Some pictures of my DRSSTC primary from conception to completion. See the primary design page to see how I did it.
Laid out with a compass and a pencil, cut out on a scroll saw. Isn't math
cool!?
Primary posts cut with the tablesaw jig discussed in the "Primary Design"
article.
I wrapped the strike rail on with wire, I think it's really attractive; but
it proved to be too close to the secondary later.
Closeup of the primary winding.
I was really pleased anentetically with my primary, although there are several frustrating "features" in this first one. First of all, I measured wrong, and I didn't realize until I had cut every thing out, so I thought I'd just go ahead and try it. So, the coupling was too high. Secondly, I laquered it to keep it from oxidizing. I really hate that. It's almost impossible to get a good connection in a new place, and you wind up scraping all the varnish off, which looks like crap. I have to do something, however, because it will oxidize if I don't. I'm thinking a thin coat of oil? I don't know. I talked to other coilers with nice primaries, and they just shine theirs up with steel wool for pictures and 'thons. I've got to find a better way to keep it looking nice.
My GDT, a couple of the CT's and the controller circuit without ICs.
The trim for the box. I make this from scrap aluminum that we pulled out of
the "bus" when we were building it. The aluminum in the upper right
corner is a sample. It had some sort of wallpaperish plastic on it, and the
only way to get it off was with the wire brush on a grinder. I liked the finish
that it left, so I kept it.
A closeup of the completed interruptor. What kind of moron doesn't clean the
fingerprints off the object before he takes a picture? Doh! The box was made
out of the same stuff as the trim. The label was done with the Gootee process
for PC boards. It was the third try that was the charm IIRC, so don't lose
hope. I couldn't find a good simple way to attach the circuit inside the box,
so I just wrapped the board in bubble wrap and crammed it in. Works beautifully.
Picture of the front display
Mock setup of the main components.
The power indicator after drilling and installation. I designed this power
indicator and it's analog. It works just fine, but I believe it would be better
if I had designed a digital one with comparators.
The coil in "test fit"
More pics to come, soon I hope. I've got it running, but it was in like 5pcs and looked horrible. I didn't have the heart to take it's picture. She needs a new primary before I can get her tuned properly, and I'll post pics when I get her put back together.
Scope Shots:
This scopeshot really freaked me out the first time that I saw it. This is
a shot of an unloaded GDT, the ringing is terrible, hence the concern. However,
all this mess calms down when you load the GDT with a transistor.
This is much better.
Brighter shot of trace.
"Zoomed in"
Ok, the last three shots are what you will probably be looking at alot. They are of loaded GDT signals across the gate/source of the 'FET/IGBT. There are several "problems" with my results. The measurement is set 10V/div. I've got ringing at the end of the pulse, and at the tops of the signal where it overshot. "Ringing is okay as long it is outside of the active region" per EVR, and that makes perfect sense. I did not worry about it on my driver because it is *just* out of the active region. If you have ringing that is in the active region during the interruptor cycle, you need to clean this up. However, the couple cycles of ring is not good at the end either. This will heat the transistors resulting in switching losses. I'm not to worried about it on this coil, because the IGBTs are running cool, but if I were going to make a bigger coil, I would like to clean this up. You are going to have overshoot, but to get it out of the active region increase the voltage to the UCC's or increase turns ratio on the GDT. IIRC, you can clean up the ringing at the end by fiddling with the DC blocking cap value on the primary side of the GDT. I have also heard about putting a resistor somewhere, but I don't remember where that is.
Here is a scopeshot of the current in the primary. 400A peak.
A picture of some plasma during testing. Plasma acts differently than I'm used to, it "snowflakes" when it hits the glass. It's really beautiful. I took lots of pictures to attempt to capture this effect, but no avail. You can almost see it in this one. The DRSSTC power arcs are really neat too; the banjo effect is perfect, no gaps, perfectly distanced; and can be precisely controlled with the interruptor. Sweeeet! Plus, if you're good with the knobs, you can make music... Man, I will never go back to SGTC!
To be continued...
Currently, this project is a bit on backorder. I need a new primary because I mis-judged the size that I needed. I have not had time to get to that unfortunately, but I'm itching to get to it. And although it works, there is something funky with my OCD circuit.
To date, my longest spark was 8-10" estimated, and to tell how far out of "tune" I was, I was running 600A+ peak IIRC. Stinko effieciency, I know, but I need a new primary to hit either of the poles. Unfortunately, I couldn't get a good picture, and wasn't that interested in getting one ATM. I estimate that had I been in tune, I should have been getting 20"+ sparks. I didn't have all the parts for my OCD, so I wasn't using it. Now I only get about 4" (200-250A peak). Oh, yeah. Important note: without the OCD, I lost about 5 IGBTs, some at embarrasing voltages. With it, I have lost none, even with maximum bridge Vin. I would highly recommend getting the OCD to work before you start to tinker with it.
(05/28/06)
Finally some time to spare! I've been working on my new design for my primary
all afternoon. I think I've finally landed on a good design, we'll see how
it goes tomorrow (Memorial Day, perfect for big sparks!). If Terry's ScanTesla
works, it ought to be perfect. It seems to, it's one awesome progam. It designed,
built, and tested over 125,000 tesla coils and spit out the good ones for
me to look at in about 2hrs. It even spits out Excel spreadsheets so that
you can look at estimated waveforms and plot values against each other. Looking
through the data, the calculations seem to be pretty accurate, which is getting
me pretty excited about tomorrow. I then ran the information through my DRSSTCpolecalc
that I wrote and the specs check out there too, so I plugged my numbers into
the other half of my program and played with them until I got a primary size
I liked. Then after making sure my programming was correct (by running it
against WinTesla) I opened up MandK. I was looking for a K of .185 and a primary
inductance of about 19.8uH that ScanTesla suggested. I returned with K=.295,
Yikes! So after raising the secondary up 2.5 inches I came up with K=.1868.
So, here's the plan for tomorrow:
New primary 7.5" diameter, .25 'fridge tubing, .2" spacing, 10.5
turns needed; building for 12 to be safe. Secondary will be raised approx
2.5" to compensate for coupling. Actually, I will run it through MandK
a few more times to get a more accurate value before I finish. NO LAQUER this
time, I'm going to try some light oil. This time, no sharp edges on the strike
rail. (Duh, but they were an accident the first time.) Then, it's off to making
some sparks! We'll see how it goes, right now it's 11:45, I've got to get
up at six to put a roof on our solar kiln (for our sawmill), so I had better
get to bed.
BTW, ScanTesla was a booger to find. Look here: http://drsstc.com/~terrell/modeling/ That's where Terry keeps it. Oddly enough, there's no link on www.DRSSTC.com for ScanTesla that I can find.
(05/29/06)
We got the roof on the kiln and it looks great. And around 2:00 it started
raining harder than I've seen in years! As far as coiling goes though, it's
been a disappointing day. Not without hope however. I built a beautiful new
primary and got some good pictures of the building process. Then, I assembled
the coil, but the performance was exactly the same as with the first primary.
???! For some reason ( I figured out why later) with all my new primary turns,
it really liked turn 1. Turn 1?!? Something ain't right here. After poking
around some and doing some more testing, I realized that it's driving the
coil about 100Khz+ low... Come to find out, I paralled the primary
capacitors for a total of .3uf at 4kV instead of what I thought I was doing,
seriesing them. So my primary tank is resonating at like half my
secondary's resonant fq. Man what a moron! I'll fix it tomorrow.
The Solar Kiln, oriented to catch maximum rays.
None of this explains my OCD troubles, however, I still don't know what's wrong with it. For the longest time, it was hitting 50A and cutting out, now I've got it to do 100A. I've got some ideas, but haven't tried them out yet. Either it's the weird primary configuration that's messing with it or it has something to do with shielding. I suspect the shielding because if I touch the shielding while the coil is running, I get little sparks and the OCD triggers. Sometimes it gets stuck there for a couple seconds too. Connecting the main sheilding to RF ground improved performance a little, you couldn't see the performance change visually, it even wasn't much on the meters, but you could hear it run more smoothly.
New setup as suggested by ScanTesla
Work in the morning will be:
Fix primary capacitor
Pray the OCD works better now. If not, figure out why it's being annoying.
Fingers crossed...
(5/30/2006)
It's working! I killed my variac (this my children is why your're supposed
to use a fuse. duh!) and my oscilloscope, and 4 IGBTs today, but I'm having
luck. I fixed the variac and the coil is working nicely. The OCD does not
work at all now, still not sure what is wrong... Suffering from heavy primary/secondary
arcs, though they have not damaged an IGBT yet.
Near the end of the day, I accidently did something really cool with my interruptor. See video. I touched the underneath of the board and accidentally caused extremely long on times. It has a deep throaty sound, I wish the camera could have gotten that too.
(5/31/2006)
WAHOOO! I've got 27" out of the cheapest IGBTs I had!!! ( I mentioned
on the forum they were lousy, but I was wrong. I just wasn't treating them
correctly.) The MSRP on the FGA40N60UFDTU is $3.90, and I was running about
150A through them easy. I ran them up to 250A at one point I think. I also
found the FGH30N6S2 is also a pretty nice one (MSRP $3.30). It was suggested
by the Fairchild rep, and they work nicely though neither of these are as
powerful as the International Rectifier IRFG4PC50UD or the HGTG40N60A4 from
fairchild. The FGA's easily handled 600W, but I couldn't push them any farther
because my variac is only rated for 320W :). I'll have some better numbers
soon! I think, for sure, this coil will run on the $4 IGBTs from Fairchild
with room to spare. If I were to build a bigger coil, I think the IRFG4PC50UD
would be my favorite. They're MSRP $11.43, but I found them at Arrow Electronics
for $4.36 ea.
My oscilloscope is fixed, the fuse blew, but I didn't have another. I got some on my lunch hour today. Thank goodness she's okay!!! The OCD is working great too, I hunted down the problem with my scope, I had a problem just after the rectifier. It's working AWESOME now. The only IGBT I killed today was when I attempted to turn on the unit without a variac. The current rushed into the bridge capacitors and the spike killed both my IGBTs. Oh... that's why they all tell you to use a variac on the bridge. Everything is looking up! I'm using this opportunity to put the coil all back together and get things permanent.
Dang it! All that fun and no pictures!? Sorry guys...
(6/11/2006)
By this time, I'll bet you guys think I'm lying. I swear I'm getting sparks,
just hang on. :) Eventually, I WILL get pictures.
Last sunday, I upped my primary current to 300A and was getting nice long sparks, and was attempting to take pictures. I'd been running continous at 300 something watts for several minutes, with GREAT sparks; and was still getting bad pictures, when BOOM! + flash + shapnel hitting stuff + me ducking under the tripod... (Ok, so maybe there wasn't any shrapnel, just a little bit of molten solder.) Apparently, I didn't make enough clearance because the wire going to the MMC jumped over into the drive circuit. Killed everything in the bridge expect 3 diodes. Even part of the wire was toasted, and the solder was blown off the diode that it arced to. "Well," I thought, "I wanted to redo it anyway..."
The week went by slowly, this was my first week back to college, Summer semester. Phbbt. Looks bearable though. At work, we got 16 tons of books in, all which I had to load on the shelves by hand. Then, this Friday we spent the afternoon cutting down oaks to mill on Saturday. On Saturday, we got up around six-seven and began milling the logs. 800 something board feet of the most beautiful white oak I've ever seen!!! That's like 2,000 dollars in wood! (Provided that it dries correctly.) Needless to say, I was dead tired at the end of Saturday. If this keeps up, I might just grow some muscles. I'll have to peel the girls off like ticks! *daydreams* Huh-huh. Yeah right.
Sunday, back to business! After church, I rebuilt the H-Bridge on a new board, and I fixed some annoying problems. The bridge is completely and easily removable now, which is how it was designed to be in the first place. The entire doubler circuit is on board now, and I have hard-wired the GDT. I like this setup MUCH better, I will include pics soon of both the fried board and the new one. Now the IGBTs just slide in and screw down. EXcellent! My 12ga wire was getting hot in the past, (estimated RMS 20something amps) so I switched it out with heavier wire.
I hooked it all up, and most everything that I could have plugged in backwards I did. After figuring all that out, I remembered my variac cratered again when the bridge blew up, even with the breaker attached. (It's got a weak winding) So, after repairing that, it began to work beautifully! I turned it up about halfway just to be safe, and was getting, I don't know, about 12" streamers. Reaching for the camera, I saw the current start to skyrocket. Uh, oh...
Hmm... Interrupter turned off, 12ish volts to the bridge, but 2A power draw! Ick. IGBTs ok, diodes ok, no shorts, I don't think I've got shoot through...
Aw crap. Some <insert synonym for tired fool here> put my doubler caps in backwards! Gosh, you can hear them sizzling in there too... *Winces* Well, there goes 10 bucks, good thing I bought extras. I guess I'll fix them sometime this week? *Hope. Hope.* Right now I'm going to bed to finish recupperating from yesterday before I have to get up at 4:00.
Boy, I hope I get this thing finished before nursing school; I register Wednesday. Come August, I won't have any free time (or money) for like two years. When's retirement?? LOL. :o)
(6/16/06)
Well, registration was ...interesting. What have I done?! :o) You mean I just
paid 3,000 dollars for you to take away all my free time for 3 months? Just
kidding, it actually looks like I'm really going to like it, although the
studying looks intensive.
Friday. I lied to my dad and told him I was going to work on my tesla coil while he went to bed, I cleaned off the back porch of the shop. 2 1/2hrs later it looks great, Happy Father's Day! We'll see what he says in the morning. After that, though, it really was coil time!!!
I pulled out the toasted doubler caps (shorted inside to 3k ohms each) and put in fresh ones. This baby works like a dream! AND I FINALLY GOT PICS!!! Because my variac won't take more than 320W, I can't turn stuff up as high as I'd like...
My longest strike caught on camera. 26" long.
About 20" I'm about to figure out the camera...
Another 20" shot
I have no doubt that once I get the variac situation worked out, this thing can hit 35-40". You can tell, as soon as I get it going good, the breaker trips in the variac. Humpf. I'll get it put together properly (right now it's in about 10pcs) and move it so maybe I can get longer sparks. Right now I can't help but hit 20" 'cause that's how close the ceiling is. Every so often it will launch one outward that will drift up and hit the ceiling. My longest stike from this happening is 27" point to point.
Get this! Running 180W, I can get 18.5" occasional ground stikes. Running 240, I can get 22.5 often! Running over that, I can't tell because the ceiling's too close. That's pretty darn good compared to a SGTC, I haven't checked the numbers against other DRSSTC's yet. Oh, and primary current was running 120A with streamers and peaked to 200-220ish during a ground strike on both 180W and 240W. Another funny thing is that it likes to *jump* power levels. For instance, it was really hard to measure at anything but certain intervals. It would *pop* into place until it decided to jump to a higher wattage. Strange, but I think I've heard Steve talk about this.
I also find that I suffer from heavy primary-secondary arcover unless I use a long enough breakout point. Then I can do anything I want without flashover.