# Proximity induction circuit and circular magnetic accelerator

Discussion in 'Electronic Design' started by jhead, Jul 3, 2007.

I am wanting to build a circular magnetic accelerator using a
proximity induction sensor to discharge the capacitors, that will
activate the electro-magnet coils just before the ball bearing reaches
the coil.

My question is this what kind of circuit will I need to build to use
an induction sensor to trip a "switch" and send power to the coil
nearest the steel ball (there will be an array of coils around the
plastic tube)?

I would rather not use a relay, as there would be moving parts, and
the switch would have to work quite rapidly once things got going.

I'm thinking that I may have to have several banks of capacitors as
there may not be enough time between discharges to charge the
capacitors array back up.

And what concepts should I further explore to make this work?

2. ### whit3rdGuest

Presumably you are pulsing magnets; you have to both turn them
ON when the ball is approaching and OFF when the ball is about
to depart. The problem is solved in some particle accelerators,
by modeling the acceleration of the particle and setting
accurate time delays to the multiple acceleration stages.
Since the acceleration is intended to be one unit per stage, your
times will be in reciprocal of the order of a quadratic series (1/M**2
for M = N, N+1, ...N+P).

The full capacity of your accelerator is reached when the ON/OFF
cycle is too slow for the fast-moving ball.
If you're pulsing magnets in the vicinity, DON'T use an induction
sensor.
The pickup-noise problem is... severe.

The circuits similar to what you are looking for are used for the
magnetizing of permanent magnets and/or surge testing of equipment.
Typically, they use powerful thyristors or IGBTs. Those devices are
quite expensive.
The relay contacts will be welded together by the surge current, unless
this is a special relay designed for this kind of operation.

DSP and Mixed Signal Design Consultant

http://www.abvolt.com

4. ### defaultGuest

Search for "coil gun" on the Internet. The idea is to put a piece of
steel in a plastic tube energize a series of magnets to propel the
steel out the end and into a target.

Depending on how many joules you need to switch it can be
inexpensively done with SCR's (thyristors) or IGBT's if they cycle
time needs to be very short (small loop).

http://www.coilgun.info/home.htm a place to start

5. ### neon

1,325
0
Oct 21, 2006
you will ned a LM555 generator whereby the design allow frequency canges and a ripple counter to run all your coils. coils like capacitors store energy s you will reach a limit somewhere whereby it will just resonatebasicaly stop time and distance is the criteria.

Thanks for the suggestions. I will be exploring optical sensing
methods, as any induction sensors would be swamped, as was basicly
pointed out.

7. ### MooseFETGuest

You also need to look at how you do your switching. Ideally, the coil
current will be snapped on just before the ball gets to the coil and
off just as it passes the middle of it. A sharp turn off, will
actually repel the ball out of the coil.

Ideally, the energy from the coil ends up back in the storage
capacitors. This will save on the heating of the system.

For anyone interested, here is my 3d rendering of my pre-prototype
idea:

9. ### John PopelishGuest

For a steel ball, there will be two completely different
effects taking place that can exert force on the ball. At
low frequencies, where the magnetic field has time to wait
for the surface eddy currents to die down, so the magnetic
field can pass through the ball, there will be forces caused
by the permeability of the steel. Those forces always act
in the direction that will increase the total magnetic flux.
The other and higher speed effect is the reaction between
the applied magnetic field and the magnetic field created by
the induced current, circulating in the surface of the
conductive ball (eddy currents). Since eddy currents
inhibit changes in the flux already passing through the
ball, this force can act as an attraction or a repulsion,
depending on the polarity of the external field, compared to
the one produced by the eddy currents. This effect is a lot
more complicated to describe in a few words, but, for high
speed rail machines, is the dominant effect available to
produce force, unless the moving body is relative non
conductive.