Re: New DRSSTC first light and a question

["Tesla list" <tesla@xxxxxxxxxx>]

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