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Re: New DRSSTC first light and a question



Original poster: Jimmy Hynes <jphynes@xxxxxxxxx>

Hey,

I think your main problem is the feedback winding.

"To obtain the feedback I run one of the primary leads through a
toroid core. The feedback winding is one turn on the core."

If the turns ratio is 1:1 (or maybe 1:2 if one 'turn' means passing through twice) then the feedback sees as much current as the primary, and the voltage drop needed at that current is quite a bit of power. Use a lot more turns on the feedback! I use 2 transformers cascaded to get 1:1000

If you're using primary feedback, active current limiting would probably be a good idea. My little DRSSTC uses the same IGBTs as you and couldn't quite do 600A at 360khz, but can do at least 600a at 180khz. A half bridge of those IGBTs at 330v rails and 400A peak has gotten me 37" so far, just do get you an idea of how much they can do.



On 9/17/05, Tesla list <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx> wrote:
Original poster: Terry Fritz <<mailto:vardin@xxxxxxxxxxxxxxxxxxxxxxx>vardin@xxxxxxxxxxxxxxxxxxxxxxx >


Hi Skip,

DigiKey sells nice little CTs right off the shelf:

<http://drsstc.com/~terrell/pictures/CTshield.JPG>http://drsstc.com/~terrell/pictures/CTshield.JPG

DK#  237-1097-ND  $6.67
120A 10kHz to 200kHz
Saturation, current, frequency response... are all ready "all figured
out" for you ;-)

These will easily do 200 amps peak.  If you need more current,
perhaps you can tap into the MMC cap for a lower current leg (the
current thought say 1/4 of the MMC strings).  Dan and some others i
think used secondary feedback where the currents are far less.

I use a bit of grounded brass tubing for a RFI shield too.

Put the burden resistors way back at the electronics to reject noise:

<http://drsstc.com/~terrell/pictures/CTwiringBad.gif>http://drsstc.com/~terrell/pictures/CTwiringBad.gif

http://drsstc.com/~terrell/pictures/CTwiringGood.gif

<http://drsstc.com/~terrell/schematics/CurrentMeasurement.gif>http://drsstc.com/~terrell/schematics/CurrentMeasurement.gif

http://drsstc.com/~terrell/schematics/ProtectionCard-1.2.pdf

Be super sure to see this note...

<http://drsstc.com/~terrell/notes/TerrysDRSSTCnoiseFIXES.pdf>http://drsstc.com/~terrell/notes/TerrysDRSSTCnoiseFIXES.pdf


Happy to see another joining the DRSSTC club :-)

Cheers,

        Terry




At 04:46 PM 9/17/2005, you wrote: >Hi all >Here is a quick spec on the new DRSSTC >I used Dan's full H bridge driver but with primary feedback driving >four IRG4PC40W IGBTs >Secondary: Dia: 4.5", 1000 turns #26 >Primary: Dia: 6.5", 5 turns #10 >Cap: .04 >Top load: 2" x 8" toroid >Resonant Freq: 285 khz >Power: DC using a full wave bridge on 115vac input. I expect to go >to 240vac input >At 40vac input the output spark is over 6" > >To obtain the feedback I run one of the primary leads through a >toroid core. The feedback winding is one turn on the core. > >Problem: The toroid core get VERY hot running at 40vac input. Too >hot to touch. Is there a better way to develop the feedback???? > >I would appreciate any suggestions. >Skip