Electric Fence Zapper

[oztules]

"For those interested Machine A takes exactly 31 pulses to blast the 3 test resistors (47 Ohm 2 Watt) so that handsome size sparks fly out of them."

Looks like I have created a monster   ... next stop for you is a tesla coil.... get down and make some real sparks. 

It is not like those ignition coil things, these things can pull some serious power... albeit for micro seconds only.

Interestingly, I wound a etd49 coil the other day from microwave secondary wire... and it didn't oscillate, checked resistance, no apparent short... wound again... same thing..... in fact got curious, and rewound 6 times with  wire from that secondary.......each time..... nada ......nothing.

I have no explanation.... none.. Rewound with wire from a different microwave transformer... and worked straight away.... tore that off and wound again from the same different transformer, and worked again...... then tore that off and wound from the first transformer..... no go again.

I have no explanation as to why there is a difference between the wires in these microwave trannies. This is the first one to defy the rules in such a decisive manner. When you can load up 500 turns, and not get a peep out of the oscillator, but the DC resistance is the same as wire that works..... well gobsmacked......Zubbly was right... it is magic stuff this electricity.

So I am confounded yet again.



.....................oztules

[David HK]

Hello Oztules,

Nice to see your'e alive and kicking. How about a dry joint problem for the above scenario? Alternatively connect it to a safe 240/120 volt circuit and see what happens?

Machine B now has its triacs and a re-mounted capacitor. I hope to finish the ETD coil some time this week - at the moment I am busy helping my daughter with her last diploma essay which is due in today (Monday).

I have some more interesting PCB layouts of the circuit which cover an 8 and 12 Triac version. This is achieved by playing around very carefully with the layout of components on the PCB. Both versions provide for a clip-on type heat sink for the TIP 31.

My local expatriate acquaintances are intrigued with the machine and some have said there is a market for this type of thing in Malaysia. They are all awaiting to see what Machine B produces.

My next door neighbour is local Chinese and he has told me that opportunist burglary is rife all over China and such an item would be useful to a lot of people. I have seen electric fences powered by mains voltage around some residences in Shanghai so it makes you think.

Very wet, humid and warm/hot here in HK at the moment.

The weekend should see new photographs and interesting reading.

Dave

[madlabs]

Howdy,

So I got distracted by a water system controller I built, you can see it in another thread. However, just yesterday I saw the bear on my driveway, so it's time to get back to to this project.

Wow, David and Oz, lots to catch up on in this thread. A quick question though David, any chances of buying a board from ya? Tons to do and even though I'd enjoy it if I can short cut this project I would.

Really nice work you two!

Jonathan

[David HK]

Hello Madlabs,

I wondered what happened to you. The answer to your question is yes.

Could you please wait a few days before going further because I am about to complete Machine B and hope to put up photographs and details this weekend. I am interested in comparing the performance of both machines since they differ slightly in terms of coil turns, wire thickness and main transformer bobbins.

I managed to finish the secondary winding of the Machine B ETD 49 coil yesterday (Thursday) so I should be able to complete its final assembly today Friday. The only hiccup is that today is the last day for the last essay for my daughters year long Diploma course so its a case of me helping her and everything else has second priority.

Nevertheless, there will be some interesting photographs and text to look at in the next few days.

David in HK

[madlabs]

Davis, no problem on the wait. Take your time. I have a few days of installation and programming of my current project and then I have to string wire on the fence. But I am very pleased that I can buy a board from you! That is going to shave some time off!

Jonathan

[David HK]

Oztules,

I need some expert advice.

Both machines have ceased working. Here is the story.

I completed the winding of the ETC coil for Machine B and fitted it in. I set up the machine for its first test and on the output side I place the usual 3 pieces of 47 Ohm 2 Watt resistors in series. I turned on the power supply and instantly all three resistors cracked out for three pulses and then stopped.

I changed the board into Machine A since I knew that coil had worked faultlessly previously. Nothing happened - no sparks output.

I put the PCB back into the Machine B and applied power and as usual one can hear and see on an AVO meter the capacitor rise to ~ 600 and then click as it discharges and repeats the cycle again.

According to one of your earlier notes the suspect could be the secondary on the main transformer so I have unwound it and gone over it carefully with a magnifying glass and cannot see any evidence of shorting or wire break.

My suspicion therefore lies on the Diac and Triacs. The Diac I am using is a small blue thing (about the size of an 1N4148 diode) the number is Diac  32V, DO-35 from RS components. The triacs are Triac,TO220AB,BTB12-600B.

Whilst generally examining the PCB and applying power I discovered that if I placed just one resistor across the output it would fire and the usual flash and crack of blue erupted. This suggest the Diac is working but, perhaps, not all the triacs. At the same time there is not enough punch to blast three resistors in series.

What number Diac are you using?

Any thoughts??

Dave


 

[David HK]

Sunday lunch time.

Both machines working. The output from the mains transformer is only sufficient to blow one 47 Ohm 2 Watt resistor. Three resistors in series remain intact.

Chief suspect - the triacs.  If it is these items are they failing then why?

How can seven triacs be switched simultaneously? The answer is expected to be - they can't. How about one big mother triac BTA40-600B  Triac (600V, 40A). OPicture below:-

[David HK]

Will buy a very large triac as mentioned above and test it sometime Monday.

Dave

[oztules]

Not an expert, but this is what occurs to me at this point.
The 7 triacs is fine, many years of testing has shown them to be a good system. They cannot all switch at the exact time, but so close to it, I have not been able to see any spread on the scope to show that this is the cas or not..

If they fail. it is usually the one closest to the output track,..... rare, but that is the only one I have had fail on two ( of many) boards over a number of years. The triac you picture will be destroyed in a few pulses..... tried them. I even used 150A 1500v scr and triacs, but the seven parallel seemed more robust.

Any diac will do the same job really,  and if a traic fails, it will fail short circuit, and the oscillator will just have a low freq squeal, and not rise, as all the power will direct into the transformer, not the cap.

So, what could be wrong.... check the primary windings connection/s............... are both bifilar windings connected, or has one been lost. This would account for losing half the output. It cannot be the triacs as I see it. They either  run, or they are short....no  in betweens.... ditto for the diac... never seen one blown so far.

Try another cap, in case there is a loss of capacitance..... else try the other transformer. The device is so simple, I can't find a complicated answer for you.

Big storage...... going to big low impedance tranny......... makes big spark.... simple really, so it must be either storage, or the transducer. The triacs will dump all the energy they can, only the small toroid and the two caps on the transformer primary can make any difference. The fact that it was viscous for the first few sparks, means the toroid seems to be not too restrictive...... so really means cap and tranny are the only ones left..... just can't find it in me to blame the triacs I'm afraid.... been wrong before too...




...................oztules

[David HK]

Oztules.

Thanks for the note - all read with great interest.

I took the Machine A ETD coil apart this morning to examine it - seems okay, and then re wound it for 500 turns. I also put in some thin magnet paper between the primary and secondary as there is adequate room.

Try another capacitor - will do, everything is worth a second test at the moment.

One 47 Ohm output test resistor on its own still produces a heck of a large spark and flash to the point where the mounting board seems to recoil.

How about the weather? Temperature here is 32 C and the humidity is at 65%.

I wonder if the spade type connectors are insufficiently contacting between male and female?

When you test with 47 Ohm resistors how many in series do you use?

Dave

[oztules]

I use 1, 2, or 3 in series for fun... or a 470r.   500 ohms impedance is the a fairly normal standard for fence tests.... medium load from grass build up etc.

Without a fence current/voltage tester it is hard to gauge what is actually happening. The resistors arc, and carbon up. They can give spectacular pyrotechnics, or just zap, it depends on how the carbon deposits and breaks down.

A smallish spark, can also be due to a low impedance high current  path(>40A) and so pull down the voltage, or big sparks with not so low impedance, and so current may only be 13 or 20 amps, and voltage stays high (>6000-8000v)... so it is hard to quantify by just the looks. The power may be similar, although the lower the impedance of the spark track, the higher the reactances in the tranny, and power output will suffer more with this combination.

 The more iron in the tranny, the better... even though it is saturated, but  the resistor sparks will vary ... sometimes rapidly as the breakdown path changes. After a while, they seem to settle down in a particular pattern.... however the physics arrives at it, will depend on more variables than I can ponder.

......oztules

[David HK]

Another hour head scratching and thinking.

Both machines seem to have insufficient power stored to zap three in-series resistors. When I have finished with a machine I always short down the capacitor with a test lead and resistor to ground for safety. Previously when the Machine A was working fine I could always hear the small crack and see a small flash as as the resistor touched the capacitor connector. Now when I short out I don't see or hear these.

Your comment "Any diac will do the same job really,  and if a triac fails, it will fail short circuit, and the oscillator will just have a low freq squeal, and not rise, as all the power go will direct into the transformer, not the cap". 

Machine B oscillator has a healthy growl to it whilst Machine A is quiet - almost silent just a slight whine - apart from a tick every second or so. 

Enough for Sunday!

Dave

[oztules]

"I could always hear the small crack and see a small flash as as the resistor touched the capacitor connector. Now when I short out I don't see or hear these. "
This is a function of where in the cycle you stop the machine.

At first you just stop it well after the last spark... and your a bit unused to the rate......so the caps are near full, and go splat.....once you get used to the rhythm, I suspect you now naturally turn it off just after the last spark, and at this point, there is no charge in the cap to discharge...... simple to check, measure the cap voltage before you discharge with your lead. Now turn it off just before you expect a spark, now you will see 500-600v, and it will have plenty of yelp.

In short, I think it is a familiarity breeds contempt thing, not electrical.

"Machine B oscillator has a healthy growl to it whilst Machine A is quiet - almost silent just a slight whine - apart from a tick every second or so.  "
This is purely a function of how the ferrite mates to the other ferrite..... dribble a spot of super glue into the ferrite interface, and it will all go silent. It is the physical interface of the ferrites that make the noise, and a very slight movement of the ferrites in relation to the former... which is loose around the ferrite.... but a drop of super glue will silence the both of them.

You may not have a problem to solve yet, it may be as previously stated, that it is working fine, but you can't measure it. I have thought that some of the ones I made were weak just as you have.... until I measured the current and the voltage, and changed my mind...... I may also have mentioned.... every one of mine were different in behavior,...... no two the same.... but all in the same ball park.



............oztules

[David HK]

Oztules,

After thinking about it all night .............

Both machines work, both have the same performance on one resistor. Observation - seems not to have enough power energy to zap 3 series resistors. Conclusion - am putting 600 volts into a 450 v AC rated capacitor. There may be some internal damage to the capacitors, it is after all these things that hold the energy.

Will buy a new pair later this morning.

Regarding the noise from the oscillator. As an experiment I purchased different ferrites. In Machine A they are 525 uH - the quiet machine. In Machine B they are 3,800 uH (noisy machine) , this must account for something.

Will post in a few hours.

Dave

[oztules]

........ 450vac is 630vdc... rectified and filtered.... so caps are fine voltage wise...... try 2 in parallel, this should increase the current, and double the pulse time
All my caps are 450vac, and they last for years and years.

These caps have a physical isolating layer (plastic/paper etc)... I suspect there is a fair margin built into the rating as well.

It maybe that your power transformers are over wound for the core size, but i suspect that they are working pretty well. If you can get a measurement tool for the job, you will get a better idea.


................oztules