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Marko

Thu Feb 23 2006, 08:46AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Well most of heavy hardware (no electronics yet) is complete but I have lots of unanswered quesions.

Up for criticism.
Secondary with that toroid resonates at about 300khz.
Small coil but I don't need some giant for the beginning. Schematic is still in 'development'

Standard interrupter will be used (NE555 + SG3525)
Driver is half bridge (i must spare my igbts) for now no primary feedback will be used used (maybe will be added later).

Its made on wooden/atxsmps box (im too lazy to make standoffs) but i tried to make it look good

I want to ask about the primary, is heavy copper wire (2,5mm dia) enough or I should use some pipe (5mm) ?
Il make adequate standoffs for primary but I must know what to use for it first.

Reaching

Thu Feb 23 2006, 12:01PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

for your very first drsstc i would use a bigger secondary or thinner wire to drop the frequency to around 150khz(maybe a bigger toroid). many people think of small coils for the beginning, but in drsstc duty, higher frequency means more problems. you will be fine with 2,5mm primary wire, but i would use the thicker wire(pipe) i you have it on hand, it will make things less problematic.
for your driver you can go with the simplest design for drsstcs, secondary base feedback (74hc14) driver ics and interrupter. nothing more is needed for the beginning.

Marko

Thu Feb 23 2006, 01:43PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

To drop frequency (with 10pf toroid) to about 150kHz i would have to use 0,2mm wire wich is incredibly fragile and it would be impossible to wind.
Coil must be mobile and compact so I cannot have bigger secondary (it is actually far too big even now)

I have some pipe and wire too, I can use any of these
Wire seems too thin to me but pipe is difficult to bend, I think pipe will win

Reaching

Thu Feb 23 2006, 02:51PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

whats the difficulty in winding 0,2mm wire? 75% of my coils use 0,2mm wire, its easy to wind. i alredy wound a secondary with 0,1mm and with 0,05mm,thats hard to wind.

you will get into trouble if you try to make a halfbridge drsstc on 300khz

HV Enthusiast

Thu Feb 23 2006, 03:28PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

I agree. First a first DRSSTC, you want to keep the fres to less than 150kHz. This should be easily attainable and also portable at the same time.

Check Steve Ward's coils for his secondary dimensions / wire sizes. He has a couple small ones that are less than 200kHz i believe.
Dan

Marko

Thu Feb 23 2006, 03:34PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Now it must be 300khz, there is no posibillity to make another or bigger secondary (as said this one is even oversized physically)
I used about 0,1mm wire for 'micro' coils 1,5cm in diameter and it was pain, wire broke several times (had to be fixed ugly way

)

And I don't see big problems driving it to 300khz, if so many small coils work around that frequency (I admit its somewhere on a roof for drsstc)
Now coil is in exact 1/4 wavelength frequency, I can increase toroid size (or put another on the top) if it is really necessary, I cannot have some monster coil because I have to drag it around , so i must be statisfied by what I have.

vasil

Thu Feb 23 2006, 04:48PM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

Ok, this is what you have....
Just keep low the ON time and the pulse rate, and dont allow many strikes to ground. Use many primary turns, with smaller guage for current limiting. maibe you will be lucky...

Marko

Thu Feb 23 2006, 05:07PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Ok, this is what you have....
Just keep low the ON time and the pulse rate, and dont allow many strikes to ground. Use many primary turns, with smaller guage for current limiting. maibe you will be lucky...

You are reading my mind...

I saw lots of small DRSSTCs operating at 300kHz, what I tought is to use very low on times and give good cooling to igbts.
Yust on anothe topic guy says about his excellent 300khz DRSSTC, used fullbridge of 40N60s...
I really hoped this wouldn't be a real problem, needed a small coil and tought it will live if so many others live.
Maybe i could use H bridge instead?

Also I heard that its far beter to use low ON time than limiting the current, to increase efficiency.

Good that you said what problems are, thanks everybody.
Il update this when I finish my schematic, I do not intend to use any feedback for now, so it will probably change a lot...

HV Enthusiast

Thu Feb 23 2006, 05:34PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

wrote ...

I saw lots of small DRSSTCs operating at 300kHz

Which ones did you see?

Marko

Thu Feb 23 2006, 06:45PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

For instance

And this one operates fine in mhz range, but its small enough to withstand it.

If it is really impossible even with warp IGBTs then its good that you said

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