Author Topic: High power electric fence transformer and fencer.  (Read 11425 times)

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Offline oztules

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High power electric fence transformer and fencer.
« on: October 10, 2015, 10:40:29 pm »
It would appear that there is some interest in fencing units.
For those folks that want a high impedance toy fencer using a ignition coil or similar, stop reading now... this is not for you.

If you want to build a fencer that can do 70-100 kms of fence, and can transform 12v into 10000 volts@150-200kw, then this is for you... yes ytou read that right, over 100000 watts is easy, 200000is doable, and I have seen 250000 watts when I have turned it up too far.

This means we will be pushing out up to 40 amps@ many thousands of volts if the fence is heavy ( grassed), and probably only 5-15 amps@ 9000v into a lightly grassed fence. The normal/standard measuring level is 500 ohms.... I happen to have lots of 560 ohm 20 watt resistors, so I use them for testing most times..... the current will be volts/560, the power will be  volts x current.

The transmission will be DC,  but will behave as a high frequency AC wave front, so there will be different voltages along the fence... sometimes higher than where it connects to the fence miles away. It will depend on the fence, the surroundings, the loads, and the inductive and capacitive effects of the fence.

We get to change some of the behavior by changing the impedance of the transformer primary, and the path to the primary from the cap and triacs.

The lower the impedance of the transformer, the shorter the discharge time will be, and the higher the power. The down side is that the spike is so thin, it is easier to stymie with resistive and inductive loads in the fence, and generates a fair bit of RFI ( radio interference )

To stop this we shape the waveform by using  an inductor in series with the primary to "slow" the current down a bit ( widen the wave and make it less steep), and some capacitance to help with the shape too. This pulls the peak voltage down, and widens the wave.... makes it a bit more sine like... if you stretch the imagination a bit ( lot)

The circuit board looks like this.

4600-0

A better one can be found here: http://www.anotherpower.com/board/index.php/topic,731.msg10716.html#msg10716, with a circuit that is almost right above that thanks to Dario

That thread will give you plenty to go on to build the unit.

Here we will concentrate on the transformer... the important bit.
 
Ok, we need a microwave transformer, and we can use it a number of ways.
....... the victim....

4602-1


We can use it like a normal EI transformer, but real estate gets pretty fine in the winding window, and we can make one just as good and lighter if we modify it slightly. It is going to be saturated anyway, so good transformer theory is dead..... so we get the transformer and start by cutting the weld on one side so we can "open" it.... like this..,.,

4603-2


So now we need to undress it from the coils.... I use a 50 ton brake press normally, but this time I will use a vice and the trusty chisel

4604-3

And remove the first coil......


4605-4

 then the chokes ( this was a ferro resonant transformer, and was designed to run saturated anyway) and the heater winding/coil for the magnetron

4606-5

and then the secondary

4607-6

So we now have choices.... we can cut it up like this:

4608-7

or we can get to this by cutting off one end instead..... both will get us  a C core style.... some of the advantages of the torroid is there somewhere too.

So I cut it to look like this:

4609-8

Either one will end up with a C core, but there is more meat in thicker laminates using it like this..... and less cutting too......

Off to the next post..... winding the thing.



.,.........oztules














Flinders Island...... Australia

Offline oztules

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Re: High power electric fence transformer and fencer.
« Reply #1 on: October 10, 2015, 11:18:06 pm »
Moving right along........

We need to make a former to wind the primary and secondary on. I choose the thickness of the laminates I am using here to match the "I" laminates of a much bigger transformer.... that way I can stack them up to the thickness I need, and the width is how many plates on the thing I am building.... poorly said, so a pic says it all.... oh and use the lathe@38rpm for winding.... lazy now..

But first we will cut some transformer paper to the size we need.... like this:.... about 92mm wide.

4624-0

and the thing we will wind it on is a stack of bigger "i" laminates in the chuck:

4625-1

The big advantage of using laminates as the core... is you can tap some of them out when you need to release the core from the windings..... very important.... no good winding it, only to find you cant get the thing off the former without destroying it... been there done that....

First we wind two layers of paper over the former, and tape them up. We  want double  insulation and then some for this... particularly if you choose the 240v version.... we don't want punch through ... ever.... So two layers of paper, and then tape it fully.....

4626-2

The tape is not so much for insulation, but to give the wire a purchase on the former so it does not move sideways easily.... it stays where you wind it.
So here we have two layers of paper, and the tape is half way there..... now we have something to wind on.
So we wind on 22 turns in this case of 2mm wire in two in hand, to use up near 90 mm of former... ie we want to use up the whole length 2 in hand... so thats the 88mm used for 22 turns ( each turn takes up 4mm wide).

4628-3

We then put paper over that 2 layers thick for double insulation again, and tape it up again... like this.

4629-4

Now we have the primary double insulated from the core and the secondary we can start... 10:1- 15:1 will be fine or thereabouts.... We will use 1mm wire, so we will get perhaps 80 turns per layer or 240 turns for three layers..... so here we go.

First layer then taped at both ends to keep things in place..

4630-5
Then we need to put a layer of paper on there and tape it up again.... this will give us insulation between layers... VERY IMPORTANT!

Then the second layer

4631-6

And then more paper ( 1 layer is enough) so we now have all layers insulated from each other wqith at least 1 layer of transfromer paper, and two layers around the inner and outer of the primary. This is why this style of winding is used in HV applications..... it won't short internally,,, well not for the last 10 years anyway in a marine environment.

then tape up and then the last layer and tape it up too... it does not need paper over the outer unless your flush with the stuff and don't know what to do with it.... but it won't help anymore, it is for between layers really.

We end up like this:
4627-7

We then push out the former ( in pieces ), and put the C core in

4632-8


were out of space.....


...............oztules














Flinders Island...... Australia

Offline oztules

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Re: High power electric fence transformer and fencer.
« Reply #2 on: October 10, 2015, 11:36:57 pm »
Were back....

Now we have the transformer windings on the c-core.

A few things, we need to make sure that there is no easy path for the voltage to ground out, so transformer paper needs to be placed under the core paper between the steel and the primary and the ends.... like this at both ends.....

4633-0

and some anywhere you feel there is any possibility of arcing... even here:

4634-1

I use plastic coat stripped from 2.5mm building wire to cover the high tension out put leads..... seems to be enough for the last 10 years, and easy to do... ie:

4635-2

Then something to hold it together until you epoxy it up or coat it with enamel etc.

4636-3

So testing on a 12v unit, we get 9700 volts into a 560 ohm load..... for 17 amps or so... standard fence conditions... but thats still 17x9700 or 168kw of power from a tiny 12v battery every second..... not too shabby.

4637-4



On the 240v board, turned down a bit, we get this:

4638-5


Have fun....


4639-6


..................oztules
Flinders Island...... Australia

Offline burctankal

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Re: High power electric fence transformer and fencer.
« Reply #3 on: January 22, 2017, 07:40:06 pm »
Hello Oztules;
I want to make your electric fence device, but i'm not sure if the pcb layout given above is 12v dc or 240v ac?
Thanks.

Offline oztules

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Re: High power electric fence transformer and fencer.
« Reply #4 on: January 24, 2017, 02:59:01 pm »
Thats for 240v.... which voltage are you after?

....oztules
Flinders Island...... Australia

Offline burctankal

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Re: High power electric fence transformer and fencer.
« Reply #5 on: January 24, 2017, 04:29:38 pm »
Quote
If you want to build a fencer that can do 70-100 kms of fence, and can transform 12v into 10000 volts@150-200kw, then this is for you...

I'm looking for 12v dc. I've read your post twice and thought that the pcb is for 12v. Unfortunately I've build it yesterday and did not work with 12v  :) If you do not mind can you please give me a little help for the 12v version.
Thanks,




Offline oztules

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Re: High power electric fence transformer and fencer.
« Reply #6 on: January 25, 2017, 04:03:45 am »
Very sorry. At that time there were posts all over the place about the two versions across a few sites, so I got slack/confused perhaps.

Here is the 12v version.
The step up  transformer was wound on a etd39 ferrite, with 18t ,18t and 350turns. The dots/pads give the start of the coil orientation.

The 350 turns are not terminated, as they can be redirected to their respective end diodes.. Different winding will give better results so it is able to be varied.

 ( i had trannies wound for other boards of other orientations)

6757-0


........oztules

Flinders Island...... Australia

Offline burctankal

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Re: High power electric fence transformer and fencer.
« Reply #7 on: January 25, 2017, 04:10:42 pm »
Thank you so much Oztules. There are some points I can't understand:
     For the 240v version: -How a 600v capacitor can be charged fully with 240 vots. What is the idea there? Is the voltage of the capacitor climbing up to 600 volts or stays at 240 volts after it is fully charged?
     For the 12v version:  -How much voltage should I get from the output of the first transformer to charge the big capacitor?
                                       -Can I drive the primary of the first transformer with a logic mosfet. If so what should the pwm frequency and                               duty cycle be?
Thank you for you help

Offline oztules

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Re: High power electric fence transformer and fencer.
« Reply #8 on: January 26, 2017, 12:54:09 am »
sine wave 240v is actually 240x1.414=340v when rectified and stored in a cap. The doubler circuit takes that to 680 if left to it's own devices, but the trigger pulls in before that and discharges it... probably in the 500-600v range set by you.

Output from the free running oscillator is probably in the 1000v range. It is not pwm, it is a scroungy wild ac looking thing. The frequency changes with the load.


.......oztules
Flinders Island...... Australia

Offline burctankal

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Re: High power electric fence transformer and fencer.
« Reply #9 on: January 26, 2017, 05:12:54 pm »


I'm planning to use a micro controller for checking day-night    situation, battery status, control the shock timing and for many other things. Because my little transformer will not have a feedback coil, I'm after driving the primary with a logic mosfet (IRFZ44N) which is connected to a micro controller. Is that possible sir? Will the square wave applied to mosfet's gate work to charge the main capacitor? Is the schema shown above true?
Thank you so much for your help