Electromagnetic Ring Launcher -- Building a Science Museum Classic: Page 4 of 4

The Jumping Ring or Electromagnetic Ring Launcher experiment is a staple of science museums and physics class rooms. Here's how to build your own right in your home.

2N2906

PNP transistor

70348161 

Q3

TK32E12N1

Power MOSFET

70017262 (equiv   IRFB61N15DPBF)

R1

180 Ohm

Resistor,

70024696

R2

100K

Potentiometer

70153741

R3

1k

Resistor

70648011 

R4

4.7 Ohm

Resistor

70023927

R5

10 Ohm

Resistor

70183308 

R6

20k

Resistor

 70183654

R7

4.7K

Resistor

70650980

R8

10 Ohm, 25W

Power Resistor

70201458 

 

 

2-pin Terminal, 4 pcs

70086275 

 

 

Heat Sink – 2 Pcs

70115166 

PS1

15V, 800 mA

Power Supply1

70231086 

PS2

 

24V, 4.5A

 

Power Supply 2

 

70177388 

S1

ON/OFF

Switch

70192043

S2

ON/OFF

Switch

70192043

L

~238 uH

Coil with ferrite core

 

C

8.2 uF + 8.2 uF

2 capacitors paralleled

70260082

 

 

Binding post (Red) 2pcs

70210915

 

 

Binding post (Black) 2pcs

70198054

 

 

BOX

70148724

 

 

Ferrite Cylinder – 2 pcs

Fair-Rite #2643625202

Other items those needed for the project are, screws, nylon screws, hook-up wire.

Comments

Note that with a 15 Volt supply to the 555 and R1 at 180 Ohms, you'll have over 80 milliamps running through R1 into the discharge pin during the discharge cycle. The discharge transistor may well come out of saturation at that current, resulting in substantial power across that transistor. You run the risk of destroying your 555. The ST datasheet for the NE555N shows a worst-case saturation voltage of 480 mV at only 15 mA when operating at Vcc=15V. You have more than five times that current.

Hello William: I think your information is wrong. If you take a closer look at the data sheet of NE555, you will see that at Vcc=15V, Idisch=15 mA, Vsat has a minimum to a maximum value of 480 mV. Furthermore, take a closer look at the footnote, even if you take a lower value for R1, there is an internal current limit. At 80 mA, the collector emitter voltage Vce of the discharge transistor is less than a volt. Now considering the duty cycle calculate the power dissipation and consider the therm

thermal resistance Rthja. you will find the package (DIP8) temperature is well below the maximum allowable range. Practically, I ran the circuit for quite a long time, without overheating or damaging the IC NE555

Does the circuit being resonant limit the rate of current increase in the coil? I've only ever made a launcher (not for hovering) and needed to get the current in the coil to maximum before the ring left the field. I dumped about 30A @ 240V into the coil. My launcher gets the ring 2m to 3m into the air at room temperature. When the (aluminium) ring is cooled in liquid nitrogen then it reaches the top of a three storey atrium - about 10m. It's used for university demonstrations.

Hello John: Nice to know your wonderful experience. The detailed analysis of a similar circuit is published in the journal "Physics Education" Jan., 2016. The use of resonance gives us the advantage that if the supply current is ~2A, actual coil current is ~8 to ~ 10 times. So, we need a smaller DC supply. Furthermore, at higher frequency, the upward force is also higher, as it gives larger phase difference between induced voltage and current in the ring

Wow! I built one of these in 7th grade. I must have been about 13. The core was made of laminations of black stove pipe iron: sheet metal strips varnished so they wouldn't conduct eddy currents. The strips were 1" x 12", laminated into a core 1" x 1" x 12". The ring was a stack of aluminum sheets, about 1.5" ID and 4" OD. The coil was a few hundred turns of AWG 18 or 20 wound between two 1/8" masonite spacers maybe 3" apart on one end of the core. Ring never hovered but did fly off impressively

Hello Laurence, It is nice to know your experience. This jumping ring effect really makes lot of kids curious, even today. I was also fascinated when I was a kid, but never tried anything at that time like you. Thanks for your comments.

Can you post more info on making L1? The photos show a toroidal coil with about 25 turns on it, but the text says 40 turns on a cylindrical core - at least that's what I get out of it.

Hi Mark: I wrote the instruction for an air core coil, it will work, Though, in the photo, you can see I used a toroidal ferrite core with few turns on it. I do not recommend doing it, because most of the toroidal core you buy have high permeability and high hysteresis loss at the frequency of our interest. I used the core, as I have it at my disposal which has a low permeability and low loss. However finding a similar one in the supplier's stock is a time consuming job. Rather, it is better to

make one with air core. Though the number turns are larger, it will not affect the normal operation. If you have a ferrite rod, you can also make the coil with 10-15 turns on it. this is also better than choosing a ferrite toroid. The purpose of the coil is only to prevent transient high current. I have a pretty bad experience with various types of toroids. Most of these heat up and hamper the normal operation by consuming extra power.

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