Forgot to mention that what you are proposing to do is like wanting to apply 48 volts to a 12 volt light bulb. Yes you can over-volt bulbs to get more light but at some point they change from just being brighter bulbs with shorter life to behaving more like flashbulbs. Hit the motor with enough voltage and you might not get any revolutions out of it before it goes up in smoke.

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stevez

 

I am not sure that 50 ma is the right current but I did want to more directly answer the question - and I have a moment to do that now. You said the current was 50 ma, the desired inductance was 18 microhenries and the application suggests relatively low frequency.

30 ga wire will handle 143 ma using a standard of 700 CM/Amp. 30 ga wire is pretty small but we'll start there.

#26 powdered iron mix is good for dc to 1 mHz.

A T-50 core is 1/2 inch inside diameter and just a place to start. A T-50-26 is a T-50 core made from #26 material. The "AL" value from the table for this core is 320. You can wind as many as 81 turns of 30 ga wire in a single layer on this core.

Crank thru the formula and it tells me that 24 turns of #30 wire will yeild a little more than 18 microhenries of inductance. Since the core can handle 81 turns this solution is rational.

I've just walked you thru the simplified process of inductor design. This is by no means all encompassing but is a good method for hobbyists.

50 ma doesn't fit with the magnitude of your project so realize that once you determine what current you really need you'll have an idea of how to design the inductor.

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stevez

 

Hmm....Actually, i don't know if the current that the inductor suppose to carry is 50mA. That was an estimated value by Bogdan. However, now i really have some ideas on how to design that inductor and thanks to you stevez

From what i get here,things that i should look for are the tables and formulas to get a certain inductance at a rated current and voltage for toroid based cores. Actually, that was what i'm looking for so far but i haven't get them. If you techies out there know where to get them, please inform me here or email me at boisol@tm.net.my.

However, what about the other cores? for example air-core? What's the difference in using toroidal core and the other types of cores? Another example, what's the difference between an 18uH air-cored inductor and 18uH toroid-cored inductor at a same rated voltage and current?

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The truth is out there......

 

An air core inductor with a value of 18 microhenries would be fairly large - maybe 2 inches in diameter and 4 inches long. It would not be self shielding so the surrouding magnetic field might impact or be impacted by other things nearby.

References that I have are ARRL Radio Amateur's Handbook and Amidon Associates handbooks. I have no idea how much of this stuff is available on-line.

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stevez