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I have derived a formula and a diagram which helps to find the length/diameter quotient of a coil with cylindrical core if the diameter of the wire as well as the maximal current and the maximal allowed B field are known.
This diagram can be used in the following way: H/n is the wire diameter if there is a single winding layer (H=coil length, n=number of windings). B_max is known (1.2 T for iron, 0.3 T for ferrite). The max. current i_max must be specified; then the quotient H/n * B_max / i_max can be calculated. This is the value at the ordinate of the diagram. If you estimate µ_r , you can read out the quotient H/D on the abszissa.
Heres a pic of a Ford model T pri coil , 4 7/8" long ,bundle of wires for the core, with 216 turns. 1.9 mH According to old english, a 'fascist of wire' , they made 60 million of them , set of 4 each car.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
Tesla's 433702 is different from using gaps in the iron wire core. (His intent was to build a make a self-regulating quadrature transformer to run 3 phase motors on single phase power without resistance losses)
"You might put some gaps in your annealed wires too - that is where the energy is stored after all, and it will also reduce a tendency to saturation"
These gaps might tend to lead to 're-arrangement' of the core at a periodic rate (buzz) unless cemented them into a non- moving mass. This would be like winding the coil on a tube filled with iron filings, (coherer)
Registered Member #3447
Joined: Fri Nov 26 2010, 11:10PM
Location: North Jersey
Posts: 97
Sorry for never responding -- I must have been really busy. Thank you all for the great discussion, as usual.
The arrangement is now: Variac -> 120:1 PT -> bridge rectifier -> 2uF cap -> Output (see here)
I had thought that an LC filter would reduce the ripple voltage and decrease the stress on the capacitor.
Now I just think it's not worth it, introduces ringing that bangs on the bridge, and reduces output voltage. Since the load is current regulated, I'm not gonna worry about it. Thanks All.
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