Re: DRSSTC - I think I heard Cross Conduction...

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Sue Gaeta <sgsparky@xxxxxxxxxxx>

Cool! Those numbers actually make more sense to me now that I am actually 
in the middle of this DRSSTC stuff.

The numbers are probably not going to be that exact because some of the 
energy gets radiated, rather than "sparked", but I think that is probably a 
very good representation of what is happening.

I think it's a good idea to get these things tuned as best as we can 
because if they are too far off, energy would be reflected back into the H 
bridge. From what I was seeing though, it looks like I have a pretty good 
sized bandwidth, since adding a two foot clip lead to the 8" torroid didn't 
really change things all that much. I wonder if I would have that large of 
a bandwidth if I had a much larger tank cap, and fewer primary turns 
though. Too narrow of a bandwidth could make the primary be out of tune 
when you get those 6 foot streamers! I don't have that problem for a number 
of reasons! :-) :-(.

Then again, maybe because of the coupling that is typical of TCs, reflected 
power isn't as much of a problem as it is with transmitter circuits. That 
seems to be the case since there are so many working DRSSTCs out there ;-)

After looking at my puny little 15" streamers, I started to ponder about 
power. Those short streamers look like they could set fire to anything that 
touches them, and I am afraid to go near them! That sharp, loud 100hz buzz 
adds a bit to the intimidation factor, but those things look mean! They are 
probably very powerful, but I need to get the voltage up a bit to get them 
to start hitting chandeleirs, and bed frames!

Sue

Tesla list <tesla@xxxxxxxxxx> wrote:
Original poster: Terry Fritz

Hi Sue,

I posted this chart from a simulations awhile back:


Cpri Ip (peek) Vs (peek kV) Streamer Power (W)
130 183 233 666.07
135 124 222 488.42
140 129 220 570.26
145 141 226 620.93
150 167 242 650.85
155 191 252 666.07

Here you can see the dip in primary current that also tends to dip the
output voltage. But running at the dip point is the most efficient. You
may actually see long sparks with the tuning off but at the expense of much
more primary current. Not sure how real these simulations are, but if you
see that the lowest input current point also produces the best sparks, that
would be a good thing :-)

Cheers,

Terry

At 06:58 PM 2/20/2005, you wrote:
>Get used it! It always happens that way. I have blown many 20A MOSFETs to
>bits, but I still have the original 10 amp fast blow fuse that I started
>out with!
>
>And everyone thought I was crazy when I said we should be using MOSFETs as
>drop in replacement for fuses :-)
>
>I have replaced all my MOSFETs with IGBTs now. Not that I thought I would
>get better performance, but I just wanted to see if burning IGBTs smelled
>any different >:]
>
>I started playing around with my coil again last week, and I added a
>0.186uF cap in series with the primary. It is now officially a DRSSTC. My
>tuning was way too high from where I predicted it should have been when I
>swept the primary tank arrangement with the signal generator, which was
>odd. The interesting thing that I noticed was that a dip in average H
>bridge supply current, and an increase in spark length (obvious) coincided
>with resonance. Just like a real transmitter! People don't usually talk
>about tuning for a dip in supply current in this arena, but I just found
>out that it does apply here. Yes, I am pulsing the driver at 100 Hz, but I
>am talking about average current.
>
>When I build the bigger H bridge, I have to look into why I can't use as
>much top loading as Steve W. uses. I have enough extra turns available to
>get it in tune, but I get smaller sparks, and it draws much more current :-(.
>Sue
>
>I am beefing up the traces, but I don't think anything could stop it once
>it lets go. But the breakers and fuses did not trip so the IGBTs blew
>themselves out of the circuit very quickly. Good since that really helps
>limit damage. I am using the little IGBT as fuses in that case and they
>almost worked. Maybe I need smaller IGBTs ;-))
>
>Cheers,
>
>Terry
>