Re: Inductor question

To: tesla-at-pupman-dot-com
Subject: Re: Inductor question
From: Esondrmn-at-aol-dot-com
Date: Fri, 6 Sep 1996 17:37:31 -0400
In a message dated 96-09-06 02:26:21 EDT, you write:

<< ubject: Inductor question
 
 I am playing around with a variable inductor that has a 4" diameter
 sliding core packed with 20 pounds of welding rods (idea compliments of R.
 Hull) that I plan on using to regulate the current in my 50A controller,
 and I have a few questions.
 
 I don't really have the right wire to wind it with yet, so I just wound it
 with some heavy wire (2 or 4 gauge maybe with fairly thick insulation) 
 that I had to see how it works.  There aren't a lot of turns in the 13"
 winding length, so the inductance is pretty low, but I noticed that the
 difference between the core being totally out of the winding and totally
 in is less than a factor of 5.  Is this reasonable for 20 lb of iron
 welding rods or could something else be screwed up?  Using Wheeler's
 formula for the inductnace of an air-core solenoid, I compute a value
 that's pretty close to what I measured with the core out, but I would have
 thought that the iron would have made much more of a difference.  Would
 winding a coil with 6 gauge magnet wire (which would give me a much higher
 inductance to start with) make more of a difference?
 
 Thanks in advance.
 
 Steve Roys. >>

Steve,

How much inductance is your experimental coil producing?  When Scott Myers
and I were talking about this earlier this year, Glenn Cerny measured his
welder core for us and found 22.4 mh core all the way in (lowest power) and
8.2 mh core all the way out (highest power).  That is less than a three to
one ratio.  We decided at the time that we would like to build a variable
inductor that would produce 5 to 25 mh.

I haven't done the calculations but I think the form needs to be longer, say
maybe 20" and I would use a wire with thin insulation to get the spacing as
tight as possible.

Ed Sonderman