Paul's Tesla Coil Blog

The final bits.

2013-08-12T22:50:00.000+01:00

Hi. This must be the last job on my Tesla Coil build. I need to make an earthing point on the main Tesla coil body. Most of the earth leads in my Tesla are connected to the earthing point on the neon transformer. These are

1. Connection to the strike rail underneath the primary coil perspex covering disc.
2. Connection to the lower terminal on the secondary coil.
3. Connection to the central rail on the Terry filter.

So I need to connect this point to my earthing plate on the conservatory wall. I could just run a wire from the earth plate through one of the vent holes in the Tesla base to the earth terminal on the neon transformer. The problem with this solution is that it would be impossible to remove this lead as the ring terminal needed on the end of the wire will not pass through the vent hole. Even if I enlarge the vent hole it would still involve removing one of the perspex walls of the base unit to attach/detach this wire.

After some thought I decided to fit an earthing point on the outside of the back perspex wall of the main Tesla unit. This would consist of 2 copper terminal lugs, one mounted inside, one mounted outside, connected through the perspex by a M6 bolt.

Above is the hardware for the terminal, I will probably replace the stainless M6 bolt with a homemade copper stud but will need to procure an M6 die first.

I made a small lead that finishes in a ring terminal to connect to the new earth point. I fitted the lead to give me a better idea where to site the hole for the terminal.

Marked up the point to drill the 6mm hole. I drilled the hole freehand, there were no obstructions and it was pretty easy to keep the drill at right angles to the perspex.

Result was a nice neat 6mm hole. My OCD placed it on the centre with the vent holes and level with the end of the neon transformer.

Here's the hardware fitted. I used 2 of the copper lugs from Alan at teslastuff.com. These are the best quality electrical lugs I have seen.

The terminal was connected to the short lead from the neon transformer earth point and the perspex sidewall replaced. Job done.

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More "Ground" Work on the Tesla Coil

2013-08-09T22:24:00.001+01:00

Hi again. Over the last couple of days I have been working on the grounding system for my Tesla. As mentioned in my last post, I had already sank one copper rod in the lawn. Plan was to get another couple of rods form B+Q and have 3 ground points spread across the lawn. Slight problem, I sank the first rod several weeks back and I now can't find it!

So 3 rods were purchased from my local B+Q. The rods are about £12 each, they are 1m long 10mm diameter copper plated rod with a nice copper terminal clamp.

The 3 grounding wires will pass through the conservatory wall and meet in the pattress box. They will pass through 3 separate holes drilled with a super long 8mm masonry bit.

I removed a small piece of turf (about 18" square) and dug out some earth down to about 10". Here's a picture of the first hole. The wire will be sank under the turf by cutting a line with a spade and easing the turf up and pushing the wire under (a trick learned watching Virgin installation engineers).

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The copper plated rod was hammered into the centre of the hole. You have to fit the clamp onto the rod before you sink it as the hammering will splay out the top of the rod making it impossible to slide the clamp over afterwards. The grounding wire was attached using a solder ring terminal and the hole back filled and turf replaced.

Above you can see the position of the second ground wire. The process was repeated exactly the same as the first ground point.

And here is the 3rd and final ground wire laid out. All the wires run into the gravel filled trench that runs around the conservatory wall. You can see Karel (wife) covering the two completed grounds.

Here's the last rod being sank. Think I was pretty lucky that all the rods went in without to much trouble.

Here are all the 3 wires in place. Next job is to wire up the grounding plate in the conservatory wall.

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Grounding point for the Tesla Coil

2013-06-02T22:19:00.000+01:00

I am going to need some way to ground my Tesla coil. Obviously dumping these high voltages into your household wiring isn't a good idea. I have heard of several other ways, one suggestion was to ground to your cold water pipes (thanks Mike), others include wire mesh lied flat on the floor etc. I wanted a neat and more permanent solution. I am going to install 3 copper grounding rods into my lawn. These four foot rods are available from B+Q, I have already sank one into the centre of the lawn, the other 2 will be close to the lawn edges as far from the central rod as possible. I have some really meaty 5 awg silicon coated wire which will run from the submerged tops of each rod, under the lawn to the wall of my conservatory.

The 3 wires will run under the drainage gravel around the edge of the conservatory and will run up the wall just to the right of the wall basket.

They will pass through the wall and come together in a single pattress box mounted in the conservatory wall.

The box will be sank into the wall just behind Milo to the left of the double plug socket. There is no existing house wiring to the left of the sockets, the mains wiring travels clockwise around the conservatory. I measured up and picked a drilling point on the outside wall which would bring me out central between the plug socket and the corner in the wall.

Drilled through with my super long 8mm masonry bit, slowing down and reducing pressure approaching breakthrough to prevent blasting a hole in the plasterboard.

I threaded a short piece of the 5 awg silicon wire through the hole just to check hole size was OK.

Here's the components for the earthing point, a 26mm deep single pattress box and a 100mm square 3mm thick copper plate. There will be some kind of terminal central in the copper plate, not decided on it's final design yet.

I masked up the plate and marked up the positions for screw holes to mount the plate to the back box. The 3.5mm holes were drilled and countersunk.

You can simply put the pattress box over the hole for the wire, draw round it and the remove the plaster. I used my Dremel with a spiral cutter, it made short work of the plaster, took about 60 seconds to work around the outline of the pattress. The cut out plaster can then be remove with an old flat bladed screwdriver or chisel.

I attached the copper plate to the pattress box and placed it into the cut-out. I am not going to permanently fit the back box yet. I will do it when I address the wiring to the 3 grounding rods.

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Bonding the Secondary coil acrylic end caps with Dichloromethane

2013-06-02T21:13:00.000+01:00

Got lots of Tesla related stuff done this weekend. Firstly my little bottle of Dichloromethane turned up from from APCPure, a solvents seller on eBay. This meant I could glue (if that's what you call it) the toroid mount to the top cap of the secondary, and the small blanking plug to the bottom cap. I have never used Di-chlo before so was a little apprehensive. I knew if you get it anywhere else other than the bonding surfaces it marks your lovely clear acrylic. Anyway it went OK, I don't think I used quite enough as I ended up with air gaps but the bonds are absolutely solid.

Here's a shot of the toroid mount bonded in place, you can't really see the offending air gaps and the bond is good and completely seals the central hole used for mounting on the winding jig. Glueing the blanking plug to the base cap went much the same. A slight change of design here, I glued the blanking plug to the bottom of the end cap so it protrudes from the base of the secondary. I will adapt the Tesla base so the plug acts as a central locating pin into the primary mounting disc.

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Work on the Secondary Coil End Caps

2013-05-29T23:26:00.000+01:00

I was hoping to finish off the top and bottom coil end caps today but this didn't work out. I needed to bond an acrylic plug into the central hole in the bottom cap. This is to close up the hole needed to mount the coil in the winding jig.

I also trial fitted the eight nylon bolts that will hold the coil down onto the Tesla body.

Here's a close-up of the plug in place. I also planned to bond the toroid mounting assembly to the top cap of the coil. This would, again, close up the hole needed for the winding jig.

Bonding was going to be achieved by using Tensol acrylic cement which a had purchased a while back from Trent Plastics. When I dug out the bottle the liquid was thicker than I had anticipated. From videos I had seen, bonding sheet acrylic was done using a water-like solvent that used capillary action to penetrate between two close fitting acrylic sheets. The liquid I had was like syrup and there was no way this would seep into a fine gap. I assumed all Tensol was the same and you know what they say about assumption. After a bit of investigating I think I have Tensol 12 which can be used for bonding gaps between rougher cut acrylic pieces. Tensol 70 is the version more suited for close fitting sheet acrylic but it was averaging out at £40 and minimum qty 500ml. Too much and too much. More homework was needed.

Here's what I found out. These water-like acrylic cements don't actually "glue" things together. It's more like a weld. The solvent dissolves the surfaces of the two pieces and the molecules merge from either side. The solvent evaporates and the two pieces become one. The solvent in these cements is Methylene Chloride also known as Dichloromethane. It's pretty nasty stuff but apparently it's all you need to bond close fitting acrylic and you can get it from eBay or Amazon. I paid £4.79 for 250ml, delivery was almost £8.00 because of it's hazardous nature. It should turn up tomorrow so will try it and let you know.

Anyway, crack on. I bought some shorter (12mm) cheese head slotted M4 nylon screws to fix the top and bottom caps in place. The 20mm bolts are a bit excessive!

Secondary Coil Ground Terminal

2013-05-27T23:40:00.000+01:00

I have just finished the lower electric connection to the secondary coil. As explained in previous posts this connection is made up of a 70mm x 23mm copper plate on the side of the secondary coil. The plate will be glued in place using 2 part epoxy. After deciding the final position of the copper plate I surrounded the area with masking tape, not really to offer any protection to the surrounding area, just as a guide. The inside of the area was deeply scored with sharp craft knife to produce a good key for the epoxy.

The copper plate was tinned (to aid soldering) and then the lower lose tail of the windings stripped of varnish and soldered to the copper plate. I used my new Dremel VersaTip to do the tinning and soldering. I bought it really to use as a small blow torch for tinning and delicate metal work, however I was very impressed with its soldering capabilities.

Here's a shot of the tail end of the windings attached to the copper terminal. The back of the plate was cleaned up with a brass wire wheel on the Dremel 8200 then cleaned with meths to remove all soldering residues. I removed the masking tape from around the scored hatchings on the coil, this would allow me to position the plate better by eye.
I mixed up a blob of 2 part 5 minute epoxy glue and applied it to the back of the copper terninal plate. Forgot to mention I had cross-hatched the back of the plate to aid bonding.

I positioned the plate onto the coil and lined it up parallel with the windings and made sure the lose tail was positioned nicely around the coil and taught. I held in position for about 5 mins while the epoxy hardened.

The plate got warm as the epoxy went off, so easy to judge when it was safe to release pressure. I neatly positioned the tailing winding wire so it made a nice spiral from the end of the windings to the copper terminal.

Then I used a small brush to cover the tailing wire with insulating varnish which will protect and hold the wire in place on the form. I gave the tail wire 3 coats.

Here's the finished terminal. Think it looks pretty good.

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Winding the Secondary Coil for the second time.

2013-05-23T22:09:00.001+01:00

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.

Secondary Coil Design and Begin

2013-02-24T20:51:00.000+00:00

Today I started prepping for winding the new secondary coil. I have already worked out winding wire diameter and number of turns as explained in previous posts. I have chosen a design to work to with the help of Stefan Kluges excellent pages on producing the ultimate secondary coil, pages can be found at http://www.capturedlightning.org/hot-streamer/stk/tc/coilbld.htm.

The first job I had to do was to construct a rectangular copper plate that I will use as the bottom electrical contact to the secondary coil. It provides a very large area for electrical connection rather than just a small point of attachment. I thought it best to produce this plate first so I could confirm that the starting and finishing points for the winding were appropriate. I found a nice piece of copper sheet in my stock which was perfect.

These are the winding figures I planned to work to.

Length of turnings =1050*0.64

=67.2

Total form length =80cm

Windless portion =12.8cm

Windless portion bottom =4cm

Windless portion top =8.8cm

As you can see I have 4cm from the bottom of the coil form to the start of the windings. This is the gap that the copper plate will sit in. Here's the diagram from Stefan's page.

A good size for the plate was 70mm by 23mm so I masked up the piece of copper and marked up the dimension. Then, using a pair of 6" tin snips, I cut out the copper plate.

The corners of the rectangle need to be rounded so I nipped them off with the tin snips and finished them off with a flat file.

The copper sheet was quite thin and so very easy to work. My coil form is already fitted on my coil winding jig. I placed a piece of masking tape 4cm from the base to represent where the windings would start. This helped me choose the initial dimensions of the copper plate.

This plate will eventually be bonded to the coil form using 2 part epoxy so it needed to be bent gently to match the curvature of the coil form.

Above is the finished plate in its approximate final position. Next job is to wind the coil. I am guessing that will be a 2 hour job so maybe I'll tackle that one evening next week.

One last thing. The kittens are driving me mad as they now use my Tesla coil as a shortcut from the settee to the living room door. So a trip to Bury Market to get some black vinyl material and a bit of trimming with scissors and we have the Tesla kitten guard.

Kitten Guard

Patent Pending

Didn't take long before its first test!!

Lulu

A turn around the secondary coil. Again.

2012-12-16T22:24:00.001+00:00

Hi everybody, not done a post for ages. Been busy with a bit of decorating and think I have not been looking forward to re-doing the secondary coil so have kept putting it off. I think it's time to finish the secondary so I can get on with testing and finally fire up this monster. Plus I think I need to move the Tesla to a safer area, at the moment it's in our freshly decorated living room which used to be pretty safe place where it wouldn't get damaged. Not anymore! Sadly we lost our old cat, Coco, a couple of months back but acquired 2 little rescue kittens, Milo and Lulu. They are mad. I haven't yet worked out if Perspex is claw proof and my Tesla looks like the worlds biggest scratching post.

If you want to see Milo and Lulu live take a gander at http://cats.damow.net from 10am till 4pm weekdays or anytime after 11pm any day. Live webcam of our kitchen (cats bedroom).

Anyway on with the Tesla. I have finalised the design for the windings on the secondary coil. The goal was to reduce the number of turns and this was achieved by increasing the diameter of the magnet wire on the secondary and reducing the length of the windings. I used JAVATC to generate the figures I needed.

With 1050 turns on the secondary resonance should be achieved by tapping the primary coil at turn number 11. The predicted resonant frequency is just over 180kHz and can be seen in the data below.

The new secondary coil blank is installed on my trusty winding jig. So glad I decided not to sell the jig on eBay after completing the first doomed secondary.

I made a small change to the winding jig. I replaced the original 148:1 motor/gearbox with a 50:1 unit. This should speed up the winding process, last time it took over 3 hours. The motor/gearbox units are produced by MFA and can be obtained from Maplin in a variety of ratios.

I have already purchased a few bottles of varnish to coat the coil after the windings are done. I am using the same as last time, it's made by a company called AEV (Advanced Electrical Varnishes) and is known as Ultimeg 2000/372 a high build Alkyd air drying anti-tracking varnish. The easiest place to get it is from Brocott on eBay but it's expensive in small amounts (£4.50 for 100ml plus p+p). You can also buy it from Hi-Wire Ltd for about £28 plus p+p but the smallest qty is 5 litres.

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New Toroid mount System

2012-06-18T23:16:00.000+01:00

I have started work on the new toroid mounting system which differs in design from the method used on the first secondary coil. This time electrical connection to the toroid from the top of the secondary coil will not pass inside the coil form but will gently spiral around the mount and then finish as a copper disc which will be in direct contact with the underside of the toroid. The final system incorporates good secondary coil design taken from Stefan's Tesla Pages and the fast easy assembly of my first design.

Above is a quick sketch showing the basics of the new mount. Here we see 3 acrylic disc which are 107mm in diameter and 15mm thick. The middle disc has an central 25mm hole. All bolts are nylon with the center bolt being M8 and the four others are M6. The diagram only shows the 2 side M6 bolts, there are another 2 front and rear. The bottom disc will be Tensoled to the top cap of the secondary coil and the four holes will be threaded to take the M6 bolts. The middle and top disc corresponding holes will be 6mm clearance holes with the top disc holes being countersunk. The central hole in the top disc will be threaded M8. The copper electrode disc will sit on top of the uppermost disc (probably bonded to it) and the the toroid mounts over the M8 bolt sandwiching the copper plate. The copper plate is soldered to the copper tail of the secondary with the tail gently spiralling (with some excess) around the toroid mount. This system will allow extra acrylic discs to be fitted to adjust the spacing between the toroid and the secondary coil.

I ordered four discs from Trent Plastics. The 3 required for the construction of the mount plus an extra to be inserted as a spacer. All the discs were the same apart from the one with the 25mm central cut-out. Above you can see the top 3 discs including the extra spacer. The lefthand disc has just been drilled to form the four 6mm clearance holes and the central hole which will be threaded to M8.

I the stacked the drilled disc on top of the other 2 and taped them tightly together. This allowed me to use the existing 6mm holes in the top disc as a template to drill 6mm clearance holes through the other 2 discs. After this was done I the added the fourth disc to the botton of the stack of disc, again taping it tightly to the others. I then passed the 6mm drill down each hole with just enough pressure to mark the center of the drill bit on the bottom disc. The stack was then separated and I could use the drill dimples on the surface of the bottom disc to centre the 5mm drill bit before drilling.

Here I am taping the four 5mm holes in the bottom acrylic disc to accept the M6 nylon bolts. Remember, this is the disc that will be bonded to the top cap of the secondary.

After removing all the protective masking tape I did a quick trial assembly just to make sure everything lined up OK.

And here's the mount in situ, not bonded yet, that will have to wait till the secondary is wound. That's the next job.

Making the Second Tesla Secondary Coil

2012-06-17T21:56:00.002+01:00

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.

Secondary Coil (Take 2)

2012-06-05T22:20:00.000+01:00

A couple of weeks back I spent a few of hours playing with my oscilloscope. I had seen a few articles on the web showing how to measure the resonant frequency of the primary and secondary coils with an oscilloscope so I thought I would give it a try. The easiest one to measure is the secondary coil, to do it accurately you need to remove the primary coil and simulate streamers from the toroid as these change the resonant frequency. I was not looking for this degree of accuracy at this stage, really just having a go to get a rough idea.
I disconnected the earth lead from the bottom of the secondary coil and connected the coil to the signal generator built in to my oscilloscope.

I plugged a probe into channel one and Damien held the it approximately 3 feet away from the secondary coil.

I set the signal generator to a sine wave of 5v amplitude and starting at 100kHz as I guessed resonance should be between in the range 100kHz to 200 kHz.

The volts per division on channel 1 was set to 10mv and time/div set to 1us. I began to slowly increase the frequency of the signal being supplied to the secondary coil. You can see from the pic above that the trace was flat as 128kHz was passed. This remained the case most of the time as the frequency was increased, there were some signals picked up, presumably harmonics of the true resonance. To my amazement at 175.4kHz the flat trace suddenly transformed into a perfect sine wave, signifying we had hit the resonant frequency of the secondary coil.

As I said this was only done for experimental reasons and in no way to get an accurate resonant frequency, but it did get me thinking more about the relationship between the secondary and primary coils. I had read a lot of references to JAVATC while looking for information about Tesla coil tuning. It's a website based program used to help in the design of Tesla coils. It works by entering lots of component specs and various physical dimensions of the Tesla coil you have built or plan to build. When the program is run it calculates the resonant frequencies of the primary and secondary coil and displays the %tune between them. It can also be used to automatically tune the primary coil to the secondary, in this mode the program will output the correct tap point on the primary (in number of turns) to get resonance with the secondary. It took me a while to work out and gather all the different data required to test my own Tesla coil build but after a lot of measuring I entered the data into JAVATC.

CRAP!!!
According to the software I needed to tap my primary coil at turn 16 to get resonance with the secondary coil. That would be a slight problem. I only have 12.5 turns on my primary!!! The reason for this was a lack of understanding when turning my secondary coil. I had opted for a larger secondary coil during the build after choosing a few other upgrades. I had failed to upgrade the magnet wire gauge used to form the windings. The 0.4mm diameter wire I used on the larger secondary had resulted in far more turns than required. There is only one thing for it, build another secondary with less turns.

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Testing the Synchronous Spark Gap Circuit

2012-05-17T23:13:00.000+01:00

Tonight I have just done a little bit of testing. I wanted to make sure all was OK with the spark gap circuit so first I made sure everything was physically OK. I checked that the disc holding the four tungsten spark gap electrodes was fastened securely to the mandrel. Also that the tungsten electrodes were secure and the spark gaps were set at the correct distance (0.5mm + or - 0.2mm).

All was fine so I proceeded. I plugged the main power supply module into the mains and connected the phase shift module to it. Then connected the phase shift module to the SSG circuit iec socket on the side of the main tesla base module. The main supply to the neon transformer was left disconnected as, at this stage, I only want to test the SSG circuit.
Turned the phase shift module to its minimum setting, a final check then I threw ON/OFF switch.
The SSG motor hummed into life and spun up to full speed very quickly. I sat and watched for a while. Nothing seemed to be smoking or melting and the motor was running smooth. There was virtually no vibration, the electrode disc seemed to be balanced very well. I decided to give the phase module a try and rotated the variac knob a few degrees. Obviously there was no viewable change to the rotation of the SSG but I could hear the motor lose and regain its lock on the frequency each time I changed the position of the phase shift variac (well I think that's what I was hearing). On further increasing the phase module the SSG motor would completely lose lock and stop but regain and restart when the setting was reduced. By this time perspex case around the phase shift module was starting to cloud up with what looked like condensation. A good time to end this first test run.
After unplugging and further inspection I concluded that the fogging was just solvent being driven out of the varnish on the coil windings in the phase shift module.
I wanted a visible confirmation that I was actually achieving some degree of phase shift. First, I thought if I illuminated the SSG with a fluorescent strip light I might be able to "see" some phase shift as the phase shift module is adjusted due to the (50HZ) flashing of the strip light. Unfortunately no access to a strip light prevented that little test. After explaining what I was trying to achieve Damien came up with an idea. He could create a 50HZ strobe with a simple little program on an Arduino microcontroller.

Damien explains:

A 50Hz wave has a period of 0.02 seconds. This is composed of half-on and half-off output. Repeat this procedure and you get a fairly accurate 50Hz square wave. Hook this output to an LED and you have a simulated strip light running at 50Hz. While it isn't in phase with the mains (Unless you're really lucky when you turn on the Arduino!) and it's not massively accurate because of the inherent overheads introduced by the delays in the microcontroller and timers, it's a good way to get a strobing effect and get an idea whether the phase-shifter is working or not. Back to dad...

Here's a pic of the little unit Damien put together. We switched off the lights and fired up the SSG circuit.

Without adjusting the phase module the Arduino strobe was shone on the spinning electrode disc. The strobe effect worked well, the electrodes appeared to be rotating anticlockwise very slowly. This was due to the slight difference in frequency between mains and the Arduino strobe. If the frequencies were exactly the same the electrodes would appear static. I adjusted the phase shift module and this resulted in a change to the slow rotation of the electrodes. This change only occurred during the adjustment of the phase shift module. I think this pretty basic test is a good indication that there is a change in phase. Below is a video of the process, it's just about possible to see the moving electrodes as the phase module is adjusted, it was more obvious to the naked eye. I think the video camera frequency also combines with the other frequencies to complicate matters.

Tesla Coil Extras

2012-05-13T23:18:00.000+01:00

Well it was nearly finished.... I am sure I will keep on posting extra additions and also experiences of my first fire-ups and tunings. First addition was mentioned in my last post, the safety bleed resistor for the large 40uF capacitor in the SSG circuit. This was quite a quick fit, the resistor is only small so I decided to fit it on the side of the module that held the 40uF capacitor. I made 2 identical mounting posts out of 10mm diameter brass rod. The posts are 25mm long and the resistor sits in 3mm diameter horizontal holes 12.5mm up each post.

The resistor legs are clamped by M3 grub screws at 90deg to the mounting holes. Electrical connection to the capacitor are ring terminals onto M4 allen key bolts (stainless of course) into the tops of the mounting posts.

I made up the wires to the resistor starting with female 1/4" piggyback blade connectors which meant I didn't have to amend the existing wires to the SSG, they could just plug into the piggybacks.

While the weather was good I decided to sink the grounding rod in the middle of my back lawn. The rod is 1 metre long and I thought it would take several attempts to sink it as the garden seems to have a thick layer of industrial rubble just under the surface. Must have been my lucky day as I hammered the rod well below the surface on the first attempt. I removed a small square of turf before I started. You can just see the refitted turf in the above pic. Next dry weekend I will run the earth lead from the rod under the lawn turf to the patio.

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Tesla Coil Finished!!

2012-05-07T22:30:00.000+01:00

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.

Tesla coil ground connections

2012-05-06T22:59:00.003+01:00

Today I decided to finish some of the electrical connections. Firstly I needed to complete some ground connections, 3 to be exact, and when I say ground I mean literally ground not mains earth ground. These are :-

1. Strike rail to ground.
2. Secondary coil to ground.
3. Neon transformer to ground.

I decided all 3 of the above will start from the ground post on the neon transformer as this has a large enough post to accomodate the multiple ring terminals.

You can see this terminal in the pic above, it's the lower terminal with the blue sheathed wire attached. In this pic I have removed the perspex side panel.

As the 3 grounds will exit the lower level perspex box I needed to drill 3 holes in the perspex side panel. I masked up the side panel so to protect the perspex and so I could mark my drill points. The welding wire for the grounds is 8mm in diameter but I decided to drill 12mm holes so the wires could pass through with the ring terminals attached. This would make assembly and maintenance much easier.

The left hole would house the secondary coil connection, the right the strike rail connection and the centre would be to the grounding spike. I marked the top on the masking tape mainly to show this side is the outside as the panels do fit better one way than the other. I drilled the three 12mm holes and then removed the masking tape. But unfortunately failed to note which side was marked top. So I took my best guess and offered up the panel and proceeded to refit the mounting bolts. Guess what?

Wrong way! the bolts did not line up correctly and the result is shown above. The perspex corner post cracked. The bolts did feel a little tight, I should have realised the panel was the wrong way round. Took me an extra hour to make the replacement post.

Here's the side panel and new corner post back in situ. Now to make up the wire lengths required for the two ground connections.

The first is the strike rail connection. The wire end at the strike rail fastened inside a copper lug so I impregnated the copper strands with solder to stop the wire end disintegrating due to repeated clamping. The other end terminates in a ring terminal which was also soldered.

Next I did the ground connection to the lower end of the secondary coil. Both ends of this wire were fitted with ring terminals, again soldered.

Above you can see the routing and end connections of these two ground wires.

I am not going to fit the wire to the ground spike yet, there's no point as it will just get in the way. It will pass through the central hole in the side panel and attach to the ground post of the neon transformer thus connecting the neon transformer, strike rail and secondary coil to ground. The ground spike will be situated in the middle of my back lawn. It will consist of a 4 foot copper rod driven fully into the ground. I will run the connecting wire under the turf across the lawn and out on to the patio.

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Primary Slider Clamp

2012-04-29T23:51:00.000+01:00

Todays horrible weather gave me a good excuse to do some more work on the Tesla. My next task is to make some kind of easily moveable clamp for the outer connection to the primary coil. It needs to be easily moveable so you can adjust its position (tap point) on the primary coil. The position of the clamp on the primary coil determines the energised length of the primary coil and hence its resonance. The tap point is moved so you can adjust the resonance of the primary to match that of the secondary coil. Well there's the basic tech stuff, here's how I made the clamp.

I started off with a chunk of copper that I picked up off ebay for about £8. It was about 3" long, 1" wide and 3/8" thick. The clamp would have to be of an unusual design because of the perspex disc that covers the whole of the primary coil. I will have to clamp onto the primary coil from below and, depending on the eventual tap point, may have restricted access due to the perspex disc underneath the primary.

After taking a few measurements I made a quick drawing using iDraw on my MacBook just to work out if this design was feasible. I decided this design should work even if the tap point is in the more inaccessible places on the primary coil. The length and shape of the righthand end of clamp may change as the design develops.

The copper block was marked up and sawn into the rough shapes required. The parts were cut slightly larger than required as they would be milled down to the required dimensions.

The off-cut removed was marked up to form the second part and roughly sawn out again oversize to allow for milling.

I fitted a 10mm milling bit and did the first lengthways run to produce the correct thickness required (6mm).

Here's a vid of a bit of the milling process. Milling copper is pretty easy as it's quite soft, I had to use the milling vice because the small height of the pieces I was working on. It's good practice to clamp work as close to the milling bed as possible so any slop in the bed is reduced to a minium. I couldn't do this with these pieces so I kept cut depths small.

After milling the two pieces were clamped together and drilled at the intersect to form the clamp jaws. The primary coil is 1/4" tubing so I used a 1/4" drill bit to form the jaws. To get the jaws to clamp tight on the tube I will remove some of the material at the vertical intersect just below the drilled hole.

A test fit of the piece works fine. It's a tight fit between the coil and the perspex disc underneath so I will mill another 0.5mm off the bottom of the lower assembly.

This picture really shows the need for this particular design of clamp especially if the tap point lies inside the external diameter of the primary coils support disc. Next session I will reduce the clamp thickness, join the two pieces together with some kind of slide mechanism and add the electrical connection.

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Electrical connection to the Primary Coil

2012-04-24T22:40:00.000+01:00

A few weeks back I made a very nice copper clamp pin which would be used to connect the inner end of the primary coil to the HT lead from the synchronous spark gap (SSG).

The hole at the top will accomodate the inner end of the primary coil and the threaded section will pass through a hole in the primary coil support disc and then the electrical lug will accept the HT lead to the SSG.
First job today was to drill the hole for this clamp pin.

The picture above clearly shows the primary coil support disc, it's the white disc sitting under the radial primary combs. It's white as it still has its protective coating and a layer of masking tape. To drill the hole needed I would need to remove this disc so after marking the hole position I started disassembly. I removed the toroid, the secondary coil and the primary coil assembly which only took a few minutes. The primary coil support disc was removed by undoing the 8 allen key bolts (stainless of course) that screw through the disc into the perspex support columns. I drilled the 9mm hole required for the clamp pin and then removed all the protective coating from the primary coil support disc.

The primary support disc was refitted and the clamp pin slipped over the inner end of the primary coil and the grub screws tightened. The primary coil assembly was then lowered down onto the support disc making sure the clamp pin threaded end lined up with the clearance hole. It did!!

Above is a close look at the clamp pin in situ. Very happy with design, it allows an easily removable electrical connection to the primary coil.

A shot from underneath shows the copper lug bolted to the threaded end of the clamp pin.

I've done a few more pics of the assembled tesla base as this is the first time all protective coatings and masking tape have been removed.

And finally a full length shot with the secondary and toroid back in place.

Fitting the phase shift Transformer

2012-04-23T21:45:00.000+01:00

Another rather productive day. On holiday at the moment so spent a few more hours on the Tesla build. Today I managed to get the step down tansformer mounted in the base of the phase shift module.

As you can see it mounts directly onto the base disc. If you remember the step down transformer was originally mounted on the second level of the Tesla base. The pic below shows its original position.

I removed the whole module including the perspex base. After separating the transformer from the base I used the old base to mark drill points onto the base disc of the phase shift module. After drilling these holes I fixed the transformer to the base disc using the original ceramic pillars.

This left a couple of jobs to finish up. Two M12 flex glands were fitted by drilling two 10.7mm clearance holes and tapping out to 12mm. I also drilled six 12mm holes in the top disc, these are purely for ventilation. There are 7 similar holes in the base around the transformer and as the base stands on small cork pads air should be able to circulate up through these holes and out the vent holes in the top.

I took a picture of the main power module and the phase shift module together just to show you how I have tried to design them with the same look.

Still have wiring to finish up and few other touches to the phase shift module but I think I have achieved a matching module.

Here's the module that replaces the repositioned step down module. It's a rather large 40microfarad capacitor and is part of the phase shift circuit.

The capacitor has a central M8 mounting bolt which screws into a vertical perspex 8mm thick square. This square is bolted to the perspex base and is reinforced by a secondary perspex square flush up against it and also bolted to the base.

Again, just a bit of wiring needed to finish off.

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Finishing the Phase Shift module casing

2012-04-22T23:38:00.001+01:00

Hi Tesla fans. Today I spent several hours on the phase shift module case. Last post described marking out and drilling the top and bottom perspex discs. I've not been looking forward to the next task but today I decided to get on with it. The phase shift module will contain the 2 Amp Variac and the 110V step down transformer, this means the perspex tube required is quite tall at 195mm. This presents a problem as it's too tall to fit under the chuck of my mill/drill and that means I would have to freehand drill the holes to take the 3mm bolts that fasten the end discs onto the tube. Doesn't sound to bad? Well remember that the perspex tube walls are 5mm thick that only leaves 1mm either side of the 3mm bolts. Now thats why I haven't been looking forward to this. I picked 15mm long M3 socket head screws to use to bolt the top 8mm thick perspex to the tube. This meant they would only protrude 7mm into the tube walls and the holes required for tapping could be kept reasonably short. Drilling went pretty well. I taped the top disc to the tube end so I could use the pre-drilled holes in the disc. I found the best way to keep as vertical as possible was to stop frequently an reposition 90 degree to the work. That way I could try to keep vertical in multiple planes.

The resulting tap holes were pretty tidy, at least none of them had broke through the tube walls due to being so far off the vertical. The 8 shallow holes were tapped out to take the M3 bolts (stainless of course).
My last excuse for a lull in my Tesla activities was the purchase of a Sony PS Vita. This months excuse was a little more impressive, took a quick snap of it before attempting the holes for the base disc.

A Peugeot RCZ GT 200. Second childhood, third mid-life crisis. Whatever!!

The base was taped to the tube and drilling was just a re-run of the top. The base disc is black 5mm perspex, black as clear would be pointless for the base, slightly thinner than the top as the top needs extra thickness to support the carry handles.

Here's the assembled phase shift module case. Next to it are a couple of lengths of 1/2" diameter aluminium rod. I will use these to make the carry handles. Below is a pic of the main power module containing the 10A Variac. I am trying to create the phase shift module in the same style.

The 2 aluminium rods were cut to 108mm and 17mm long flats were milled on each end. I drilled 6mm holes central on the flats on each end.

The handle will be supported on 22mm lengths of 6mm ID 8mm ED aluminium tubing. To allow the handles to sit flush on the tubes 8mm seats were milled on the underside of the handles centred on the 6mm mounting holes.

Below is an assembled handle. The supporting tubes fit nicely into the 8mm seats. I will be using socket head screws in the final asssembly (stainless of course).

I span up the handles on my lathe and used varying grades of emery clothes to create a nice brushed finish.

I fitted the 2A variac to the top disc incorporating the handles. The plastic bolts were the only long bolts I had to hand but I now know I need 4 60mm socket head bolts for the final assembly (stainless of course), off to ebay to source some.

Building the Phase Shift Module

2012-03-11T21:55:00.002+00:00

Hi there, it's been over a month since I last posted (blaming the purchase of a PS Vita). Haven't done anything with the tesla so you've not missed anything. Last post I did was about the 2 Amp variac purchased for phase shifting. I am still in phase shifting mode so I bought some perspex to house the new module.

The phase shift module will be housed in the perspex tube and will look similar in design to the tesla power source module I constructed. It will contain the 2 Amp variac and the 240v to 120v step down transformer that, at the moment, is mounted on the second level in the tesla base. This change in design is due to some advice I obtained from the very clever people at http://www.pupman.com. The advice was to step down the voltage to 120v before the phase shifting variac, hence the step down transformer will have to be external of the main tesla and it makes sense to house it within the new phase shift module.

Above is a pic of the present situ of the step down transformer. This will me removed and replaced by a module that houses the large capacitor needed in the phase shift circuit. Tonight I started on the housing for the new phase shift module. As usual the plastic was masked up ready for marking up and drill. The top and bottom of the housing will be held in place by 3mm allen bolts so first I marked up the holes needed.

I marked up both discs, then realised I could tape both discs together to drill at the same time. Both discs are 185mm diameter, the top disc is clear 8mm thick, the bottom is black and 5mm thick. I went for 8mm thick on the top as this disc will have the rather heavy 2 Amp variac bolted to it.

Here's both discs taped tightly together ready for drilling the 8 3mm clearing holes for the bolts.

Drilling went without any mishaps. If you want a few tips on drilling perspex take a look at my Drilling and Tapping Perspex page. The top disc needs an additional 10mm hole drilling dead centre to allow the variac shaft to pass through. After drilling this hole it was possible to rest the variac on top of the disc with the shaft passing through the hole to allow the marking of the four 6mm holes needed to mount the variac to the perspex disc.

2A Variac for Phase Shifting

2012-01-28T22:42:00.002+00:00

Last week I took delivery of the first item needed to create the phase shift module. I was going to rely on mechanical adjustment for phase shifting but after a lot of reading up I have decided that the ability to adjust phase remotely while the tesla is operational is a must. If you are pretty new to Tesla coil building (like me) the subject of phase shifting can sound quite complicated. In simple terms, the synchronous motor rotation is locked to the sine wave of the AC power supply meaning that the spark gaps always present themselves at the same point on the sine wave. Without any phase shift the same AC sine wave is applied across the capacitors meaning that the spark gap may not present as full charge is reached in the capacitors. Phase shifting allows you to advance/retard the sine wave to the synchronous motor so you can present the gaps when full charge occurs in the capacitors. Without phase shifting you can only alter this timing by physically rotating the motor in its mount or rotating the spark gap disc relative to the motor shaft. Both of these being impossible (or very dangerous) to do while the TC is in operation and can be very difficult to quantify adjustments.
To make the phase shifter we use a variac wired as a variable inductor, a motor run capacitor and bleed resistor.

First to arrive was a 2A panel mount variac. I bought it from a seller on eBay called Wattbits. This is the second variac I have bought from these guys, the first was a 10A version that is the main power source for the Tesla coil.

Here's the 10A version in the power supply module.

The 2A version is physically about half the size. I want the phase adjust module to look similar in design to the power supply module so I have ordered a length of 185mm diameter clear acrylic tubing and a couple of 185mm acrylic discs for the top and base.

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Primary Coil Clamp Pin

2012-01-21T21:43:00.002+00:00

I spent sometime yesterday trying to figure out a good way to make the required electrical connection to the innermost end of the primary coil.

As you can see in the picture the connection needs to clamp onto the end of the 1/4" copper tubing and then pass through the 12mm perspex disc underneath the primary coil. In this pic the disc is still covered with protective plastic coating.

This is a side on pic taken level with the primary coil. You can see the anti-strike perspex disc above the primary coil and the 12mm thick disc below. After long consideration I decided that I needed a fitting that would clamp on to the end of the primary and have a protrusion that would pass through a clearance hole in the 12mm disc below. This "protrusion" would need to be threaded to allow a copper lug to be fitted on the underside. I had bought a drawing app for my ipad called iDraw and thought I would throw a quick design together. I've used this app before for designing the toroid mounting pin, it's not the most technical drawing app but it matches my abilities.

I started with a small length of 16mm diameter round copper bar. I turned down 25mm of it to a diameter of 8mm and then the next 25mm to 14mm diameter.

I cut the turned section off with a hacksaw then cleaned up the cut end in the lathe finishing the 14mm diameter section to a length of 22.375mm.

Here's the finished blank. Next I drilled the hole for the 1/4" copper tube (6.75mm drill bit used) and the holes for the clamping M3 grub screws. Decided to deviate from the plan and have 2 clamping grub screws at 180 degree to each other.

Using an M8 X 1.25 die I cut threads on the end of the 8mm diameter section (about 15mm of threads) and then cut the M3 threads for the grub screws.

Here's the finished article fitted with an M8 stainless nut and copper electrical lug.

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Connecting the Variac to the mains

2012-01-15T21:31:00.000+00:00

Today I finished the wiring to the SRSG (synchronous rotating spark gap), added IEC female connectors to the two outputs from the variac and slapped o a 13amp plu onto the input to the variac. Although I'm not yet ready to test the Tesla coil charging circuitry I can now test the variac up to full voltage.

Here the variac is plugged into a 230v mains outlet. The SRSG 240v feed from the variac module is connected to the correct input on the Tesla coil base. The main Tesla coil feed (0v -110v) is left unconnected but tapped by the volt meter.

The variac dial was set to zero and the on/off switch thrown. The synchronous motor spun up immediately and the meter continued to read zero. Rotating the variac knob resulted in an increase of RMS AC voltage on the meter.

The reading were as expected and hoped. The printed scale around the variac knob isn't that accurate, but I didn't really expect it to be, it's really just a guide. Think I will mark on a couple of accurate markers.

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Checking the Variac with the Oscilloscope

2012-01-15T00:35:00.001+00:00

Started on a little more of the wiring today. My task was to add a feed wire from the variac unit which would supply 240v to the SRSG feed transformer. This wire would just tap into the input feed after the on/off switch within the variac housing. I thought it would be a good idea to test the variac electrical connections before adding anymore wiring. The safest way to do this was to use the function generator on my oscilloscope to supply a low amplitude (about 5v) 50Hz signal across the input terminals of the variac and test the output with one of the channels on the oscilloscope.

Here's the setup I used. The function generator is plugged into the inputs of the variac and also channel 2 of the oscilloscope. The oscilloscope probe is connected across the output of the variac and feed into channel 1 on the oscilloscope. With both channels set to the same volts/div and the scope set to dual trace (shows both channel traces on same screen) it's very easy to see to compare input and output of the variac. Far safer than slapping a plug on the variac, plugging into the mains and hoping all is OK.

You can see from the video when the variac control knob is set to zero there is no output. As the knob is rotated the flat trace rises till it reaches the same amplitude as the output of the function generator. This is the required result and shows that the variac is functioning correctly. When in use with the tesla coil I will only need to use about half the range of the variac as the NST is rated at 110v. Tomorrow I will add the wiring for the SRSG.

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