Off Grid Living / Camping > Utilities
Electric Fence Zapper
philb:
A CRC book of Chemistry and Physics has a good spark table that can tell you how much voltage it takes for a 1 inch spark. 10 mA is a very hot fence charger. Most of the professional chargers are significantly less.
I would guess it is enough voltage to p**s a bear off bad enough I wouldn't want to be in the same county.
If you use a smooth wire to carry the voltage, you may want to wrap it around barbed wire or something pointed to get through the bear's fur.
I had a "Super Safe Leakage Tester" to check distributor caps, coils and wiring for cracks. It was made in the '60's. You could hold your finger an inch from insulation on the test leads and see a blue spark. It was almost all voltage and no amps so no shock. The other settings would drop the voltage and raise the amps. That would make anyone holler and end up on their knees. I never could understand why it said super safe. :o
oztules:
Don't ever consider using barbed wire with an electric fence.... it is very very illegal, and downright dangerous.
Having said that, I have delved into ignition coil fencing units before, and can say they do work to some extent.
If your fence is clean, and short (around a haystack etc) they are fine.
If you wish to do any good with a loaded fence, they are useless.
It is far better to build a tiny multivibrator to change the 12v to 400-600 volts, store that in a capacitor and then discharge that into a low impedance transformer.
The ignition coils solution is a very very high impedance solution, and mostly unsatisfactory for most uses..... thats why no commercial solutions use them.
If you want a circuit for this I can provide a simple very effective board design for you. It can do up 10000 volts at 40 amps... good for a 70km- 100km of wire fence.
You will need a small ferrite transformer, and a microwave transformer core or any other reasonable sized core, and wind your own transformers.
Using this system, you can store the charge from the small multivibrator into a capacitor, and then discharge it into a decent core to develop lots of watts for a small time period..... less then 10/millionth of a second or so....... its a bull stopper.
I have seen up to 400000 watts from this design.... it is simple and very cheap.
DONT US BARBED WIRE EVER!!!! with an electric fence...... getting caught /tangled on a hot barbed wire fence is deadly to some people with iffy hearts and can easily kill a cow in this instance.
No one uses high tension coils anymore, they are next to useless because of the tiny current they produce. Any fence load (grass etc) will knock it down very quickly. A low impedance solution burns the grass (kill not burn ) off the fence.
A 15ma solution will totally wipe out an igntion coil solution...... plus the unloaded voltage is illegal as it will be in the 20000v region... 10000 is the limit here and NewZealand.... I assume it is there too.
..................oztules
madlabs:
Oz, Phil, All,
Turns out I musta done something wrong measuring the current draw of the circuit. It actually draws less than 1mA except for the LED blink. Tough to determine voltage from distance unless you have a proper spark gap with spheres. As to bears, luckily I live in northern CA where all we have is small black bears not known for attacking people. But they are known for climbing apple trees and destroying them.
The fence is quite short, only around 700 feet. I actually do have mains (inverter) power out there. Oz, I'm quite interested in your circuit and board. By any chance do you use Eagle? If not, even a jpeg would do. Or I can use your art to make an Eagle version. I have no problem doing some xfrmr winding. Out of curiousity, how many wraps of what gauge?
Thanks!
Jonathan
oztules:
Jonathan,
12vdc is fine, 240ac volts is fine, 110ac volts is not fine, and would need a little step up transformer to get to the higher voltages needed for storage..... a step up will use some extra magnetising current, but apart from that no change.
I use two boards, one for 12vdc, and another for 240vac. The ac one uses a simple voltage doubler/rectifier to get the 640 volts, the 12v uses single transistor with small ferrite to make the 600v+
When we store this in a capacitor, we can get the energy from 1/2 C (in farads)xV (volts)^2.. 1/2 capxvoltage squared.
We then use a simple diac discharge circuit into an scr/triac... so as the charge voltage rises, we use a sample to trigger the diac at say 600v, and this discharges all that energy into a core.
The tiny ferrite I use is an e49 core, with about two lots of 18 turns of 1mm wire for the primary. One winding for the feedback to make it silly simple, the other primary as the switched primary. The secondary can be 400 turns of spiderweb, as it is small current high voltage.
The power transformer I use are the microwave ones... free so cheap I suggest.
When you dump up to 60 joules into a core (even a 1kw core) it will saturate to hell, but it does not matter for this one shot system.
It consists of 9 turns 2 in hand 1.8mm to 2mm wire (about #12 or #13 AWG) for the primary, and about 200-260 turns for the secondary, I use 1mm wire for that.
The transformer can be just welded/epoxied back together as it was originally for the microwave duty, don't need to do the I E thing.
The power transformer needs to be neatly ( side by side wire) wound with each layer separated by motor/transformer paper. This will give us reasonable isolation between each layer and stop the enamel from trying to keep isolation between each layer, the paper does that. We need to leave 3/16th inch of paper over/past each winding layer for the same reason.
It's simple, easy, and very effective technique for very high voltage transformers...... then epoxy the transformer too keep moisture out and you have a very commercial grade fencer for a 5-20 dollars instead of a thousand dollars.
I will do an article for you if you wish. The circuit board is done with protel, never liked eagle.
Try to get picture or gif of unit and board today, maybe article in a few days.
................oztules
A tiny 15ma fencer can use as little as a few uf capacitor into a small transformer for light fencing, and same circuit into a 100-200uf capacitor with a bigger core will get you up into the hundreds of thousands of watts, and draw over an amp..... this will light up a many many tens of miles fence, burn off the grass, andstill pull over 8000v @ 30 - 40 ampsinto a 300 ohm(heavy) fence...... same board and circuit etc.
Wolvenar:
At a friends place I setup a store bought fencer on a bird feeder post in an attempt to scare off a repeat offender bear raiding it.
I set a pipe in concrete within a couple pvc pipe/concrete layers.
I don't remember the specs of this fencer but I do know it worked.
To set this up you have to know this fird feeder is on the edge of a retaining wall.
When I replaced the feeder I made it high enough that the feeder itself could not be reached by the bear on its hind legs.
When the bear came for his nightly raid he noticed he couldnt just reach the feeder.
He touched the pole with his paw and was rather surprised, recoiled looked around then decided to rear up on hind legs to push the pole down since he could not reach the feeder any more.
Well I wish I had it on video. He pushed into the pole got zapped then fell completely into it like he lost control of his balance, face first into the pole and off the side of the 4' retaining wall.
That bear got up and ran like hell away, never looking back.
He still sticks around the area but wont come even close to the house anymore.
I don't have a lot of images of this I guess but.
The inside pipe, the other 1' pvc was placed in cement in the ground and this placed in it, and more cement.
A shot of the retaining wall, but not a good one to show its height.
Before the new setup.
This had a feeder with a zapper to keep squirrels off.
The bear had taken this down earlier and broke a few perches.
I had to fix that as well as a few places squirrels chewed.
They took immediate advantage of the fact it was down and they could get to it in ways they wouldn't get zapped
So in this case a fencer deterred a good sized bear rather well.
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