Electric Fence Zapper

[Wolvenar]

Awesome David!!!
Looking forward to the details, I might have to build one, if I ever find time.

Thanks guys for pursuing this and sharing with us here.

[oztules]

Nice to see it done. I hope you don't sample the output ......... although in some macabre way...... it is always funny watching someone else touch the output.

? there is a core in that power transformer ... isn't there?  It will work  without, but it will stress the triacs unnecessarily if there is no core at all. The resistance of the primary is very low, and a bit of inductance would be a good thing.... and the current transfer will be better.

Well done, and nice to see my crazy stuff work for someone else.



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

[David HK]

Yes, there is a core inside the main transformer. The original laminates were 'E' type so I cut out the centre section of the E and stuffed it in.

And like all things in life it has now stopped working because, I believe, of a short in the main transformer secondary. I took the thing 'down town' and let one of the local old Chinese boys do the secondary winding and he was insistent on using masking tape as the insulator between layers.  I hadn't got the heart to stop him as he was doing me a cheap favour. I think this is the reason for the secondary failure.

My plan is to unwind the the secondary and rewind it much more carefully with proper transformer (magnet) paper between layers and also avoid contact (lying against perhaps is a better description ) with the start end of the coil.

Nevertheless, this thing really whacks out some power and the three 47 Ohm resistors in series at the output end were not at all happy with serious blue arcing coming out of the sides. Having seen this I have no intention of touching the the wire for a quick look see.

Will report back next week when I have sorted out the main transformer.

Oztules, while your around, what does the variable resistor do? I have twiddled it and see little effect.

So far so good. learning as I go, as usual.

Dave in Hong Kong

[oztules]

The variable resistor changes the step off voltage, but as I mentioned previously somewhere, I use too low a value to make much difference, it is really for fine tune at 250k, if you increase it to 1m or more, you will have more control, but the timing will change markedly too, and you may be inclined to not bother replacing a fixed resistor, and let it pulse too quickly...... that, and I had oodles of 250k things around the place at the time.

Best to get the capacitance you want, then work backwards to find the right values to give you the step off, and timing right, and just a bit of twiddle with the pot. The divider resistors and transistor selection of the oscillator will change the charging power, and the divider and pot can fine tune the step off and timing.

It makes short work of my 47R 2watt resistors, they survive for maybe half a dozen pulses at most before rupturing and spitting blue fame along their length.... and spit off a bit of enamel to boot. too... careful with the eyes, sometimes it is quite good at ejecting the enamel off the coating of the resistors.

It is a bit scary too.

I suspect the secondary is toast. If you put the two output wires within a few millimeters of each other, they will arc straight through the enamel of the wire... makes for big sparks as the energy transforms the lacquer into plasma.

If you can hear the oscillator wind up, and hear the grunt of the transformer, and it cycles again, you can be sure the secondary is the number one suspect.....number two is your flywheel diodes are short.
If the oscillator just starts to wind then holds a low frequency, it's the triacs . If it goes halfway up the pitch scale, then the one of the rectifier diodes are shot.

Measure the cap voltage is another way, it it rises to 450v-600v, then all is well with the charging side, and it has to be the transformer or or flywheel diodes. If your using 6a04 diodes or better then the transformer is number one suspect


EDIT: just looked at your picture...... flywheel diodes look very small.... what are they.... look more like 4008 etc.... in which case they are probably shot to hell. They don't have the surge capacity to hold this thing down.

edit2: Yes just looked at your schematic, and in small print I see 4007 diodes..... they will not survive long at all. Fix this before you tangle with the transformer. Almost guaranteed the diodes are toast and short.... my old eyes missed that before.... sorry.... look at this:






.... see the big fat diodes there.

Stay wary my friend.


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

[David HK]

Your right about the diodes not lasting, I have blown two already (1N4007 types).

Will see what I can do to replace the lot. 


Thanks also for your last note on the things to look and listen for when the things blows a gasket.

I have some ideas to make a significant improvement to the insulation of the main transformer secondary and will attempt that in the next few days.



Dave

[David HK]

Oztules,

Thank you for the last set of notes.

I have changed the diodes – big mothers aren’t they!

The main transformer was shorted in the secondary coil, so I unwound it back to the start. I then rewound it very carefully and each winding layer is now separated by a piece of good quality transformer paper. After reassembly, I connected it up again and it works.

I suspect the thickness of the transformer paper has changed the performance a little. Previously, with the ultra thin masking tape separator between the winding layers, the sparking over the three 47 Ohm 2 Watt resistors in series was spectacularly vicious and frightening. With the latest wind using modestly thick transformer paper the sparks just make it out of the surface of the resistors. Nevertheless, the power being produced must be substantial just to make this happen.

For your information I am keeping the circuit schematic up-to-date and have revised it to include the latest information on the diodes and the triacs (non insulated tab type).

Secondly, the PCB layout has been updated to take into account the larger size of diodes. I will post the final circuit schematic and PCB layout in the next few weeks after all the experimental work has been completed.

I now have one more PCB and will build another identical machine in the next week or so.

Dave

[oztules]

It should run without breakdown now.

I have yet to see a transformer failure... so your a first.

 I have seen diodes and  triacs fail in the early days, but not any more now the teething problems have been teased out. Some have been  running for four years now.

The sparks... it could be your man wound tighter than you, or the extra space is giving a looser coupling. You can remedy this by using only half the primary as the first winding, and the other half the last winding. Then the secondary is trapped between the primary layers, making the coupling very tight.

The other thing you may find, is the humid weather over there has gotten into the resistor body in the intervening period since last use/terror.... perhaps because of the ash/carbon  on the surface, and that if you use three new ones, they may well behave like the originals for a bit. This behavior changes radically from scary to fairly benign, depending how the resistor is being destroyed.

You may find the dynamic loading has changed markedly, rather than losing as much power as you surmise at this stage. If you had a meter that did current and voltage, it would tell you all.



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

[David HK]

For reference this Sunday morning (5th May 2013)

Volts                  13.7  (From RE system)

Current draw     0.34A

Watts                4.65


Dave

[David HK]

Hello Oztules,

Another week of updating and learning.

The first PCB now has five LT6A4 diodes – photograph somewhere below. I expect its overkill, but the machine works fine with them. I left D1 as a normal 1N4007.

I did a continuity check on the toroid and discovered that there is a short between the ferrite coil former and the wire. I have subsequently wrapped two new ferrite rings with insulating tape and then carefully wound 1mm diameter wire onto them. A second check reveals no continuity problem so I have given both of them two dips in varnish and will replace the one on the first PCB when drying is complete.

I am now making up a second PCB which will avoid many of the shortcomings and pitfalls made on my first attempt. There are two interesting comments to make with this second unit.

Firstly, I have wound on 15 turns of two-in-hand 1 mm diameter wire onto the ETD 49 bobbin. That’s all it could take in a single pass. I have since covered this with ‘thin’ magnet wire paper. The Start and Finish ends are right this time so it should work when all is complete.

On the first ETD 40 coil I used 0.8 mm diameter wire and obtained 18 turns of two-in-hand. I then ‘semi-bundled’ the secondary directly on top of the primary (no paper separator) and laboriously wound on the wire turn by turn and achieved 604 turns with room for more ~ 20 to 30.

On this second coil I intend to adopt the same procedure and see what can be achieved in the way of turns between 400 and 600.

I have been to the local scrap yard and discovered piles of transformers that range from small two-hands-to-pick-up, to slightly bigger units that need two or three men.

Initially I thought that the second transformer I purchased was the same as the first, but after dismantling it, it is about 33% bigger although the width of the bobbin is the same. A photograph appears below. My question about this is:-

If I wind the same 11 turns of 1.8mm wire for the primary and 400 turns of 1mm for the secondary I will end up with a larger copper mass. What does this do to the voltage, and/or the power output?

Other improvements to the PCB design are very cosmetic and not easily seen by the naked eye, but are:-

Two adjustments to component spacing, and new positions for the larger LT6A4 diodes and associated through holes.

I have also made up an Option B PCB layout which puts the TIP 31 on the left hand side of the board and incorporates through holes for a clip on type heat sink for it. I don’t actually know if this is really necessary, but there is room on the PCB to accommodate the feature if required.

The board design ‘as is’ has room to accommodate one or two more triacs. Is there any merit in adding more?

This is a really interesting project.


Dave

[David HK]

My apologies, I failed to include this photograph in the above set.




David HK

[oztules]

Ok, more triacs the better the current capability.

More turns on the power transformer does not mean better performance. The back MMF of the secondary will work against you.
Probably 200-250 turns is probably even a bit too much..... You may do better with a bit less. Remember the amps in the secondary are very very high >40 amps at full loads........ and lots of turns means lots of amp turns.... big back MMF may cruel your expected gains. Open circuit, it will be impressive, but under load may  drop well below a 200 turns version.... experiment and see where the gains drop off. Every core is different with my stuff, as my microwave trannies seem to be all different.

The core will saturate whatever the core I suspect, so it is something we just have to live with. Bigger is better.... but at what weight?

The whole thing is a big compromise.... but it does work, and different combinations of ratios will yield different results... not all expected either. It is very interesting really, and tells you a lot about magnetics and wave forms if you don't do the serious calculations ( which are out of my comfort zone in reality). Good learning tool really.

More turns on the etd49 really only yields faster rise times for the cap in most cases, more turns on the power transformer may not give you the load capabilities you may expect..... possibly far from it..... I suspect Rossw could tell us both a lot more about this if the truth be known.




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

[David HK]

Oztules,

Thanks for the note it was very interesting reading. You are right about compromises. Today I spent a minute or so working out voltages to the ETC 49 primary, the number of primary turns, and the number of turns on the secondary to see what voltages would be apparent (mathematically).

In Excel once the formulas are set up its easy to change parameters. I was curious to see what would happen in a 24 volt application and started off working out the voltage divider changes that would be needed to avoid blowing the TIP 31.

After putting the 24 volts into the ETD coil mathematics and projecting the same onto the main coil a lot of winding turn changes are needed to keep the theoretical output below 10,000 volts. So yes, its an interesting machine that one could spend months or perhaps years tinkering with and recording the data obtained.

Found my biggest capacitor in Hong Kong today - 70uf  475 volts AC.

I shall carry on with the second machine and keep folks posted as I go.

Judging by the "hits counter" this thread seems to be of interest to a great many readers so its nice to see a useful idea for a machine slowly being exposed in text and photographic form.

Keep in touch.

Dave

[oztules]

By the time we finish this, this will be the most scrutinized circuit in the universe.

"In Excel once the formulas are set up its easy to change parameters. I was curious to see what would happen in a 24 volt application and started off working out the voltage divider changes that would be needed to avoid blowing the TIP 31. "

As a very rough rule, double the two divider resistances, and it will probably work with all other things exactly the same.
Remember, your power transformer will not care what you run the thing on, it will still get fed 600v only... the diac and diac divider network sees to that, so the power tranny does not change in any way.

The ETD49 can stay the same if you want, just change the divider resistances and it will still work.... although doubling the winding of the primary/halving the secondary will help with impedance matching some.

Luck with transformer calculations.... the oscillator is frequency varied, pulse width varied, and amplitude varied in each cycle.... it is roughly a square wave that changes the frequency from low to high as the load changes, the pulse width changes from wide to thin as the voltage rises, and the amplitude of the wave changes from low to high as the voltage rises in the cap..... how to figure that is beyond me... I use the suck it and see method The universe is a complex place, and I'm not bright enough to fathom it all at once. So 24v operation will require very few changes to work the same.... watch the temp on the transistor as you fiddle the resistances on the divider.

I am wary of spread sheet and modeling in general if ALL the parameters are not fixed in cement. The moment we make an average value, or assumption because we can't give a definite value to something, or there are things at work we don't understand... and so we use some constant to make it simpler... the more useless modeling is... the biggest problem is that it looks so good, we are inclined to believe in them..... at our peril. See economic modeling, and environmental modeling.... never even come close to the truth, and never will as we don't understand most of the forces at work in both cases.... so they allocate a mean value and move on...

The output transformer defies models that normal transformers would use, as it relies on the impedance of the input winding, not the turns to dictate the pulse width, which in turn controls the rate of change of the field... which controls the EMF generated in the secondary. Thats why 200 turns will beat 400 turns on the secondary with any decent load. The currents are very high, and the back MMF is very pronounced, and the whole lot saturated... what a mess to calculate...best of luck with that.

"Found my biggest capacitor in Hong Kong today - 70uf  475 volts AC."

If your after sheer grunt in the output, you can parallel caps, or increase the voltage and series parallel a few caps. The  energy stored has a V^2 component... so doubling the capacitance is double the energy, doubling the voltage is quadrupling the energy. The triacs may need upgrading with more capacitance, and really will need upgrading if doubling the voltage.


You can play with it endlessly, but be careful of the business end, it packs quite a wallop.



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

[David HK]

Your up early today.

I am just about ready to start house cleaning and thereafter its my BBQ/Roasting spit cleaning ready for a pork loin roast on Friday (public holiday here). The fare will be pork loin roast with the skin on (crackling), roast potatoes, mashed potatoes, carrots, peas, perhaps cauliflower, gravy and apple sauce. All washed down with beer, wine and whatever. Wish you could come.

My BBQ/roasting spit is all stainless steel and has slowly been built up over 15 years. This includes the BBQ table, forks, tongs, trestle, auxiliary table, and countless other small things that make it a nice talking point when guests arrive. The fuel is charcoal which is common in China and Hong Kong. I may put up a photo next Friday or Saturday.

Thank you for the additional notes, I wish there was a set of machines easily available to observe all the wave forms, voltages etc that you mention. I was thinking of writing a begging letter to China Light & Power to see if the company engineers might have a curiosity interest and help with measurements.

Anyway the next task is to finish machine No. 2.

Dave

[David HK]

Update for Saturday 25th May 2013.

Machine B is coming along as the photograph below illustrates. There are minor differences with Machine A and cover:-

Coil wire thickness and the number of turns, a larger capacitor, and a home made main transformer coil bobbin.  For this I have resorted to 9 turns of two-in-hand 1.6 mm primary wire, whilst the secondary is re-used 1 mm dia wire (ex transformer) and exactly 224 turns. This allows the In and OUT wires to be the furthest apart on the bobbin.

Remaining work is to wind the secondary on the ETD 49 bobbin and populate the Triacs on the board with spacers and bolt on the Tabs.

This machine should have a greater output than machine A.

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.

I am toying with the idea  of replacing the main transformer coil on Machine A with another home made bobbin which is only wide enough to accommodate 9 turns of two-in-hand 1.8 or 1.6 mm primaries. The existing primary is 11 turns.

Eventually I will document the exact differences between both machines.



David HK