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Magnetic levitation

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LAN_403

TheMerovingian

Tue May 09 2006, 12:35PM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

I have determined the formula for current given voltage, duty cicle, diode voltage drop and coil resistence (frequency and inductance doesn't seem to play a role)

It is used to set the max duty cicle on the tl494

I(rms) = (V * Df - Vd)/(R*(1+Df))

Vd is the diode voltage drop
Df is the duty factor (Ton/Toff or D/(1-D) where D is the duty cicle)

It is slightly less then expected using the simple V*D/R formula and it is due to the diode voltage drop

Setting Vd to zero produces the simple formula V*D/R that is good for a worst case estimation

Tesladownunder

Tue May 09 2006, 04:42PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Reaching wrote ...

.. does anyone know if its possible to levitate a copper or aluminium disc stable via eddy currents(induction)?

It is possible to levitate a dish shaped copper or Al disc vertically but the power is large and the dish may be close to melting. I've not been able to manage it but 50Hz is rather low to work well.

You can in fact pick up non-magnetic washers with an AC electromagnet with an additional copper washer added to the core. Now a levitator for aluminium objects would be really cool

Peter

Reaching

Tue May 09 2006, 05:30PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

it works with 50hz and with a relative low current (around 5Amperes)
heres a video of a levitating heatsink, ok not really i need something to hold it in place.
the coil is directly connected to Mains, like a transformer

Hazmatt_(The Underdog)

Tue May 09 2006, 10:37PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

when are you guys going to start making maglev led clocks? You know, spins while being levitated. That'd be pretty fun!

cjk2

Tue May 09 2006, 11:21PM

Registered Member #51 Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263

After some tweaking, it seems that to fix the stability problems, all I needed to do was lower the frequency a little. Perhaps to make it stable, the frequency has to be kept near the max frequency of the field effect sensor. Im not sure, but it is working very well now.

GimpyJoe

Tue May 09 2006, 11:29PM

Registered Member #316 Joined: Mon Mar 13 2006, 01:30PM
Location: Marietta, GA
Posts: 212

It would be neat to put the whole thing in a vacuum and set the magnet spinning, just to see how long it would go. you would probably have to connect the coil to an aluminum bar which would connect to the base of the chamber, to sink heat.

Tesladownunder

Wed May 10 2006, 01:07AM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Reaching wrote ...

it works with 50hz and with a relative low current (around 5Amperes)
heres a video of a levitating heatsink....

Thats a nice shot. With 550W input something will melt eventually though

My display maglev has spun for up to 90 minutes in air. Needs a very deft flick of the wrist though to keep it in the right spot but still rotating fast enough.

A 625k MPEG of the rotating magnet is here.

Peter

cjk2

Tue May 16 2006, 02:28AM

Registered Member #51 Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263

I consider the project 95% done at this point.

Tesladownunder

Sun May 21 2006, 04:42AM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Neat stuff. I am starting to get inspired to make one for a display at the University on their Open Day in a few months. My museum one is just a bit too much to drag down for the day.

This time I want BIG. Perhaps levitating a really big spanner or perhaps a notebook computer or radio. Or for real cool a small magnetic levitator.

I just need to get my other 500 projects out of the way first....

Peter

TheMerovingian

Fri Jul 14 2006, 01:00PM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

I have made a levitator with this principle , except using one error amplifier as buffer for limiting the duty cycle, using a PNP bipolar driven dyrectly by the tl494, and using a diode to kill the offset of the amplifier, making the amplification easier with less offset voltage. I have only problems with the magnet overheating (max current 1.3A, "usual current" 900mA). Maybe i should use more turns. Anyway it is able to levitate a supermag structure weighting 80grams at 1 cm from the core.

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