I was trying to make a device which can vibrate – so I took inductor, some 220uH 22uH, put 12V pulsed current through it (~10Hz), and put neodymium magnet – I was expecting to feel 10Hz vibration of a magnet in my hands when holding it 1mm from the inductor – but I haven't feel anything.
I tried 2 different magnets, result is the same.
What I did wrong? Is that due to the fact that my inductor is 'cored'?
Best Answer
The inductance and frequency are almost certainly totally unsuited to the drive level provided. Unless you are providing 1000's of amps of drive (at which stage you'd need welding goggles to view the inductor) then you need a different arrangement.
The current through an ideal inductor will increase linearly with time when a constant voltage is applied.
Here
L = 220 uH = 2.2E-4
t = 1/2 of 10 Hz cycle = 0.05 = 5E-2second
V = 12 Volt
Most available power supplies are not capable of this sort of current :-).
For operation at around 10 Hz you need a MUCH larger inductance value. The inductor may not be much larger physically but it will have a very large number of turns comparatively. For a physically very small inductor the wire will become very fine, resistance will be high and resistance will start to play a very significant part.
To use the existing inductor at sensible power and current levels you would need to increase the frequency substantially and the resultant pulses would not be able to b sensed as vibration. For example, to reduce peak current to ~=2.7A would require operation at 10 kHz.
To start to experiment in this area the easiest way is probably to dismantle a small relay. This will usually have a laminated core, DC operates currents in the 10's of mA's to 100s of mAs range and would produce "pull in" forces that are noticeable.
Note that you can use a spring loaded "pole piece" to get mechanical vibration. Your magnet will successively provide attraction and repulsion on subsequent cycles. As the magnet will also be attracted to the core material you may still need to utilise a spring if you want approximately symmetrical attraction and repulsion forces.
* ADDED COMMENTS *
There are a number of comments on other answers. I opine that the basic core shape is OK but that the material and amp-turns are wrong. So -
Start with pulling almost any small relay apart as per my suggestion. They have done the work of optimising core and using VERY fine wire and many turns and ... .
Once you have a feel for it try your own. The core you are using MAY work with many many turns of the finest wire you can find BUT ideally you want a core with MUCH higher "permeability". This will greatly increase your inductance for a given ampere-turn product. A core of soft iron wires would work very well. Metal (iron) powder also.