# Using a screw-in fluorescent light bulb as an electric fence pulse charge indicator

#### FredFlintstone

Joined Apr 30, 2022
23
I recently set up an electric fence around my chicken coop. It uses a 0.1 Joule charger that pulses every second. The charger has a tiny indicator light that flashes each second, but I would like a brighter indicator that I can actually see from a distance of 100 feet or so.

Some time ago I was told that I could use a screw-in fluorescent light bulb, with the electronics removed, to flash each time the fence charger sent a pulse. This would be a great solution for me if it works, but how? Is this as simple as wiring the bulb between the fence and ground? If so, would it reduce the charge imparted to an animal?

#### crutschow

Joined Mar 14, 2008
29,773
Is this as simple as wiring the bulb between the fence and ground?
Yes, I believe so.
If so, would it reduce the charge imparted to an animal?
Anything that takes power from the fence, would reduce the charge, but it may be negligible.
You might put a large resistor in series with the bulb to reduce that, if needed.
You could increase the resistor value until the bulb is too dim to readily see.

#### FredFlintstone

Joined Apr 30, 2022
23
Thanks crutschow. Maybe you know the answer to this question:

When I removed the electronics from my screw-in fluorescent bulb I found a pair of wires coming from each end of the twisted fluorescent tube -- similar to the way a standard 4' long fluorescent tube has a pair of pins on each end. From what I recall about fluorescent light bulbs, each pair of pins/wires is connected to a filament-type heating element inside the tube.

If this is correct:

Can I simply twist each wire pair together, then solder a couple of insulated leads with alligator clips to the twisted connections, thus creating an easily removable fence flasher?

#### Dodgydave

Joined Jun 22, 2012
10,301
You need to put the filament ends in series, and then it should work then select the best resistor to prevent loading on the fence.

#### crutschow

Joined Mar 14, 2008
29,773
Can I simply twist each wire pair together, then solder a couple of insulated leads with alligator clips to the twisted connections,
Yes, you can just ignore the filaments and use them as electrodes, since there are only there to ionize the mercury gas when operating from low voltage.
The fencer voltage should be sufficient to directly ionize the gas and give a glow.

Joined Jul 18, 2013
25,190
When I removed the electronics from my screw-in fluorescent bulb I found a pair of wires coming from each end of the twisted fluorescent tube -
You mention a ES CFL bulb, but where does "each end of the fluorescent tube" come in?

#### crutschow

Joined Mar 14, 2008
29,773
You mention a ES CFL bulb, but where does "each end of the fluorescent tube" come in?
Most fluorescent bulbs have a connection at each end.
For a spiral bulb they just are both in the same direction (below):

#### MisterBill2

Joined Jan 23, 2018
11,876
I know that it is also possible to flash a four foot tube with a high voltage pulse against the outside. And I have ignited a 4 foot tube that had a steady DC voltage across the ends that was not enough to make it light by applying a spike from a flyback thransformer pulsed with a 0.1 microfarad cap charged to 250 volts. The wire from the transformer was wrapped around the tube about 3 turns near the end not tied to the transformer.
The tube flashed and stayed conducting, loading the supply down to about 65 volts, I think. The supply was a 120 volt mains powered full wave voltage doubler with selenium rectifiers and 80 MFD capacitors.

Joined Feb 20, 2016
4,134
I was going to suggest something like @MisterBill2.
Try just winding a bit of wire around the outside of the lamp and connecting that to the fence.
And another loop of wire around the other end of the lamp to ground. Or connect the tube's wires to ground.

#### MisterBill2

Joined Jan 23, 2018
11,876
I was going to suggest something like @MisterBill2.
Try just winding a bit of wire around the outside of the lamp and connecting that to the fence.
And another loop of wire around the other end of the lamp to ground. Or connect the tube's wires to ground.
That should work. The forward conduction of a glow device is much lower than atypical fence charger. For the 4-foot tubes that I was experimenting with it seemed to be about 65 volts, not enough to be an effective fence charger.
What are you protecting the coop from? Some creatures will learn to jump over the wires.

#### FredFlintstone

Joined Apr 30, 2022
23
The fencer voltage should be sufficient to directly ionize the gas and give a glow
Before disassembly I tested my CFL bulb by screwing it into a standard light socket and it worked. Then I removed the electronics, connected the wires from one end of the tube to the charger's fence terminal, and the other end to the charger's ground terminal ... but the CFL bulb did not light.

So maybe the pulse duration of this charger is too short?
Or the pulse itself is too weak?

What are you protecting the coop from? Some creatures will learn to jump over the wires.
So far my cameras have picked up foxes, cats, raccoons and opossums. Foxes and cats can easily scale or jump a short fence, but neither can scale the 8-foot tall posts that support my chicken roosts. So my main concern is to discourage raccoons and opossums, both of which are great climbers and can easily scale the posts.

I set up an 8-inch tall "test fence" around the coop, about two feet outside the supporting posts, with charged wires at 4 and 8 inches off the ground. So far I have watched cats and raccoons (and one of my dogs) curiously inspect and then completely avoid these wires. It almost appeared that they could sense the electric pulse by nosing close to the wire but not actually touching it, and from then on they simply avoid it ...

But opossums seem undeterred by the fence wires, as I have watched them walk or run beneath or in-between the wires several times. If I didn't know better, I might think that opossums are immune to the shocks produced by the fence. But maybe they are simply not getting enough of a shock to stay away.

My next test will be to run a ground wire in between the charged fence wires. If the earth itself is too resistive to allow a full-powered "zap" to drive away opossums, the ground wire might help by providing a better return path to the charger's ground terminal.

When I'm done testing, I will eventually build a permanent 4-foot tall welded wire fence, with electric wires installed just outside this fence at several different heights. This should discourage almost all ground-based predators, assuming the charger itself is producing enough zap.

#### Dodgydave

Joined Jun 22, 2012
10,301
What is the make of the fence pulser, you may be able modify it for more output..
try using a neon bulb with a 180K resistor.

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#### crutschow

Joined Mar 14, 2008
29,773
but the CFL bulb did not light.
I'm surprised you couldn't see anything.
The pulse should be strong enough, but apparently not.

Perhaps a neon bulb with a suitable resistor in series with each, would give you a sufficient flash to see.
They have flicker-flame, large neon bulbs which may also work.

#### MisterBill2

Joined Jan 23, 2018
11,876
For raccoons and possums I suggest a neon sign transformer. Yes, it may well be lethal but for some predator types that is the only effective choice. Hopefully your chickens are not in an area frequented by children or other people.
The alternative will be the charged wire on top of the fence, with the metal fence connected to the charger ground terminal. A very good connection will assure the most shock energy gets delivered.

#### crutschow

Joined Mar 14, 2008
29,773
I suggest a neon sign transformer.
Only if your property insurance has a high payout for accidental death by negligence.

#### FredFlintstone

Joined Apr 30, 2022
23
For raccoons and possums I suggest a neon sign transformer.
In another thread I suggested that this one:

... might be safe enough to use around humans since its voltage is substantially lower than most NST's, and more importantly it outputs only 30mA, which seems so low to me that I would think it safe for humans to touch. But I was discouraged by others from using a NST so I decided against this unit. Then again ...

Two years ago a guy on YouTube who "fixes and upgrades" fence chargers produced this video where he actually used this exact NST to fix an old weed burner fence charger. This does not mean that I trust either him or this NST, but I still wonder if 30mA is actually dangerous enough at 3kV to injure or kill a human.
Hopefully your chickens are not in an area frequented by children or other people.
No one but me ever goes near them, especially at night when the charger will be on.

The alternative will be the charged wire on top of the fence, with the metal fence connected to the charger ground terminal. A very good connection will assure the most shock energy gets delivered.
I plan to do exactly this, eventually, but first I would like to see some evidence that the charger I bought, or the one I replace it with, will actually deter opossums on the ground ... and so far I continue to see a small one run underneath my test fence wire with apparently zero reaction. It's as if he feels nothing on his back rather than an electric shock.

This brings up a question:

Can I increase the output of my charger simply by adding a bigger capacitor in parallel with the existing cap? The guy in this video did it, and it seemed to work for him.

#### crutschow

Joined Mar 14, 2008
29,773
it outputs only 30mA, which seems so low to me that I would think it safe for humans to touch.
May not be fatal, but GFCIs typically interrupt the circuit at less than 10mA, so I would be leery of 30mA.

To use that transformer I would interrupt the input about once per second (as the Weed Burner fencer in the video does), with the on-time of about a tenth of a second.
That likely could be done with a solid-state output timer (mechanical relay types would not last long) to control the mains voltage to the supply.

#### MisterBill2

Joined Jan 23, 2018
11,876
The higher voltage does mean that current will flow, regarless of some resistance. And consider that power does the damage and 0.03Amps X3000 volts is 90 watts.

#### FredFlintstone

Joined Apr 30, 2022
23
To use that transformer I would interrupt the input about once per second with the on-time of about a tenth of a second. That likely could be done with a solid-state output timer (mechanical relay types would not last long) to control the mains voltage to the supply.
That's almost exactly how I imagined using that NST when I first saw it -- cycle the input power -- rather than trying to cycle the output power which would probably be impossible, at least for me.

But I was assuming the use of a mechanical relay which, as you mentioned, would burn out too early, so THANK YOU for mentioning solid-state output timers! I found a limited number of them online but they seem to be rather costly. So if I build this theoretical fence charger I might use the NST mentioned above which costs $11.00, plus this solid state relay which costs$5.50:

... plus a 12vdc power supply and a 12vdc digital timer, both of which I already own. This means only four easy-to-assemble off-the-shelf components and a total cost of less than \$20. This doesn't mean I'm going to do this of course, but at least it gives me a functional plan for a DIY fence charger that's probably a lot more powerful than the one I just bought which cannot even light up a CFL bulb.