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Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
Goodchild wrote ...
Mads Barnkob wrote ...
Primary capacitance size has a larger role in arc thickness as this is were the energy released for each strike comes from.
You know this is interesting that you bring this up because I'm not convinced that is true. I have built both very low impedance DRs and very high impedance DRs and I don't find that to be the case. With regular DRs I notice no difference in streamer thickness vs the size of the tank cap.
Furthermore if this was true this means a very very small tank cap (say maybe 10nF) should make very weak thin sparks, this can't be true as shown by QCW operation. With only 10nF you get sparks thicker than a regular DR that has a tank cap an order of magnitude larger.
I'm curios to what lead you to your conclusion?
I did only write a larger factor, not how large :)
But if we stick to DRSSTCs, my observation is that a smaller coil have to run longer, with more primary cycles, to get thicker arcs with their low capacitance mmc as compared to a larger coil running few primary cycles with a large mmc capacitance. All in all it properly sums up to the "same" RMS current if size factor is taken in too.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Thanks for the replies. Well, my VTTC running a "half wave" RF envelope produces ~60cm sparks with only 6kW of peak power, and a DRSSTC running uninterrupted on half wave rectified mains needed some 4-5kW to make 40cm sparks... So the difference in peak powers between "QCW-type" coils and pulsed coils seems to be really big.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Dr. Dark Current wrote ...
Thanks for the replies. Well, my VTTC running a "half wave" RF envelope produces ~60cm sparks with only 6kW of peak power, and a DRSSTC running uninterrupted on half wave rectified mains needed some 4-5kW to make 40cm sparks... So the difference in peak powers between "QCW-type" coils and pulsed coils seems to be really big.
Well that's also because it's a VTTC, if you look at a QCW which is the same operation only with solid state you will find it take about the same amount of power to make the same length sparks as a regular DR. Well maybe a little bit more but defiantly not as much as VTTC.
I'm not exactly sure what the cause of this is, but if I had to guess I would say that the extra losses from the filament and the way the tube operates in general are to blame.
Mads, this was my original conclusion as well I must have just misunderstood the way you worded it. High tank impedance dose need more cycles from the same spark length, but in the end it average to the same overall power per bust.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Goodchild, my 2nd SSTC (my last non-DR coil) makes 40cm sparks with 22A of peak current, which is around 4.5 kWp. From my experience the "half wave" SS coils take a bit more of peak power than VTTCs, but not much more.
Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
Voltage is a big factor isn't it? My DRSSTC I ran at the lab that did 6-7ft sparks was running 390VDC (lower due to vdrop) at 410A... I noticed on my fullbridge, the diff of 2 foot to 6 foot was little effect on primary current...it's like at a certain voltage it stops rising primary current yet voltage still climbs...
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Dr. Dark Current wrote ...
Goodchild, my 2nd SSTC (my last non-DR coil) makes 40cm sparks with 22A of peak current, which is around 4.5 kWp. From my experience the "half wave" SS coils take a bit more of peak power than VTTCs, but not much more.
I was comparing coils with resonate tanks such as QCW, VTTC, and DR. From what I have seen SSTCs tent to be just as bad as VTTC just as you have observed.
However the mode of operation of a QCW and VTTC are very alike and that's what I was comparing as far as power. QCW tend to be much better than the VTTC even though they operate in the same manner with just different switch types (Tube vs IGBT).
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I think what makes the tube coils operate somewhat differently is the parallel resonant tank circuit used, which very likely alters the RF power envelope.
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DRSSTC peak powers and spark length
Well, my VTTC running a "half wave" RF envelope produces ~60cm sparks with only 6kW of peak power, and a DRSSTC running uninterrupted on half wave rectified mains needed some 4-5kW to make 40cm sparks... So the difference in peak powers between "QCW-type" coils and pulsed coils seems to be really big.
