I am trying to reproduce an electric fence unit that was discarded by a neighbour. It was left open in all weathers and very muddy. I've cleaned it enough to identify components and draw the very amateurish circuit diagram below.
I have built the circuit onto pro board. The problem seems to be that the triac is not triggering output pulses. The 230v LED is supposed to flash with each pulse. The original transformer was wound onto a UFY ferrite nucleus core, but that is smashed and the windings damaged beyond repair. The original output was 10Kvolts. I have substituted the original transformer with fairly hefty TV LOPT Flyback Transformer.
I would be very grateful for any advice as to why the fence unit is not pulsing/firing.
Many thanks.
Julian.

 

hi Julian,
Welcome to AAC,
Is the 240Vac source via a mains isolating transformer.??
E

 

I think you need to re- examine the schematic. Doesn't look correct to me.

 

hi Julian,
Welcome to AAC,
Is the 240Vac source via a mains isolating transformer.??
E

Thanks Eric, It's supplied directly from the mains.

 

I think you need to re- examine the schematic. Doesn't look correct to me.

I just made a sketch of the components and used 'TinyCad' to make it more readable.
Can you let me know what does not look correct?
The original circuit was just built on a piece of paxolin board, so it was very easy to identify the components.
Please see attached photos of the same circuit board from the same model fence unit.

 

h Julian,
I would strongly recommend that you use a isolating transformer, as you maybe aware the project is potentially lethal.

Do you have any electrical training ?

E

 

have substituted the original transformer with fairly hefty TV LOPT Flyback Transformer.

I doubt that transformer has an isolated secondary.
If so then that circuit can be lethal to anyone touching the fence.
As stated, you need an isolation transformer.

 

h Julian,
I would strongly recommend that you use a isolating transformer, as you maybe aware the project is potentially lethal.

Do you have any electrical training ?

E

Eric, Yes I started out as a Radio and television engineer in the 1960s. Then on to aircraft radars.
My workbench supply is protected with an RCD circuit breaker that reacts within 40 milliseconds.
I agree that this bit of kit is dangerous. On the original plastic box there is only a warning of the 10 Kvolt output.

 

I doubt that transformer has an isolated secondary.
If so then that circuit can be lethal to anyone touching the fence.
As stated, you need an isolation transformer.

The original Tx just had the primary and secondary windings onto a 16mm ferrite UYF core, so no isolated secondary!

 

hi Julian,
I would like to draw your attention to Item #7 of AAC's UA's.
E

7. Safety & Closing of Threads. While everyone is responsible for their own safety, the moderating staff, on a case by case basis, will close discussions if they get the impression that one of the members appears unwilling or unable to appreciate the risks in what they are attempting.

 

I think D5 is actually a neon, and I wonder if D8 might be a diac. Is T1 a thyristor, or maybe a triac used as a thyristor?
Reorganise is a bit and it doesn't look so wrong.

 

The original Tx just had the primary and secondary windings onto a 16mm ferrite UYF core, so no isolated secondary!

If the primary and secondary windings are not physically connected, then there is isolation.

But a TV flyback may have them connected together.
You can easily check that with an ohmmeter.

 

I think D5 is actually a neon, and I wonder if D8 might be a diac. Is T1 a thyristor, or maybe a triac used as a thyristor?View attachment 236501
Reorganise is a bit and it doesn't look so wrong.

Thanks Ian, D5 is a 230 vac Led, and D8 is definitely a zener diode. T1 is a TRIAC , a BTA 140 600v. The one I've put into the circuit I'm working on is a BTA 140 800v that I can't get to trigger!

 

If the primary and secondary windings are not physically connected, then there is isolation.

But a TV flyback may have them connected together.
You can easily check that with an ohmmeter.

I can't check the original Tx because it is so damaged, however with the flyback Tx there is no continuity between the two windings.

 

hi Julian,
I would like to draw your attention to Item #7 of AAC's UA's.
E

7. Safety & Closing of Threads. While everyone is responsible for their own safety, the moderating staff, on a case by case basis, will close discussions if they get the impression that one of the members appears unwilling or unable to appreciate the risks in what they are attempting.

Again Eric, after 50 odd years working with EHT I do fully understand the risks involved as as mentioned my workbench mains supply is more than adequately protected.
I am completely on board with your concerns and amazed that these electric fence units are on sale to the general public.

EDIT: Just to be clear those photos of components wired to that paxolin board are from the current fencer units on sale, not the Pro Board that I am working with.

 

Thanks Ian, D5 is a 230 vac Led, and D8 is definitely a zener diode. T1 is a TRIAC , a BTA 140 600v. The one I've put into the circuit I'm working on is a BTA 140 800v that I can't get to trigger!

It won't trigger with a zener, because the gate current will just be the current through the 1.5M resistor.
It needs a breakover device (a diac) to discharge the capacitor into the triac gate to give enough trigger current.

 

It won't trigger with a zener, because the gate current will just be the current through the 1.5M resistor.
It needs a breakover device (a diac) to discharge the capacitor into the triac gate to give enough trigger current.

Thank you Ian, you are probably correct. It looked like a standard zener diode (see photos in post #5).
I'll pop in a diac sometime today and post back into this thread.

 

Thank you Ian, you are probably correct. It looked like a standard zener diode (see photos in post #5).
I'll pop in a diac sometime today and post back into this thread.

The only clue is in the part number! (although some do have a single band in the middle rather than towards the end)

 

The only clue is in the part number! (although some do have a single band in the middle rather than towards the end)

You were absolutely correct Ian! I received a batch of DB3 diacs today and placed one in the circuit and the triac is now triggering.
As pointed out above a flyback Tx is not really the way to go, so my next quest is to calculate the amount of turns needed for the primary and secondary windings onto a 16mm ferrite U core. Again as mentioned the original Tx was smashed so apart from identifying the wire gauge there was no way to count turns.
Any calculated guesses would be gratefully received.
Coil winding is not a problem as I am just resurrecting my very old Kolectric coil winder. (photo below)
Thanks again all,
Julian

 

@Julian104

If you need help with inductors, here are two things that will help:

Inductance Calculations
Author: Frederick W. Grover
ISBN-10: 048647440-2

And from one of the most brilliant people I've ever had the pleasure of learning from:

http://ludens.cl/Electron/Magnet.html
http://ludens.cl/Electron/trafos/trafos.html