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Tesladownunder

Sun Feb 19 2006, 02:57AM

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

I got this electromagnet as a throw out via the Uni Chemistry Dept where I gather it was used for magnetic resonance stuff. Probably weighs 50kg. It is ancient and uses cotton covered wire and solid iron square bar so is not for AC.
Run at only 150W, here the power is much greater than my 1 inch NIB magnets.
In the pic below a drill is supported by the spade bit between the pole faces.
I haven't tried a higher power yet but might if I have something to show such as plasma in a neon tube or liquid oxygen.

Peter

1140317823 10 FT0 Magnetphysics140wdrill

Marko

Sun Feb 19 2006, 01:29PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Seems really huge compared to that drill...

If you have any ferrofluid left it may be interesting to try it at full power

Maybe its a good idea to varnish that wire a bit to stop cotton degrading..?

Tesladownunder

Sun Feb 19 2006, 06:31PM

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

Ferrofluid. Hmmm.. I should have thought of that since I have a new unopened lot.

The coil resistance is about 1 ohm each side. I have no idea how much it will take before saturation - presumably around 2 Tesla for iron. I will have to make up a little gauss meter to plot a B/H curve.

I might see whether the forces on Bismuth are noticeable as well. Waving a copper bar through there gives very noticeable slowing.

Peter

Marko

Sun Feb 19 2006, 06:51PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

2 tesla i horrid amount of flux, doubt its that big...

It actually turns all energy input into heat, you can drive it to saturation it would not be a big problem as long as it can dissipate enough heat...

Wire seems thick btu I dont know how much can cotton insulation take, varnishing may help...

Variac + high power diode bridge, maybe ''few'' huge smoothing caps??

Tesladownunder

Sun Feb 19 2006, 07:02PM

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

Wiki says iron saturates at 2.2 Tesla.

The cotton insulation is probably fine - after all it must have lasted about 50 years. The insulation requirements are low because the turn to turn voltage is low and limited only by resistance and not inductance. The coil is inches thick and each one has 7.5 volts across it.

I have a supply that will handle much more DC current. Unfortunately parked at the back of my shed and as accessible as Pluto. I will need it for more serious experiments.
Or I could parallel the coils and run from the same supply pictured at 15 V 36A (rated 15.5V at 40A)

Peter

Marko

Sun Feb 19 2006, 07:13PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Ok for iron i tought for magnet, at full power :)
Or maybe it really could, in magnetic resonance there are often used magnets of several tesla (but really huge, superconducting magnets) ???
Gauss meter is a good idea if you can get one...

..ferrofluid

Bjørn

Mon Feb 20 2006, 01:00AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

The strongest electromagnets traditionally have been water cooled copper coils since superconductors does not like strong magnetic fields. There are also hybrids that combine the two to reach even higher levels.

Did you try to run the drill to see if the bit got hot?

Tesladownunder

Mon Feb 20 2006, 01:14AM

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

I am not going to be levitating frogs with this.
Thinking about the design of a hybrid coil (I recall superconductor for outer coil and standard for the inner coil) gives me ideas for augmenting this field with a can crushing type of coil in the air gap. It may not work though due to the proximity to the iron cores.
I would like to measure multi tesla fields in real time and will have to look it up.

Peter

Simon

Mon Feb 20 2006, 02:51AM

Registered Member #32 Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549

You could try a putting a glass of water between the poles and then turning the thing on. I've heard of people bending the meniscus of water with NIBs (but I've never noticed it happening for me).

Dave47

Mon Feb 20 2006, 01:48PM

Registered Member #84 Joined: Thu Feb 09 2006, 01:06PM
Location: Dallas, TX
Posts: 47

My Master's thesis involved electron spin resonance. The test setup used one of the big 60s era Varian magnets like the ones that BjÃ¸rn described. The power supply was huge, water cooled, linear, and ran about 100 amps (maybe more... I can't remember exactly). All that, and its max field was ~1 tesla. Resonance was then achieved with ~11GHz of microwaves generated by a Varian Klystron and about half of the max field strength.

The small ones I believe are useful for NMR and you only need a a few 10s of MHz of RF to make them work.

David

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