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 #61373
Joined: Sat Dec 17 2016, 01:45PM
Location: San Antonio, TX
Posts: 87
I read somewhere that resonance only makes the relationship between voltage and current change (in or out of sync), but not really boost power, which somehow makes the arcs longer. I also notice that my MOTS get hot real fast and draw 1.5 to 2x the current on primary without resonant caps. I don't know if all that extra current draw is just the power factor or if there is another reason why.
The resonant caps make the output arcs much brighter and longer, so the voltage must be much higher?
Does resonance increase the current output also?
How can current and voltage be out of phase if voltage pushes a current?
Registered Member #61375
Joined: Sat Dec 17 2016, 05:45PM
Location: Norway Aalesund
Posts: 13
Hi ScottH You are woundering about the magic of electricity i think.. Faraday found out that a current want to stay in its state, and oppose any change.. This is natures "conservatisme", any change is unwanted.
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
I don't know the entire story, but my understanding is that it cancels out the reactance (or, AC resistance) of components in your circuit.
A microwave oven primary has quite a bit of inductance; A random measurement I found online showed 63 mH of inductance.
At 60 hz that calculates out to be about 23.75 ohms of reactance, on top of the resistance of the wire, and the resistance + reactance of the secondary.
However if you run the transformer in resonance that reactance drops to almost zero, and then you're just fighting the resistance of the wire.
That's how DRSSTC's can get such incredible arcs; both the primary AND secondary are driven in resonance with eachother, so the maximum power outputs you can get are limited only by the resistance of the wires, and your power supply.
Please correct me if I'm wrong anyone by the way. I'm PRETTY sure this is how it works, but... I have been wrong before.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Yes, resonance can cancel out series impedances, resulting in higher power output. Of course this comes from higher power input, there's nothing magical going on.
In the case of a MOT, the shunts create a leakage inductance which limits short circuit current. Putting a capacitor in series with either primary or secondary can cancel some or all of this, resulting in higher short-circuit current flowing.
Voltage and current with be in phase at a resistor. At a capacitor, current will lead voltage by 90 degrees. At an inductor, voltage leads current by 90 degrees.
You might combine this last two to see that if a current flows through both an inductor *and* a capacitor in series, the voltage across each will be in anti-phase, so reducing the impedance of the pair. When the individual voltages have the same magnitude, the total voltage will be zero, the pair are resonant, and the remaining series impedance is due to only the resistive losses in the components.
If you combine an inductor and capacitor in parallel, so they see the same voltage, then their currents are in anti-phase, and the terminal current of the combination will be less than the terminal current of either of them. At resonance, no input current is required to support any circulating current between the two, until losses get in the way.
Registered Member #61373
Joined: Sat Dec 17 2016, 01:45PM
Location: San Antonio, TX
Posts: 87
Dr. Slack wrote ...
Yes, resonance can cancel out series impedances, resulting in higher power output. Of course this comes from higher power input, there's nothing magical going on.
In the case of a MOT, the shunts create a leakage inductance which limits short circuit current. Putting a capacitor in series with either primary or secondary can cancel some or all of this, resulting in higher short-circuit current flowing.
Voltage and current with be in phase at a resistor. At a capacitor, current will lead voltage by 90 degrees. At an inductor, voltage leads current by 90 degrees.
You might combine this last two to see that if a current flows through both an inductor *and* a capacitor in series, the voltage across each will be in anti-phase, so reducing the impedance of the pair. When the individual voltages have the same magnitude, the total voltage will be zero, the pair are resonant, and the remaining series impedance is due to only the resistive losses in the components.
If you combine an inductor and capacitor in parallel, so they see the same voltage, then their currents are in anti-phase, and the terminal current of the combination will be less than the terminal current of either of them. At resonance, no input current is required to support any circulating current between the two, until losses get in the way.
Does resonance work with the MOTS wired in parallel as well? By terminal current, do you mean the current drawn by the primary? Can you explain how current and voltage can be out of phase?
I thought a voltage drives the current, making power. When the current is out of phase with voltage, does VxA=W if they aren't working together at the same time?
If possible, do you know roughly how many Henries of inductance the secondary of a large MOT has?
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Does resonance work with the MOTS wired in parallel as well?
Yes
By terminal current, do you mean the current drawn by the primary?
I mean the current drawn at the terminal of whichever component I'm talking about, so the inductor, the capacitor, or the combination of the two
Can you explain how current and voltage can be out of phase?
Current and voltage are independent. It's only when you are driving a resistor that they're in phase. If you're driving a current into a capacitor, then the voltage is the time integral of the current/C. If you're putting a voltage across an inductor, then the current is the time integral of the voltage/L.
I thought a voltage drives the current, making power.
For a resistor
When the current is out of phase with voltage, does VxA=W if they aren't working together at the same time?
No. That's where you get power factor coming into the equation. For a capacitor or inductor across a supply, the voltage and current are in quadrature, no power is dissipated, the power factor is zero, you have a finite VA, but zero W.
If possible, do you know roughly how many Henries of inductance the secondary of a large MOT has?
Never measured one. Here's a rough estimate though for one I have. Core area 70x35mm, approx magnetic length 260mm, assume iron has ur of 2000, guess at 2200 turns. H field for 1 amp one turn = current/length = 1/0.26, B field = u*Hfield = 4pie-7*2000/0.26, flux = area*Bfield = 0.07*0.035*4pie-7*2000/0.26, inductance = n^2.flux = 114H. Of course, should the iron saturate, the ur and hence the inductance will plummet.
The other important inductance in a MOT is the leakage inductance. That's the inductance due to the shunts, that appears in series with the MOT. This is the inductance that's resonated out with a series capacitor. I don't have an estimate for this inductance.
Registered Member #61373
Joined: Sat Dec 17 2016, 01:45PM
Location: San Antonio, TX
Posts: 87
Dr. Slack wrote ...
Does resonance work with the MOTS wired in parallel as well?
Yes
By terminal current, do you mean the current drawn by the primary?
I mean the current drawn at the terminal of whichever component I'm talking about, so the inductor, the capacitor, or the combination of the two
Can you explain how current and voltage can be out of phase?
Current and voltage are independent. It's only when you are driving a resistor that they're in phase. If you're driving a current into a capacitor, then the voltage is the time integral of the current/C. If you're putting a voltage across an inductor, then the current is the time integral of the voltage/L.
I thought a voltage drives the current, making power.
For a resistor
When the current is out of phase with voltage, does VxA=W if they aren't working together at the same time?
No. That's where you get power factor coming into the equation. For a capacitor or inductor across a supply, the voltage and current are in quadrature, no power is dissipated, the power factor is zero, you have a finite VA, but zero W.
If possible, do you know roughly how many Henries of inductance the secondary of a large MOT has?
Never measured one. Here's a rough estimate though for one I have. Core area 70x35mm, approx magnetic length 260mm, assume iron has ur of 2000, guess at 2200 turns. H field for 1 amp one turn = current/length = 1/0.26, B field = u*Hfield = 4pie-7*2000/0.26, flux = area*Bfield = 0.07*0.035*4pie-7*2000/0.26, inductance = n^2.flux = 114H. Of course, should the iron saturate, the ur and hence the inductance will plummet.
The other important inductance in a MOT is the leakage inductance. That's the inductance due to the shunts, that appears in series with the MOT. This is the inductance that's resonated out with a series capacitor. I don't have an estimate for this inductance.
So why is the primary current draw much less when the secondary is in resonance, if resonance makes it act like the shunts are not there? Also, why don't my transformers get hot when resonating and putting out much more power? When I run the Mots with no caps, they overheat fast and blow the fuse.
Other YouTube videos measuring draw current with vs without caps show that the primary current draws more from the wall with resonant caps, but the opposite is true in my case as my setup probably pulls 20a at 120v (caps) vs 32a (no caps). Can you explain how that works? Thanks.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Post schematic diagrams of how you have caps connected to the MOTs. As I said, you can resonate different inductances, it's not clear what you are doing.
Registered Member #61373
Joined: Sat Dec 17 2016, 01:45PM
Location: San Antonio, TX
Posts: 87
Dr. Slack wrote ...
Post schematic diagrams of how you have caps connected to the MOTs. As I said, you can resonate different inductances, it's not clear what you are doing.
I don't have one, but I'll explain. I have 2 Mots with primaries wired in parallel. I have 2 sets of 2 Mocs each wired in parallel connected to each HV output. Since it is wired in phase, I wired the HV output wires from the 2 Moc sets to one wire. There is the Neutral HV terminal, which is wired to the Earthed body of the Mot. Both Mot transformer bodies (cores) are sitting on a foil base so they make contact with each other.
I experience the same things when they are wired in anti-phase/ anti- parallel (Moc HV outputs are not wired together in this configuration, they arc to each other).
The caps are .75uf each. Overall capacitance of the 2X2 cap setup totals .75uf
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
You've left out some connections. You draw the output arc (a) in series with the capacitor, to ground or (b) the capacitor is to ground, and you draw the arc across the capacitor?
you can use ascii art to draw a schematic if you *really* can't be bothered to install LTSPICE and do a screen cap
___________
| | |
MOT == z
__|_____|_____|____
but SPICE is kinda handy to have on your computer anyway
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.
Does resonance in a MOT actually boost power output?
