Re: [TCML] Source for 1H air-core inductors

[jimlux <jimlux@xxxxxxxxxxxxx>]

Ed Phillips wrote:
> Resistance?
>
> Current handling capability?
>
> Ed

Ballparking here using Wheeler's equation
6" diameter, 6" long, 3000 turns is just under 1 H..

3000 turns * 18" average turn length = 4500 feet
40 ga is 1000 ohms/1000ft  (roughly.. 10ga is 1 ohm/1000ft, 40ga is 
1/1000 the area)

So 4500 ohms DC resistance, or something around there.

40 AWG is about 30kft/lb, so we're looking at less than 1/4lb of wire.

What about if you just buy a 1/4 lb spool of 40AWG wire.


Sticking with the idea of 3000 turns in the size of a standard wire 
spool... one might look at a pound of AWG 30.  Resistance would be about 
450 ohms.

Half pound spools, 1600ft of AWG30 Beld-Sol are $45 from Mouser.

ACtually, though the spools might be too small, which reduces the 
inductance.

A one pound spool of PolyThermaleze might be closer to what you want.


Didn't someone measure the inductance of a standard 500ft spool of AWG12 
THHN?  500 ft/1 ft turn (average) = 500 turns works out to about 26 mH..


Current handling is going to be determined by allowable temperature rise..
we can sort of estimate here, too..
Let's say we can tolerate a 100C rise.  We're looking at basically a 
solid lump of copper with some plastic, so let's call it 250 grams of 
copper, which has a specific heat of .38 J/(K*g), or, inverting, 2.5 
degree grams/Joule.  250 grams, so overall rise in our spool will be 
2.5/250 = 0.01 degree/Joule

Say we push an amp through this beast.  That's a dissipation of 
(assuming my AWG30 case) 500W, so in a second, we get a 5 degree 
temperature rise.  In 20sec, we've got our 100 degree limit.




> "That's huge indeed.
>
> Mine are just a little larger than two human fists held together.
>
> Wound with #40 AWG wire.
>
> D.C. Cox"
>
>
>
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