Electric fence charger

[Stumpy]

Can you point me in the direction of a plan for an electric fence power
supply. Ideally a diagram and a parts list. The retail models to deter
dogs from jumping fences are ~1KV and .5mA they also claim about 1/3 of a
joule.

 

[default]

Can you point me in the direction of a plan for an electric fence power
supply. Ideally a diagram and a parts list. The retail models to deter
dogs from jumping fences are ~1KV and .5mA they also claim about 1/3 of a
joule.

http://www.uoguelph.ca/~antoon/circ/hv/hvpulse/hvpulse.html

or

www.homepower.com/files/electricfence.pdf

 

[Stumpy]

That was actually 5mA. Thanks for the very clear links.

 

[Stumpy]

I was in too much of a hurry to build my own, so I bought a model that puts
out 1.2 Kv intermittently. It is in an urban location and I'm worried about
liability.

Is there a neon or LED bulb that can pulse with a rating up to ~1.5 kV for
an indicator?

 

[Don Bruder]

I was in too much of a hurry to build my own, so I bought a model that puts
out 1.2 Kv intermittently. It is in an urban location and I'm worried about
liability.

Liability for what? Hang a few of those "Warning: Electric fence" signs
on it, and there went whatever liability there might be.

Side note:
The output of an electric fence charger (assuming a "store-bought" unit,
as opposed to some homebrewed-from-a-car-coil unit) will give you a
high-voltage (Anywhere from 5KV to 15KV or even more, depending on
brand/maker/age) "bite", yes - After all, it's designed to do exactly
that. But it's also (A) Too short a duration pulse to mean anything
other than "SHIT! THAT SMARTS!", and (B) too low an amperage to mean
anything unless somebody is stupid enough to wire a cardiac patient to
the fence and power things up. Even then, it's not *LIKELY* - just
*POSSIBLE* - that anything worse than "SHIT! THAT SMARTS!" is going to
come of it. Granted, it wouldn't be any fun, but it's not likely to be
harmful in any lasting way.

Is there a neon or LED bulb that can pulse with a rating up to ~1.5 kV for
an indicator?

Any standard small neon should give you at least some flash for each
pulse of the fence if you wire it from the hot wire to ground. I
wouldn't sweat over it, though - Simply assume that once it's plugged
in, it's just like a gun: Loaded and could go off anytime. Only unlike a
gun, if it goes off on you, it's only going to result in a cuss, not a
fatality. It won't take you (or anyone else, right down to the youngest
kiddie that might come along) long to learn not to mess with the wire.

 

[Stumpy]

Liability for what? Hang a few of those "Warning: Electric fence" signs
on it, and there went whatever liability there might be.

It's hand labeled now, Store bought signs tomorrow.

Any standard small neon should give you at least some flash for each
pulse of the fence if you wire it from the hot wire to ground. I
wouldn't sweat over it, though - Simply assume that once it's plugged
in, it's just like a gun: Loaded and could go off anytime. Only unlike a
gun, if it goes off on you, it's only going to result in a cuss, not a
fatality. It won't take you (or anyone else, right down to the youngest
kiddie that might come along) long to learn not to mess with the wire.

I assume Radio Shack can come up with a bulb, just wondering what to ask
for.

It is a good idea for me to do something more active than a sign because I
don't want a wife or offspring to come from the inside and expect it to be
turned off, or to open the gate at night and get a surprise.

 

[Don Bruder]

I assume Radio Shack can come up with a bulb, just wondering what to ask
for.

Rat-shack (AKA "You've got questions, we've got blank stares and cell
phones you-need-some-batteries-with-that?") should have them, but I
wouldn't bet on the droids to know what you're talking about. Just look
for a small neon lamp - An "NE-5" unit would likely be ideal.

Failing that, go to your local hardware store or whatever that sells
Flourescent light starters (the little tin cans with two pins on them to
plug into the fixture - Last time I bought any, they were almost
literally a dime a dozen) Inside the tin can is a capacitor and a small
neon lamp (I think the type is even "NE-5" - bonus mode!) that would be
ideal as an HV indicator light. Wire one leg to the hot wire, the other
leg to ground, and watch it flash. For that matter, depending on the
output of your particular fence charger, it might not even need to be
physically wired to the system - Getting it within a few inches of the
wire may be all the "connection" needed to get it to flash with each
pulse of the charger - kinda like you can stand under high-tension wires
with a flourescent tube in your hands, and have it light up without
being connected to anything.

It is a good idea for me to do something more active than a sign because I
don't want a wife or offspring to come from the inside and expect it to be
turned off, or to open the gate at night and get a surprise.

Speaking from 40 years of living with electric fences, that's *ALL* it
will be: An unpleasant surprise. I'd expect it to happen once, *MAYBE*
twice if you've got "slow learners" in the family. For the kiddies, it
may result in a session of bawling, but... <shrug> Oh well... Just like
they get burned once and don't mess with the stove anymore, they'll get
tagged by the fence once, and won't mess with it again. (But unlike the
stove, the fence poses no significant risk of third degree burns or need
for reconstructive surgery...)

 

[James T. White]

Is there a neon or LED bulb that can pulse with a rating up to ~1.5
kV for an indicator?

I don't think you will have much luck putting an idicator directly on
the charged wire as it will likely shunt the high voltage pulses to
ground and prevent the electric fence from having the desired "bite".

 

[Jasen Betts]

["Followup-To:" header set to sci.electronics.basics.]

I was in too much of a hurry to build my own, so I bought a model that puts
out 1.2 Kv intermittently. It is in an urban location and I'm worried about
liability.

Is there a neon or LED bulb that can pulse with a rating up to ~1.5 kV for
an indicator?

a neon could do it, but ther's probably enough voltage there to run a small
xenon tube and they're much more visible.

Bye.
Jasen

 

[default]

I was in too much of a hurry to build my own, so I bought a model that puts
out 1.2 Kv intermittently. It is in an urban location and I'm worried about
liability.

Is there a neon or LED bulb that can pulse with a rating up to ~1.5 kV for
an indicator?

I wouldn't know for a fact, but my guess would be any ne-2 lamp with a
fairly large series resistor might work. They use between 20K to 100K
for neons working from 120 VAC. I'd use a few series resistors to
prevent arcing around the resistor.

If you kludge something together and seal it - take care that the air
inside is dry or condensation will provide a path for voltage the
first cold day that comes along.

If the voltage spike has a fast rise time, it might work by just
connecting both wires from the neon lamp to the fence and depend on
capacitance to ground to flash the lamps.

When I was a kid I got the idea that it would be neat to light a neon
with static. My aunt had this killer carpet and walking over to the
radiator was a sure fire way to get a surprise. NE2 and NE45 lamps
would only flash once, not very brightly, and burn out . . . The
correct size resistor is necessary even with very low current sources.
They do make neon gate hooks for cattle farmers. What I've seen is a
neon lamp mounted in a cylindrical yellow plastic housing. It has a
hook on one end (the gate side) and loop on the other with some larger
flanges to keep one's hands from slipping off and onto the wire

The idea is that in order to safely cross the fence you unhook the
wire and step over the fence, then replace the wire. It doesn't have
a ground connection that I could see so it either depends on
capacitance to light the lamp or is in series with the fence and drops
the 65 volts or so the neon needs to light.

Your signs won't be visible in the dark . . .

An LED probably wouldn't work. They require a few milliamps to run,
your charger probably puts out 1-2 milliamps. There's also the
(probability) possibility that inductive ringing in the output of the
charger or length of fence wire would be more than enough to break
down the ~4 volt reverse voltage Leds can withstand.

A second cable with low voltage "walk lights?" Or a small cable with
a number of LEDs running from a LV source?

Is it the idea of neon lamps flashing and lighting the perimeter that
appeals, or just the gate?

 

[Stumpy]

I wouldn't know for a fact, but my guess would be any ne-2 lamp with a
fairly large series resistor might work. They use between 20K to 100K
for neons working from 120 VAC. I'd use a few series resistors to
prevent arcing around the resistor.

If you kludge something together and seal it - take care that the air
inside is dry or condensation will provide a path for voltage the
first cold day that comes along.

If the voltage spike has a fast rise time, it might work by just
connecting both wires from the neon lamp to the fence and depend on
capacitance to ground to flash the lamps.

I bought a couple of 120volt neon panel lamps. Rated 1/2 watt @ 120v. This
should mean P=IE, 1/2=I*120 .:. I=4mA That seems awful high for a dim
little lamp.

Using that value the resistance of the bulb is I=E/R, 4mA=120/R .:. R=
30kohms

So a voltage divider requires 9*30K=270Kohms

If I buy a 270Kohm resistor it needs to pass 4mA. That would require a 6
watt resistor (P=IE, .004*1.5K=6)

That's ridiculous. What am I doing wrong?

Your signs won't be visible in the dark . . .

Good point. I'm planning on putting the lights panel mounted on the sign
itself.

A second cable with low voltage "walk lights?" Or a small cable with
a number of LEDs running from a LV source?

Too expensive!

Is it the idea of neon lamps flashing and lighting the perimeter that
appeals, or just the gate?

Just the gate, where any law abiding citizen might expect to gain access.

 

[Don Bruder]

Is it the idea of neon lamps flashing and lighting the perimeter that
appeals, or just the gate?

Just the gate, where any law abiding citizen might expect to gain access.[/QUOTE]

The solution becomes even simpler: A hot wire doesn't need to be a
continuous loop - Simply run the wire UP TO the the posts on either side
of the gate, and terminate it right there. Hook the charger to the wire
anywhere happens to be convenient, and you're in business. As long as
all the wires that are supposed to be hot are in contact someplace, your
entire fence will be hot, and no need for worrying about the gate.

 

[Stumpy]

The solution becomes even simpler: A hot wire doesn't need to be a
continuous loop - Simply run the wire UP TO the the posts on either side
of the gate, and terminate it right there. Hook the charger to the wire
anywhere happens to be convenient, and you're in business. As long as
all the wires that are supposed to be hot are in contact someplace, your
entire fence will be hot, and no need for worrying about the gate.

No, the gate has a charged up piece of hardware cloth on top to prevent the
dog from going over. Someone could reach for the latch with one hand and
touch the charged up portion at the same time.

I realized my concern about impedance was a waste of time. I might as well
just put 10 of the lamps in series since they are rated at 1/10 of the
supplied voltage. The local Rad Shack only has 4 amber bulbs so I might as
well get a few green and some red ones to give my sign a classy, christmassy
type decor.

 

[Don Bruder]

The solution becomes even simpler: A hot wire doesn't need to be a
continuous loop - Simply run the wire UP TO the the posts on either side
of the gate, and terminate it right there. Hook the charger to the wire
anywhere happens to be convenient, and you're in business. As long as
all the wires that are supposed to be hot are in contact someplace, your
entire fence will be hot, and no need for worrying about the gate.

No, the gate has a charged up piece of hardware cloth on top to prevent the
dog from going over. Someone could reach for the latch with one hand and
touch the charged up portion at the same time.[/QUOTE]

Ahhh... Now we have one more snippet of needed information that wasn't
provided to begin with.

And I go back to the "they'll only do it once or twice" school of
thought.

I realized my concern about impedance was a waste of time. I might as well
just put 10 of the lamps in series since they are rated at 1/10 of the
supplied voltage. The local Rad Shack only has 4 amber bulbs so I might as
well get a few green and some red ones to give my sign a classy, christmassy
type decor.

As mentioned, simple neon bulbs, like an NE-5 or similar, will likely
flash *WITHOUT* needing to be electrically connected to the wire - Just
placed "close" to it. Use the legs to attach them to the wire like
twist-ties, and I'd expect them to flash brightly each time the charger
pulses.

Keep in mind that the charger isn't putting out continuous juice (or at
least, it SHOULDN'T be - "constant" chargers went out decades ago) It's
pulsing, and the pulses are *SHORT* - Very possibly too short to
usefully light a non-discharge type bulb.

I still say the simplest solution is posting a wanring sign at the gate,
and letting the fence "train" anyone coming in.

 

[Rich Grise]

I was in too much of a hurry to build my own, so I bought a model that
puts out 1.2 Kv intermittently. It is in an urban location and I'm
worried about liability.

Is there a neon or LED bulb that can pulse with a rating up to ~1.5 kV
for an indicator?

If you can get a naked neon bulb with leads sticking out, you could just
dangle it by its leads from just one of the fence wires - a spike like
1.2KV should fire neon just by capacitance to air. =:-O

Cheers!
Rich

 

[Stumpy]

I don't think you will have much luck putting an idicator directly on
the charged wire as it will likely shunt the high voltage pulses to
ground and prevent the electric fence from having the desired "bite".

Good point. I used 10 neon bulbs and then added 2 10Kohm resistors in
series to reduce current. I have difficulty measuring the actual voltage
because it does not stay constant long enough to get a real reading. My
digital multimeter is useless and I don't really trust the ancient analog
one.

One thing I do know is that the dog has touched the fence 3 times and has
not done so again. I was too wimpy to grab the wire. I touched the wire
above the 2 resistors and after 10 bulbs - it was very unpleasant. I don't
want to do it again.

I'm a little embarrassed about how tacky the sign looks. I probably should
have looked for a 300Kohm 10watt resistor and just used 2 bulbs.

 

[Don Bruder]

I don't think you will have much luck putting an idicator directly on
the charged wire as it will likely shunt the high voltage pulses to
ground and prevent the electric fence from having the desired "bite".

Good point. I used 10 neon bulbs and then added 2 10Kohm resistors in
series to reduce current. I have difficulty measuring the actual voltage
because it does not stay constant long enough to get a real reading. My
digital multimeter is useless and I don't really trust the ancient analog
one.

One thing I do know is that the dog has touched the fence 3 times and has
not done so again. I was too wimpy to grab the wire. I touched the wire
above the 2 resistors and after 10 bulbs - it was very unpleasant. I don't
want to do it again.

I'm a little embarrassed about how tacky the sign looks. I probably should
have looked for a 300Kohm 10watt resistor and just used 2 bulbs.
[/QUOTE]

Word of advice from an old hand with electric fences: When in doubt as
to whether it is or isn't "hot", touch it with the *BACK* of your hand -
The resulting "jerk" if it is turned on will (usually) fling your hand
away from the wire, rather than onto it, reducing the duration of the
"zap" (although not having much effect on how hard the "bite" feels)

Another method that gramps swore by was pick a fresh green blade of
grass, at least 3-4 inches long, and lay that on the wire - If it's hot,
it'll "zing" you, but the bite won't be anywhere near as bad as direct
contact.

Of course, there's always the "grab a stick" method - Using a stick or
similarly non-conductive object, push the "hot?" wire to within about
1/8-1/4 inch of something grounded and hold it there for a couple fo
seconds (to give the charger a chance to pulse at least once). If it
says "SNAP!", it's hot.

 

[default]

If I buy a 270Kohm resistor it needs to pass 4mA. That would require a 6
watt resistor (P=IE, .004*1.5K=6)

That's ridiculous. What am I doing wrong?

Try point four milliamps. I see in Jameco they list their ne2 lamps
at point six milliamps.

Wattage? You only need to dissipate the average power not the peak
the charger can put out. There's probably a 1:100 duty cycle you're
dealing with.

The dog will have learned and the fence will be moot . . .

I had this cat . . . the former owner let the cat in the second floor
window, so it didn't understand doors but insisted I open the window.
That got old fast and was hard on the screen. I rigged a auto spark
coil in series with a car signal lamp and flasher and laid two tracks
of wire down on the window sill. The cat learned in just one day.

 

[Stumpy]

Try point four milliamps. I see in Jameco they list their ne2 lamps
at point six milliamps.

Wattage? You only need to dissipate the average power not the peak
the charger can put out. There's probably a 1:100 duty cycle you're
dealing with.

The dog will have learned and the fence will be moot . . .

I will keep the fence active. Maybe the dog is smart enough to know what
the flashing lights are for.

I did notice all the suggestions about freestanding lamps. It's a very
interesting proposition, but I can't understand no clear reference to
ground. Would you have to respect the combined load and limit the number
used? Heck - you could put an infinite amount on a charged up wire and
get no current lighting.

 

[default]

I will keep the fence active. Maybe the dog is smart enough to know what
the flashing lights are for.

I did notice all the suggestions about freestanding lamps. It's a very
interesting proposition, but I can't understand no clear reference to
ground. Would you have to respect the combined load and limit the number
used? Heck - you could put an infinite amount on a charged up wire and
get no current lighting.

The dog can probably make the connection between the lights and shocks
relatively quickly. Animals are a lot smarter than we credit them -
they just don't have the same priorities or abilities that we do.

Then you just need the lights?

There's no magic with operating gas discharge lamps with only one
connection. High frequency (20 KHZ and up) high voltage electricity
has a relatively low X sub C (capacitive reactance - expressed in ohms
but applied to AC).

AC will pass through a capacitor even though there is no DC path
between the leads. The higher the frequency, the lower the resistance
to AC, or/and the higher the capacity the lower the resistance to AC.

Remember seeing "plasma globes?" Low pressure gas breaks down at a
lower potential than high pressure gas - that and the capacitive
reactance makes the arc follow a hand brought near the globe.

Neon tubes and lamps have a partial pressure of gas in them and ionize
fairly easily. (Too low and it won't work - too high and it won't
work).

Getting back to fences and neon lamps . . . your fence charger almost
certainly develops a high voltage low current pulse by using the
collapsing magnetic field of a transformer to generate the voltage.
The faster the collapse the higher the voltage. The more turns of
wire the higher the voltage also.

With that type of generator, you have a fast rise time that is "rich
in harmonics." The faster the rise time the more/higher high
frequency present. That and high voltage may be enough to break down
the gas in the neon bulb and ionize it. The capacitive reactance to
ground and nearby grounded objects, completes the return path for the
electricity.

There is no free lunch - but if it works at all there should be no
limit to the number of neon bulbs that will flash when the spike comes
along. The bulbs are just turning some of the energy that would be
lost to capacitive reactance anyway (actually it may take a smidgen
more energy because the surface area is greater - make a capacitor's
plates larger and you increase the capacity and lower the capacitive
reactance).

It won't be as bright as with a hard wire connection - but you really
have to try it and see what happens.

Tesla coils can light fluorescent lamps from twenty feet away without
wires using similar principles.

Touching an ordinary incandescent lamp to a high voltage terminal on a
working spark coil will light the lamp with a faint blue glow (partial
pressure of nitrogen in the bulbs - so they work like plasma globes).

Some lamps light green when subjected to high voltage high frequency -
vacuum filled bulbs with 100,000 volts on them produce X-rays, and
flint glass fluoresces green with X-rays.