Different methods of strengthening a magnetic field.

[gramps1]

Hello!
Lately I've been experimenting with the ways an electromagnet effects a Rare Earth magnet. The electromagnet we used was taken from a vibrator massager, probably 50s vintage. The resistance of the coil is 96 ohms and consumes about 1.25 amps when operated on 120 volts AC. When the electromagnet is energized, a small Rare Earth magnet will vibrate (probably in harmony with the 60 hertz AC). If the magnet is held in the palm this vibration can be felt as far as 12 inches from the coil. However the coil runs hot and is burning a hot of amps.
How can we reproduce this effect with a different coil and or power supply design that only uses perhaps 125 milliamps?
Thanks, Gramps

 

[FinBurger]

You'd have to give a sketch of your setup, so that we can see what kind of solenoid/motor you are trying to make.

 

[Tom.G]

Wire a 25W incadescent light bulb in series with the electromagnet. This will limit the current.

 

[gramps1]

Hi FinBurger,
I hope this will suffice for a sketch
Photo of the electromagnet.

The experiment consists of holding a rare Earth magnet 10 inches above the electromagnet and noting the extent of the field by feeling the magnet's vibration in the palm of the hand.
Tom.G,
We will try that but I think it would reduce the magnetic field.
Edit we want to .maintain the same field strength but use less power.

 

[Tom.G]

FIeld Strength: directly proportional to Current x Turns

Modified of course by the material used for the core, and, as others have mentioned, the dimensional aspect ratio of the windings.

 

[FinBurger]

Hello!
Lately I've been experimenting with the ways an electromagnet effects a Rare Earth magnet. The electromagnet we used was taken from a vibrator massager, probably 50s vintage. The resistance of the coil is 96 ohms and consumes about 1.25 amps when operated on 120 volts AC. When the electromagnet is energized, a small Rare Earth magnet will vibrate (probably in harmony with the 60 hertz AC). If the magnet is held in the palm this vibration can be felt as far as 12 inches from the coil. However the coil runs hot and is burning a hot of amps.
How can we reproduce this effect with a different coil and or power supply design that only uses perhaps 125 milliamps?
Thanks, Gramps

Hi FinBurger,
I hope this will suffice for a sketch
Photo of the electromagnet.
View attachment 283148
The experiment consists of holding a rare Earth magnet 10 inches above the electromagnet and noting the extent of the field by feeling the magnet's vibration in the palm of the hand.
Tom.G,
We will try that but I think it would reduce the magnetic field.
Edit we want to .maintain the same field strength but use less power.

So, the coil here has a core that is shaped like an "E". The magnetic circuit runs up through the middle arm, has to jump through the air, and then runs down the outer arms to close the loop. The magnetic field feels about 4000 times less magnetic resistance in the iron as in the air. So, to increase your magnetic field, you want to make the air gap smaller.

Add a pole piece of soft iron that almost bridges the gap. You should find that this increases the inductance of the coil, and that will reduce the ohmic (heat) loss.

By the way, when you put the permanent magnet on the core, you raise the possibility of saturating the iron's magnetization, and this makes it a poor magnetic conductor. This will reduce the inductance, and thus increase the ohmic loss (which is what you saw).

Lastly, what is your final goal? If it is to make a vibrator, then you need to optimize the whole electromagneto-mechanical system. That is, the movable mass that the coil will be pulling on should be suspended on a spring such that its resonant frequency (simple harmonic oscillator) is close to 60 Hz.