Here is my end of this week roll up.
In the above note I mentioned that I would devote time to collecting parts and other related work.
Most of the parts have been ordered through RS Components Hong Kong and will arrive in the middle of the week ending 27th April 2013.
I did discover one mistake with the triacs I ordered. I selected a type that had insulated tabs whereas in this design I need non insulated tabs. You will see later how I link the tabs with a bolt and copper spacers to a thick copper winding wire that lands on the board. In helps make up for insufficient contact area on the middle leg of the triacs.
Documentation has been useful and I now have an Excel file with multiple sheets showing different things. In one sheet I have drawn up a table showing wire diameters and the theoretical number of turns that can be done on the width of the ETD 49 bobbin. I have subsequently wound a bobbin with 0.8 mm wire and discovered that instead of the theoretical 20 turns of 2-in-hand, I can only achieve 18 turns in a single pass. The difference is of course due to enamel thickness on each wire plus a minor amount of slippage space due to the single pass and non over-lapping requirement.
Other documentation covers capacitor energy values in Coulombs and Joules. Another deals with the inescapable fact of dollar cost which does not bother me too much since this is an advance birthday present.
The coil winder metalwork alterations are more-or-less completed except for an arm to hit the counter each revolution. This should be in place by the weekend.
The PCB layout has been refined with minor cosmetic improvements but without change to the overall layout. Warning text has been added for obvious reasons.
A good size mounting board has been obtained and is yet to be equipped with stand off rubber feet.
The elusive 50uf 600 volt capacitor continues to be a problem and in the whole of Hong Kong I have found one shop that sells high voltage capacitors which are mostly for very expensive sound systems. The cost is in the Cleopatra’s dowry range. As an interim measure I still have a 50uf 450 volt capacitor which is easily purchased locally.
On the subject of AC working voltages and DC working voltages for capacitors, this URL touches on the subject
http://armyintelligence.tpub.com/IT0351A/IT0351A0015.htmOne other thing on large AC capacitors - the one I have is filled with vegetable oil. Does it make any difference if this is laid horizontally or vertical for operation?
On the subject of testing I have some 1 Ohm wire wound Powerohm resistors which I found in a local scrap yard. One is used as a dump load for Ghurd’s famous contribution to electronic science, and the others are waiting for rainy day use. The relevant website is here:-
http://www.powerohm.com/resistorLanding.aspx?partNumber=WR100Are three of these any use for testing the main coil output? If not, the local pigeons that roost in my mango tree and crap all over the backyard floor are in for a shock.
Back to documentation again. I have cut out most relevant thread entries and pasted them into an MS Word file. Thereafter I have spent a couple of hours amalgamating everything into a logical story based on a typical 12 VDC system. It covers quite a lot of what has been written above in note form.
I have also taken the time to study other commercial electric fence systems sold as well known brands in the US of A and Australia. I have created an Excel table for Model, Distance and Cost for Gallagher (USA) electric fence machines. The longer the distance the more expensive they become.
The PCB design now has six mounting holes – one in each corner and two roughly middle board.
The wiring links to the PCB have been “planned” to cater for two types of connection – solid and reliable soldered wire connections, and, push-on and pull-off spade type. I am wary of the push and pull spade type because enormous pressures can be applied to the circuit board if they are stubborn in each direction. The presence of two centre board mounting and locking down holes will go some way to alleviating this problem.
The fence line testing instrument sold in Australia seems like a nice bit of kit and someone has obviously put a lot of thought into its design.
I note in one comment on this topic Oztules mentioned the use of lower value capacitors for shorter distances. Is it possible to make up any form of table relating one to the other? Also, apart from different capacitor values, what would be the knock on effect in changes to the circuit generally?
So it has not been an unproductive week and the next one should see a significant move ahead.
David in HK