What size core for choke?

[Sch3mat1c]

Ok, sounds about like "wasteless", 28mm wide leg and 50mm stack. I get around 800T for 23ga. wire on this... which might be.... 200mH? But then, running through the inductance formula with l = 8", A = 2.2 in^2 and mu = 1000, I get 5.75H.

Tim

 

[Geek]

800T will get him closer to 9H in practise.

 

[Prune]

Well then, how much of a gap do I leave between the E and the I?

 

[Sch3mat1c]

Let's see, 800 * .5 = 400 ampere-turns, the table in this book says about .01" (two sheets of heavy (i.e. 5mil) paper).

I think normal thin, ruled writing paper is around 3 mil, so 3 or 4 layers of that would also do it.

Tim

 

[Prune]

I assume that I wind all layers in the same direction (say clockwise), but that it doesn't matter if I'm winding from left to right on one layer (along the bobbin) and from right to left on the next one, so I don't have to cross after each layer to get back to the left side?

 

[Sch3mat1c]

Exactly.

 

[Prune]

Due to the thickness of the plastic bobbin and paper-impregnated-with-nailpolish insulation between each layer (at turn on before the subsequent capacitance is charged the choke will see the full voltage across it), I'm expecting about 540 turns -- I've got five layers at around 54 turns each, and I think I can fit another five. Due to the less turns I'll use only one sheet of heavy paper and nail polish for the gap (and the stacks are not quite perfectly aligned anyway.

As long as I have at least 3 H in the end it should be OK.

 

[Prune]

I got about 550 turns with all the insulation, so I made the gap a bit smaller. Resistance measures at 8 Ohms, and the simulator shows only a couple of Watts are dissipated in the application, so I guess it won't get hot enough to burn the paper insulation