Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: RyanGuyardo on 15/10/2010 16:09:05

Title: Neodymium magnet vs high steel carbon in homopolar motor. How?
Post by: RyanGuyardo on 15/10/2010 16:09:05

I'm experimenting homopolar motor using both neodymium magnet and high steel carbon magnet, once at a time.

The problem is, what are the differences  between these magnets in terms of strength, electricity conductivity, or anything related to homopolar motor, as they are almost equally strong?

Anyways, both of my magnets give me almost equal rotational speed as well.

Title: Neodymium magnet vs high steel carbon in homopolar motor. How?
Post by: Soul Surfer on 15/10/2010 16:16:36

This is a rather specialised question that is probably more suited to the technology area.  I doubt if there are many people around who could answer you without a lot of research which you could probably do yourself just as effectively.

Title: Neodymium magnet vs high steel carbon in homopolar motor. How?
Post by: daveshorts on 15/10/2010 16:28:29

They will vary depending on the exact model of magnet you are using even within a type of magnet. In general the rarew earth magnets are a lot stronger, hugely stronger than a conventional carbon steel magnet.

A good way of getting a first approximation of their relative field strengths would be to try pulling them both off the same piece of steel, and see how the forces compare (if they are the same shape and size).

Conductivity you are probably in a better position to measure yourself.

Title: Neodymium magnet vs high steel carbon in homopolar motor. How?
Post by: RyanGuyardo on 15/10/2010 16:35:11

Thanks, good idea, daveshorts!

P.S. move this post to anywhere it suits the most, it's okay.

Title: Neodymium magnet vs high steel carbon in homopolar motor. How?
Post by: Soul Surfer on 15/10/2010 17:20:56

Here is a very old paper giving some design information and results for a homopolar motor

http://dspace.mit.edu/bitstream/handle/1721.1/11803/32785690.pdf?sequence=1

Title: Neodymium magnet vs high steel carbon in homopolar motor. How?
Post by: RyanGuyardo on 15/10/2010 21:11:02

I'm using one AA battery for each homopolar motor. It gets hot not even after half a minute and the voltage drops at a steep gradient, from 1.5V to 1.3V in about 2 minutes. My homopolar motor is about the same as this, http://www.youtube.com/watch?v=3aPQqNt15-o (http://www.youtube.com/watch?v=3aPQqNt15-o), starting from 30th sec, not the last spiral shape one.

Is it acting like a short circuit while i attach my copper wire to let it start spinning cause I'm planning to use li-po battery to replace my AA battery for a longer running period, but if it acts as a short circuit, it's going to explode.

Title: Neodymium magnet vs high steel carbon in homopolar motor. How?
Post by: syhprum on 15/10/2010 21:54:33

You should use a current limited PSU to get consistent results.

Title: Neodymium magnet vs high steel carbon in homopolar motor. How?
Post by: RyanGuyardo on 16/10/2010 21:40:43

F = BIL sin(theta)
B is the magnetic field strength
I is the current
L is the length of wire
theta is the angle between the magnetic field and the wire.

I'd like to increase the speed or my homopolar motor and I found this equation on website. Is it the same as the Lorantz's Force equation which uses cross product?
where
F = Eq + vq x B
F is the force (in newtons)
E is the electric field (in volts per metre)
B is the magnetic field (in teslas)
q is the electric charge of the particle (in coulombs)
v is the instantaneous velocity of the particle (in metres per second)
× is the vector cross product