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electric fence generator: concept review

earckens

Member
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

Super Moderator
Most Helpful Member
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 :D Although I suspect someone else will have posted it by then.
 

earckens

Member
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 :D 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.

Eric Gibbs E_Fence1.gif

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

fencechargercircuit.png

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

tvtech

Well-Known Member
Most Helpful Member
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.
 

dr pepper

Well-Known Member
Most Helpful Member
Beware that the energy level from an ignition coil can be dangerous, fencers can be as high a voltage, but limited energy.
 

shortbus=

Well-Known Member
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

Well-Known Member
Most Helpful Member
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

Super Moderator
Most Helpful Member
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

Well-Known Member
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!
 

crutschow

Well-Known Member
Most Helpful Member
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

Well-Known Member
Most Helpful Member
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

Well-Known Member
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
 
Last edited:

Nigel Goodwin

Super Moderator
Most Helpful Member
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 :D
 

crutschow

Well-Known Member
Most Helpful Member
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

Well-Known Member
Most Helpful Member
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.
 

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