How Can We Change The Polarity?

What you need is an H-Bridge. Imagine your coil as the cross bar of the H and switches on the four vertical posts of the H. Connect the two top posts of the H to 24V. Connect the two bottom posts of the H to ground. If you close the switches on the top right and bottom left, the current will flow right to left through the coil. If you close the switches on the top left and bottom right, current will flow left to right through the coil. This is a common means for driving motors when you want to drive the motor forward and backwards. The switches are normally transistors or MOSFETs.

If you google H-bridge, or motor control, you can find out all you need to know.

5kHz is right in the middle of the audio band...I don't think your device will do much .

What are you hoping to achieve, the iron core may vibrate a little but not much as it will be so heavy....compare it to a loudspeaker.....

Del

talovida,

Mark the + and - terminals and leads as such then invert them but instead of directly attaching the leads to the terminals. First flash them this will reverse the polarity.

One of the considerations is the INDUCTANCE of the coil you've created. Switching at 5kHz, you basically have a 5kHz square wave, and fundamentally AC rather than DC. The higher the frequency, the higher the inductive reactance, so, regardless of HOW to switch, a larger issue may be, WHAT WILL BE THE EFFECT?

If you want to try an experiment, use an audio frequency generator with a square wave function, and a good audio amplifier. (watch the DCR of your coil so you don't present too much current draw on the amp at lower frequencies). Gradually increase the frequency at watch the effects. At low frequencies, as has been said before, the coil will act like a transducer and you will here the signal, but as you sweep higher and higher, the sound will reduce (at some point the sound will die quickly because of the mass), but, I think if you examine it magnetically, you will also find the energy dies pretty quickly also because of the increasing impedance.

If you measure the inductance, you can calculate the reactance at 5kHz and compare to the DCR. All else being equal, the amount of magnetic force is directly proportional to the amount of current.

Depending on what you are trying to activate / motivate, you might consider some very small electro-magnets and coils if you want to work at 5kHz.

There are several other issues of the steel (or iron), its permeability, at what point it saturates, and so on, because this governs the way the magnetic field will form and collapse at different frequencies.

KEEP EXPERIMENTING, but, as much as possible, try to consider all the sciences behind what you are doing, and BE CAREFUL. I once nearly lost a finger being careless with a magentizer.

Good luck.

Some quick calculations indicate your coils are about 1.8 inches OD and have a DCR of about 6 ohms. IF it were an air-core inductor (and it clearly is not), the inductance is about 20mH. Given this (and there is more to consider) the impedance of this coil at 5kHz would be about 630 ohms, so your current would be 1/100th of that using DC, and your magnetic field AT PEAK would also be 1/100th of what you experience with DC.

Be aware this is NOT ACCURATE, but just to give you an indication of what is happening at these frequencies.

One way or another you need to start with a square wave, but, think about it a bit. Do you want a 2,500 Hz. square wave or a 5,000 Hz square wave (a 5,000 Hz square wave reverses polarity 10,000 times per second)?

The characteristics of the coil are going to seriously filter the signal, as pointed out by DCaD; so an audio amp might be a good way to get up and running quickly (just replace the speaker terminals with the two ends of the coil. But again as DCaD says don't expect to be able to drive much power into the coil.

In fact, on reflection: the square wave will be filtered so much by the electro magnet, you might as well start with a sine wave. So you can get started with a tone generator for your PC like the one Blink pointed us to in the beat frequencies challenge.

http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=3829

Click on < DOUBLE TONE GENERATOR > at top

click on < 2000-07-01 >

download dgen.zip