# Testing an Electric Fence Unit

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#### Western

##### Member
Does anyone know how you should test an electric fence unit ... under a realistic load ... short of asking the kids to "touch this wire" !

Farmer tells me that it has the built in ability to throttle back the power if there's an overload ... to the point of shutting down if too severe.

He says that it is doing that now ... even with very little fence attached.

I did find a Gallagher load tester advertised, that has a 100 ohm and a 500 ohm load ... but no extra info to explain what I should be seeing.

The unit in question is a Thunderbird MB1750R and supposedly good for 135km of fence!

Output 13.72J at 142 ohms resistive load.

Whoops ... I see I posted this in the wrong section ... sorry.

#### JimB

##### Super Moderator
Whoops ... I see I posted this in the wrong section ... sorry.
Moved it for you.

JimB

#### crutschow

##### Well-Known Member
You could look at the fencer output with a high voltage probe and an oscilloscope (you could make a ≈100:1 probe by soldering ten 10megΩ, 1/2W resistors in series connected to a 1 megΩ oscilloscope input. Put the resistors in a plastic sleeve for insulation.) .
It likely outputs several thousand volts when operating normally.

#### unclejed613

##### Well-Known Member
when i was 12, we were out camping, and while we were on a hike, i heard this "thunk...........thunk...........thunk" sound. what i found was a box mounted on a fence which was open on the side towards the fence. inside the box was a lantern battery, a relay, and an ignition coil. as i leaned to get a closer look, i put one hand on the fence.... "THUNK" boy did that hurt....

#### KMoffett

##### Well-Known Member
My dad used to check the electric fence by garbing the fence wire tightly with his hand. Not loosely, as the spark hurt worse than the shock. I would watch his arm jump each time the fencer pulsed. That was not the "weed cutter" type. OK, I still test 9V batteries with my tongue, but was not willing to try his trick with the fence.

Ken

#### ronsimpson

##### Well-Known Member
Does anyone know how you should test an electric fence unit ... under a realistic load
Yes. I have a younger brother ..... He still does not like me.

You could look at the fencer output with a high voltage probe and an oscilloscope (you could make a ≈100:1 probe by soldering ten 10megΩ, 1/2W resistors in series connected to a 1 megΩ oscilloscope input. Put the resistors in a plastic sleeve for insulation.) .
If the scope is set to "AC" the divider will not work right and burn out the scope's front end. Don't rely on the scope's 1meg resistor. You should put a resistor at the bottom of the divider.

I have seen circuits with three 10meg 1 watt resistor in a string and a neon bulb at the bottom.
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#### Western

##### Member
You could look at the fencer output with a high voltage probe and an oscilloscope (you could make a ≈100:1 probe by soldering ten 10megΩ, 1/2W resistors in series connected to a 1 megΩ oscilloscope input. Put the resistors in a plastic sleeve for insulation.) .
It likely outputs several thousand volts when operating normally.
Thanks for that. Never even though of it but I do have a couple HV probes from back in my tv fixing days. I still need to add a load to see what happens ... but should make it safer to monitor.

when i was 12, we were out camping, and while we were on a hike, i heard this "thunk...........thunk...........thunk" sound. what i found was a box mounted on a fence which was open on the side towards the fence. inside the box was a lantern battery, a relay, and an ignition coil. as i leaned to get a closer look, i put one hand on the fence.... "THUNK" boy did that hur
Ouch !! ... Funny how some of those experiences we never forget.

My dad used to check the electric fence by garbing the fence wire tightly with his hand. Not loosely, as the spark hurt worse than the shock. I would watch his arm jump each time the fencer pulsed. That was not the "weed cutter" type. OK, I still test 9V batteries with my tongue, but was not willing to try his trick with the fence.
I won't do either, I'm a sook. Someone conned me into testing a 70 volt battery out of a weather balloon control box with my tongue when I was just a kid. I think that explains it.

I do remember during my apprenticeship while we were doing EHT supplies on B&W TVs ... one of the guys told us how one of the lecturers used to say it wouldn't hurt you ... and to prove it, used to pull out his willy and draw some arcs. He'd get arrested for that now ... and half the class would end up in therapy.

If the scope is set to "AC" the divider will not work right and burn out the scope's front end. Don't rely on the scope's 1meg resistor. You should put a resistor at the bottom of the divider.

I have seen circuits with three 10meg 1 watt resistor in a string and a neon bulb at the bottom.
Thanks Ron. I got caught once using my scope on a mig welder (many years ago) ... fried one probe. At least I can use my HV probe ... I just need to work out a suitable load.

#### KeepItSimpleStupid

##### Well-Known Member
The way I heard you test fence chargers is you tell someone to go pee where the wire is located.

#### gary350

##### Well-Known Member
I test my electric fence with a 6" long piece of grass. Hold the grass with 2 fingers then touch the tip of the grass to the electric fence wire. Now very slowly slide wire up grass closer to your fingers the grass acts like a variable resistor when you get closer you start to feel the tingle of the electricity. Slowly go closer the shock gets stronger you can stop anytime you want. I usually slide wire along grass to about 2" from my fingers that is were I stop. Easy, quick & painless. You don't need any fancy  tester if the fence shocks you will shock animals too.

#### gary350

##### Well-Known Member
The way I heard you test fence chargers is you tell someone to go pee where the wire is located.
I grew up on a farm my uncles & friends were playing cards and drinking beer one Saturday night at my uncles house. Uncle had an electric fence around his back yard to keep a cow in the back yard so he did not have to mow grass. 1 of the guys got up from kitchen table and went out the back door to pee off the porch. Electric fence wire was only 12" front right side of porch the guy peed on the wire it locked up all his leg & arm muscles he froze in place and screamed for 20 seconds until pee was gone. Then he fell on porch like a dead person it nearly killed him. LOL. I was about 12 years old than that was 57 years ago. That would have made a good video for YouTube.

#### unclejed613

##### Well-Known Member
i almost forgot... i don't see a wire from the fuse holder to the circuit board in either of the pictures above. it looks like there's only one wire connected to the fuse holder.

#### schmitt trigger

##### Well-Known Member
Just thinking about it makes me cringe!

Pee, being rich in salts, should be a very good conductor.

#### Ylli

##### Active Member
Just thinking about it makes me cringe!

Pee, being rich in salts, should be a very good conductor.
Yes, but according to the tests run by "MythBusters", the urine stream quickly breaks up into droplets and becomes discontinuous. Broken wires don't carry current.