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I'm a noob in electronics. Actually, I'm asking here in Stackoverflow for my physics experiment :)

I need a AC power source that has a range of approx. 20V - 250V. I'm using this source to power an electromagnet that is constructed by using enamel coated copper wire of 0.3mm

I need to be able to generate sine waves with frequencies of approximately 100 hz - 3000 hz.

I found that normal function generators do not have enough voltage & power to support my experimental setup. Slidac was also something I considered, but since it transforms the voltage from the input source of 220V, the output current becomes too high in cases of low output voltages.

Thanks a lot in advance.

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  • \$\begingroup\$ 20V to something like 40V : normal signal generator + hi-fi amplifier. For higher voltages : ditto plus a mains transformer in reverse. (But remember with a N:1 transformer, the amplifier will have to drive N^" times the load current) \$\endgroup\$
    – user16324
    Commented Feb 9, 2015 at 23:26
  • \$\begingroup\$ I'm confused about your last comment: "the output current becomes too high in cases of low output voltages." What? \$\endgroup\$
    – Greg d'Eon
    Commented Feb 10, 2015 at 3:40
  • \$\begingroup\$ @Kynit Since Slidac just transforms the voltages, in order to match the electrical energy, the current raises a lot, which burns up my electromagnet. (The Slidac I have received input power from 220v, 1A source) \$\endgroup\$
    – MinSik CHO
    Commented Feb 10, 2015 at 23:43
  • \$\begingroup\$ Right. But the current from a 220V source and the current from a 20V source transformed to 220V would be the same, right? \$\endgroup\$
    – Greg d'Eon
    Commented Feb 11, 2015 at 0:35

2 Answers 2

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Modern professional audio power amplifiers are available for rent from some music stores and most PA System rental companies. These are available with maximum output voltage depending on how much power the amplifier has.

For example, a Crest Audio CA-1200 is rated to provide 2400 Watts RMS into an 8 Ohm load (bridged output). That works out to 300 Vac RMS. That is: the output voltage is adjustable from zero to 300 Vac at max power.

There are many other similar amplifiers from a variety of manufacturers available - I mention this one only because I have used it in the past.

I'm suggesting an amplifier like this because they are usually readily available from rental houses for a low-cost daily or weekly or monthly rental fee.

Note that in order to achieve this output voltage, you have to switch the amplifier to what is called "Bridge Mode". This is where the output signal comes from the two HOT output terminals on the amplifier. One channel provides up to 150 Vac, the other channel provides the exact same signal except 180 degrees out of phase. The sum of those voltages gives you the 300 Vac available.

The consequence of this is that both of the output terminals are live with respect to ground. Your question doesn't indicate whether this is a problem or not. It usually isn't but you need to be aware of it.

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  • \$\begingroup\$ Yes, given your requirements, you definitely want a multi-kilowatt audio amp AND DO NOT TOUCH THE TERMINALS WHEN ON!!! Even if there's no signal, the potential for the amp to fail DC is not worth discovering by touching it. \$\endgroup\$
    – AaronD
    Commented Feb 10, 2015 at 0:06
  • \$\begingroup\$ Also, measure your magnet to make sure that it won't break the amp. >=4 ohms should be fine for any amp in non-bridged mode. >=8 ohms should be fine for bridged. If you find one that will drive 2 ohms, that's even better, but don't count on it. \$\endgroup\$
    – AaronD
    Commented Feb 10, 2015 at 0:08
  • \$\begingroup\$ Thanks for your comments. Actually, the current does not need to be strong, as the magnetic flux itself does not need to be strong. I need sufficient voltage only so that the reverse current generated from the induced current does not alter the waveform of the signal greatly. \$\endgroup\$
    – MinSik CHO
    Commented Feb 10, 2015 at 23:48
  • \$\begingroup\$ Is there anything like this: youtube.com/watch?v=O3VZJg8CCvs I'm trying to make same setting as this vid and do some experiments with more parameters. Thanks. \$\endgroup\$
    – MinSik CHO
    Commented Feb 10, 2015 at 23:49
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As Dwayne mentioned you want a power amplifier. You feed it with your signal generator which gives you the signal shape and frequency, it provides the power.

Next you need to compute what the impedance of your electromagnet is across those frequencies. You will find that the resistance of the wire to the magnet, and the magnet itself, makes a simple RL circuit. Once you know the impedance you can compute your current flow an power dissipation.

Since you are doing this with a magnet are you trying to vary the magnetic flux?

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  • \$\begingroup\$ Yes, I am. I'm trying to alter the magnetic flux in sinusoidal waveform. Actually, youtube.com/watch?v=O3VZJg8CCvs this is the experiment I'm trying to regenerate - I'm trying to introduce some more variables to this phenomena. I think he uses Slidac in the vid. With low amps needed, is power amplifier with high watts ok? Thanks. \$\endgroup\$
    – MinSik CHO
    Commented Feb 10, 2015 at 23:51
  • \$\begingroup\$ What you are calling a Slidac is what I think of as a rheostat then that will probably work. If you just hook it up to your coil it is like hooking up one side of a transformer and not the other. You will consume the "magnetization" energy of the core material (it gets warmer as you swap the field, just like a transformer) but it will only consume as many watts as you pull out of it through interaction with the magnetic field. \$\endgroup\$
    – Chuck
    Commented Jul 10, 2015 at 20:37

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