snip
>>>and with 39 feet of wire in it, since #10 has a resistance of about 1
>>>milliohm per foot, it'll have a resistance of 39 milliohms.
>>>
>>>Now, let's say that this thing can dissipate 100 watts, continuously.
>>>
>>>Since:
>>>
>>> P = I²R
>>>
>>>then:
>>> P 100W
>>> I = sqrt --- = sqrt --------- = 50.64 ~ 50 amperes,
>>> R 3.9e-2R
>>>
>>>the voltage across the coil would be,
>>>
>>> E = IR ~ 50A * 3.9e-2R ~ 2 volts
>>>
>>>and its IT would be 50 amperes * 100 turns = 5000 ampere - turns.
>>>
>>>Google "ampere-turns" for some rather more detailed info.
>>
>> If an electromagnet is thermally limited, and you plan to fill the
>> available winding window, I think it doesn't matter what size wire you
>> use. So size the wire to match whatever power supply you have, to get as
>> many watts into the coil as it can stand.
>>
>> It's like a transformer. A 100 VA transformer is the same size whether
>> it has a 120 volt primary, a 240 volt primary, or a dual primary.
>
> A persuasive argument but would it not be the case that if
> you wound with wire half the diameter of #10 say #16 that
> there would be 400 turns with .16 ohms resistance (both four
> times as much as with #10) but half as much current for the same
> power level since 25*25*.16 = 100 so there are 10000 ampere turns
> which is twice as much as before.
Prove to me that 400 turns of #16 is the same length of wire as 100 turns of #10 wire. Assume a 1" diameter core and 2" length. I've looked for an online calculator, no luck so far. Mike