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Fun on the farm

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ruddycrazy:
G'day Guy's,
                   A few weeks ago found the cows decided they could just walk thru the fence and come crap in yard so got onto the owner of them and said time for an electric fence mate or I'm having rump steak for dinner. 8) So I had enough insulators and duly installed them on the fence and the next day Bill helped with the high tension wire I had here for the hot wire. He supplied a 240 volt fencer along with a 300watt inverter but I found it chewed through the batteries in a day.

                 Thought about that old Dick Smith fence kit I put together years ago so got it out and decided to give it a test. Well at the start it worked then started bridging in the high voltage transformer which is 250 turns of 0.25mm wire with 7 turns of 0.4mm wire. Well duly got on and wound up another only to find that bloody bridged out too. So wound another one and GRRRRRR same bloody thing. Decided to have one last go and found Murphy was around as only had enough 0.25mm wire left for 8 layers instead of 10. So did 6 turns on the primary to compensate. YAY it worked from the first ball and was throwing a 10mm spark gap nicely then several pulses of bloddy bridging then it worked again. Anyway left it running for an hour and it looked like every few minutes it would bridge for a few cycles then work again. So went and put on the fence and with my trusty $5 multimeter set to 1000 volts checked the hot wire and YAY the electric fence is working.

               The fence kit was featured in the silicon chip mag back in '99 so when I finally found the kits I got 2 of them and still have the second to build. Gotta say the circuit is a beauty based on a 555 with a LM358 switching a triac into the first transformer. Then 340 volts is put thru a 7uf cap then onto this high voltage transformer where 3.6Kv is the output. Must of soldered in and taken out that transformer several times and the circuit just keeps working.

              I reckon I will have to make jig for winding the next one as I won't stop until I get one NOT bridging. I reckon using a toroid for the design would of been so much better and bloody easier to wind too. As the circuit olny uses 50mA @12 volt it is purfect for this power pauper the idea is a set and forget project just to keep the boss happy as cows munching on young fruit trees has me sleeping with the dog.

Cheers Bryan

tanner0441:
Hi

I built a few fences and in the UK they specify 10,000V for 10mS  and from memory 5 joules max.

When I needed one in a hurry I used a 4 pole relay through the NC contacts and an electrolytic to control the pulse spacing and an old car ignition coil with a 0.1uF across the contacts  (to help the coil ring) used to pulse the coil.  Worked a treat keeping Stallions from mares, with enough left to run a fox wire round the hens.

Mind you it ticks on a MW radio for about half a mile.

Brian

clockmanFRA:
Here, in Rural Normandy, France, the locals reckon that Sheep take 10 hours to work out the electric fence is not working.
The local cows take 24 hours before they work out that they can escape, which is about once a week, so we don't get many speeding motorists around these parts.

Oh yes, Snails the edible sort, take 20 minutes to work out the electric is off, and then all 200,000 do a runner, says our man from the snail farm up the road.    :P

ruddycrazy:
G'day Guy's,
                    Went for a walk up the hill this morning and found it's still working nicely with the battery on 12.5 volts which aint too bad in my opinion as it was 12.7 volts went I installed it. My mate who owns the cows will be coming around with his fence tester gadget as he is keen to have a look at it after I told him of the current draw of the unit.

Below is a schematic of the circuit and T2 is the one for the high voltage so I reckon with another transformer or toroid a few more turns on the secondary should get a much higher voltage. I do think the southern nutter on that remote island may be able to shed some light on this subject too. 8)




Next jobbie is making up a circuit to monitor the pv panel and voltage so I can see how it performs over time and I will be building the next one with the thought of getting a much higher voltage so I can get a hot wire right around the farm.

Cheers Bryan

oztules:
To hot wire the farm, you will need to get up in the 500-600v range@25uf before you dump it into the transformer.

It is best to use a much higher turns L1 and use about 4uf across the transformer primary, this will shape the waveform much better for transmission, and noise, and shock in the output scr or triacs.

I make simpler more powerful units that have hit over 40amps@8000volts ( thats a lot of watts ). They use 1 transistor, and 5 triacs and not much else. They have run for the last 7 years at least.

The trick to making the power transformer is to use something big for a start.. I use microwave transformers.

Slit the thing apart, get rid of all the windings, we only want the laminates.
Make a former ( I use wood).... For the primary, about 18 turns of 1.2mm or more 2 in hand to take up the width of the former.
For the secondary, about 230 turns.
1. Isolate the primary with transformer paper .
2. wind the first layer of 1 turn thick of secondary.. maybe 40 turns side by side, no overlapping... very neat.
3. put a layer of transformer paper over that, then wind the second 40 turns or whatever fits for each single layer.
4. Make sure you are about 3mm back from the edge of the paper with each tidy layer. This makes it very very hard to jump, as the spark has to get past the 3mm, then back in op the layer under or over it for another 3mm.... wont happen, even with 13000v they don't compromise.

5.When you have your 5 or 6 layers done, more transfromer paper on top, then tape it up.
6. Get some epoxy or lacquer and lacquer it. I use epoxy.....
7. Use more transformer paper in the E slots, and place the winding on the transformer laminates core. You want there to be transformer paper stopping arcing where ever there is an opportunity.
8. Re-weld transformer and your done. This should last forever if you do it neatly, and with purpose. I have not seen it arc.... ever, and thats testing to over 14000v.... there are quite a few out in the field, and our moist marine environment would show up the weakness very quickly.


..........oztules

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