Re: OLTC (was Fwd: Hmmm...)

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

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

Hi Brian,

At 08:30 AM 8/17/2002 -0700, you wrote:
>> Subject: Geez...
>> Date: Sat, 17 Aug 2002 01:47:16 -0400
>> 
>> Hey,
>> 
>> I am a dope. Since it was 3AM I neglected to do any
>> math on Terry's power supply. I was only referring
>> to the first stage of the setup, where he charges up
>> the 47uF cap. Even though he may not get 1300V on
>> the 47uF cap, If he opens the IGBT while the 150mH
>> coil is charging, the inductor becomes the source,
>> and its polarity reverses. This will place a greatly
>> negative potential on the end of the coil connected
>> to the IGBT, so that the total voltage across the
>> IGBT consists of DCin - Vc + V(150mH). It is the
>> voltage kick from interrupting the coil that is the
>> problem, which works out to overvoltage the IGBT
>> unless you provide an alternate current path for the
>> kick pulse. Hence the afforementioned diode of my
>> last post...

There may indeed be better resonant modes and such that could be used.  In
this case, I just picked the easy one ;-)  Also voltage doublers may be
possible:

http://hot-streamer-dot-com/temp/ON-LINEVoltageDoubler.jpg

>> 
>> Depending on the type of IGBT you have, it may have
>> some built in body diodes which will clamp a few
>> millijoules of inductive energy before overheating
>> the die. It's OK for an occasional surge, but not
>> for repetitive abuse.

They have big beefy 200 amp HEXFRED diodes in the reverse direction.

http://hot-streamer-dot-com/temp/irg4pf50wd.pdf

>> 
>> For some reason I cannot get a clear pic of the
>> schematic, so I am working a bit in the dark. Is the
>> IGBT in the first section ONLY used to turn on the
>> supply, then stays on until the ozone fills the room
>> and it is time to go out for a cig? If it is only an
>> on switch, then why not just use a triac on the AC
>> input side of the bridge? Is is a lot less to worry
>> about just to turn the thing on (but it must stay on
>> until the 60HZ half cycle is complete). There are
>> also optoisolators with small triacs that can be
>> used to trigger the larger power triac (the ON
>> switch).
>> 
>> Or, is the supply turned on just long enough to
>> charge the 47uF cap, then the supply is turned off,
>> then the 47uF cap is discharged into the primary of
>> the output coil, then the cycle repeats again by
>> turning on the supply to again charge the 47uF cap?
>> If this is the duty, I can see why you would want an
>> IGBT for the power switch.

The IGBT array performs the same function as the spark gap.  The array
turns on for about 100uS every 8.333mS  This completes the primary LC
circuit and also discharges the primary cap to get ready for the next
firing cycle.

>> 
>> This is a very novel idea which I would like to
>> learn more about. Has someone posted an article on
>> the operational theory behind this setup? I am
>> throwing out a lot of guesses and think it's time
>> for me to hush until I learn more. :)

Mostly just making it up as I go along and people add suggestions ;-))

Here is a text file of posts on this subject:

http://hot-streamer-dot-com/temp/Off-LineTeslaCoils(OLTC).txt

Here is a web page:

http://hot-streamer-dot-com/OLTC/

You can also see older and the latest posts here if your not on the list:

http://www.pupman-dot-com/listarchives/2002/August/threads.html

http://www.pupman-dot-com/listarchives/2002/August/maillist.html

All the posts start with "OLTC".

You can send posts direct to me at:

twftesla-at-qwest-dot-net

Cheers,

	Terry



>> 
>> -Brian
>> 
>> 
>