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Registered Member #54926
Joined: Mon Apr 27 2015, 07:18PM
Location: Limburg, the Netherlands
Posts: 6
Hello fellow coilers, I am planning to build my first DRSSTC. I have some experience with spark gap coils and small sstc's. But since DRSSTC's are quite different, I would like to ask you for some help.
First of all, I don't have a specific size I want, it just needs to be impressive for its size. I am planning to use a CM300DY-24NF half-bridge to do the heavy lifting, with 325V at the bus (no doubler - rectified 230V ac, could go for a doubler if advised). For the MMC I will be using CDE 942 series caps for 225nF at 4KV, this could be increased to 300nF since I have some spares.
My question is about the secondary size and wire diameter. My current design uses a 12,5cm dia, 65cm high coil, with 32 AWG wire for 2600 turns. Since I am using a big (slow) igbt, my guess is I should keep my Fres relatively low. I've put this in JavaTC, which gives me this output:
Does this look any good? I have the feeling 32AWG wire would be too thin. I could change this to 30AWG for an Fres ~100kHz, but will my cm300 brick be able to handle this? Any comments on this or other specs would be greatly appreciated! Thanks.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Anaesthetix wrote ...
Hello fellow coilers, I am planning to build my first DRSSTC. I have some experience with spark gap coils and small sstc's. But since DRSSTC's are quite different, I would like to ask you for some help.
First of all, I don't have a specific size I want, it just needs to be impressive for its size. I am planning to use a CM300DY-24NF half-bridge to do the heavy lifting, with 325V at the bus (no doubler - rectified 230V ac, could go for a doubler if advised). For the MMC I will be using CDE 942 series caps for 225nF at 4KV, this could be increased to 300nF since I have some spares.
My question is about the secondary size and wire diameter. My current design uses a 12,5cm dia, 65cm high coil, with 32 AWG wire for 2600 turns. Since I am using a big (slow) igbt, my guess is I should keep my Fres relatively low. I've put this in JavaTC, which gives me this output:
Does this look any good? I have the feeling 32AWG wire would be too thin. I could change this to 30AWG for an Fres ~100kHz, but will my cm300 brick be able to handle this? Any comments on this or other specs would be greatly appreciated! Thanks.
I too am building my first coil, your specs are somewhat similar to mine, im using cm300dy-24h but im going to be using a voltage doubler since it will give you twice the bus voltage and almost double the output if you are wanting long sparks this is what i would recommend.
I also believe a HD aspect ratio of 4:5 is important too. Here are my my specs.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
Anaesthetix wrote ...
Hello fellow coilers, I am planning to build my first DRSSTC. I have some experience with spark gap coils and small sstc's. But since DRSSTC's are quite different, I would like to ask you for some help.
Welcome to the forum, you are in the right place for advice on building DRSSTC :) You should add you other coils to the show your Tesla coil thread that is a sticky in this forum.
Anaesthetix wrote ...
First of all, I don't have a specific size I want, it just needs to be impressive for its size. I am planning to use a CM300DY-24NF half-bridge to do the heavy lifting, with 325V at the bus (no doubler - rectified 230V ac, could go for a doubler if advised). For the MMC I will be using CDE 942 series caps for 225nF at 4KV, this could be increased to 300nF since I have some spares.
With CM300 bricks you properly would have your current limit set at 800-1000A, this would give you some good 2 meter sparks.
a 225nF/4kV MMC is too small voltage rating vise for a CM300 coil, using my MMC calculator I would use a MMC at 300nF/8kV, 4 in series and 8 strings in parallel to have a MMC that fits the ratings of a coil running 1000A at 80kHz.
Anaesthetix wrote ...
My question is about the secondary size and wire diameter. My current design uses a 12,5cm dia, 65cm high coil, with 32 AWG wire for 2600 turns. Since I am using a big (slow) igbt, my guess is I should keep my Fres relatively low. I've put this in JavaTC, which gives me this output:
Does this look any good? I have the feeling 32AWG wire would be too thin. I could change this to 30AWG for an Fres ~100kHz, but will my cm300 brick be able to handle this? Any comments on this or other specs would be greatly appreciated! Thanks.
You secondary specifications look fine, I am however wondering if you are only using a small topload, since you still have a rather high resonant frequency compared to the number of windings. DRSSTCs like larger toploads than SGTC, they need more capacitance to feed the growth of sparks and to withstand the spark load that will pull the resonant frequency down more with a small topload.
Some day it is my plan to upgrade this DRSSTC from 60N60 IGBTs to a fullbridge of CM300.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Mads Barnkob wrote ...
a 225nF/4kV MMC is too small voltage rating vise for a CM300 coil, using my MMC calculator I would use a MMC at 300nF/8kV, 4 in series and 8 strings in parallel to have a MMC that fits the ratings of a coil running 1000A at 80kHz.
My coil is going to be similar spec to this but with a voltage doubled 230v bus my MMC was going to be 8KV rated, will this be enough for my coil?
Im also confused about current limit when people quote 1000A. What part of the system is drawing that much current? It cant be the secondary because that is usually in the micro ampers range at that such high voltage.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
nzoomed wrote ...
Mads Barnkob wrote ...
a 225nF/4kV MMC is too small voltage rating vise for a CM300 coil, using my MMC calculator I would use a MMC at 300nF/8kV, 4 in series and 8 strings in parallel to have a MMC that fits the ratings of a coil running 1000A at 80kHz.
My coil is going to be similar spec to this but with a voltage doubled 230v bus my MMC was going to be 8KV rated, will this be enough for my coil?
Im also confused about current limit when people quote 1000A. What part of the system is drawing that much current? It cant be the secondary because that is usually in the micro ampers range at that such high voltage.
Below the MMC calculator, all the equations used are listed, here is the specific for your question about supply voltage vs. MMC rating
MMC Zc, impedance: Zc = SQRT(ESR^2 + Xc^2). ESR is the combined ESR for the MMC. Xc is the MMC reactanse from above.
Voltage over MMC: Voltage over MMC = Zc * primary peak current
As you can see, the voltage across the MMC is only a product of the impedance and current.
The peak current that we talk about limiting is the current that circulates in the primary circuit, through IGBT switches, primary coil and primary capacitor. The voltage and current rise in each switch cycle of a DRSSTC is explained here:
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Mads Barnkob wrote ...
nzoomed wrote ...
Mads Barnkob wrote ...
a 225nF/4kV MMC is too small voltage rating vise for a CM300 coil, using my MMC calculator I would use a MMC at 300nF/8kV, 4 in series and 8 strings in parallel to have a MMC that fits the ratings of a coil running 1000A at 80kHz.
My coil is going to be similar spec to this but with a voltage doubled 230v bus my MMC was going to be 8KV rated, will this be enough for my coil?
Im also confused about current limit when people quote 1000A. What part of the system is drawing that much current? It cant be the secondary because that is usually in the micro ampers range at that such high voltage.
Below the MMC calculator, all the equations used are listed, here is the specific for your question about supply voltage vs. MMC rating
MMC Zc, impedance: Zc = SQRT(ESR^2 + Xc^2). ESR is the combined ESR for the MMC. Xc is the MMC reactanse from above.
Voltage over MMC: Voltage over MMC = Zc * primary peak current
As you can see, the voltage across the MMC is only a product of the impedance and current.
The peak current that we talk about limiting is the current that circulates in the primary circuit, through IGBT switches, primary coil and primary capacitor. The voltage and current rise in each switch cycle of a DRSSTC is explained here:
That calculator is useful, it looks like i will be OK up to around 700A, although i dont know if i will be going over that limit if i push it to the limit which i will want to get the longest sparks possible in the end.
I didnt think that 700-1000A would ever be possible on the primary, thats alot of current! I take it that this is measured in very short bursts per cycle, since the wall outlet is only able to supply me about 15A but is it different for DC?
Registered Member #54926
Joined: Mon Apr 27 2015, 07:18PM
Location: Limburg, the Netherlands
Posts: 6
Thank you very much nzoomed and Mads for your input.
Mads Barnkob wrote ...
Welcome to the forum, you are in the right place for advice on building DRSSTC :) You should add you other coils to the show your Tesla coil thread that is a sticky in this forum.
Thank you. I'll be sure to post my other coils soon! My small sstc is getting a revision currently.
Mads Barnkob wrote ...
With CM300 bricks you properly would have your current limit set at 800-1000A, this would give you some good 2 meter sparks.
a 225nF/4kV MMC is too small voltage rating vise for a CM300 coil, using my MMC calculator I would use a MMC at 300nF/8kV, 4 in series and 8 strings in parallel to have a MMC that fits the ratings of a coil running 1000A at 80kHz.
Mads Barnkob wrote ...
The peak current that we talk about limiting is the current that circulates in the primary circuit, through IGBT switches, primary coil and primary capacitor. The voltage and current rise in each switch cycle of a DRSSTC is explained here:
Okay, I'll order some more capacitors. 2 meter sparks would definitely be impressive. Using the theory for voltage rise with a halfbridge at 325V (half bridge without doubler, so it switches 325V - 0V, other end of primary kept at 162,5V) gives me a little over 6KV after 10 full cycles. This would give me a max current of 850A with 15uH primary and Fres 75kHz. So if I switch to a full-bridge or a half-bridge with doubler, am I correct in saying that the voltage rating of the MMC would need to be doubled?
Mads Barnkob wrote ...
You secondary specifications look fine, I am however wondering if you are only using a small topload, since you still have a rather high resonant frequency compared to the number of windings. DRSSTCs like larger toploads than SGTC, they need more capacitance to feed the growth of sparks and to withstand the spark load that will pull the resonant frequency down more with a small topload.
I've tried adding a bigger topload (15cm * 60cm) which gives me Fres=75kHz. I've also tried adding a second toroid, but this only changes the Fres with a percent or so. The revised specs:
Mads Barnkob wrote ...
Some day it is my plan to upgrade this DRSSTC from 60N60 IGBTs to a fullbridge of CM300.
That is one pretty coil you have there! Inspires me even more to build one of my own.
What part of the system is drawing that much current? It cant be the secondary because that is usually in the micro ampers range at that such high voltage.
Big TC arcs with a meter or more length draw several amps of current.
I take it that this is measured in very short bursts per cycle, since the wall outlet is only able to supply me about 15A but is it different for DC?
Yes, the high bridge current draw is buffered by the big electrolytics on the bus.
@Anaesthitix:
Using the theory for voltage rise with a halfbridge at 325V (half bridge without doubler, so it switches 325V - 0V, other end of primary kept at 162,5V) gives me a little over 6KV after 10 full cycles. This would give me a max current of 850A with 15uH primary and Fres 75kHz. So if I switch to a full-bridge or a half-bridge with doubler, am I correct in saying that the voltage rating of the MMC would need to be doubled?
That would be the case if the primary would ramp up current for the full 10 cycles you assumed. If you wouldn't change the capacitance of the MMC, that would also imply doubling primary current. Usually arc loading limits primary current long before the 10 cycles end, but only if the coil is properly tuned. The trick is to tune the coil in such a way, that you won't hit the OCD. That or the OCD will also prevent the MMC from acquiring too much voltage.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Anaesthetix wrote ...
[/quote1442751372] I've tried adding a bigger topload (15cm * 60cm) which gives me Fres=75kHz. I've also tried adding a second toroid, but this only changes the Fres with a percent or so. The revised specs:
That is the same size im going for in my coil too.
Should be easy to make with ducting, but does anyone know where can i get a spun one of these from?
Im thinking of making it myself, but dont think it will be easy.
Registered Member #54926
Joined: Mon Apr 27 2015, 07:18PM
Location: Limburg, the Netherlands
Posts: 6
Uspring wrote ...
@Anaesthitix:
Using the theory for voltage rise with a halfbridge at 325V (half bridge without doubler, so it switches 325V - 0V, other end of primary kept at 162,5V) gives me a little over 6KV after 10 full cycles. This would give me a max current of 850A with 15uH primary and Fres 75kHz. So if I switch to a full-bridge or a half-bridge with doubler, am I correct in saying that the voltage rating of the MMC would need to be doubled?
That would be the case if the primary would ramp up current for the full 10 cycles you assumed. If you wouldn't change the capacitance of the MMC, that would also imply doubling primary current. Usually arc loading limits primary current long before the 10 cycles end, but only if the coil is properly tuned. The trick is to tune the coil in such a way, that you won't hit the OCD. That or the OCD will also prevent the MMC from acquiring too much voltage.
Okay, thank you! I'll probably go for a doubler then, will do some tests on lower bus voltage anyway, to see how it behaves.
nzoomed wrote ...
That is the same size im going for in my coil too.
Should be easy to make with ducting, but does anyone know where can i get a spun one of these from?
Im thinking of making it myself, but dont think it will be easy.
I'll make my toroid from ducting. Always used that for my other coils, it looks and works great. If you try to spin one yourself, let me know how it worked out for you. It would be awesome to be able to make these yourself.
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First DRSSTC; questions about dimensions
