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Re: Photos of Components

Original poster: "Gerald  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Ben,

Original poster: "Medina, Benjamin (UMR-Student)" <bamxbb@xxxxxxx>

Note: The Tesla list does not accept file attachments. So I stuffed all Ben's pictures he sent at:




These are some photos of the Primary, Secondary, Capacitor, and Rotary Spark Gap. I would like to hear your honest opinion about these. Your comments will be appreciated.

If you notice, the strike rail of the primary is soldered. I know there has to be a gap so we plan on doing that over the break. Also, we could only get a 50' roll of 0.25"OD refrigeration copper tubing so you can also notice the solder spots (splice). There is actually 2 spots. I bought a 10' roll thinking it was going to be enough but it wasn't, so we bought another

It's amazing how fast that used up. I had to use two rolls of 50ft and still ran out. Yes, you will need to cut the strike rail. I counted 14 turns. You may want to test the resonance of the secondary with toroid and primary with Cp independently before you put it all together. This will require a scope and signal generator to measure. I can help with the procedure if you need. I will presume that the soldering is good enough. I first tried to use a propane torch with no sucess, so I used a 150 watt solder iron used to solder sheet metal on solid wire small enough to fit inside the cu tubing. I used plumbers acid flux on all pieces and fed rosin core solder to sweat the joint.

10' roll.

If you notice, there are a couple of "white spots" or spacing between some of the wounds. This happened when I was first winding the 22 AWG wire using the lathe. It gets better as we go up the secondary.

This is probably OK for your first coil. The important thing is the turns dont overlap. If you do take out the spaces (not hard to do if you are careful not to let the wire get too loose), you may want to coat the windings with polyurythene when you are done. Lathe will be handy to get the coating even.

12"x12" glass plates with aluminum foil. I am definitely going to get the MMC caps. I still haven't decided from where though. But I have a couple of links I hope I can purchase these from. Should we even try our coil with these glass plates or just go with the MMC caps (for the 1st trial)?

I dont know your time schedule or budget. Terry Fritz knows a place to buy the caps that can probably get them to you within a week. Advantage of MMC is low loss, controlled capacitance, self healling case of punch thru, high current rating. I'd highly recomment the 942C series of CDE caps. These caps are rated at 2000Vdc so your string should have at least 12 in them (total of 24KV breakdown). I use strings of 14 so I can let the resonant rise go to 28KV and not have to worry about the caps. Exceeding the peak current ratings is how these caps can fail. The 0.15 uf caps are rated for 432 amps peak and cost about $2.50 each. They typically can take twice the voltage so a lot of margin there. If you want to make an MMC, let me know what capacitance you are shooting for and I can help with the string size and cap value. For your 15KV 30ma NST, a capacitance of 5.3 nf will resonate with the inductance of the NST at line frequency. Static gaps need about 1.6* Cres (~8.5 nf) and SRSG want about 2.8*Cres (14.9 nf). One string of 12 will be 12.5 nf and one string of 14 will be 10.7 nf. A 10Mohm 1/2 watt bleed resister across each cap is highly recommended to equalize the voltages and bleed off any charge once powered down. Terry has the Digikey part number for the resisters and they can get you resisters quickly.

If you have a capacitance meter, then you can measure what you've built going the glass route. I noticed that you are using a thicker plate glass than I used (thats good). I was using a 4.5KV transformer for my first coil and the glass took the voltage OK. With your 15KV NST, the peak voltage will be 21KV with no resonant rise and you might check to see if your thickness will take it. I have heard that if the glass goes, it goes with a bang and maybe shatters if not taped together well. On the foil, I would bring out the full width of the foil plate to connect to (helps improve the connection). You might extend the foil to say 4 inches outside of the glass and then use it to roll up over the wire you use to connect with. Then you can just clamp the rolled foil on to the bared wire for good contact.

Spark Gap
1/12 hp, 115 V, 3 A, 3000 RPM, 60 Hz motor from QUANTUM.
1/8" think pure tungsten electrodes (had a hard time trying to cut the tungsten into small pieces . You can notice the irregularity at the ends of the tungsten in the rotor disk). What do you think of the idea/setup? I want to remove that copper wire used for the connection and use another type of wire or strip. What do you suggest? 22 AWG wire? Brass strip?

For some reason I can download the pic of the sparkgap. If you still plan on using the ARSG, I would recommend that you don't go below 240 bps and use the terry filter and properly set safety gaps. Problem with 120 bps on an asynchronous rotory, is you have no phase control and if it happens to fire at zero crossing and stay there for a while, the core will begin to saturate and the NST inductance will go down. Even thou you thought you were operating at larger than resonance, the reduced inductance will raise the resonance back to 60 Hz and then you will get uncontrolled resonant rise on the voltage. The safety gap should fire or the MOVs in the terry filter will conduct to stop the voltage rise at the gap setting or the MOV voltage that you designed for (in my case, I use 16 MOVs to limit the voltage to 29500v). A MOV is like a zener diode and the ones Terry uses are 1800V MOVs.

Trick on cutting tungsten: use a new file and file a grove around the rod. Then snap break at that point. You can use a disc sander to finish off the ends. I cant comment on your setup (cant get the picture), brass sheeting works great for high current connections. 22 awg is way too small for the high current path. Use JAVATC tool to simulate your design with the cap you have chosen, the primary geometry, the coil size and toroid size that you want to use. Let it auto tune and it will tell you how many turns of primary to tap at. SInce you only have 14 turns, I would adjust the toroid size until you get to 10 turns. This will give you some adjustment headroom. Also note the PEAK CURRENT calculated by javatc for your primary. This will tell you if there is a current problem with the cap string. Once the streamers form the added capacitance it presents to the top load will lower the tuning of the secondary. Its nice to have a few extra turns of primary to compensate for.

Good luck,
Gerry R