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Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Ash -
An automotive distributor won't work as an RSG for a spark-gap coil.
1. The current in the HV side of an automotive ignition system is a few tens of milliamps, while in a spark-gap Tesla coil the current in the tank circuit can be hundreds of amps. The soft brass electrodes in the distributor would vaporize in short order.
2. A distributor is sealed, and would would nearly instantly fill with hot, ionized air and would stop quenching.
3. You'd still need to devise some means of driving the distributor at a controlled speed, especially of you wanted a synchronous RSG that had the mechanical "timing" of its electrodes synchronized with the sine wave of the AC line voltage.
The only commercially-made rotary spark gaps that I am aware of are from turn-of-the-century spark-gap radio transmitters (expensive collector's items) or RSG's from WW-II vintage military radar systems (produce in very small numbers with a low survival rate).
It's pretty much a build-your-own proposition, and to do it right you'll need a lathe, milling machine, precision rotary table, and the engineering and machinist skills to design and build it.
Having said that, numerous Tesla coil builders who have the equipment and the skills to use it have built beautifully designed and constructed RSGs.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
I disagree, Herr Zapp, you don't need much of any machinery to make a RSG It would help, but i built a srsg with some saw, a drill, and wood. The are very simple and a 120BPS rsg doesn't need to be *too* beefy to prevent it from flying apart. It may not be great for high powers, but a very simple srsg can be made out of a microwave's shaded pole motor. I have tested it a few different ways and it seemed to be truely synchronous, and it would reliable lock to the mains frequency.
However, the torque is almost non-exsistant, so a very light weight rotor with minimal wind resistance would need to be built... I made one using the fan blade with all of the blades chopped off to leave me with just a cylindrical piece of plastic that could easily be pressed onto the motor shaft. I put in a few holes in the sides of the piece of plastic and put some small bolts through the holes and voila. I cannot find a video of it, but here is the one i said i made with wood Excuse the song, i really don't have a good excuse for that. It seems that i accidentally chose the wrong audio playback speed, so it sounds like 60hz instead of 120hz, but in reality it sounded exactly like all other srsg coils.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Arcstsrter -
I specifically said that you'd need precision machine tools to "do it right".
Look on the web and you'll find examples of horrifyingly crude RSGs cobbled together from pieces of scrap using only hand tools. By "do it right", I'm talking about a dynamically balanced rotor made from high-strength, high-temperature-resistant, shatter-proof material like G10 epoxy/glass composite or LE phenolic, clamped to the motor shaft using a precision-machined aluminum or steel hub with multiple locking fasteners, with the electrodes positively mechanically secured to the RSG disk.
I'm talking about carefully-designed and constructed RSG's like those produced by Ed Wingate, Finn Hammer or Bill Wysock. Here are a few links to photos of well made RSGs:
Wingate: Wysock:
It takes more than a hammer and hack saw to build an RSG like these.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Arcstarter -
I'ts all about the level of pride you take in what you build with your own hands, rather than just meeting some absolute minimum level of functionality.
Tesla coils have no practical purpose, they are simply interesting technical amusement machines. To me, they're much more interesting if the're built like a Rolex rather than a Yugo.
Do you think the "craftsman" near Gorky Park who attempted this automotive body repair took any pride in his work?
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
Cduma, if if you don't have the tools, see if you can talk to some workshops or something in your area. They would most likely have the tools. If there is none, you could do what Arcstarter suggested but make sure to stand a good distance away from it with safety glasses on.
Herr Zapp, people are different. Some derive pride from making something functional from next to nothing (be it minimally functional or not), while others strive to build the best they can with the money they have saved up. Not everyone wants to spend a fortune obtaining the tools and/or materials to build something that works. There is no "right way".
Why not wait for cduma's response before we all get up in arms about nothing?
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Persanally, I agree with Herr Zapp here. Things like RSG's have to be done right (at least from the point of view of recommending someone else to do it). Stuff that's 'cobbled together' and spinning at 3000 RPM or so needs to be 'relatively' safe.
I still think it is 'possible' to modify an automotive distributor, but it would need a modified rotor arm, presumably with tungsten welding electrodes, and modifications to the cap, again tungsten inserts. It would also need forced air cooling, maybe inlet through the 'now redundant' centre connection, with holes drilled in the base for outlets. It would also still need to be driven synchronously, I'd reccomend 1500 RPM, but it should be ok at 3000. Also, as Herr Zapp points out, you'd still not get as high a power throughput as one designed and built from scratch.
I'd also recommend looking at Ritchie Burnett's page:
(I did a bit of googling on the subject last night)
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Buy rotary spark gap
It would help, but i built a srsg with some saw, a drill, and wood. The are very simple and a 120BPS rsg doesn't need to be *too* beefy to prevent it from flying apart. It may not be great for high powers, but a very simple srsg can be made out of a microwave's shaded pole motor. I have tested it a few different ways and it seemed to be truely synchronous, and it would reliable lock to the mains frequency.
