Electromagnetic Ring Launcher -- Building a Science Museum Classic: Page 3 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.

its inductance and resistance were measured using LCR meter. Two ~8 micro Farad capacitor were paralleled to make ~ 16 micro Farad and the combination was connected in parallel with the coil. Now the resonance frequency can be calculated using the well-known formula:

Resonance frequency can also be measured using an oscilloscope and a function generator. This procedure can be found many places in the net.

Detailed specifications are given below.

Diameter (coil former): ~27 mm, length: 16 mm, number of turns, N: 50 ~ 60, wire size: # 14 AWG. Ferrite cylinder of diameter ~16 mm was inserted through the coil (two cylindrical ferrite rods were attached using nylon screws and stand-offs). Measured inductance is ~ 110 mH ( ~235 mH, with the ferrite core inside). Measured resistance ~ 0.1W,  with C = 16 mF measured resonant frequency, fr ~ 2.6 kHz

 

 Fig.5. Coil with 16 micro Farad capacitor in parallel. A copper ring is shown through the extended ferrite cylinder.

The whole system consisting of the boxed circuit-PCB, power supplies and the coil; which is shown in Fig.6.

 

Fig.6. Photograph of the complete system

 

 

Test Procedure:

To set the condition for optimum operation, the coil-Capacitor circuit should be set at resonance. Without using any expensive equipment, we can easily make sure of this condition following the block schematic as shown in Fig-7.

 

Fig.7. Setup for resonance

Before connecting the 24V supply we have to make sure that the 10 Ohm resistor-shunt-switch (S2) is open. Now connecting the 24V supply  to an Ammeter in series with the circuit, the potentiometer R2 is slowly turned from high to low, which causes frequency to go from low to high. As the frequency goes up the current goes down and we can see the ring starts to levitate. At resonance, the current goes to the minimum at ~ 1.2 A. At the resonance, the copper ring levitates ~2 cm  above the coil. Now if the 10 Ohm resistor is shorted by closing S2, the ring jumps out of the ferrite rod. Keeping the switch S2 closed, if power switch S1 is turned ON from OFF, the ring jumps tens of centimeter above the rod. All of this tests are shown in the video. The circuit can be even run at voltages higher than 24V. If driven by 48V, even much higher jump is seen.

Oscilloscope waveforms are shown in Fig.8 when the coil is at resonance.

Fig.8. Waveforms at the MOSFET Gate, Drain, Coil-high side and across coil, when the coil is driven at resonance.

 

Parts List

 

Part

 

Value

 

Description

 

Allied Part #

C1

0.01u

Ceramic Capacitor

70079249

C2

0.1 uF

Ceramic Capacitor

70095155

C3

0.1 uF

Ceramic Capacitor

70095155

C4

0.1uF

Ceramic Capacitor

70095155

C5

0.1 uF

Ceramic Capacitor

70095155

C6

100uF

polarized capacitor

70187892

C8

100uF

polarized capacitor

70079479

D1

FFPF30UA60S

Fast RecoveryDiode

70078639 

VS-15ETH06FPPBF

D2

18V

Zener Diode

70061620 

IC1

NE555N

Timer IC

70550780 

L1

5uH

Inductor

~ 40 turns on 1cm dia. plastic tube

Q1

2N2222

NPN transistor

70725575 

Q2

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.

Pages

Add new comment

By submitting this form, you accept the Mollom privacy policy.