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My first DRSSTC - Video added

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LAN_403

Goodchild

Fri Aug 06 2010, 08:39PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

I'm sorry if I came off as critical, I'm just trying to help, any way it doesn't matter how you do it, in the end it will work or it won't work and that will decide how the final coil will be designed.

I'm just trying to give you some info that I learned from my time building DRSSTCs, so that you spend less time blowing shit up and more time making sparks.

Good luck to you

teravolt

Sat Aug 07 2010, 07:20AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

well Luca it looks like I will be asking the electronics questions from you. I am using Steve's new drive PCB but with a couple changes on the bridge. I am using 2 UCC27201DDA half bridge drivers to drive 4 IRFS3004-7PPBF ultra low ohm FETS. Unfortunately the fet's and energy storage caps for the bridge get hot at 500 khz with 10ms burst. I think that they are on in the linear region to much if the time because I have dead time. I have had another PCB made so I run my transformer with Push pull instead with a bridge. my goal is to build a DRSSTC that does about 450khz and is modulated at the power input with a D-type amp like Steve Ward's QCW coil. it is a busy project

I hope you finish the thread to he end of your coil.

Herr Zapp

Sat Aug 07 2010, 08:15AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Luca -

One comment on your MMC.

Usually, (looking at your MMC photo) the horizontal interconnections between the individual strings of caps are NOT recommended. Visualize what happens if a single cap fails as a dead short: the other caps now see a substantial increase in peak voltage. In an MMC that is built without the interconnections between each string, the only capacitors that are overvoltaged (and possibly destroyed) are the remaining capacitors in the original string that contained the shorted capacitor.

However, with the grid-style interconnections, if a capacitor fails shorted, now ALL the capacitors in the entire MMC are subjected to overvoltage, and ALL may fail.

With the "independent string" construction, you will need to add bleeder resistors to EACH cap.

Herr Zapp

dmg

Sun Aug 08 2010, 06:13AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627

Luca wrote ...

5- Let's see... I want to touch with my hand this assumption... In case, probably I will switch to fairchild 40N60...

I thought the 40N60's (SOT-227 package) where no longer in production?

Im a bit worried though about thier ratings, pushing that much current into devices that can disapate only around 200-300W, could they possibly overheat themselves to death at too high ON time?

Luca

Sun Aug 08 2010, 02:41PM

Registered Member #2481 Joined: Mon Nov 23 2009, 03:07PM
Location: ITALY
Posts: 134

Gatedbreakdown wrote ...

I thought the 40N60's (SOT-227 package) where no longer in production?

Im a bit worried though about thier ratings, pushing that much current into devices that can disapate only around 200-300W, could they possibly overheat themselves to death at too high ON time?

I have found some of these devices in a surplus store. I think that they are used but they should be ok (and cheap)

Anyway, for a DRSSTC use they are ok, they have been pushed up to 800Apk. Usually power dissipation is not a big problem in DRSSTC, the duty-cycle is extremely low (typ 1-2%) so the average dissipated power is quite low. Usually overcurrent kills the IGBT before overheating in DRSSTC use.

regards,

Luca

dmg

Mon Aug 09 2010, 02:09AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627

Thats good,

main reason I was saying this, is that just from the looks of the package it seems just easier to work with, will dissapate more efficiently, and can be cooled easier compared to its TO-274 counterpart.

Also, as far as I know off, the 40N60 TO-247 doesnt have an isolated mount like the SOT-227.

Luca

Fri Sept 10 2010, 09:46AM

Registered Member #2481 Joined: Mon Nov 23 2009, 03:07PM
Location: ITALY
Posts: 134

Hi all,
I have been quite busy in this period, I have just had the time to wind the secondary...

I also applied a thick layer of insulating varnish on the coil, it resulted quite non-homogeneous but it should not be a problem, it's more an aesthetic issue...

I have also measured the primary self-resonating frequency, it's 95kHz, with the primary tapped at 5.5 turns, JavaTC is really a reliable simulator!

Next step is to build the topload and final assemply.

Reagrds

Luca

Luca

Mon Dec 06 2010, 08:38PM

Registered Member #2481 Joined: Mon Nov 23 2009, 03:07PM
Location: ITALY
Posts: 134

Hi,
I havent updated this post for a while, but I made some progress...

The coil is almost done, I need to finish some protections (line filter) and other details...

However, I powered the coil with a small transformer (30Vac 100VA) because I'm still waiting for the variac, and I have obtainded 24cm sparks to a grounded object

See annaxed pictures

Regards,

Luca

Luca

Mon Jan 03 2011, 09:48AM

Registered Member #2481 Joined: Mon Nov 23 2009, 03:07PM
Location: ITALY
Posts: 134

Finally, I finished my coil.

As soon as I powered it, I relized that the coil was strongly overcoupled, since I had racing sparks already at 1/3 of the varac...
Calculated k was aroud 0.17...

I rised the secondary few cm more and the situation somehwaht improved but at 50-60% of the input voltage I still have some racing spaks...

Calculated k now is 0.13... I will try rising the secondary another couple of cm, but I am worried to have a too low coupling...

However, the coil is pretty efficient, since at 60% of the input voltage (around 150Vac) I get up to 120cm sparks toward grounded targets... If I manage to push the variac to 100% without racing spaks I should reach 160-170 cm !

Current in the primary lies between 550-600 A and occasionally it trips the OCD protection during heavy ground strikes (OCD set to 650A). I found that increasing the inup voltage the primary current rapidly increases to around 500-550 A and then once strong break-out is reached primary current remains almost constant even if I further increase the input voltage. Is it something already known?

Here you are some pics

Regards,

Luca

radhoo

Mon Jan 03 2011, 12:01PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

those purple sparks look great on the old furniture background. nice work!

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