# I am building an electric fence driver and need to know if has too much or too little power

#### antrowe07

Aug 30, 2019
5
So I'm not as much worried about the circuit as much as I am the size of the flyback transformer and mosfet,i am testing with an IRF640 and a small Canon flyback transformer from an old laser printer and it will produce arcs of about 3/4 of an inch. I'm using a pulsed power supply of 19v. I thought the pulsating was the circuit but when I change the power supply it stopped pulsating and it would make continuous arcs. I really just need to know if what I have will harm people or animals too much.. Thanks in advance

#### duke37

Jan 9, 2011
5,364
Electric fence drivers vary widely in the power of the shock. They are specified in terms of energy rather than volts or amps, A small fence would be adequatelt powered with 0.1J but a long fence in Australia may use 10J (but Australians are tough). The energy is normally provided from a high voltage capacitor which is charged to the correct voltage (300V) and discharged through a transformer (about 1:20) You must leave a blank time between pulses for the victim to withdraw before the next pulse. Normally the pulses are spaced at one/second. In the UK a notice must be displayed tp warn little chilldren and other animals.

The voltage must be high enough to punch through hair or fur. A long fence will have a considerable capacitance which needs to charged at each pulse

Your circuit shows a rectangular box, I assume this is a 555 which produces continuous pulses. I have not worked out the frequency. If your transformer can store 0.1J then your circuit could be used with the FET pulsed at one second intervals. There is nothing to control the FET current which could be excessive if the output is shorted.

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,792
Your electric fence definitely needs to be pulsed with a sufficient interval between pulses to allow whatever is being shocked to disengage from the fence. If excited continuously, lethal results could occur. Only Government entities are allowed to use lethal force in this manner.

#### Nanren888

Nov 8, 2015
623
In some places electric fences in urban areas are banned. I guess you;re not in an urban area.
Fences for cows might be quite different, or set differentlt, from those for smaller animals.
.
Discharging from a capacitor is a good concept as you can calculate the maximum energy delivered.
.
A monster 58 Joules.
https://am.gallagher.com/nz/product/6564/fence-energizer-m5800i

100 Joules
https://am.gallagher.com/nz/product/6585/fence-energizer-m10-2c000i

As a guide, commercial units will cause removal of teeth, if the victim gets the pulse right.
Farms often need big ones are weeds grow up into contact with the wire & sap some of the pulse energy down the fenceline.

#### antrowe07

Aug 30, 2019
5
In some places electric fences in urban areas are banned. I guess you;re not in an urban area.
Fences for cows might be quite different, or set differentlt, from those for smaller animals.
.
Discharging from a capacitor is a good concept as you can calculate the maximum energy delivered.
.
A monster 58 Joules.
In some places electric fences in urban areas are banned. I guess you;re not in an urban area.
Fences for cows might be quite different, or set differentlt, from those for smaller animals.
.
Discharging from a capacitor is a good concept as you can calculate the maximum energy delivered.
.
A monster 58 Joules.
https://am.gallagher.com/nz/product/6564/fence-energizer-m5800i

100 Joules
https://am.gallagher.com/nz/product/6585/fence-energizer-m10-2c000i

As a guide, commercial units will cause removal of teeth, if the victim gets the pulse right.
Farms often need big ones are weeds grow up into contact with the wire & sap some of the pulse energy down the fenceline.

100 Joules
https://am.gallagher.com/nz/product/6585/fence-energizer-m10-2c000i

As a guide, commercial units will cause removal of teeth, if the victim gets the pulse right.
Farms often need big ones are weeds grow up into contact with the wire & sap some of the pulse energy down the fenceline.[/QUOT...yes I am in a very urban area,thanks for ur response but I was kinda just wanting to make my own for learning g purposes,i looked at the fence chargers u recommend but they say they are not available in my region lol

#### antrowe07

Aug 30, 2019
5
Your electric fence definitely needs to be pulsed with a sufficient interval between pulses to allow whatever is being shocked to disengage from the fence. If excited continuously, lethal results could occur. Only Government entities are allowed to use lethal force in this manner.
I messed up in the first thread,what I meant to say was with the 19v power supply for some reason it was pulsating but when I changed supplies it ran a continuous arc with no pulse,i plan to look around for an actual fence driver circuit as I was hoping to use the 555 flyback circuit I posted,,I already have a store bought 2 mile charger and just need something bigger,like I said I think I'll look for a different circuit just to be on the same side..thank you for your time and response

#### antrowe07

Aug 30, 2019
5
Electric fence drivers vary widely in the power of the shock. They are specified in terms of energy rather than volts or amps, A small fence would be adequatelt powered with 0.1J but a long fence in Australia may use 10J (but Australians are tough). The energy is normally provided from a high voltage capacitor which is charged to the correct voltage (300V) and discharged through a transformer (about 1:20) You must leave a blank time between pulses for the victim to withdraw before the next pulse. Normally the pulses are spaced at one/second. In the UK a notice must be displayed tp warn little chilldren and other animals.

The voltage must be high enough to punch through hair or fur. A long fence will have a considerable capacitance which needs to charged at each pulse

Your circuit shows a rectangular box, I assume this is a 555 which produces continuous pulses. I have not worked out the frequency. If your transformer can store 0.1J then your circuit could be used with the FET pulsed at one second intervals. There is nothing to control the FET current which could be excessive if the output is shorted.
Thank u for your time and response,with the information i now have I believe I'll just go look for an electric fence driver circuit instead of the flyback circuit I intended to use,i planned to add a cap if needed and I misspoke when I asked,,it actually had a pulsed output but only while using a certain power supply. I figured out the power supply was bad and using a different supply gave me continuous arcs..to be safe I will look for a different circuit and a transformer that isn't a flyback,,once again thank you very much

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