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.
Registered Member #1747
Joined: Wed Oct 08 2008, 12:57PM
Location:
Posts: 6
Hi, This is my 1st post here, so Hi to everybody:)
I have recenlty stopped work on my gas turbine to concentrate on my tesla coil (i must have a subconcious love of building things that are dangerous)
I have a MOT which i am planning to re-wind for a 15kV supply. The secondary has already been removed.
I have wound high voltage transformers (up to 6kV) before but ive had plenty winding area and space to fit additional insulation between the windings, here it will be tighter.
I have 0.767v/turn open curcuit from the transformer (both measured with a few turns and calculded from the 300 primary windings at 230v) so for 15kV i need about 19600 turns.
My open window area is 43mm x 20mm, take that down to 42 x 19 to allow for some turns of Polyimide tape (RS components 468-421 70microns thick, 4.8kV insulation voltage) as insulation and winding holding.
Using wire with a maximum overall diameter of 0.165mm (0.132mm dia copper, or 35-36AWG or 38-40SWG) i can wind 250 turns allong the 42mm dimension. for 19600 turns, ill need 78 layers, these being a total thickness of 13mm. I have 19mm which leaves me with 5mm for insulating tape layers and any possible inaccurate winding layering. Theoretically at 0.07mm thick, i can fit 70 layers but i think thats optimistic. If i taped every 3rd layer, that would give 26 layers of tape.
Every 3rd layer would be 575v so i shouldnt have any issues(?)
My wire supplier (Comax) has gave me data sheets which shows the insulation on that wire is 0.021mm thick and has a breakdown of 110v/micron giving me a maximum of 2300v between any two wires. (see data attatched)
How often should i place additional layers of insulation which will be the 70micron tape able to withstand 4.8kV? Is every 3rd or so layer excesive?
Will i even need additional layers of insulation? I think so just due to breakdown of air around the wires.
Depending on the answers, i may go for more windings to get as high a voltage as possible (up to a max of 20kV perhaps(?)) by balancing windings with insulation.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Hi, sorry but I think 15kV is absolutely unrealistic for a MOT. You will have big problems with corona and even if it holds for first few seconds, it WILL arc over sooner or later. 15kV is going to jump more than 2cm in air and even more by surface tracking, so you would need to make sure that there is more than ~3cm of insulation tracking surface between winding and core.
The enameled wire will indeed stand a lot of voltage, but that's only assuming there is NO scratch or nick in the enamel. It's true that a non damaged enameled wire will stand more than a kilovolt.
If you can wind the layers on top of each other, with turns side-by-side and can make sure the wire does not slip near the lower layers, you would theoretically need no insulation between the windings. The best way to secure the layers in place is to varnish them before winding the next layer, this way the turns are held in place and won't slip.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
I would consider a couple of options;
1) Use a center-tap winding... e.g. 7.5 - 0 - 7.5 kV This will reduce the probability of flashover to earth/frame/core/primary etc. (i.e. just like a Neon Sign Transformer)
2) Put the transformer under oil ! I find it difficult to insulate a dry high voltage transformer. It's also easier to repair.
3) Consider a lower voltage. 5 - 0 - 5 kV for example would be significantly easier due to corona problems. For the same power throughput the spark gap would need to be a little better due to lower primary impedance but there would be very little overall performance change.
Registered Member #1747
Joined: Wed Oct 08 2008, 12:57PM
Location:
Posts: 6
Hi,
Thanks for your replies,
Dr K, I had considered this but thought that by wrapping the windings effectively creating 15 of 1kV winding sets would deal with this issue. If at all times i kept all connections potted or wrapped so as to minimise the chance of it happening.
Sulaiman, would you advise winding it as two separate coils, side by side where high's are on the outside and the grounded sides are closest to the core.
I see what you are saying about 5kV - 0 - 5Kv. My thought was, whilst i had the oppertunity to go for a higher voltage and get a higher energy (v squared) into the caps then i should try and acheive it.
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.