[Amps] Edge wound inductors

[Larry]

Tom W8JI wrote:
> 
> The factors that affect optimum form factor of an inductor 
> would fill a good sized book, but the edge wound tape does 
> two good things besides the obvious mechanical tap 
> attachment advantage.

I don't see the tap advantage. If a round conductor coil is wound and 
supported in a similar manner, then the same type of clamps can be used. 
  I have some of these made for standard coils and they work just as 
well as the ones for edge wound. If you choose to make the tap 
permanent, it's difficult to solder to the edge wound but if you have 
tubing you can just drill a small hole and poke a suitable wire in it, 
then silver solder.

> 
> First, the turn-to-turn center spacing can be smaller 
> without increasing turn-to-turn capacitance to the value of 
> tubing. Turn-to-turn capacitance kills Q in high reactance 
> inductors. A more compact length increases mutual coupling 
> from end-to-end and reduces inductor physical length for a 
> given inductance and current rating.

I understand the above and agree with the theory, but in practice I have 
not seen the expected results. Most likely I just don't have enough data 
points.


> 
> Second, eddy currents decrease. This also increases 
> inductance for a given size and reduces heat and loss 
> resistance.

Why would eddy currents decrease? Are you referring to the currents 
produced by the turn-to-turn capacitance?

> 
> Measuring edge wounds and tubing or round wire in a good 
> test fixture with good gear at HF, I find edge wounds have 
> about the highest Q of any inductor I've ever 
> tested...generally up in the area of Q=1000.

I have measured many inductors at HF with good test equipment. I have 
only a few edge wound inductors that I have measured but all of them 
measured at around 250-350 as best I can remember. I can wind similar 
sized round conductor coils that can easily beat that number.

Tom, I think I asked you this a few years ago, but please refresh my 
memory. How do you measure Q's that high. It's been my experience that 
above Q's of 500-600 in the HF range, the test fixture has more of an 
influence on the measured Q than the coil parameters do.


> 
> While we can do very well with tubing in low or moderate 
> reactance inductors and we might not need the additional 
> component Q when the operating Q of the system is low, there 
> isn't much bad about them and they are easy to find and easy 
> to work with. They even work well in the rain.

They don't work for crap in the snow!

OK, I'll give you the Q even though I don't see it in the small sample 
set I have. But the I still have a problem with the implementation. If 
you start with an inductor with a Q of 600 and position it a half inch 
away from the chassis and other metal objects, the Q is going to drop 
drastically and I doubt if you wind up with an installed Q of 75. If you 
start out with a much smaller inductor with a lower initial Q and 
install it in the same volume, it will be affected far less and you 
might actually wind up with a higher installed Q. I see no reason to go 
out of your way to use an edge wound inductor in these cases other than 
it's photogenic appeal. If you have one and it fits well in the chassis, 
great. But to go out of your way to spend more money just to shoehorn in 
an edge wound makes no sense to me.

73,

Larry - W7IUV
DN07dg - central WA
http://w7iuv.com