of the inductive component, the load o f the coil would be much less than the load imposed by a lighting circuit. So I thought that combined with the correct capacitor and perhaps the addit ion of a small snubber circuit (a small resistor in series with the capacit or) would cut down on the sparking. Perhaps I'm way off base here. Does an yone have any opinions on this or has anyone ever done this? This uses a st andard automotive ignition coil".

Reply to
captainvideo462009

Before solid state fence chargers, many used an interrupter like the an automotive turn signal interrupter. They were exposed on the front of the box so they could be replaced.

The most reliable fence charger was one that came with the 132 acre Dairy farm Dad purchased in 1957. It had a motor that rocked a mercury switch back and forth to supply power to a transformer that energized the fence. You could build a similar unit.

Paul

Reply to
Paul Drahn

lots of designs, and of course we could go solid state but the simplicity of this one really intrigues me.

closing of the flasher points used in this application would quickly burn t hem out. I was thinking that in spite of the inductive component, the load of the coil would be much less than the load imposed by a lighting circuit. So I thought that combined with the correct capacitor and perhaps the addi tion of a small snubber circuit (a small resistor in series with the capaci tor) would cut down on the sparking. Perhaps I'm way off base here. Does a nyone have any opinions on this or has anyone ever done this? This uses a s tandard automotive ignition coil. Thanks, Lenny

http%253A%252F%252Fgardengalbevy.files.wordpress.com%252F2013%252F01%252Felectric-fence.jpg%3Bhttp%253A%252F%252Fgardengalbevy.com%252F2013%252F01%252F22%252Fbasics-of-electric-fencing-informed-farmers%252F%3B822%3B691

Was this a 6 or 12 volt coil? And I'm assuming then that you're talking abo ut an automotive ignition coil and that the current through the switch wasn 't that great? Lenny

Reply to
captainvideo462009

Yeah, especially if they are Jewish doctors.

It's better to give that one life to my profession than die in some raghead country fighting another imperialistic war for US/Israel.

Reply to
Phoena J.

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