Author Topic: Powerhouse electric fence machine  (Read 3466 times)

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Offline David HK

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Powerhouse electric fence machine
« on: February 06, 2014, 04:40:14 AM »
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.



Offline rossw

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Re: Powerhouse electric fence machine
« Reply #1 on: February 06, 2014, 05:46:36 PM »

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?

No. The diodes and caps after it form a voltage-multiplier, which requires AC. A diode as you suggest would stop it working entirely.

Quote
Diodes 1, 2 and 3, appear to be fast avalanche types – can anyone suggest a type and value number?

I doubt they need to be anything particularly special save for the PIV.
Given the output voltage, I'd use at LEAST thousand volt diodes. They likely don't need much more than 1A, but if you can find say 3A/1600V I'd use them.

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Resistors – All resistors shown in the circuit are one watt size irrespective of value.

Likely what was on hand. You'd probably need to calculate out the values.. Are the "8 x 5M6" connected in parallel or series? If they're in series, they will be dissipating almost nothing - just don't go too small or you'll risk getting flashover.

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AC capacitors 0.1 Ohm – would 400 Volt types be adequate?

0.1uF I guess you mean! 400V would be only just barely adequate. Since they're basically straight across the mains, I would probably specify 630V (240V AC has a peak value of 340V, which doesn't leave you a lot of headroom)


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I have placed all circuits on one board with a noticeable gap between the power generation and the High Tension side.

A common practice for this is to put a slot on the board and/or a "guard trace". (The guard is grounded)


Quote
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?

I believe the things you are describing are in fact the VDRs. 7 in parallel on the "low side", 7 in parallel on the "high side", and thus forming a divider to provide the "middle" (lower output).

The "protection" for the neons is in fact the 4 x 100K 1W resistors.


Offline David HK

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Re: Powerhouse electric fence machine
« Reply #2 on: February 06, 2014, 06:05:16 PM »
Ross,

Thank you for your useful notes which I will follow up.

Before posting on the forum I contacted the moderators and 'Cory' replied with the recommendation that this post should be in the Off Grid Living section, so I have followed that advice.

However, the other electric fence thread is in the Solar (heating electric) section and has achieved in excess of 9,000 hits, so its obviously a popular subject. Having written that  do you think this new thread should remain where it is, or, put it in the Solar (heating electric) section so that it sits alongside the other similar thread?

I have also drawn up the circuit schematic and will post that in due course.

Dave

Offline rossw

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Re: Powerhouse electric fence machine
« Reply #3 on: February 06, 2014, 06:17:38 PM »
However, the other electric fence thread is in the Solar (heating electric) section and has achieved in excess of 9,000 hits, so its obviously a popular subject. Having written that  do you think this new thread should remain where it is, or, put it in the Solar (heating electric) section so that it sits alongside the other similar thread?

I expect the hits on the other thread have come through people finding it via search engines, and as such the content should be indexed and found pretty much regardless of which section you put it (as long as it's not a members-only area of course).

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I have also drawn up the circuit schematic and will post that in due course.

Ahh, excellent. I was looking for it. Your comments said "circuit" but all I could find was "PCB layout".

Offline David HK

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Re: Powerhouse electric fence machine
« Reply #4 on: February 06, 2014, 07:18:11 PM »
Here is the schematic which I have checked against the hand drawn circuits. I have no way of knowing if the hand drawn circuits contains any errors, so if the experts can check - that would be helpful.

The PCB and circuit schematic are both drawn using Express PCB and Express Schematic software in case anyone needs to know.

Missing values of components will be entered later and also printed as a bill of materials.

Dave

Offline David HK

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Re: Powerhouse electric fence machine
« Reply #5 on: February 20, 2014, 10:04:44 PM »
Can anybody offer a guess if the 900 Volt rating for the Varistors mentioned in the hand written notes is a 'maximum' or 'minimum' value.

This web site offers a selection that may fit the purpose - 

http://enecomponents.com/product3.php?id=813

Dave