AC powered Led Zeppelin electromagnet

[nbontra]

I've posted on here a few times concerning the electrical problems I continue to encounter for my video installations.

And yet, here's another one.

If anyone remembers, I posted a month back or so concerning the use of an audio signal from a home audio receiver to open and close a small electromagnetic valve. I tried a few methods and was unsuccessful, but after blowing the fuse in my multimeter I'm back at it again.

I threw the receiver on Phono, and started up my LP of Led Zeppelin I. Metering the the speaker wire on the ACV setting, I believe Robert Plant managed to get around 30 volts before my mom demanded to know "Just what I thought I was doing". The receiver I'm using still had about 10 percent more until maximum volume, so I'm pretty confident I could get around 40 volts. I think it was the loudest I've had my speakers, and boy did it sound good.

So, my question is this: Can 30 AC volts provide enough power for an electromagnet? From what I've read up on, it's largely dependent upon how many/how tightly wrapped the coils are. Store-bought electromagnets like this one are often powered by 6 DCV, is that something that can be powered with AC as well?

http://scientificsonline.com/product.asp_Q_pn_E_3113200

If so, then would I just connect the speaker wire directly to the electromagnet? Or will I need to get an AC to DC converter?

I realize that these are probably all basic electrical knowledge questions, and really appreciate anyone who helps me out. If I need to clarify any part of the setup or a diagram would help, please let me know.

 

[berkeman]

Your speakers are themselves electromagnets:

http://en.wikipedia.org/wiki/Speakers

You can use AC or DC to energize electromagnets. You should at least try to make your electromagnet look like a speaker (in terms of AC impedance and DC resistance), so that you don't hurt your audio power amp by connecting it to your electromagnet experiments.

 

[nbontra]

You should at least try to make your electromagnet look like a speaker (in terms of AC impedance and DC resistance), so that you don't hurt your audio power amp by connecting it to your electromagnet experiments.

I did the math [correctly, i hope] and plugged in 8 ohms for resistance as that is what my receiver states as the minimum. That gives me:

30 volts, 3.75 amps, 8 ohms, and 112 watts at peak power.

If I understand electromagnets, the current is what determines the strength. So if I can create an electromagnet which has 8 ohms of resistance, then the amperage is going to be anywhere from zero to maybe 4.5 amps. The windings of the coil will build up to 8 ohms I'm pretty sure, but i could always add a small resistor to the connector.

Referring to "making the electromagnet look like a speaker", if I have the receiver outputting up to 30 volts, and the electromagnet's resistance at 8 ohms, do I need to worry about any other factor?

 

[berkeman]

The speaker input impedance is a combination of the resistance of the wire in the speaker coil, and the inductive impedance of the wire coils sitting around the mu of the stationary magnet. And here, I need to plead ignorance and bail -- sorry. I honestly don't know how those two components contribute to the impedance seen by the power amp. Does the wikipedia.org link talk about that at all?

 

[nbontra]

It didn't mention anything that I could see; but if the 8 ohms of a normal speaker is a nominal resistance that varies, then making a magnet with a constant resistance of 8 ohms would be seen as "the perfect speaker" by the amplifier. Right?

I'll study up on it some more tomorrow, thanks for all your help!