>>> 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.
>
> Yes by mistake I left out a factor of four due to length
> 400 turns would be about 4 times as long so that factor and
> the factor of 4 from half-diameter would give .64 ohms
> resistance rather than .16 ohms so now the calculation is
> 12.5A*12.5A*0.64ohms = 100W and 5000 ampere turns which is
> the same as with #10 wire.
>
I think it's much worse than that. I used Reg Edwards (SK) program at
formatting link
named "Multilay" to calculate the lengths of wire. Bunch of great programs. Thanks Reg. From Multilay Coil Inside dia 1" Outside Dia 8" Length 8"
400 turns of 16 gauge wire is 470 ft of wire @ .004 ohms/ft = 1.88 ohms 100 turns of 10 gauge wire id 117.5 ft of wire @.001 ohms/ft = .117 ohms
So; the current ratio will be 16 to 1. Therefore 16 x 100turns = 1600 or for #16 wire 1 x 400turns =400 The amp/turns is 4 time higher for the # 10 vs. # 16 I got lazy and short on time, so I may not have explained this well. Let me know if it doesn't make sense. Mike