Replace electric fencer output transformer

Thread Starter

cpgos

Joined Nov 26, 2018
21
I would appreciate some advice on how to select an electric fencer output transformer. The original transformer was found to be faulty as discussed in the thread below:

https://forum.allaboutcircuits.com/threads/electric-fencer-output-transformer.154966/#post-1335680

The original transformer is shown disassembled in the attached photo. The primary coil has two layers of 34 turns of 1.1mm wire and the secondary has four layers of approximately 160 turns of 0.2mm wire. The ratio then between the primary and secondary is 640/68 which is 9.411 or approx 1:10.

To be compatible with the control circuit presumably any replacement transformer would have to have a similar primary coil along with a similar turns ratio or is there some other requirement for a pulse transformer used in such an application as this. For example, would a relatively standard 220V to 20V mains transformer be suitable?

Best regards



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Thread Starter

cpgos

Joined Nov 26, 2018
21

Thread Starter

cpgos

Joined Nov 26, 2018
21
Thanks, I think that I understand your intention now.

The coil that you suggest would replace the entire fencer rather than just the faulty transformer.

Best regards.
 

LesJones

Joined Jan 8, 2017
2,439
Hi Max,
If I remember the original thread correctly I think the primary is pulsed with about 200 volts and does not depend on the back EMF from the field collapsing the way it would if it was driven from 12 volts. I have seen designs using a normal 12 volt ignition used in CD ignition systems pulsed with a few hundred volts so I think the coil would work but the output voltage would be too high. (Probably about 10KV) As the original transformer only had a 1:10 ratio I think the unit was designed to give an output pulse of about 2KV. This still means that that ignition coil would not be suitable. (But for a different reason.)

Les.
 

Thread Starter

cpgos

Joined Nov 26, 2018
21
Hi Max,
If I remember the original thread correctly I think the primary is pulsed with about 200 volts and does not depend on the back EMF from the field collapsing the way it would if it was driven from 12 volts. I have seen designs using a normal 12 volt ignition used in CD ignition systems pulsed with a few hundred volts so I think the coil would work but the output voltage would be too high. (Probably about 10KV) As the original transformer only had a 1:10 ratio I think the unit was designed to give an output pulse of about 2KV. This still means that that ignition coil would not be suitable. (But for a different reason.)

Les.
Thank you for your response and your comments on the original thread are accurate.

Could the 200V pulse be applied to the primary of a relatively standard 220V to 20V step down mains transformer as a possible approach to replacement?

Best regards
 

LesJones

Joined Jan 8, 2017
2,439
It could be BUT the design of the original primary winding (Now secondary) will probably not stand up to the 2000 volts that will be across it in your application. If you look at the way the secondary was wound on the original transformer you will see that it is made in 4 layers so that the insulation on the wires did not have to withstand a very high voltage. The insulation between the layers dealt with the voltage between layers.
The normal mains transformer will probably just wound straight onto a plastic former so there could be a high voltage between adjacent turns.

Les.
 

Thread Starter

cpgos

Joined Nov 26, 2018
21
It could be BUT the design of the original primary winding (Now secondary) will probably not stand up to the 2000 volts that will be across it in your application. If you look at the way the secondary was wound on the original transformer you will see that it is made in 4 layers so that the insulation on the wires did not have to withstand a very high voltage. The insulation between the layers dealt with the voltage between layers.
The normal mains transformer will probably just wound straight onto a plastic former so there could be a high voltage between adjacent turns.

Les.
Thank you for your response.

Would you agree that the only practical replacement option is to recycle an output transformer from another electric fencer?

Best regards.
 
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