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 #3925
Joined: Fri Jun 03 2011, 10:50AM
Location:
Posts: 121
hey,
i have a few questions about FBTs, etc soo -
could a voltage multiplier be used with a modern dc flyback transformer? what would be the advantage of using a 100nf capacitor in a voltage multiplier, instead of a 1pf capacitor? im not sure what the capacitance changes. how big a spark have you found to be acheiveable from a dc flyback? because i can get about a 5cm spark, but the fbt fails quickly, the first fbt lasted for hours, but the second only for 10 minutes, and the third one after about 10 seconds, (fortunately the third one is still useful, as it has different secondary windings which i can use)
and also, is it possible to cool a potted dc FBT in oil, cos i wouldnt have thought it would work very well since its sealed. finally - could i use the ferrite core from one of the failed FBTs, as the core for a homemade FBT i intend to make? it should be as simple as putting the primary on one side of the ferrite core, and the secondary on the other right?
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
alf wrote ...
hey,
i have a few questions about FBTs, etc soo -
could a voltage multiplier be used with a modern dc flyback transformer?
Unfortunately no, it needs the negative swing of a non-rectified transformer output.
wrote ... what would be the advantage of using a 100nf capacitor in a voltage multiplier, instead of a 1pf capacitor?
A voltage multiplier suffers from voltage droop as load current increases, because the capacitors have an AC impedance. With a larger capacitor the current can reach higher values before the voltage droops.
wrote ... and also, is it possible to cool a potted dc FBT in oil, cos i wouldnt have thought it would work very well since its sealed.
It might provide some benefit for longer periods of operation at somewhat higher power levels than it's designed for, but if you're going for very high power pulsed operation then the inside will heat up before much heat can make its way through the case of the transformer to the oil.
wrote ... finally - could i use the ferrite core from one of the failed FBTs, as the core for a homemade FBT i intend to make? it should be as simple as putting the primary on one side of the ferrite core, and the secondary on the other right?
Absolutely you can. Most flyback transformers use a very high permeability ferrite core (exact permeability might not be known) but they set the effective permeability of the core using air gaps of known length. Chances are this has been done and you can just keep the spacers that are already in between the two core halves. Now it's also important to point out that a flyback transformer can be driven in true flyback mode, or in a forward or symmetric converter mode. Generally speaking flyback mode can get you to a higher voltage while forward and symmetric converters get you more power. For a forward or symmetric converter you might want to remove the core spacers.
Also, for the best transformer quality you actually want to wind the secondary on top of the primary. We often see the cartoon drawings of a transformer with both windings on opposite sides of the transformer, but this leads to a higher leakage inductance. When you drive the transformer the leakage inductance on the primary side will cause a voltage spike on the switching transistor which will heat up your transistor more than it needs to.
Registered Member #3925
Joined: Fri Jun 03 2011, 10:50AM
Location:
Posts: 121
Daedronus wrote ...
The first thing to fail ( at least for me ) in a FB transformer is the diode, After that you have a lower voltage flyback, but it's AC.
I have a cople of DC flybacks like that, that now have become AC
It's easy to tell if they become AC, they will no longer power my marx generator...
hey,
right, i dont think that has happened to me, because instead of a big hot arc, i just get a 5mm or so purple crackly spark, like a static spark, with no current, so maybe the secondary has fused, and it is arcing?
so a marx generator will work with a pulsating dc input, and a cockcroft walton multiplier will only work with an ac input? could i use a mark generator to boost the fbts output voltage to 200kv, to power an x-ray tube, or would the current be too low? and, if the supply voltage is 20kv, the capacitors in a marx generator will only need to be rated to 20kv, right? aww, but atleast they will have other uses, like a plasma globe :D
I think the failure mode depends on the reason it failed, if you put too much power in it it's possible that indeed the windings have fused. When my flybacks failed I was get really long sparks, 5 - 6cm+ but with very little power, so most probably the over voltage killed the output diode.
I was still getting decent sparks after that, but far smaller, 2-3cm. I plan to make a external CW multiplier for my abused FB one of this days....
The output of a marx generator is a very intense pulse. You can get some incredible sparks from one. It should have no problems getting to 200Kv (and more), but it will be more of a flash X-Ray, not continuous.
And last, just so you know, if you play with a marx, keep any kind of electronics far from it.
Registered Member #3925
Joined: Fri Jun 03 2011, 10:50AM
Location:
Posts: 121
Daedronus wrote ...
I think the failure mode depends on the reason it failed, if you put too much power in it it's possible that indeed the windings have fused. When my flybacks failed I was get really long sparks, 5 - 6cm+ but with very little power, so most probably the over voltage killed the output diode.
I was still getting decent sparks after that, but far smaller, 2-3cm. I plan to make a external CW multiplier for my abused FB one of this days....
The output of a marx generator is a very intense pulse. You can get some incredible sparks from one. It should have no problems getting to 200Kv (and more), but it will be more of a flash X-Ray, not continuous.
And last, just so you know, if you play with a marx, keep any kind of electronics far from it.
hey,
right, hmm my failed fbt is producing big sparks also, but intermittently :-/
ahh ok, would it be possible to omit the resistors in the marx generator, to increase the pulse frequency? and with my fbt, i can draw around a 2 inch spark, and at about 1 inch, it changes gradually from a orange spark to a blue crackly one, roughly what voltage would this be? maybe enough to power an x-ray tube hopefully :P
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.
questions about flyback transformers?
