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Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
So, over the past few months I finally got motivated to attempt a Tesla coil, and started slowly collecting parts. My only other attempt was a few years ago, when I knew next to nothing about them.
For power I decided to use my 2A variac and large 8.2kV transformer, ballasted with 2 150W lighting ballasts. The transformer is protected by a filter made of four 100W wirewound resistors and a polystyrene capacitor.
The primary MMC is a single string of 12 cheap dodgy "CJE" 2kV 150nF PP film caps. I suppose they're meant to be counterfeit CDE 942C's, but they still work and hardly cost anything, so I'll ride them into the ground. I have 20x big Vishay snubber caps, 1250VDC 0.82uF, with very thick terminals, so I assume they will have a much higher RMS current rating for when I want to upgrade.
The double static spark-gap is 3 8mm brass spheres on ceramic electric fence standoffs, with a mains-powered fan. I think each gap is currently 2 or 3 mm.
The primary coil is 6 turns of 16mm^2 insulated cable, with an inner diameter of 90mm and an outer diameter of roughly 250mm. The secondary is 50mm by 290mm wound with 1410 turns of (approx) .15mm wire. I've had this secondary for ages, and cant remember the exact wire gauge.
Here's a video of the coil running at 150-220 Vac from the variac (sorry for the crap quality):
And a crappy MS paint schematic:
Now, I'm wanting to improve this coil, since I'm sure it's capable of a lot more. I have those new Vishay caps, and the power supply can handle up to 1.5 - 2kVA if the variac is removed, but I'm not sure what else I need to upgrade? The secondary wire is very thin and only has a few coats of poly on it, will it be reliable at higher power?
Registered Member #2566
Joined: Wed Dec 23 2009, 05:52PM
Location:
Posts: 147
Make/find a better toroid/topload for a start. This one is too corrugated and sprays little corona sparks everywhere. For higher power levels (>500 VA) you should make a better spark gap too.
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
Thanks, I'll start working on a better toroid. Is brass still ok for a high powered spark gap, or should I try to find some tungsten?
Also, I've heard of the idea of using a second tuning inductor for the primary circuit, which might be handy since I've only got 6 turns and when I change to the new caps and top load I may find that I need more turns to hit resonance again. However, is it more efficient to simply have a larger primary? I would think the power transfer would be a bit lower if you had a primary coil then a series inductor, rather than just a larger primary?
Registered Member #2566
Joined: Wed Dec 23 2009, 05:52PM
Location:
Posts: 147
Brass is still ok and even copper works good too. But I was talking more about design than electrode material.Multisegment SG with bigger pipe or plate electrodes or Richard Quick SG will certainly work better than your current gap (especially at higher power).However,whatever you do keep on mind your small SGTC won't tolerate more than 600-700 W of power.Yes,it is more efficient to have larger primary than tuning inductor.
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
Thanks for the help.
I just did a bit of research on pipe segment gaps and Richard Quick gaps, seems like the best solution.
For the new primary I've got the choice of thin copper pipe or some high quality multi-strand 4awg power cable, probably gonna go with the cable, since the copper pipe is quite dented.
Looks like I've got some work to do, I'll post the updated coil when it happens. :D
EDIT: When I push the variac beyond 220V to full line voltage I've noticed that the output streamers become much shorter, bushier and a lot dimmer. I'm thinking perhaps the break rate rises too high, or perhaps the gap isn't quenching properly? Either way, I seem to be losing a considerable amount of power at higher voltages.
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My Mini SGTC, I've caught the coiling bug!
