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Registered Member #55
Joined: Thu Feb 09 2006, 04:56AM
Location:
Posts: 149
I have been tuning and findling with the DRSSTC that I built around those Toshiba bricks thread is here: I think I have just about maxed it out, the coil runs great but the longest discharge I can achieve is about 45". The secondary is 21" long so thats just over 2x. How do you guys get those 3x length streamers? I am inputing doubled mains into the halfbridge so 340VDC or so. The bridge is rated for 1200V and I think I am going to replace all of the bridge components and get it ready for 220VAC doubler input. The storage caps are 450VDC 3000uf so I just need to increase the TVS string's voltage. I hope this will give me a bit of a boost.
Registered Member #76
Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458
thats a very good question, . with all my drsstc´s i get only 2x the secondary lenght except my mini drsstc5 which make nearly 4x secondary lengh streamers, so let the drsstc gurus speak out their secrets
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I got barely 1 secondary lenthg with halfbridge powered from 320V. Halfbridge simply seems to need more voltage to get going properly (I plan to switch to a fullbridge and bigger MMC now).
If I had 1200V IGBT's doubling to 650V is a must, maybe even tripler if you are ambitious
DRSSTC gods also seem to twiddle the coupling sometimes to get best compromise betwen peak current/spark output and losses..
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Its all in the tuning, at least in my experience.
Try running your DRSSTC with more primary inductance (gradually adding 1/4 turn and so forth . . .)
There are several things that will occur when you do this.
1. You will begin to notice that initially, arc length vs. input voltage will begin decreasing. So the more primary inductance you add, the less arc you will initially get vs. input voltage.
2. Primary current for the same size arc will be increased vs. lower inductance tuning point.
When this occurs, as you increase input voltage, there will be a point when the arc will simply explode into being at which point minor input voltage changes result in ever increasing arc lengths.
Just be aware, there will be a balance between peak primary current and the amount of current your devices can safely handle.
My DRSSTC III system is tuned to a point where I literally have to get about 200V DC bus voltage before any decent arc lengths occur, then it starts growing very rapidly after that.
Registered Member #76
Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458
interesting effect ive never noticed, cause i never run my drsstcs from a variac. but can someone explain why it is better to tune the primary frequency lower than the secondary fres? i noticed this by building my drsstc 6 which is running on primary feedback. the secondary resonant frequency is just below 100khz and i get best results with 80khz on the primary, but i get only a little more than 2x secondary lenght in streamers,. so my secondary is 49cm in lenght and the longest streamer i got was 1,22m.
would be amazing to see squeezing arcs like this out of a big drsstc thats my drsstc5 which has only a 15cm high secondary and is producing more than 45cm sparks ....
Registered Member #55
Joined: Thu Feb 09 2006, 04:56AM
Location:
Posts: 149
Thanks Dan. One thing I noticed with my particular coil is becasue I originally planned to use a 6" diameter secondary then switched to 4.5" after the primary was built, I can have the first primary turn even with the first secondary turn and I do not get racing ars. What I do get is an increase of power drawn and longer sparks. I usually haver the first secondary turn just about even with the last primary turn. But I have noticed as I remove spacers and bring the scondary down, while increasing coupling, performace drastically increases. I got to the point where i am now at 45" or so with the first turn of the secondary is even with about the 3rd turn of the primary (halfway down). Just for kicks last night I removed all spacers and cranked it up I got no racing arcs and huge discharges for about a minute before I blew my variac fuse which is a 10A fuse for now (should be a 20A they are on order . Does this sound right? Should I leave it at the higher coupling when seeking a higher priamry inductance taping point. Doesn't higher coupling result in lower primary current? My higher coupling is more than likey what we would conisder normal range becasue of the primary vs ssecondary diameter.
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
Take advantage of the 1200V silicon, run it at 650VDC, be sure all the components will take the extra voltage. Also be sure not to over-volt the MMC. Watch the tank current with a CT and scope, and using the caps impedance, calculate the peak voltage and make sure it doesnt exceed the DC rating at least.
My coil was getting just about 12' sparks at the NY thon last weekend (45" winding) . Limited by the ceiling rafters as usual... BTW, that was running 1250A peak primary current, 675VDC input and about 5.5-7kW (depending on pulse rate). The interrupter was set for only 7 RF cycles of drive time (it might have actually been limiting at 6 cycles). I found tuning to be critical to get the longest sparks with the 1250A limit. If tuned too high, the sparks didnt grow as long. If tuned too low, the limiter kicked in too early. Get it just right and you find a sweet spot that gives the best spark per peak tank current.
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Squeezing longer sparks out of a DRSSTC
. Does this sound right? Should I leave it at the higher coupling when seeking a higher priamry inductance taping point. Doesn't higher coupling result in lower primary current? My higher coupling is more than likey what we would conisder normal range becasue of the primary vs ssecondary diameter.
. Limited by the ceiling rafters as usual... BTW, that was running 1250A peak primary current, 675VDC input and about 5.5-7kW (depending on pulse rate). The interrupter was set for only 7 RF cycles of drive time (it might have actually been limiting at 6 cycles). I found tuning to be critical to get the longest sparks with the 1250A limit. If tuned too high, the sparks didnt grow as long. If tuned too low, the limiter kicked in too early. Get it just right and you find a sweet spot that gives the best spark per peak tank current.