electric fence generator: concept review

[earckens]

For an electric fence generator I am looking at using an old oscilloscope CRT high-voltage transformer. What is the voltage range for this kind of transformer?
Has anyone with experience in using this component for HV spike generation maybe describe their findings?

 

[Nigel Goodwin]

I would say it's probably not very suitable - too low a voltage output, and too high a voltage input (scopes don't often run off 12V).

The classic example has always been a car ignition coil.

If you search the site, one of the long time members has posted a link to a great example of a home made electric fence on his website - when his name pops back in my brain I'll come back and edit this post Although I suspect someone else will have posted it by then.

 

[earckens]

I would say it's probably not very suitable - too low a voltage output, and too high a voltage input (scopes don't often run off 12V).

The classic example has always been a car ignition coil.

If you search the site, one of the long time members has posted a link to a great example of a home made electric fence on his website - when his name pops back in my brain I'll come back and edit this post Although I suspect someone else will have posted it by then.

Hi Nigel, could it be from Eric Gibbs in his post (February 23, 2015) #8 in this thread: https://www.electro-tech-online.com/threads/solar-electric-fence.143863/ ?

I attached his schematic below; he uses a relay to periodically discharge the main capacitor and create a high-voltage spike.



In a second attachment another circuit is shown, but here an SCR is triggered to discharge the main capacitor.



What are your feasibility comments on either circuit? Or any better ideas or improvements?

 

[Nigel Goodwin]

No, came to me eventually

 

[earckens]

No, came to me eventually

Great circuit! Thanks a lot!

 

[tvtech]

That's Gary. From Canada. Great guy.

 

[tvtech]

I used to regularly check his website. He and his Wife loved travelling. Always posted photos on his site. The one with him in icy conditions acting like a Polar Bear in a freezing pond lol.

Nope haha. I'm from Africa. Don't like cold water. Imma wimp lol.

 

[tvtech]

CHEMELEC

Electronic Consulting,Hobby Projects,Pictures

chemelec.com

 

[dr pepper]

Beware that the energy level from an ignition coil can be dangerous, fencers can be as high a voltage, but limited energy.

 

[shortbus=]

Beware that the energy level from an ignition coil can be dangerous, fencers can be as high a voltage, but limited energy.

That may be true in today's fence chargers. But in the old days, they had some that were called 'weed burners" or "weed choppers". High amperage ones that would cut/burn any weed or grass that touched them. The grass or weeds would short out any smaller amperage chargers. Don't know if they still make them today though.

 

[crutschow]

Beware that the energy level from an ignition coil can be dangerous,

It's unlikely that a typical ignition coil circuit could generate enough energy to be dangerous to humans (of course the shock can hurt like heck).

 

[Nigel Goodwin]

Beware that the energy level from an ignition coil can be dangerous, fencers can be as high a voltage, but limited energy.

It's got to be fairly strong, or it wouldn't discourage cattle etc. - but because it's pulsed it's not dangerous to humans either - the energy available is relatively low.

 

[chemelec]

If you have a Considerably Constant On Time Duty Cycle, Than a Car Coil Can be dangerous.
Also is the shock actually passing through you Heart or Brain.
Also Depends somewhat on you Heart Health.

My Home Made Coil Put out a Lower Voltage, But Considerably More Current.

PLAY SAFE!

 

[Garrent47]

No, came to me eventually

Great design there, nice!

 

[crutschow]

If you have a Considerably Constant On Time Duty Cycle, Than a Car Coil Can be dangerous.

The "On Time" of typical flyback or capacitive discharge is always a very short spark.
It's not possible to appreciably increase the spark of these circuits' on-time to make it dangerous.

 

[crutschow]

If you want a lower output voltage from an automotive coil to avoid insulator problems, but with a higher output current, you can use a capacitive-discharge circuit with about a 100V capacitor charge voltage and a larger charging capacitor.

 

[chemelec]

The "On Time" of typical flyback or capacitive discharge is always a very short spark.
It's not possible to appreciably increase the spark of these circuits' on-time to make it dangerous.

Maybe you should build this circuit up and check it out for yourself.

But as I Said, My "Home Made Coil" puts out a Lower Voltage with a Higher Current

 

[Nigel Goodwin]

I think it really depends on what you consider 'dangerous'? - you can't have it all ways, it has to be strong enough to discourage animals (often cattle, who have nice thick hides), but weak enough not to harm smaller creatures (such as humans).

As for lower voltage, higher current - it's the current that kills - if the 'lower' voltage is high enough to pass a 'higher' current through your body, it's more dangerous than the higher voltage lower current. I'm fairly sure most people here (at least the older ones) will have had shocks from HT leads at various times - and any of the rural members have probably had shocks from electric fences as well

 

[crutschow]

Maybe you should build this circuit up and check it out for yourself.

I see no reason to do that since I'm quite familiar with how those circuits operate.
Are you?

 

[dr pepper]

I remember a very old electric fence that had an adjustable spark gap, you altered the gap which controlled the max voltage, as the gap jumped when it reached ionization voltage.