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Re: Inductor question


>From: Steve Roys <sroys-at-umabnet.ab.umd.edu>
>To: tesla-at-pupman-dot-com
>Subject: Inductor question
>

>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.  
>
Steve,
	I've wound a 2 3/8" ID 12" long inductor with 2 layers of
wire. I started out with #16 A.W.G enamel ran out at 3/4 of 1 layer,
used #18 for about 1/2 of a layer and finished out with bifilar #19
SCE (single cotton covered enameled). Sooooo, I'm not sure of how many
turns I have;(

	My iron core is 4 lbs 13 oz of transformer "I" sections.

It measures L= 600uH Q=1.4 aircore at 60Hz and between 8.3mH and
16.9mH iron core at 60Hz. (I'm still learning to use the Leader LCR
bridge here. The 8.3mh figure was a shallow dip, the 16.9mH was a
sharper dip) Hum, 2:1? methinks that means something;)

For short term use (~1minute) you do not need such large wire. The
500mA or 700mA per square mil wire sizing equation is for transformers
that operate day in and day out with only an 50 degree C temperature
rise (50 degrees C: memory here) I would guess that I get a 50 degree
C rise above ambient in 1 minute. For longer run times or higher
currents use larger wire. 2-4 gauge is a bit large;) 19 gauge is to
small! How about 12 gauge?

>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. 

If you are basing your expectations on a 1000 or so Al value for your
core, remember, that value is for a full magnetic path. With only a
partial circuit, you will have a much lower increase in the
inductance. I see only a 28:1 increase in my inductance. I have also
only partially filled my solenoid. Still, 5:1 seem very low.

I am going to ask, what seems to be an obvious question here, with no
slight intended. Are the welding rods that you used mild steel?
Stainless? Bronze;) I started doubting myself and checked my Bronze
brazing rods with a nydodium(sp) magnet. Not magnetic;) phew! I still
remember that info;)

How did you determine the inductance of your solenoid? LCR bridge?
Current based calculation? Based on my results tonight, I'll have to
double and triple check all my measurements using my Leader LCR
bridge.




Observed results using a home wound ballast inductor:

In use with the pig's secondary OC:

	220V through this inductor and through a 13.5 ohm ballast
resistor into the 110V tap of my 65:1 pig yields a 20kV peak 3.6ms
pulse width square wave. The pig's core is saturating. Ipri=10A.

	220V through this inductor/resistor parallel combination into
the 110V tap of my 65:1 pig yields a 19kV peak exponentially ramp and
decayed square waveform of 4.2ms period. Ipri = 20A.

note: 220V into the 220V tap of this pig yields a 10kV peak sine wave
with or without ballast.  No pig core saturation here.  It's only a
7.2kV pig; which is why I'm feeding 220V into it's 110V tap.
The magnetization current was 1.8A implying an inductance of 324mH in
the 110V "primary"

Now let the fun begin;)

	I connected my rotary gap to the series L/R ballasted pig's
secondary. Using my 10K:1 HV divider I measured 400kV peak hash ontop
of the output squarewave! To this day, I'm not sure if the 400kV was a
real measurement or ground noise. I had the pig's case grounded to my
4' ground rod and then through my RFI filters to house ground. Since
then I've put in an 8' ground rod. During this experiment I blew out 2
microprocessor controlled light switches in the house.

	I added my TC cap in parallel with the rotary gap. I then
measured 75kV peak RF hash on top of 28kV peak LF ripple on the
secondary.

	I then measured the pig's primary voltage. I saw short period,
100uS, 200-300Vpp RF hash ontop of the 60Hz 220V waveform. I also saw
long 1-1.5 -at- 2mS (notes not clear here, 1-1.5 divisions at 2mS per
division?) waveforms of 600-800Vpp ontop of the 60Hz sinewave. I did
not draw the waveforms so, going from memory, the RF waveforms were
sinewave and the LF waveforms were sawtooth.


	Regards and good coiling (no matter what size)

	jim