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Science help needed [electromagnet construction]

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Hey guys, I need to make a 12v DC powered electromagnet as strong as possible with a 100% duty cycle that won't overheat. Voltage will be continuous but not constant. Typical operation should be 8 hours continuous but figure 24/7 just to be on the safe side. Ferrofluid can be used as a coolant but prefer not to. I have an old 10w solid state guitar amp I plan to use as a power source that is currently powering a 4 ohm speaker. I have less than two weeks or so to pull this off and this project is UBER important to me. Any and all help/suggestions are welcome.
 
Quick stab at this:

10W/12V = .83 amps (from power supply specs given)

12V/.83A = 14.4 ohms (4 ohm original load would suggest more amps or less volts.)

#30 copper wire is rated for .86 amps and is 103 ohms per 1000 feet so 14.4/103 = 140 feet of #30 wire. (chassis wiring specs, not in a bundle. Would probably have to reduce this number after some experimentation)

For better magnetic field use 4 parallel turns of #36 wire?
 
OK OK I tryed to ignore this one but I can't. If you plan on using this amp, How are you going to get DC out of it. The output to the speaker is AC. Unless a lucas wiring joke is coming soon, Start over. If this is real, start by telling us what you are trying to lift, What its weight is and why a regular magnet will not work. George
 
Output is DC and I need to vary the magnetic field thus I can't use a permanent magnet.
 
Crap. you're right, it is AC. I have another amp that is DC output so I'll use that one. That one is 2 watt, 4 ohm.
 
OK so first all speakers are AC devices, so all amps that are hooked up to speakers are AC. Any significant DC current will fry any speaker coil. The only speaker that used any dc are called field coil speakers and I don't think you have ever seen one. They had 2 coils in them. One for the voice coil and one for the "field coil" that replced the permenant magnet. That said, seems like you just need a variable DC power supply if you are sure that you need a dc magnet? Not to pry but it would help if I knew what you are trying to do.(I am guessing some sort of display rather than lifting something?)
 
The amp I'm talking about is DC powered; takes 6 AA batteries. If I can use the AC output of the first amp I mentioned without burning anything up or shocking myself that would be great. I'm thinking about something like this: https://www.youtube.com/watch?v=SGoOu8cPmeM

I've made them as a kid and always used DC and was told to use DC, that's why I said DC and thought the speaker was fed DC cause it didn't shock the carp outta you.


I need to build a ferrofluid sculpture and need a variable electromagnet to achieve the effect I'm after.

Off note, I have a 1939 Zenieth radio that has a weird transformer/ coil looking thing on it, is that what you're talking about?
 
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