Quite by accident I have stumbled across a web site which provides an interesting insight to the repair of an old electric fence machine which may have been manufactured in Australia. The machine is sold under the name Powerhouse.
The URL for the website is here:- http://www.ozvalveamps.org/repairs/fencer.htm
and readers may wish to peruse it. I have spent several hours going through it to decipher the circuit diagram that some generous soul has committed to paper – in this case the Internet.
For the interest and convenience of readers I have made up a circuit drawing which is reasonably easy to follow, but owing to my lack of experience in electronics I have a few questions that someone may be able to answer.
Working across the circuit from left to right:-
Should I add in a diode on the mains supply before the 10 Watt 330 Ohm resistor to avoid circuit damage by wrong polarity connection?
Diodes 1, 2 and 3, appear to be fast avalanche types – can anyone suggest a type and value number?
Resistors – All resistors shown in the circuit are one watt size irrespective of value.
AC capacitors 0.1 Ohm – would 400 Volt types be adequate?
SCR – I have two stud type SCR’s in my rainy day box, they are IR 50RIA100 – so I assume from the datasheet that one of them should cope with voltages up to 1,000 volts or thereabouts?
I have placed all circuits on one board with a noticeable gap between the power generation and the High Tension side.
Components off board are:- the SCR, 30uf 1,100V capacitor, the transformer, and the five neon bulbs, finally the three connections for Earth, Half Power and High Power.
The only components giving me a headache are the Voltage Dependent Resistors (VDR’s) which are specified at 900 Volts. I understand the working of the VDR’s after researching You Tube and assume they are to keep the voltage within the ‘legal’ limit of 10,000 Volts. However, after studying manufacturers’ literature the common types are rated at 910 and 950 Volts DC, so I assume the scribe’s reference to 900 Volts is a guide to ‘thereabouts.’ This URL is a good reference:- http://www.elecsound.com.cn/pdf/EV4_14mm_Zinc_Oxide_Varistor.pdf
One thing that puzzles me in the URL is the photograph showing what appear to be 14 pieces of a ‘cream and white’ things that protect the neon bulbs. That is seven pieces on Full Power, and another seven on Half Power. Can anyone explain what these are?
Finally, I have also studied Neon’s and found this URL useful:-http://www.shokaifareast.com/Products/Lamps/neon_selection_guide.htm
Can anyone recommend Neon voltages for this machine?
In some ways I am dreading the response to this article and expect to be told it’s a load of crock and forget making one!
If someone comes up with a contrary view that the machine is worthwhile making I shall be pleasantly surprised.
NOTE:- The layout is provisional. Through-the-hole-pads may be changed to suit the actual size required by components.
David in Hong Kong.