Help with some old electric fencers

[canadaboy25]

So I know that this forum is more for tech stuff but I'm going to go ahead and post.

I've go these two old Holdem model 57 electric fencers and neither one of them work. One is older than the other but from what I can tell the wiring is exactly the same.

None of the lights on either unit light up when plugged in and on and I have checked all of the fuses.

These units say "clips weeds" on them and they have a removable "chopper" module (see pictures). What are these "choppers" even for? From what I can tell, three of them are the same. One is newer and the other two are older looking ones. From what I can make out on the writing, all three modules are the same. There is also one "mystery" module. It has no markings on the outside and it is about three times heaver than the other three.

My main questions are, what are these "choppers", how can I test them, and how can I test all of the other parts of the unit?

I haven't bothered to draw out a wiring schematic yet but if it would be helpful I can make one.

One last thing is that I am not asking everyone to come and tell me that this is a terrible idea and all that other jazz about it not being safe. I am aware of the dangers and I accept the risks. I also know how to be safe and protect myself from danger, just in case anyone was going to go off on me about it!

Thanks!

[stj]

Re: Help with some old electric fencers

oh jesus - dont play with those!!

it's a current-limited high voltage generator.
the can probably contains an oscillator that is replaceable incase you overload and kill it by shorting the output.
does it list the output voltage or current anywhere?
it has a 2core cable, but i can see the case needs to be earthed because there is a spark-gap on it.

[goontron]

Re: Help with some old electric fencers

open one up.

[canadaboy25]

Re: Help with some old electric fencers

oh jesus - dont play with those!!

it's a current-limited high voltage generator.
the can probably contains an oscillator that is replaceable incase you overload and kill it by shorting the output.
does it list the output voltage or current anywhere?
it has a 2core cable, but i can see the case needs to be earthed because there is a spark-gap on it.

I've looked over the thing and I can't find any output ratings.

Yea the case does get earthed and the fence connects to a terminal on the bottom.

open one up.

They are both opened...

[goontron]

Re: Help with some old electric fencers

They are both opened...

a chopper.

[canadaboy25]

Re: Help with some old electric fencers

a chopper.

Ahh yes, I should have seen that!

Before I open it up, what would be inside there? Any fluids or gasses?

[Sparkey55]

Re: Help with some old electric fencers

Ahh yes, I should have seen that!

Before I open it up, what would be inside there? Any fluids or gasses?

The chopper is used to control the duty cycle of the ac power to the primary of the transformer incase of an sustained abnormal overload on the high voltage secondary winding.

[stj]

Re: Help with some old electric fencers

the answer your actually looking for is that it should be safe, it's not a gas or liquid container.

[canadaboy25]

Re: Help with some old electric fencers

Well I've traced it around and from what I can tell the "chopper" is a bridge rectifier.

I'll have to wait until tomorrow to cut into it because it is welded shut.

[stj]

Re: Help with some old electric fencers

use side-cutters to rip the folded edge open at the base.

[canadaboy25]

Re: Help with some old electric fencers

Well I cut into one of the choppers and it wasn't a rectifier like I originally thought.

It looks to be more like a switch or something. Two of the pins are shorted together. The piece of metal connecting them broken so I patched it up with some solder and tried the fencer again but it still didn't work. On the top of the chopper module it says allow time for it to warm up, so would I need to leave it plugged in a long time before it will turn on? It seems unlikely. One of the pins isn't even connected to anything and the last pin goes to some sort of inductor.

It seems like a switch but since the two prongs are already shorted, what world the purpose be?

[Sparkey55]

Re: Help with some old electric fencers

Well I cut into one of the choppers and it wasn't a rectifier like I originally thought.

It looks to be more like a switch or something. Two of the pins are shorted together. The piece of metal connecting them broken so I patched it up with some solder and tried the fencer again but it still didn't work. On the top of the chopper module it says allow time for it to warm up, so would I need to leave it plugged in a long time before it will turn on? It seems unlikely. One of the pins isn't even connected to anything and the last pin goes to some sort of inductor.

It seems like a switch but since the two prongs are already shorted, what world the purpose be?

Current flows thru the small coil that is wrapped around the two pieces of bi-metal contacts which inturn makes contact with the other screw adjustable contact. When enough current flows to heat the bi-metal spring it bends enough to open the contacts, cools down, closes contacts. Rinse and repeat. A simple over current duty cycle limiter just as I stated in an earlier post.

[Sparkey55]

Re: Help with some old electric fencers

Well I cut into one of the choppers and it wasn't a rectifier like I originally thought.

It looks to be more like a switch or something. Two of the pins are shorted together. The piece of metal connecting them broken so I patched it up with some solder and tried the fencer again but it still didn't work. On the top of the chopper module it says allow time for it to warm up, so would I need to leave it plugged in a long time before it will turn on? It seems unlikely. One of the pins isn't even connected to anything and the last pin goes to some sort of inductor.

It seems like a switch but since the two prongs are already shorted, what world the purpose be?

Keep in mind that in order for the chopper to work properly the metal can needs to be reinstalled otherwise the bi-metal switch will not heat up within working paramenters as it was design for. A lot can go wrong with those, burned out heating element, worn contacts, cold solder joints, etc.

[canadaboy25]

Re: Help with some old electric fencers

Well now that I fixed that chopper the newer fencer lights flash and work properly.

The older one doesn't work because the capacitors are wrecked.

The problem I'm having now is that the spark is very weak.

[Sparkey55]

Re: Help with some old electric fencers

Well now that I fixed that chopper the newer fencer lights flash and work properly.

The older one doesn't work because the capacitors are wrecked.

The problem I'm having now is that the spark is very weak.

Does not need to be a strong spark to kill grass and weeds. The output might be just around 2KV or less. Not a bug zapper or cow zapper.

[stj]

Re: Help with some old electric fencers

recap it.
and remember your playing with a weapon designed to hurt things over several miles away.

[stj]

Re: Help with some old electric fencers

Does not need to be a strong spark to kill grass and weeds. The output might be just around 2KV or less. Not a bug zapper or cow zapper.

most of those devices output 5-6Kv
and it IS a cow / sheep / fox / intruder zapper.

[canadaboy25]

Re: Help with some old electric fencers

Well the reason the original owner had given them to me was because one wasn't working, but also because the other wasn't shocking as strong as it used to. That's the reason that he liked it, because it shocked so hard.

Is it possible for the transformer to weaken over time?

[stj]

Re: Help with some old electric fencers

no, it's just a pair of coils - unless one has shorted windings.
but caps age and resistors can change value

btw, these things work through the earth, if you have very dry weather they dont work so well.
and you need a very good groundspike to hook it up to.
.

[canadaboy25]

Re: Help with some old electric fencers

Well there is only one resistor and it is only hooked up to the mains power indicator light to limit the voltage. The two caps have on lead shorted to ground and the other lead on both of them go to two different prongs on the chopper.

I am just shorting a screwdriver between the hot and ground terminals. The spark used to arc much further that it does now.