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DRSSTC specifications, thoughts welcome

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Mads Barnkob

Mon Aug 08 2011, 01:38PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

A large DRSSTC build for sturdiness would be the subject here.

Supply
Retified 3 phased 400VAC for 564VDC.

Driver
Steve Ward Universal driver

Bridge
2x CM300DY-24H
4x Siemens B43550 6000uF 350V electrolytic capacitors for filtering, 2 parallel strings of 2 in series.
300x500 mm with 80 mm fins heat sink

Secondary
200 mm diameter
2500 turns 0.4 mm wire, 1100 mm winding length

Primary
Inner diameter 300 mm, Outer diameter 700 mm
8 turns 10 mm copper tubing, turn spacing 15 mm
tapped at 6.6 turns
watercooled

MMC
80x 942C
16 parallel strings of 5 in series.
0.48 uF at 10kV

Topload
250x1100 mm

Resonant frequency ~ 48 kHz
Impendance of the system is around 7-8 Ohm.

My only thought at the moment is the rather thin secondary with a high number of turns with a smaller wire than usual on a similar coil.

Your thoughts, suggestion or torch to burn it all to the ground is welcome :)

Thomas W

Mon Aug 08 2011, 02:42PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

sounds like a good and interesting idea, but why, may i ask have a water cooled primary?

Goodchild

Mon Aug 08 2011, 04:29PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

I personally prefer a fat secondary with larger wire as it will have much lower losses due to it's Q and lower winding resistance. With a large coil there is really no reason to use small wire.

Herr Zapp

Mon Aug 08 2011, 05:37PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Goodchild -

Are you aware of any systematic analysis that anyone has done on DRSSTCs, looking at resonant frequency vs losses in the switches and secondary?

For a given size secondary coilform (say 8", 10" or 12" diameter for a "large" DRSSTC), it would seem that there would be an optimum secondary wire gage that minimized overall losses, balancing losses in the tank circuit (switches, primary coil, and interconnecting wiring) vs losses in the secondary windings.

Herr Zapp

Mads Barnkob

Mon Aug 08 2011, 06:21PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Tom Williamson wrote ...

sounds like a good and interesting idea, but why, may i ask have a water cooled primary?

Water cooled primaries is becoming a necessity for longer run times at such high currents as these beast can handle, else I will risk melting the supports holding the primary or damage the primary itself.

Goodchild wrote ...

I personally prefer a fat secondary with larger wire as it will have much lower losses due to it's Q and lower winding resistance. With a large coil there is really no reason to use small wire.

I ran number through javatc for 315 mm secondary with 0.5 mm wire and a 200 mm secondary with 0.4 mm wire, here is the numbers. We are looking at about 20% difference in DC resistance and Q.

Goodchild

Mon Aug 08 2011, 08:08PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

Herr Zapp wrote ...

Goodchild -

Are you aware of any systematic analysis that anyone has done on DRSSTCs, looking at resonant frequency vs losses in the switches and secondary?

For a given size secondary coilform (say 8", 10" or 12" diameter for a "large" DRSSTC), it would seem that there would be an optimum secondary wire gage that minimized overall losses, balancing losses in the tank circuit (switches, primary coil, and interconnecting wiring) vs losses in the secondary windings.

Herr Zapp

Well I don't have a definitive answer for your question but I have come to the conclusion from what I have done and also compared to others work that you can keep the fres low and still achieve low losses. Using a bigger secondary allows you to use the bigger wire and still maintain that low fres for your switches. I personally use 24 AWG on my big DRSSTC but because of the larger secondary I'm still able to run at a fres of 31KHz. You get the best of both worlds low losses in the secondary and the switches.

Mads, 20% is a big improvement! If you have not yet wound the secondary I would suggest going with a bigger one.

On the note of water cooling, I to was planning originally to water cool my big DRSSTC as well, but because of the high impedance tank I was running it turns out that I didn't need it at all. I can run my 3/8 primary for a good 60 mins pushing out 11 feet with only minor warming of the primary winding. The tank capacitor also benefits from the high impedance tank in that it doesn't have to be rated at as high of a voltage.

This is just my point of view when it comes to building DRs there are many out there!

Mads Barnkob

Mon Aug 08 2011, 09:47PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Goodchild wrote ...

Mads, 20% is a big improvement! If you have not yet wound the secondary I would suggest going with a bigger one.

On the note of water cooling, I to was planning originally to water cool my big DRSSTC as well, but because of the high impedance tank I was running it turns out that I didn't need it at all. I can run my 3/8 primary for a good 60 mins pushing out 11 feet with only minor warming of the primary winding. The tank capacitor also benefits from the high impedance tank in that it doesn't have to be rated at as high of a voltage.

I took a look at my DRSSTC I numbers and they are double of the 315 mm secondary example, its wound with 0.25 mm wire on a 160 mm form, it performs great giving 150 cm sparks at 500A.

As I have the tube I will go for 200 mm and 0.4 mm wire.

I will prepare the primary for cooling, that is only leaving a bit more tubing, tests will have the last say on this :)

Goodchild

Tue Aug 09 2011, 12:38AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

Sounds good, what you have on hand play's a big part on choosing parts as well. I just figured if you hadn't decided yet on any of the secondary stuff it would have been good to go with a bigger one.

Good luck sounds like a fun project!

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