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Weekend DRSSTC

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LAN_403

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Sat Aug 19 2006, 01:21PM

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

okay, this project grew up yesterday, cause i have sooo many parts of my old drsstcs and experimental primaries etc liying around that i decided to use them in a quick but not dirty drsstc build and tested in a weekend. yesterday i searched for parts to use and came up with some really nice parts i found, such as

fullbridge of 40n60 igbts (almost finished)
primary with 6mm copper tubing and 7turns, inner diameter of 21cm, height of 10cm, strikerail etc (finished)
a nice hdpe case i build a few weeks ago already with a 80mm fan installed (finished)
10x wima fkp1 caps 100nf 1,6kV for a mmc of 300nF 3,2kV DC (finished)
some nice high frequency cases
yesterday i finished the driver (from my new drsstc6) and tested it ok
finished the mmc and the 1/1000 current transformer today.

still have to build the 1/140 feedback transformer and put it in a shielded case , have to wind the 2 gdts for the bridge and add some decoupling caps, tranzorbs etc to make the bridge work. here are a few pics.

(here is what i started with yesterday)

(finished driver in the small package,hehe)

(finished mmc, double sided pcb full tinned)

(the 1to1000 current transformer in a hf box

more to come very soon, still have to finish the bridge, the secondary and the toroid
secondary will be a 11x40 or 11x35cm wound with 0,17mm wire to give a fres of approx 90khz with a 10x30 toroid, but i doubt i can finish them this weekend cause i want a very nice toroid and that needs some time

Wilson

Sat Aug 19 2006, 02:55PM

Registered Member #78 Joined: Thu Feb 09 2006, 11:27AM
Location: Sydney, Australia
Posts: 133

Man! Thats an incredibly tiny driver!!

There are components on the other side of the PCB ... right?

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Sun Aug 20 2006, 12:22PM

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

small update, started to wire the things up as professional as i can, that needs some time and i have to build up a comparator charging circuit for the electrolytic cap too. dont want to use this old charging circuit i have on hand, its too stoneage like

but things seems to do great and this will be a very powerful small portable drsstc when im finished. heres a pic of the current status

heres the front

okay, not finished this weekend, but the next weekend is only 5 days away, hrhr

more updates

working on a comparator charging circuit for the 2200yf electrolytic cap. status leds for charging and ready, seems to work fine on my breadboard, now im on building it on a pcb. when it works then i can finish the complete electronics today and can make first decisions on how to make a nice toroid and secondary

update

finished the charging circuit, it charges the cap up to 250volts dc via 2 charging resistors 190ohm 8 watt and when the cap reaches 250volts a relay bridges the charging resistors, so i can pull up the bridge relatively smooth without tripping the breaker while loading up the big bridge cap. therefore there are 2 leds one shows the charging status the second led goes on when the cap is full (~310volt dc)
there are 2 switches for this device, one to switch it on and the second to switch the bridge rectifier on and start the charging , when the switches are off the cap discharges automatically through a another resistor

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Thu Aug 24 2006, 05:33PM

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

new update

had a failure in my charging circuit due to a bad voltage divider but now it works fine and everything does like it should. finished the electronics today, and tommorow i can start winding the secondary. then i can do the first low voltage testruns and when everything works i can have first full power tests on saturday or sunday. cant wait to see this beast in action.

here are two pics of the current status

(okay not industrial standard but better than nothing)

(inside full of electronics)
more to come soon

Hazmatt_(The Underdog)

Thu Aug 24 2006, 08:54PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

very very nice.

When you're drilling your PCB's don't push down so hard, its deforming the fiberglass. Just let the drill do its job.

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Sat Aug 26 2006, 07:52AM

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

started doing some first low voltage resonant tests and got dissapointed cause the thing wont start to oscillate, but no problem, i found the failure on my driver pcb, i have 2 wrong turned diodes which leads the feedback signal to ground. now i have to change the diodes and hopefully the thing will do its job. more info to come soon, and a few scopeshots if everything works after fixing the failure

started doing first testruns and got first light today with around 50volts input some 10cm discharges. after fixing some problems with my driver i can now do first tests on mains voltage, hope that doesnt end in a disaster

update

yeah, and it ended in a disaster and i cant find the failure, my fullbridge is just popping away when i test it on mains voltage. i thought it was the driver powersupply which was not enough smoothed , after fixing this i tested again, but the same failure, it is like the bridge is just turned on and ends like a bakon

, . my thought is the feedback ct which has only 115turns , but why does this thing work on 50volts with all signals ok but not on mains voltage?
now im on building a new driver version with (almost the same like steve ward describes in his drsstc guide) hope the 1/1000 ctÂ´s will fix the problem, hopefully,

Steve Ward

Mon Aug 28 2006, 10:35PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Seems unlikely that the CTs would be a problem. Ive used 1:100 CTs for feedback in the past, they seemed to work just the same as the 1:33 to 1:33 CT arrangement that ive been using more recently.

You might want to make sure you dont have some voltage transients killing the IGBTs.

williamn

Tue Aug 29 2006, 02:58AM

Registered Member #55 Joined: Thu Feb 09 2006, 04:56AM
Location:
Posts: 149

I have used 1:100cts for the feedback circuits on my past two coils and they work fine. I still use cascaded CTs for my current sense transformers becasue using a low value loading resistor casued all kinds of problems with faulty triggering. Your Cts should be fine. Could your clamping schema for feedback Ct be faulted causing your 5V logic to fry? Have you checked the operation of your logic?

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Tue Aug 29 2006, 10:27AM

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

yeah, logic and everything is fine. the only thing i wondered about was the feedback which sometimes stops at 20volt input on the bridge when i turn the on time higher or the off time lower, this problem is gone when i use 50volts on the bridge. and i dont think i kill the igbts in cause of voltage transients, okay i have not tvs on the bridge, but i never used them in my 6 drsstcs i build before, so the problem is a secret for me, .im very sure that it has to do with my high side cap charging circuit or with my driver (its a revised version of my drsstc6 controller which is a revised version of steve wards drsstc3 driver)

now a question, where should i put the ct and feedback transformer in and how does it behave , after the mmc or before the mmc ?? okay the current transformer should be mounted after the mmc to catch the real pulsed amperage but where does the feedback ct "work" better?. its like a noobish question for one who already build 6 drsstcs but 4 of them are secondary feedback which worked better for me than any primary feedback i tried so im in the thought to switch back to secondary base feedback with overcurrent protection.
i never popped a fullbridge by switching mains on it and never fried any igbts during a testrun when i worked with secondary feedback which is so "bad for the igbts" cause of no zero current switching etc, i dont share this opinion after 4 of my good igbts died so fast

williamn

Tue Aug 29 2006, 12:12PM

Registered Member #55 Joined: Thu Feb 09 2006, 04:56AM
Location:
Posts: 149

I always put the feedback CT before the MMC. If your logic is ok, I would suspect it has something to do with your gate drive, did you ever get a chance to use a scope and check for shoot through?

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