electric fence

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It's not safe because it's DC. It's safe because the duty cycle is low and the energy of each pulse is limited to the energy stored in a charged flyback transformer, sharply limiting the total amount of energy the fence can deliver.

What's unsafe is the occasional Appalachian Engineerin' method of hooking up a fence directly to an AC powerline, delivering a nearly-unlimited amount of energy through a low impedance for an unlimited duration.
 
Given the duration of the pulse, it would be hard to distinguish between pulsed AC and pulsed DC. :)

As far as clearing shorts instead of being disabled by them, the critical feature is that the source be able to deliver enough current into a short (such as vegetation) to eventually burn it out after some number of pulses. This is not, however, consistent with limiting the pain and suffering you experience when you touch the fence.
Some fence chargers will not deliver a pulse at all if there is a short on the fence wire. That makes it very difficult to locate and clear shorts.
 
Back when I was a weekend farmer, I had a fence charger that was marketed as a "weed burner". I bent over to pick up a log chain in a mud hole and touched my back to the fence. I promptly expended my entire blue vocabulary.
 
retirede said:
Back when I was a weekend farmer, I had a fence charger that was marketed as a "weed burner". I bent over to pick up a log chain in a mud hole and touched my back to the fence. I promptly expended my entire blue vocabulary.
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Bet you cleared your shorts too!:D
 
As mentioned that pulse is energy being discharged from a storage device (an inductor). The inductor may have AC applied to it, but it is the collapsing of the field when the supply circuit opens that causes a DC to flow as the field collapses, that collapse is only one direction as the charge at that instant is only a positive or negative charge and not an alternating charge.
 
enireh said:
why is safe to use dc for an electric fence and never use ac? I've heard dc holds on also
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I'm not sure where you heard that, or if its true.

But I have heard AC current is worse at making a persons muscles contract in such a way that they can't control it.

I'm really not sure if that's true either. At any rate, I've always heard its safer to test an electric fence with the back of your hand, and not the palm, because the current could make your hand close around the wire, and you may not be able to let go.

Personally, I've always thought there has to be a better way to test an electric fence.
 
kwired said:
As mentioned that pulse is energy being discharged from a storage device (an inductor). The inductor may have AC applied to it, but it is the collapsing of the field when the supply circuit opens that causes a DC to flow as the field collapses, that collapse is only one direction as the charge at that instant is only a positive or negative charge and not an alternating charge.
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Kind of like an old style automotive ignition with points and a coil?
 
ggunn said:
Kind of like an old style automotive ignition with points and a coil?
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I think that is the basic function of most of them, collapsing field creates a high voltage discharge. Those ignition systems really can hit you hard too, but never electrocute anyone because there is limited current, though there may be secondary injuries that result because of the reaction to the shock.
 
kwired said:
I think that is the basic function of most of them, collapsing field creates a high voltage discharge. Those ignition systems really can hit you hard too, but never electrocute anyone because there is limited current, though there may be secondary injuries that result because of the reaction to the shock.
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Grabbing a spark plug wire with the engine running while leaning my crotchal area against the body of the car... Yeah, I know.
 
steve66 said:
I'm not sure where you heard that, or if its true.

But I have heard AC current is worse at making a persons muscles contract in such a way that they can't control it.

I'm really not sure if that's true either. At any rate, I've always heard its safer to test an electric fence with the back of your hand, and not the palm, because the current could make your hand close around the wire, and you may not be able to let go.

Personally, I've always thought there has to be a better way to test an electric fence.
Click to expand...

Back in the day in science class we did the dead frog experiment. You would apply a battery voltage to a fresh killed frog leg, one way would make the leg contract other would expand it. It was explained if the DC contracted your muscles, you could not let go. If AC contracted your muscles they would open in the next half of the cycle. I was also told that is why AC will throw you across the room. Your muscles contract and expand in one cycle faster than we can make them do it. More voltage more push.

For testing a fence just grab a piece of grass and wet it, then lay it on the fence at the tip of the grass and slide it slowly up the wire at some point you will just start to feel the shock.
 
ggunn said:
Grabbing a spark plug wire with the engine running while leaning my crotchal area against the body of the car... Yeah, I know.
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Ouch. Once ran my exposed big toe into the exposed spark plug lead on the back of a running pushmower, with salty, sweaty hands holding the bare steel bar. Walked around about 3 hours with my arms locked in a ghoul-type pose.

Also made the mistake once of picking up and moving a TV that was on, and unplugging it with the tube leaned into my crotchal area. I guess the capacitors discharged thru the tube, because one second I'm holding an 80lb TV in my hand and the next it's on top on me on the floor. I would not recommend using one's testicles to short out or discharge a loaded capacitor. :happyno:
 
JFletcher said:
Ouch. Once ran my exposed big toe into the exposed spark plug lead on the back of a running pushmower, with salty, sweaty hands holding the bare steel bar. Walked around about 3 hours with my arms locked in a ghoul-type pose.

Also made the mistake once of picking up and moving a TV that was on, and unplugging it with the tube leaned into my crotchal area. I guess the capacitors discharged thru the tube, because one second I'm holding an 80lb TV in my hand and the next it's on top on me on the floor. I would not recommend using one's testicles to short out or discharge a loaded capacitor. :happyno:
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On a more somber note a classmate of my granddaughter worked on computers. A laptop capacitor killed him. I would not recommend discharging any cap via the body parts.
 
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