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

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!