Date: Thu Nov 2 13:55:48 2006

Author: Dale Stille

Subject: Re: jumping rings "launcher" and load (fwd)

Post:

Mike,

The breaker on the variac is a 15 amp thermal, and the building is a 20
amp magnetic.

Dale

On Thu, 2 Nov 2006, Michael Timmins wrote:

> Do you know what type of breakers you are using? Are they thermal or magnetic
> or a combination. I could be that your coil heats up before the breaker
> reaches the temperature at which it "breaks".
>
> Mike
>
> On Thursday 02 November 2006 12:57, Dale Stille 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: tap-l@lists.ncsu.edu
>>> 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
>
> --
> Mike Timmins
>
> University of Virginia
> email: mat3q@virginia.edu
> phone: (434) 924-6800
> mail address:
> 382 McCormick Rd
> Charlottesville, VA 22904
>

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