Maker Pro
Maker Pro

Help with fence charger schematic

duke37

Jan 9, 2011
5,364
Joined
Jan 9, 2011
Messages
5,364
In theory, 10% more turns will give 10% more voltage but there will be a secondary effect of additional coil capacitance. Also, making modifications to a HV transformer may give insulation problems. 10% difference in the fence voltage will be irrelevent.

You can get low voltage DC to high voltage DC convertors for little money. I got a couple but I just do not have the time to play with them at present.
 

barryg

Jul 24, 2017
17
Joined
Jul 24, 2017
Messages
17
Understand
One quick question
Is the power from the transformer on the fence charger AC or. D.C.?
I'm assuming AC but is it true that on a magneto it is D.C. And the power falling away induces a voltage by use of breaker points?
 

duke37

Jan 9, 2011
5,364
Joined
Jan 9, 2011
Messages
5,364
Transformers produce AC only. If you want DC you will need to rectify the output. I have seen a fence charger with output rectifier, I do not know the effect of this, it is possibly to counter the effect of fence capacitance.

A magneto produces AC.
For low voltage ignition, the output is shorted and the current builds up. When the points in the cylinder open, a spark is drawn until the energy in the magneto inductance is dissipated.
For high voltage ignition, the points (outside the engine) open and a high voltage winding produces enough voltage to activate the spark plug in the cylinder.

The AC is truncated, only the first half cycle is used so it looks like DC.
 

WHONOES

May 20, 2017
1,217
Joined
May 20, 2017
Messages
1,217
The 24V supply will be useful. You will need to reduce it to 12 or 15V for the control circuitry. A simple 3 terminal regulator such as an LM7815 or similar will suffice.
 

WHONOES

May 20, 2017
1,217
Joined
May 20, 2017
Messages
1,217
Haven't forgotten you. Have done a fair bit of simulation. Will post a circuit soon that will generate 12 to 14Kv.
 

WHONOES

May 20, 2017
1,217
Joined
May 20, 2017
Messages
1,217
See below schematic and graph for 15.7Kv generator. Note that you will require a spark gap between the output and you fence otherwise nothing will happen. You may create your own spark gap. The size of the gap will determine the strike voltage. Air ionises at 3Kv per mm so, if you want 12Kv set the gap to 4mm.
Also note that Resistors R1, R2 and R3 are for the benefit of the simulation and do not exist in reality so don't try to include them.
If you wish to try this out, say so on this thread and I will provide further info on construction and other bits. Note that the transformer needs to be built with some care.
 

Attachments

  • Fencer 7a.pdf
    14.8 KB · Views: 55
  • Fencer 7a graph.pdf
    49.2 KB · Views: 42

duke37

Jan 9, 2011
5,364
Joined
Jan 9, 2011
Messages
5,364
I am not able to see the schematic at the moment but it seems to me that 15kV is excessive and much more than those fencers I have played with.

What is the point of generating a lot of high voltage energy and then dissipating in a spark gap?
 

WHONOES

May 20, 2017
1,217
Joined
May 20, 2017
Messages
1,217
1) You are not dissipating the energy into a spark gap. One end is connected to the voltage source whilst the other is connected to the fence thus discharging the circuit energy into the fence when the spark gap breaks over.

2) The size of the gap controls the voltage applied to the fence by virtue of its break down voltage.

3) The circuit does not have to be run at 15kV, that is just the maximum that is achievable. What ever voltage the user decides upon is set by varying the spark gap dimension i.e. 1mm for 3kV, 2mm for 6kV and so on.

The diagrams are PDF's. Anybody should be able to read them. If not then download a reader. They are freely available.
 

duke37

Jan 9, 2011
5,364
Joined
Jan 9, 2011
Messages
5,364
1. Energy is required to create a spark, this is wasted energy.

2. A spark gap across the output should be installed. This with an inductance of six turns spaced 10mm or so, 300mm diameter will give some lightning protection. The parallel spark gap will also limit the output voltage.

3. The output MUST NOT use the mains earth. In the UK, this is illegal. Even with the output isolated, radio interference can occur. I can tell it is my brother ringing me even before he speaks.

4. PDF reading. Some rotten devil messed up my computer and I had it cleaned out, now Adobe will decode some PDF files but not all. Any recommendation for an alternative to Adobe?
 

WHONOES

May 20, 2017
1,217
Joined
May 20, 2017
Messages
1,217
Yup. A larger spark gap on the fence to ground will give some protection against a lightning strike.
Again, the generated emf is controlled by the spark gap on the output.
The fence should be grounded with a stake into the earth. A choke to ground could be a good idea as it would ring and maintain the voltage a bit longer.
 

duke37

Jan 9, 2011
5,364
Joined
Jan 9, 2011
Messages
5,364
The inductance should be connected in the connection to the fence, not to ground. This will impede the fast lightning strike and help to pass the energy through a surge arrestor (spark gap) to ground on the fence side. This site electricfence-online.co.uk shows how a coil can be supported by plastic pipe. The UK Min of Agric showed a coil some years ago which I made and appeared to be a help. I cannot find the details again.
The one I made was 6 turns or so 300mm diameter with a spacing of 10mm mounted on a wooden former.

Thanks Alec
I will look up Irfanview
 
Top