# Creating AC current from 6v DC source

1. Feb 28, 2012

Hello! I'm a long time reader, but this is the first time I've not been able to find the information I've needed already...

I have a small electromagnet that needs to have an AC current (it is essential that the electromagnet has a reversing polarity) but the source of power comes from a 6v battery.

I know I need an inverter, but all the inverters I can find are converting 12v to 220v AC - which seems to be slightly excessive (and expensive) considering that the electromagnet itself is no bigger then a penny.

Does anyone have any ideas? Is there something I can make myself, or something cheap that I can purchase?

I can use a 9v battery, if thats required, but everything about this project needs to be kept fairly small.

My knowledge of circuits and electronics is minimal, so please use small words (and maybe pat me on the head to tell me I'm doing a good job).

Many thanks!

2. Feb 28, 2012

### DragonPetter

What kind of AC current? Sinusoidal, or can you use other waveforms? What is the application?

3. Feb 28, 2012

Any kind of wave form is acceptable =).

The application is to have a bunch of these AC electromagnets with tuned resonate frequencies. The overall intention, is to have about 12 individual electromagnet + battery + resistors (to specify the frequencies) that are fairly small in size.

Any idea? I'm at a complete loss... its literally just the small scale thats making this impractical - the only power sources I can find that are small enough are always going to be DC =/.

4. Feb 28, 2012

### DragonPetter

Have you considered an oscillator? You can build them out of OpAmps or even passive circuits. Depending on the type of oscillator you can also filter the waveform to get just the fundamental frequency.

I googled "opamp oscillator" and this is the first to show up: http://www.ti.com/sc/docs/apps/msp/journal/aug2000/aug_07.pdf

5. Feb 28, 2012

Ahh, that looks interesting.

Will have to have an indepth read of that, thanks!

Does that mean I can run an oscillator through an electromagnet (as if the oscillator signal was a current) to make the electromagnet follow that signal?

I'll read up more on opamp oscillators now!

Another question though...

Is there a way of creating an AC electromagnet that carries a dense band of frequencies? Kind of like 'white noise' in the form of an electromagnet, if thats possible.

6. Feb 28, 2012

### DragonPetter

I'm not sure how to answer your question. It sounds more like an antenna than an electromagnet.

7. Feb 28, 2012

Haha! Thats a great idea!

And an antenna creates an electromagnetic field, so as long as I was able to create an antenna that is senstive to all frequencies, I'd essentially have what I'm looking for... I think. Maybe. Right...?

Thanks for your help! I'm gonna do some research into antennas!

8. Feb 28, 2012

### psparky

Silly suggestion....but you could take an old minature DC motor.....hook it to a miniature AC generator.....power the DC motor with your battery......and boom there ya go as long as the frequency is within your specs.

Silly, I know....but technically it would work!

9. Feb 28, 2012

10. Feb 28, 2012

### psparky

.....Or you could use that....sure! :)

11. Feb 28, 2012

### DragonPetter

Isn't that fixed a 3kHz? I thought you needed multiple/adjustable frequencies. If you need just one frequency and don't care what that frequency is, there's lots of CCFL backlight inverters.

12. Feb 29, 2012

### Staff: Mentor

You could generate white electrical noise and amplify it, then feed that to the solenoid to produce an electromagnet with randomly varying strength.

13. Feb 29, 2012

### cjameshuff

Buy a cheap MP3 player like a Sansa Clip that plays FLAC or WAV (or other lossless format), get some free audio synthesizer software or write a short program to generate audio files with whatever waveforms/mix of frequencies you want (within the audio range, anyway). If you want white noise, make a white noise track, want a frequency ramp, make a separate track for that. Two channels per player. Use a low-dropout 5V regulator to power them from the 6V via the USB interface, if their batteries don't last long enough and you can't find an actual 5V supply.

You want uncompressed or lossless audio, because lossy compression algorithms throw out a lot of the signal that you can't hear but which you might need. Even with this, keep in mind you're working with cheap audio hardware, not a precision signal generator. If it doesn't put out enough power, look into power amplifier circuits.