OLTC update 240BPS inductor

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi All,

As it turns out, there just is not anyway to wind a 34mH air inductor with
#18 wire without having to use about 600 feet of wire at about 4 ohms of
resistance.  I'll spare you all the torturous calculations...

http://hot-streamer-dot-com/temp/OLTC09-21-01.gif

At about 6.3 amps RMS input, 4 ohms is (I^2R) 160 watts of R heating just
in the inductor!  Worse yet, it tends to spoil the resonant charging.

So I went back to a split core toroid.  Happily it turns out to be even
lighter than 600 feet of # 18 :-))  Going from 150mH at 4 amps peak to 34mH
at 10 amps peak makes a ton of difference!!  Weighing in at 3 pounds 5
ounces, May new 34mH inductor can go to 10 amps without saturation.  It
also only has a DC resistance of 0.856 ohm or 34 watts of heat.  Better
still, it is now 240VAC ready :-))):

http://hot-streamer-dot-com/temp/OLTC09-21-04.jpg

Notice those red hands from winding 300 turns on this puppy ;-))  Sawing
the core was not easy either!  I sawed it twice to get a nice big 1/4 inch
gap.  Even though these cores are tape wound, sawing them was not a big
deal and they stay together pretty well.  Even though I was just wildly
guessing at core size and all I got lucky and it worked out just right:

http://hot-streamer-dot-com/temp/OLTC09-21-02.gif

http://hot-streamer-dot-com/temp/OLTC09-21-03.gif

I goofed up on that Req = SQRT(Rdc^2 + Xl^2) stuff...  So the core is
really 36.3mH.  Not a big deal and I decide to wait till I could actually
run it to do any fine tuning.  

The line input current looks like this:

http://hot-streamer-dot-com/temp/OLTC09-21-04.gif

"Funny" but not to bad at all.  Drawing 6.31amps at 240VAC in gives a
system input power of around 1500 watts.  Firing voltage is 580 volts and
the peak primary current is a toasty 5732 amps ;-))  That's 573 amps/IGBT!
Probably should have used 15 IGBTs...  It will be ok as long as I don't run
it too long to heat them up.

So running at 240BPS with this much "easier" inductor seems like a great
thing!  I'll see if I can get some real testing done tomorrow.  Many thank
to Richie ;-))

Cheers,

	Terry