Winding the Secondary Coil for the second time.

The new secondary coil form has been sat in my homemade coil winder for long enough. It's time to start winding.

In my last post I gave the new stats for the replacement coil. The only change I have made is to start the windings 4.5cm from the base of the coil rather than 4.0cm. This change is just to allow a little extra room at the base of the coil to accomodate the copper plate that will act as the lower electrical connection. This will mean with the same number of turns (1050) the windings will finish 0.5cm higher, 8.3cm from the top of the coil.
 Before starting the winding I thoroughly cleaned the outside of the coil with meths to remove all traces of grease. I ran a line of masking tape around the coil with the top edge of the tape exactly 4.5cm from the base of the form. This would ensure that the windings would start exactly level with the base of the form. I measured 67.2cm (total height of windings required) from the top edge of the tape and marked this point on the form with a small pen dot. I would coil tightly up to this point then loose coil to the top of the form.
Well almost ready to start. Not quite. This time there's no help available..... and believe me, its better to have an extra pair of hands when winding a coil especially if you are relying on human resources to tension the feed wire and direct the winding wire onto the coil. Manual winding requires both hands, one to feed the wire (left in my case) and the other hand to push the coils together either with a non scratch implement or the back of your finger nail. This means you have no free hands if you need to stop (or start) the winding motor. My winding motor is powered by a variable power supply on the bench the winding jig, not exactly "to hand". I would need some way to switch it on/off remotely.
Bingo. Idea.

I plugged the power supply into one off those remote control mains switches. This one is a cheap as chips version from Maplin similar to the one linked.

Here's the little controller. I can either have it close to hand or even put it on the floor and press the off button with a press of a toe.

The winding wire end was clamped under the head of one of the white plastic bolts that holds the base coil end in place. You need to have a plan in place to clamp the wire end tight when you finish the windings, I decided to clamp it with the same method as the start, using one of the bolts that holds the top coil end in place.

Time to turn.

Well it took about an hour and went pretty well. Stopped just once when I realised I had left the door open. Two kittens and turning a tesla secondary coil are not compatible. Here's a quick vid of the finished coil. I have put on a couple of coats of insulating varnish. Still needs another couple of coats.

I am really happy with the finish. The varnish has a better finish than on my first coil. Next up is a few more coats and then fitting the copper plate electrical connection at the base of the coil.

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Making the Second Tesla Secondary Coil

Well here we go with the build of the replacement secondary coil. Rather than jump straight in and build an identical secondary with thicker gauge wire and hence less turns I decided to do a little more homework on secondary coil designs. One thing had always concerned me with the design of the first secondary I built. This was the termination of the ends of the coil inside the secondary form. The top and bottom copper tails pass through small holes drilled in the wall of the secondary form and make electrical connection through the top and bottom end caps.

The pic above shows the top electrical connection on the old secondary coil. You can see the copper tail clamped into the lug underneath the perspex cap. A very neat set-up but nearly every knowledgeable Tesla site I have seen strongly advises against this. The only one who seems to prefer this method is Alan at teslastuff.com who has had great success with this design. My final decision on the design of the new coil was strongly influenced by a page at www.capturedlightning.org. Stefan really seems to know his stuff when it comes to design and build of secondary coils so I decided to proceed using many of his recommendations.
The overall length and diameter of the new coil form was the same and again it would be made from 150mm diameter 3mm thick clear acrylic tubing with top and bottom caps in 15mm thick clear acrylic. The new secondary will mount to the existing 8 mount holes in the tesla base unit so the secondary base cap is an exact copy of the original. If you want to see the original post showing construction of this you can find it here.

The pic above shows the new secondary coil form with the top and bottom caps in place.

Here is a close-up of the bottom cap of the secondary showing the 8 nylon bolts that pass through mounting holes in the primary coil support disc. The central hole is 10mm in dameter and will only be used to thread the whole form onto my winding jig. After winding the hole will be permanently sealed by a turned acrylic peg turned (very successfully) on my lathe.

The peg is a really close fit and the flat area will provide a good surface to be bonded with Tensol 12.

Above you can see a trail fit of the peg. Obviously it will be fitted on top of the base cap. The coil form is now ready to wound on the winding jig. However, not tonight, time for a quick spin in the new RCZ. Spot the new wheels.

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Tesla Coil Finished!!

Finished off my homebuilt Tesla coil today. This involved finishing the primary coil sliding clamp. It required a way to clamp it to the primary coil and the fitting of an copper lug to make the electrical connection to the MMC bank.

The above pic shows the two parts of the clamp before adding a clamping mechanism. I wanted to keep this mechanism as simple as possible as I may redesign the whole clamp depending on the eventual tap point on the primary coil. I removed a 15mm length from the right hand end of the top piece and silver soldered it to the right hand end of the lower section. I then drilled a horizontal 2.5mm hole lengthways down the centre of the block which was tapped out to take an M3 allen bolt.

This produced a simple clamping method which still permits the two parts to separate to allow for repositioning. Adding a copper lug for the electrical connection just meant adding another threaded hole on the underside of the clamp.

I cut a 1.2m length of GTO wire to complete the electrical connection from the MMC bank to the clamp. 1.2m was needed so the clamp could reach any point around the primary coil. Each end of the GTO wire was coated in solder before fitting into the copper lugs. That's it Tesla coil finished, well almost. Have ordered a 33k ohm 2W resistor that I will fit across the terminals of the 40uF capacitor in the SSG circuit and bleed the stored charge away after each run of the Tesla coil, a simple safety feature.

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Synchronous Spark Gap Module Part 1

Not done much on the Tesla for a few weeks due to the summer hols. First task is the synchronous spark gap.  The base is a piece of 8mm thick clear acrylic measuring 320mm by 160mm. I wrapped it in masking tape again to protect it when drilling and also so you can mark it up for drilling.

The motor was mounted to a small block of 15mm perspex by 2 8-32 bolts kindly supplied by Alan from Teslastuff. In turn this block was mounted to the base and supported by another block of 15mm perspex directly behind it.

Here you can see the motor attached to the perspex mounting block. The disc on the mandrel is a piece of 5mm black acrylic perspex and holds the 4 1/4" diameter tungsten rods which are held in situ with collars on the front and rear.

The tungsten rods were sourced from Teslastuff.com and the collars came from a power tool dealer on ebay, think they are something to do with router tooling.

The collars have 2 small grub screws at 90 degrees to each other and clamp the rods up very securely.

Looks a bit like ORAC

I have decided to enclose the whole assembly with clear 10mm perspex. Maybe this may help prevent strikes but mainly I just think it will look good. I will have to sort out some ventilation, perhaps a fan mounted in one of the perspex walls, not sure yet. For those of you who remember Blakes 7, I can't help thinking about ORAC as I envisage the finished enclosure.

I am using 10mm square rod as seams on the inside of the side walls which allows me to bolt the box together rather than glueing.

Our glass dinning table made a great flat surface to align the side panels.

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Terry Filter comes together

Covered the 200mm x 320mm x 5mm black acrylic Terry Filter base with a coating of masking tape which will protect against scratching while drilling and allows me to mark up all the holes. After a trial placing of all the Terry Filter components the board was marked for drilling.



The main pcb and the 2 long resistors will be mounted on 1" high ceramic stand offs which require 4mm holes. The completed Terry Filter module will also be mounted on 1" stand offs, 6 in total. With the board marked up I watched the pretty uneventful start of the British grandprix then made my way out to the garage to drill out the holes.



The board was placed on a flat piece of ply offcut for drilling which prevents the drill bit from damaging the back of the acrylic as it emerges.



When drilling lots of varying size holes I find it useful to mark hole diameters on the work. After drilling the masking tape was removed to reveal a pristine piece of black acrylic with clean tidy mounting holes hopefully in the right places.



First trial fit of the components goes well, all holes line up nicely.



Still waiting for some brass bolts and copper lugs to enable the final assembly.



The safety gap ceramic posts are held in place by 65mm nylon bolts that screw through the base and up into threads in the brass balls. I may change to using metal bolts as the nylon bolts flex and do not hold the safety gap assembly as firm as I would like.



Next job is to make the electrical connectors between the pcb, resistors and terminal posts.



Think it turned out pretty good.

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Parts for Secondary Coil

Just about to start construction of the secondary coil. First bits are here, a 1 metre length of 110mm weld pipe and a 1kg roll of 0.4mm class H winding wire. I picked up the pipe from a koi carp dealer and the wire from Brocott who also have an ebay store if you prefer to buy on ebay.



Decided to go for black piping as the copper winding wire stands out really well against the black.



The nasty looking bottle is anti tracking varnish which I will use to seal the windings, also acquired from Brocott. Winding materials were my fathers day present. Thanks Damien.

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