Wire Table

The title says it all. This is for established factual (we hope) things.

Wire Table

Postby Doug Coulter » Thu Dec 12, 2013 2:47 pm

Click the pic to get a usable size.
WireTable.gif
Terman's old table


This is from Terman's Radio Engineer's Handbook. Some other odd info - Cu has a positive tempco of resistance. It's enough to almost cancel that of silicon junction transconductance, which is why an old National Semi app note suggests the use of a copper current shunt in their cheapo wattmeter - it compensates the rest fine, thanks.

Hint - I use #10 wire for ammeter shunts around the solar system. One foot of that is almost exactly one milli-ohm (1 mv/amp). Don't use it insulated, it will get hot at 100 amp levels...of course, if you're pushing it, yet still want that big signal (eg mv/amp for an LCD panel meter) - use two 2 foot pieces in parallel.
You get 4x the heat dissipation...I actually use it about 14" long, then tie sense wires a foot apart in the middle somewhere, usually one right at one end (ground end, for whatever I'm calling ground) and adjust with a known current till it's right. Yes, the tempco means that the more amps, the higher it reads on the meter - this is not necessarily a bug...it means (to me) that I'm pushing something, like battery life in the system, so I want scary numbers once they get real big.

I put this table up because I needed it - and had to go find the book again, for some other work I'm doing with building broadband transformers to work way off ground (think fusor voltages). This lead to the old equation for approximate inductance (sizes in inches).
Microhenries = r^2 * n^2 /(9*r + 10 * l)

n being turns, r the radius, and l the length. Since I was iterating, and I have the perl programmers virtue of laziness, I wrote a script that does this one, and warns if l is too short for it to be accurate. Yeah, it's not a beauty, programming wise, just efficient (for the programmer's time, that is).

Code: Select all
#!/usr/bin/perl -w
use strict;

# a quick and dirty microhenry calculator for single-layer solenoids
# uses the old formula from Terman: L = r^2*n^2/9*r + 10 * L

my $turns;
my $diameter;
my $radius;
my $length;
my $microhenries;
my $feet;

print "Input number of turns ->";
$turns = <>;
chomp $turns;
print "Input form diameter (inches) ->";
$diameter = <>;
chomp $diameter;
$radius = $diameter/2;
print "Input length (inches) ->";
$length = <>;
chomp $length;

$feet = (3.14159 * $diameter * $turns) / 12;

print "turns:$turns\tradius:$radius\tlength:$length\n";
print ("Coil too short for this to be accurate!\n") unless ($length > (.8*$radius));


$microhenries = $turns**2 * $radius**2/(9*$radius + 10*$length);
print "\nMicrohenries = $microhenries\n";
print "Feet of wire:$feet\n"
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Doug Coulter
 
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