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Registered Member #3688
Joined: Mon Feb 14 2011, 07:39PM
Location: Europe
Posts: 38
Thanks for All the valuable Advice!
Sigurthr: I will build the Augmented interrupter, but I've never worked with optocoupling with fibers before. Is it as simple as Attaching two modules to either part of the fiber?
Does anyone have any tips for secondary winding? Any good dopes to coat it with?
@ Dr. Brownout Ahh okay that makes sense then. Very nice results indeed! 6" from 120vrms w/ halfbridge IRFP260s sounds quite accurate/reasonable based on my results if your coil has a bit lower Fres and less primary impedance than mine. Thanks for the confirmation of specs:output!
What is the approx fres of your FGH40n60 full bridge?
@MArked One: Neither have I haha. It is always better to use optocoupling with remote TC logic circuits but I've never actually done it and never had a problem wire hardwired connections. I've just used shielded cable and a metal project box and grounded the shielding (at the TC driver) or built it all on one board.
It is more of an issue for DRSSTCs to have it optocoupled as a long ON time from interference getting in to the interupter logic could/will blow up expensive transistors. SSTCs can run CW so you don't have to worry about that, interuption is optional for a SSTC but not a DRSSTC.
Secondary winding: MAKE A JIG TO HOLD THE COILFORM AND THE SPOOL. I wound my first secondary (20"x 4.5" form - 1500 turns - 18" of 30ga winding) by hand with it resting in my lap with only my fingers to hold tension and rotate the form (no jig), and it was the most nerve-racking, stressful, boring, and mind numbing 16 hours of doing something by choice in my life. A few pieces of wood, a long dowel or threaded rod, some screws/bolts, and an electric drill is all it takes. I wound my second secondary (smaller, on a smaller coilform, with half a jig and a drill) in about three minutes.
Registered Member #4104
Joined: Fri Sept 23 2011, 06:54PM
Location: Uk .
Posts: 122
My SSTC Is halfbridge of 600v 20A fets , was hitting 9" arcs with 230v and 4 x 6 inch secondary but after many fed deaths i have giveup till i get a scope ... .
For winding i used lego , made a simple jig from it then supended the secondary form between i wound my 4 x 6 inch secondary with 28 awg wire in about half hour .
I coat my secondarys in polyurthane floor varnish , 2 coats gives a nice finsh and it seems to work ok , no idea on brand though .
I also use my mains earth as my ground , I have had no interferice problems nor any stange affecs so far that im aware of ..... bit its risky as there is a TV/Console/PC in close are tao TC , Earth wire and proximity .
Registered Member #3885
Joined: Sun May 15 2011, 12:47AM
Location: Newton, Massachusetts, United States
Posts: 94
MArked One wrote ...
I will build the Augmented interrupter, but I've never worked with optocoupling with fibers before. Is it as simple as Attaching two modules to either part of the fiber?
Indeed it is! On Digikey, FB128-ND is the transmitter I use, FB123-ND is the receiver, and FB140-1-ND or FB143-10-ND are suitable fiber cables. Much cheaper than the fiber stuff I see many other people using, and I've never had any sort of reliability or durability issue with it. (Thanks to dude500 for showing me these modules)
Registered Member #3688
Joined: Mon Feb 14 2011, 07:39PM
Location: Europe
Posts: 38
I'll Ask my local tech shops if they have an affordable fiber optocoupling solution the next time I'm in town.
Twirlywirly555: thanks for the tip! I'll coat the secondary in some sort of quick-setting varnish.
On Another note: what does the "burst mode" feature do in the interruptor schematic? Am I correct in Assuming that it interrupts the output signal At regular intervals?
Sigurthr: I'll try A jig for sure. Do you employ Any method to keep the wire from tangling?
I'm including A salvaged line filter in the coil to help prevent RF junk from entering the mains wiring. Does this Approach make sense?
Registered Member #2405
Joined: Fri Oct 02 2009, 12:59AM
Location: Wisconsin
Posts: 140
Sigurthr wrote ...
@ Dr. Brownout Ahh okay that makes sense then. Very nice results indeed! 6" from 120vrms w/ halfbridge IRFP260s sounds quite accurate/reasonable based on my results if your coil has a bit lower Fres and less primary impedance than mine. Thanks for the confirmation of specs:output!
What is the approx fres of your FGH40n60 full bridge?
.
The fres of my 9" coil is 65kHZ. The tank cap is .225 made from MMC caps. Bus voltage is 340 or so depending on the variac setting. I dont have real big heat sinks on those either but they seem to handle that frequency and power level quite nice. Also that particular drive is not fiber optic, it also uses base feed back and no OCD of any kind. My new ones all have some kind of protection, even the one I am building now. I am using a full bridge of CM300 bricks and I have TVS's and zener diodes allover those bricks. I took some pics of it today with my phone if you want to see that setup.
@ MArked One: I actually left out the burst mode 555 in my iteration of his interupter, as I wasn't sure what it was for either.
I used my finger to guide the wire and keep tension on it. As far as tangling goes, it must never be allowed to slack at all, or it will jump turns and overlap or all come undone. A slight angle away from the unwound side of the form will usually help the wire lay tightly against the previous turn and prevent inter-turn spacing from popping up, but the angle is pretty critical and when doing it by hand it is neccessary to stop and fix it some times. If you can't wind the coil without stopping once then be sure to tape finished sections regularly with small 1-2" pieces of GOOD electrical tape (easy to remove and sticky) running in parallel direction as the axis of the coilform, staggered at a couple points around the circumference every couple inches of winding. This prevents catastrophic unwinding.
@Dr. Brownout Sure, I'd love to see some photos, sounds like a monster setup! Wow, 65kHz.... haha, one day I've got to stop making high fres coils! My largest secondary is only 250kHz fres (w/o topload).
Registered Member #2405
Joined: Fri Oct 02 2009, 12:59AM
Location: Wisconsin
Posts: 140
Sigurthr wrote ...
@Dr. Brownout Sure, I'd love to see some photos, sounds like a monster setup! Wow, 65kHz.... haha, one day I've got to stop making high fres coils! My largest secondary is only 250kHz fres (w/o topload).
I will upload some photos of that TO247 H Bridge along with some photos of the coil and spark pictures. I etched the board for the H bridge on two different PCBs I did not have a PCB big enough for one board, I actually had made the original layout to accommodate the 40Gn60 I think was the part number, or something like that but when I looked up the specs on those bricks they were being obsoleted so I found some leaded TO247 components and decided to make the H bridge out of those so I reworked the original layout and it worked out really well.
I had that coil at one of the Cheesehead teslathon a few years ago and it performed really well there too so its pretty robust lots and lots of protection components all over the place, however no real protection circuits. All the ones I build now have some kind of active monitoring of some type.
The coil is 9.5" diameter and has a 50" winding length the top load is 6" x 24" spun aluminum toroid But I will upload some photos of it.
Registered Member #2405
Joined: Fri Oct 02 2009, 12:59AM
Location: Wisconsin
Posts: 140
Ok here is a few photos of the coil the heat sinks on the IGBTs are small but nothing seems to get hot at all, I was really impressed how cool this coil runs, 340 Volt bus, its a 120V with a doubler the bus are 3500uf 450WVDC 525 volt surge. Fres is 65kHZ. Top load is 6" x 24" spun aluminum
Registered Member #2405
Joined: Fri Oct 02 2009, 12:59AM
Location: Wisconsin
Posts: 140
I stand corrected the Fres on this coil is 75kHZ not 65kHZ. its been while since I played with this I found some Gate drive wave forms I took and the scope is showing around 74kHZ.
The first wave form I had a lot of ringing in the signal so I upped the snubber cap size to 4700uF across the rails and it cleared it up nicely.
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Mini SSTC Inquiry - 220v?
