If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
3 parallel strings of 15 (45 total) of Cornell-Dubilier CDE 942C20P15K-F
each shunted with 1M Ohm 1 watt metal film bleeder resistors for safety - I am very unsure of this, can metal film resistors handle 2Kv? I looked around and can't find a multiple mega ohm power resistor that can handle that kind of voltage so I can use one for each string but I understand they exist.
Spark gap:
3/8" tungsten carbide rods on heatsink (have a machinist buddy making them) with a shop vac to quench gap.
Plan to build structure mostly from Lexan. Will add strike rail. Going to live dangerously and not buy a new variac - mine won't handle 1800 watts.
Registered Member #1408
Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679
She's going to be LOUD! A single spark gap will be loud enough to almost deafen you unless it's in an enclosure of some type. Considered a multiple SG?
Registered Member #3515
Joined: Wed Dec 15 2010, 03:05AM
Location:
Posts: 11
quicksilver wrote ...
She's going to be LOUD! A single spark gap will be loud enough to almost deafen you unless it's in an enclosure of some type. Considered a multiple SG?
Isn't loud part of the fun?
Might be interesting to measure it's sound pressure level. I had planned to put the primary gap in the enclosure under the coil. But could have multiple gaps - would this make tuning more difficult?
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
dithersail -
Two points: 1. If you are using standard 6" PVC SDR pipe, the actual OD is 6.625". Using 6.7" will introduce a small error in your wire length and resonant frequency calculations.
2. Your target tank capacitor value for a 15KV, 120ma NST power supply with a static spark gap is .03uF, not 30uF.
3. The 15KV output rating on the NSTs is the RMS voltage, not the peak voltage. Multiply the RMS voltage by 1.414 to get the peak voltage. 15,000 X 1.414 = 21,210 volts. So your individual strings of 15 caps only provide a voltage safety factor of 1.4X, not 2X. See the MMC design chart at:
3. Your bleeder resistor value is incorrect They should be a minimum of 10 meg ohm, not 1 meg ohm.
4. Your concern about bleeder resistor voltage rating is valid. Use the 1/2 watt Vishay VR37 resistors, 10 meg ohms (Allied Electronics, etc.). These resistors have a much higher voltage rating (3,500V) vs the 300 or 500 volt rating of common metal-film resistors. I use two in series across each cap as this gives enough lead length to connect directly across the cap leads while still maintaining a reasonable standoff distance (1/4") between the resistors and the cap body.
5. Not sure what you mean by "transformer wire", you want to use enameled "magnet wire", preferably double or triple build insulation thickness.
6. Use of a variac is HIGHLY recommended for initial tuning, especially for this level of input power. You really don't want to hit a completely untuned coil with full line voltage. If you have access to an RF signal generator and oscilloscope to at least set initial tuning, you'll reduce the risk of secondary flashover ("racing arcs") that can destroy the secondary.
7. The noise from the output streamers will be greater than the noise from the spark gap. When the coil is correctly tuned, tuned the spark gap generates a sharp sizzle, not a gunshot.
I suggest that you cross-check all your calcs using JAVATC, also available at the link provided above.
You might consider building a hinged enclosure for your spark gap, not so much to reduce the sound level but to shield the light output. Obviously you'll want to take photos of the coil in operation, and the extremely intense radiation from the spark gap (nearly identical to an arc welder) will disrupt still and video photography.
Registered Member #3515
Joined: Wed Dec 15 2010, 03:05AM
Location:
Posts: 11
Herr Zapp wrote ...
dithersail -
Two points: 1. If you are using standard 6" PVC SDR pipe, the actual OD is 6.625". Using 6.7" will introduce a small error in your wire length and resonant frequency calculations.
got it, will recalculate....
2. Your target tank capacitor value for a 15KV, 120ma NST power supply with a static spark gap is .03uF, not 30uF.
Oops, mistyped.......
3. The 15KV output rating on the NSTs is the RMS voltage, not the peak voltage. Multiply the RMS voltage by 1.414 to get the peak voltage. 15,000 X 1.414 = 21,210 volts. So your individual strings of 15 caps only provide a voltage safety factor of 1.4X, not 2X. See the MMC design chart at:
Got it. Are these caps OK at 1.4x?
3. Your bleeder resistor value is incorrect They should be a minimum of 10 meg ohm, not 1 meg ohm.
Thanks I was unclear about this.
4. Your concern about bleeder resistor voltage rating is valid. Use the 1/2 watt Vishay VR37 resistors, 10 meg ohms (Allied Electronics, etc.). These resistors have a much higher voltage rating (3,500V) vs the 300 or 500 volt rating of common metal-film resistors. I use two in series across each cap as this gives enough lead length to connect directly across the cap leads while still maintaining a reasonable standoff distance (1/4") between the resistors and the cap body.
OK got it, I'll order those - I was going to mount the tank caps on a sheet of lexan drilled for the leads, with the resistors underneath on the other side of the lexan......
5. Not sure what you mean by "transformer wire", you want to use enameled "magnet wire", preferably double or triple build insulation thickness.
Yes, magnet wire - can you suggest a good source?
6. Use of a variac is HIGHLY recommended for initial tuning, especially for this level of input power. You really don't want to hit a completely untuned coil with full line voltage. If you have access to an RF signal generator and oscilloscope to at least set initial tuning, you'll reduce the risk of secondary flashover ("racing arcs") that can destroy the secondary.
I'll see what I can get my hands on - I do have an oscilloscope but not a RF generator....
7. The noise from the output streamers will be greater than the noise from the spark gap. When the coil is correctly tuned, tuned the spark gap generates a sharp sizzle, not a gunshot.
I suggest that you cross-check all your calcs using JAVATC, also available at the link provided above.
You might consider building a hinged enclosure for your spark gap, not so much to reduce the sound level but to shield the light output. Obviously you'll want to take photos of the coil in operation, and the extremely intense radiation from the spark gap (nearly identical to an arc welder) will disrupt still and video photography.
All great advice, I really appreciate it. I'd rather be successful first try........
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
dithersail -
All good.
For your magnet wire, there are many sources. Since you are going to put a fair amoint of effort into this coil, I'd recommend either Ham swap meet or spending the money for new commercial magnet wire. Be very careful of eBay "hobby wire", as this may be commercial magnet wire that has failed the insulation pinhole test or has out-of-spec insulation thickness. The stuff I've found at Ham swap meets us usually first quality industrial surplus or overstock.
The C-D 942 caps will survive with a 1.4X voltage safety factor, but more margin is better. You are going to have a fair investment in the cost of the caps, so I'd be very conservative. Four strings of 20 caps each is pretty conservative, but will set you back a few more $$.
I'd recomend NOT directly mounting the caps on a drilled piece of polycarbonate, or any other plastic. I've seen several MMCs built this way that "failed" because of surface tracking (insulation breakdown) across the surface of the plastic. Much better is to mount the caps on "turret standoffs", or even home-made standoffs constructed from 1" threaded nylon standoffs mounted on a 3/8" thick plastic panel. High density polyethylene is best from the point of insulation performance, but acrylic, polycarbonate, or polystyrene will work.
Registered Member #3515
Joined: Wed Dec 15 2010, 03:05AM
Location:
Posts: 11
Thanks for the pic - very informative I can emulate. I do have access to a supply of HDP. I don't know of any ham swap meets in our area - I'll ask around. Maybe I can find a source online.
Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
I got wire from magnet4less once. I got the 32 gauge, heavy build, and as I was winding, I noticed that the wire was not all the same color. And I kept finding these hard lumps on the wire, which when picked off, I found compromised the insulation! Of course, this could only happen after I was 75% done with my coil...
So I left a very poor review, which seems to have disappeared from their site! Very honest and professional, no?
Maybe it was a problem with the very fine wire, or maybe all their stuff is crap, all I know is that I'm never buying from them again.
I will be winding with wire from Parawire for my big coil in the next few days. I think it's 26 gauge or so. I believe Arcstarter has had good experiences with this company, and from what I can see with the wire on the spool, it looks fantastic! Will report back with final results when I actually finish with the stuff.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
Check design of first spark gap coil?
