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4hv.org :: Forums :: General Science and Electronics
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Strong magnet

Author Post
Sun Feb 19 2006, 02:57AM Print View
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.


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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..?
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Sun Feb 19 2006, 06:31PM
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.

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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??
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Sun Feb 19 2006, 07:02PM
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)

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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...

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Mon Feb 20 2006, 01:00AM

Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2024
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?
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Mon Feb 20 2006, 01:14AM
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.

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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).
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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 Bjørn 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.

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Mon Feb 20 2006, 04:08PM
Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424
The Bitter magnets use massive amounts of power as well as water to cool them. Still if only 10 tesla is required for paramagnetic levitation and if the bore size is dropped to 3mm istead of 32 mm, I wonder how feasible this is on a home experimenters scale.

There needs to be a gradient of magnetic field as well which is sufficiently steep and with a stable centre. One end of a magnet would suffice rather than an iron cored bipolar magnet like my one described here.

Suspending a water droplet with a tiny tadpole may have to suffice though.

Maybe a few experiments on how much current can be put through a heavy wire under water flow before it disintegrates might be interesting as a start.

Cooling water flow. Hmmmm... Our pool pump is only a few feet away with a 1.5kW motor.

With the lack of a ferromagnetic core, running it through the can crusher setup would be feasible for a pulse of considerable power.

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Mon Feb 20 2006, 04:49PM
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Im afraid that with water will destroy cotton insulation, varnishing could help...
Or if you can establish a good waterflow around iron core only?

If you connect that to can crusher the solid core will acutally tend to be a 'can' (it will make huge eddy currents and dissipate all the energy)
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Mon Feb 20 2006, 05:40PM
Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424
I am not thinking of modifying this coil or getting it wet. Heck I haven't even made it slightly warm yet. A new air cored coil with integral water flow is what I was thinking of with the working volume very small to still allow a lot of power in a small space. I dont have access to 6MW though.
Sort of more like 5kW in a soft drink can size with high flow water through it and pushing the copper to the limit.

Just thinking about Ferrofluid. The spikes seem proportional to the field or field gradient - have to think about that one. Might be a handy way to record this directly although a hall effect device would be best if I can find one with the range.

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Sun Feb 26 2006, 07:20PM
Registered Member #131
Joined: Fri Feb 10 2006, 09:25PM
Posts: 185
Nice try bismuth or pyrolithic graphite.
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