Date: Thu Nov 2 16:46:17 2006
Author: Michael Timmins
Subject: Re: jumping rings "launcher" and load (fwd)
Given the numbers quoted, I get a power factor of ~.01 for Dale's setup. So
this is probably the reason the breaker survives. I remember the first time
someone told me that there was no real current going through a transformer
not under load. I didn't believe them till I tried it. It's very
However, I would still be careful telling people to plug their air core
solenoids into an outlet without doing a quick calculation or at least using
a variac as a check.
On Thursday 02 November 2006 15:34, Dale Stille wrote:
> Cliff, JZ, and all,
> JZ has hit the nail on the head here I believe. This is the reasoning I
> have been using ( although not entirely convinced so not with my usual
> fervor ) to explain this. Cliff.....I used a regular BK meter to measure
> the amps but it only went to 20 amps.....and so then I pulled out the old
> "clamp-on" meter. It was passing 67 amps when I shut it down due to the
> heat buildup.
> But, no matter what is really happening, that AC electromagnet demo sure
> works good.......
> On Thu, 2 Nov 2006, Gerald Zani wrote:
> > My reasoning to Dales Dilemma:
> > The inductance has pushed the current out of phase with the voltage.
> > Without the inductance that current would easily blow the breaker. But
> > the reason you can put 60 or 70 amps through a 15 or 20 amp breaker is
> > that current is imaginary and not real. It lags the voltage by 90
> > degrees because of the inductance. The real current is brought down by
> > the sine of the angle between the current and the voltage.
> > A wise saying from my tech school daze:
> > "ELI the ICE Man. "
> > Meaning:
> > ELI:The voltage Leads the current in an inductive load by 90 degrees.
> > ICE: The current leads the voltage in a capacitive load by 90 degrees.
> > A purely inductive or purely capacitive load will draw only imaginary
> > power and will not dissipate real power. It is the resistance that draws
> > real power.
> > NO?
> > Am I wrong? -- JZ
> > At 12:57 PM 11/2/2006, you wrote:
> >> ---------- Forwarded message ----------
> >> Date: Thu, 2 Nov 2006 11:31:11 -0600 (CST)
> >> From: Dale Stille
> >> To: "John Cockman, Jr."
> >> Subject: Re: [tap-l] jumping rings "launcher" and load
> >> John and Mike,
> >> You got my curiosity going now.....so I did some real measurements on my
> >> coil. The demo we routinely do with this is to show this as an
> >> electromagnet with and without the coil. We routinely turn our variac
> >> up to about 80 volts for both of these demos. You can't do it for
> >> extended periods because the coil heats up pretty fast. So, when I
> >> measured the current when used without the coil it shows we are pumping
> >> 60 to 70 amps through this for the short time we use it. Curious,
> >> because the room circuit breakers are 20 amp breakers and the breaker on
> >> the variac is a 15 amp breaker......and yet we have blown neither of
> >> these doing this demo in the 20 years I have been here. And before you
> >> say the breakers aren't working.....we know they are because we have
> >> other demos where we do break them on a routine basis. When we insert
> >> the coil and repeat the demo, then our current is down to 10 to 15 amps.
> >> According to your reports it shouldn't work......and yet it does. And
> >> it is also not just a single special coil that does this. I have built
> >> 4 other coils of this design since I have been here and they all work
> >> the same.
> >> Later,
> >> Dale
> >> U of Iowa
> >> On Thu, 2 Nov 2006, John Cockman, Jr. wrote:
> >>> L = r^2*n^2/(9*r+10*l)
> >>> r = radius of coil
> >>> l = length of coil
> >>> n = number of turns
> >>> Inductive reactance XL = 2*pi*f*L, where f=60hz
> >>> Impedence Z = (XL^2 + R^2)^1/2 where R is the resistance
> >>> You probably want V/Z to be less than an amp.
> >>> John
> >>> ----- Original Message -----
> >>> From: Krishna Chowdary
> >>> To: email@example.com
> >>> Sent: Thursday, November 02, 2006 10:09 AM
> >>> Subject: Re: [tap-l] jumping rings "launcher" and load
> >>> I knew I was forgetting something obvious. Thanks to all who reminded
> >>> me about the inductive reactance of the solenoid+core itself
> >>> contributing to the overall impedance of the circuit.
> >>> Followup question: clearly if the inductance is too small, I _would_
> >>> blow a fuse or melt something. The inductance is related to the number
> >>> of turns on the solenoid, solenoid geometry, and any conducting core
> >>> filling material. If I were to do this with just a simple air core
> >>> solenoid, does anyone have experience with dimensions, number of turns
> >>> per unit length, wire gauge, etc.to get a reasonable inductive load at
> >>> 60 Hz? Again, my goal is to plug an air core solenoid into a wall
> >>> outlet safely.
> >>> Again, thanks for your input.
> >>> --
> >>> regards
> >>> -Krishna
> >>> Krishna Chowdary
> >>> Department of Physics & Astronomy
> >>> Bucknell University
> > Gerald Zani e-mail: Gerald_Zani@brown.edu
> > Manager of Demonstrations phone: (401) 863-3964
> > Department of Physics FAX: (401) 863-2024
> > Brown University Providence, RI 02912-1843 USA
> > http://www.physics.brown.edu/physics/demopages/demo/
> > http://www.physics.brown.edu/physics/userpages/staff/Gerald_Zani/index.ht
> > Do a little more of that work which you have confessed to be good,
> > Which you feel that society and your most Just Judge rightly demand of
> > you. Cultivate the tree which you have found to bear fruit in your soil.
> > If you have any experiments you would like to try, try them.
> > Now's your chance.
> > Henry David Thoreau, Journal entry, 1850.
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