Solenoid electromagnet is getting hot instead of magnetic

Thread Starter

eculver

Joined Jul 21, 2020
2
I am working on a project using magnetorheological fluid (MR Fluid).
Right now, I have a setup for testing the Mr fluid with two syringes connected by a small piece of ptfe tubing. I can lock the fluid when holding a neodymium magnet to side.
My goal is to replace that magnet with a solenoid magnet that the tube passes through so that I can lock the fluid at will. My problem lies with the magnet design.
I have tried using soft steel pipe that is a snug fit around my tubing with washers on both ends as a spool. I then use about a thousand turns of 24 gauge wire around said spool to create my magnet. Running it with 12 volts was drawing about 1.2 amps and not creating a strong enough field to lock the MR fluid, and when i tried turning the voltage up, it increased the amp draw but the magnetic proceeded to get very hot. I have also tried forgoing the pipe and wrapping the wire directly around the tubing with similar results. What can I do to make the magnet stronger, and stay cooler?

Details on materials
Ptfe tubing is 0.25" od
steel tubing is 0.5" od 0.25" wall
power is benchtop powersupply with 30v 5a max

Any advice is appreciated.
 

Irving

Joined Jan 30, 2016
940
Think about the direction of the magnetic field.

The magnet is polarised through its faces, so held to the tube the magnetic field passes through the fluid

The electromagnet produces a magnetic field along its axis, it passes along the soft iron core. There will be virtually no magnetic field inside that cylinder. A solenoid has a solid core.
 

crutschow

Joined Mar 14, 2008
25,247
The electromagnet produces a magnetic field along its axis, it passes along the soft iron core. There will be virtually no magnetic field inside that cylinder. A solenoid has a solid core.
But a solenoid core is hollow, and it's the magnetic field in the hollow that attracts the solenoid core.
 

Thread Starter

eculver

Joined Jul 21, 2020
2
Thank you for the advice. due to limitations on space I can not fit a solenoid on the side. I dont know a lot about magnets, but would wrapping the wire through the length of the tube so that instead of seeing a densly packed slinky on the outside you would see a large number of parallel lines along the length of the tube achieve a similar effect?
 

BobTPH

Joined Jun 5, 2013
2,495
Two things:

The magnetic field will be proportional to the number of turns and the current. To get more field, more turns is a good thing.

Secondly, does the direction of the field make a difference? If you put the pole of your neodymium magnet facing the tube, that would be transverse to the flow, whereas a solenoid around the tube would be parallel to the flow.

Bob
 

Irving

Joined Jan 30, 2016
940
But a solenoid core is hollow, and it's the magnetic field in the hollow that attracts the solenoid core.
Yes, but the field in this instance with a soft iron core is all in the core, no in the space inside the core. Without the core, the air solenoid produced a much smaller field, and its in the wrong direction. Compared to that rare-earth magnet its probebly a few 100 time smaller.. An axial field won't lock the fluid AFAIK.

1595351575343.png
 

ElectricSpidey

Joined Dec 2, 2017
1,191
A simple test of this theory would be to turn the neo magnet 90 degrees and see if it stiffens the fluid.

Or place the electromagnet you already made perpendicular to the tube.
 
Last edited:

Irving

Joined Jan 30, 2016
940
Lets try some math.

1000t of 24awg for sake of argument 2" long = 50mm

dia 24AWG = 0.02", therefore 100t per layer, 10 layers

B = 4pi*10e-7 * turns/length * I = 4pi*10e-7 * 1000/.05 * 1.2 = 0.03Tesla

A rare-earth magnet ~ 1.4Tesla


QED
 
Last edited:

DNA Robotics

Joined Jun 13, 2014
571
In a solenoid, the magic happens in the inside gap.
The North & South poles are on opposite sides of the gap.
The magnetic field is created in the exterior armature and the gap is where it will magnetize your fluid.
Its late. Maybe someone can explain it better.

Solenoids.jpg
 
Last edited:
Top