160mm DRSSTC project

[Mathieu thm]

Hello everybody,

For a long time, I always wanted a DRSSTC but it was unimaginable for me to build one.
I started to make some small SGTC including a big RSGTC that I still have, and I started to do small SSTC.
A few months ago I built my first "little" DRSSTC to begin, which I never would have thought of when I was 12.
Now that I've built a little DRSSTC to understand how it works, and have fun, I am embarking on a project that I would love to do for a very long time, a fairly large DRSSTC.

Since it's a pretty big project, I started doing CAD design to see what it could look like and avoid as many mechanical problems as possible.
Here are the plans I was able to make with SolidWorks :





The box should be 46x25.5 cm (not counting the wheels and the primary support).
The entire DRSSTC should be about 1m40.

Some specs (it's not final, it can still change) :

• Toroid: ~150mm minor diameter, ~700mm major diameter
• Secondary : 160mm, 73cm winding with 0.315mm copper wire
• Secondary frequency : 74kHz
• I don't know yet exactly how the MMC will be (maybe Dawncap 3000v 0.47uf in 5s2p configuration)
• For lGBT, I don't know exactly, maybe cm300 or skm300 depending on price and availability, I do not know yet if I make it work in 325v or with a voltage doubler in 678v
• Driver :UD2.7 of profdc9
• Bus capacitance: maybe 2x6800uF (or 6800uf with the voltage doubler)

I have already started a little, starting with the secondary circuit,
Here is some photo:



I will try to start making the aluminum case, and of course I will post the progress !

[davekni]

I will try to start making the aluminum case, and of course I will post the progress !

Only concern that comes to mind is aluminum case top ring looks too close to primary coil.  See this post and many following ones related to the same issue with a large coil:
https://highvoltageforum.net/index.php?topic=1430.msg11047#msg11047
Top of aluminum frame makes shorted turn.  Issue in above link is that 8020 is anodized, so has a thin nonconductive coating on sides.  Initially frame top isn't quite a complete shorted turn due to this anodization.  Arc from secondary broke down this thin oxide layer.  Then the much higher current induced from primary coil melted screws.

[Mads Barnkob]

Great material and looks like you are well prepared for building a coil like this

I think you should add longer legs from frame to platform that supports the primary coil. A total height of 140 cm for a CM300 coil, that can easily do 2-2.5 meter sparks, will just give you a lot of ground strikes and not take advantage of such a powerful bridge.

Your wheels on the base is going to give you stability problems, the foot print is simply not large enough for something that is this tall. I have made the same mistake on both my DRSSTC 1 and 3. For my large coil I simply had to build a support frame of 4 pieces of 2 meter long wood frame, to give it a large enough foot print. Somehow there is never a even surface where you are going to run a Tesla coil, as its mostly outside

A 5s2p MMC of 0.47uF capacitors is only going to net you around 0.188uF, that is too small for such a coil, in my opinion. Did you take your design for a ride in the MMC calculator? https://kaizerpowerelectronics.dk/calculators/mmc-calculator/

In my guide, I recommend 0.3 to 0.6 uF for a 160mm coil https://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/mmc-tank-capacitor/

[Mathieu thm]

Only concern that comes to mind is aluminum case top ring looks too close to primary coil.  See this post and many following ones related to the same issue with a large coil:
https://highvoltageforum.net/index.php?topic=1430.msg11047#msg11047
Top of aluminum frame makes shorted turn.  Issue in above link is that 8020 is anodized, so has a thin nonconductive coating on sides.  Initially frame top isn't quite a complete shorted turn due to this anodization.  Arc from secondary broke down this thin oxide layer.  Then the much higher current induced from primary coil melted screws.

I think you should add longer legs from frame to platform that supports the primary coil. A total height of 140 cm for a CM300 coil, that can easily do 2-2.5 meter sparks, will just give you a lot of ground strikes and not take advantage of such a powerful bridge.

I originally wanted to insulate the upper part of the chassis like the brOdin coil, but that's a good idea, I would put longer legs from the frame to the platform that supports the primary coil to gain some height, and to avoid problems with the primary coil.

A 5s2p MMC of 0.47uF capacitors is only going to net you around 0.188uF, that is too small for such a coil, in my opinion.

I suspected that the MMC would have too small a capacity, I would try to make an MMC in this range of 0.3 to 0.6uf.

Your wheels on the base is going to give you stability problems, the foot print is simply not large enough for something that is this tall. I have made the same mistake on both my DRSSTC 1 and 3. For my large coil I simply had to build a support frame of 4 pieces of 2 meter long wood frame, to give it a large enough foot print. Somehow there is never a even surface where you are going to run a Tesla coil, as its mostly outside

Thanks for this information, this can indeed be quite an annoying problem.

[Mathieu thm]

I started to look at how much it could cost me to make the UD 2.9 of profdc9, but I noticed that it works in pulse skip, I also looked at the UD 2.7 of profdc9 and it would cost me almost the same to do the UD 2.7 (without pulse skip) or the UD2.9 (with pulse skip).

I wonder if it can be a good idea to make the pulse skip controller, or I keep it simple with the UD 2.7.

The pulse skip mode really brings a plus for this coil size ?

I imagine the pulse skip mode adds maybe more stress on the IGBTs,  so maybe it's better to stay with UD 2.7 ?
I don't know at all if it can be a good idea to use the pulse skip mode, what do you think?

I also started looking at the IGBT bricks, after looking at the table on the IGBT page (which is very useful !) : https://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/igbts/
I saw the CM300DY-24H bricks which I think might work well with my setup, I read several threads on where to buy IGBT bricks, so I looked on eBay for IGBTs and found several sales, one of which I spotted: https://www.ebay.com/itm/282631487695

I also looked at the SKM300GB125D: https://www.ebay.com/itm/322570650877 but I'm thinking of using the CM300s

Are there any special things to pay attention to when selling IGBT bricks ? Are there many counterfeits ?

[dbach]

Hey,

Im not sure if theres a better way to do this but i would be happy to sell you 2 cm300dy-24h bricks for nearly half that price, I can confirm they are genuine as well.

Most bricks on ebay will be genuine but make sure they are functional and also not in too poor condition.

Kindest regards,
Davis

[Mathieu thm]

Im not sure if theres a better way to do this but i would be happy to sell you 2 cm300dy-24h bricks for nearly half that price, I can confirm they are genuine as well.
Most bricks on ebay will be genuine but make sure they are functional and also not in too poor condition.

Thank you for the answer, it's an interesting offer, but the problem is that I live in France so I think the shipping can be very expensive

[futurist]

Nice work so far!

Are you planning CM300 half-bridge or full-bridge?
Check out my similar 160 mm coil https://www.highvoltageforum.net/index.php?topic=78.0
I'm using SKM400 half-bridge with 340nF MMC, originally I had CM200 half-bridge and both worked great
 

I would suggest you use CM300 half-bridge with voltage doubler for your coil, especially with 240 VAC mains here in Europe
Mine survived 7 years of occasional use and I'm sure the inverter won't fail anytime soon. I recently rebuilt it, changed DC power supply and rewired everything- now I'm waiting for some good weather to test everything out

[Mathieu thm]

Check out my similar 160 mm coil https://www.highvoltageforum.net/index.php?topic=78.0

Very nice DRSSTC ! Interesting way to cool IGBTs

Are you planning CM300 half-bridge or full-bridge?

I planned to make a full bridge with two CM300 which will maybe CM300DY-24H.

[Mathieu thm]

Good evening everyone,

Here is a little update, I finished making the aluminum frame and there are some changes compared to the planned plan.
I increased the height of the frame by a few centimeters (30cm instead 25cm originally planned),I will also extend the length of the bars between the frame and the primary coil (I think 15cm rather than 5cm originally planned).

Here are some pictures of the frame :

[Hydron]

Having the aluminium frame rails form a full loop without any insulating breaks may not be the best plan, see here for some fun times another coiler had: https://highvoltageforum.net/index.php?topic=1430.msg11047#msg11047
(I suspect at the power levels of a smaller coil it won't be quite as spectacular as the bolt-burning seen on that coil!)

If it were me building the coil I'd look at putting a few insulating breaks into it, maybe get some pieces of FR4 from a cheap PCB vendor to make insulating versions of the fixing plates.

[Mathieu thm]

Having the aluminium frame rails form a full loop without any insulating breaks may not be the best plan, see here for some fun times another coiler had: https://highvoltageforum.net/index.php?topic=1430.msg11047#msg11047
(I suspect at the power levels of a smaller coil it won't be quite as spectacular as the bolt-burning seen on that coil!)

If it were me building the coil I'd look at putting a few insulating breaks into it, maybe get some pieces of FR4 from a cheap PCB vendor to make insulating versions of the fixing plates.

You're right, I've already planned to make an insulation so as not to have a closed loop, I haven't done it yet because I'm thinking about how I could do it properly

[Mathieu thm]

I received the pcbs of the ud2.7c, and I took the opportunity to take some Hydron "gate drive" pcb :



After soldering all the components on the ud2.7c, here is the result :



I plugged it in and tested it and everything seems to be working fine 

Now i have some question about Hydron gate drive pcbs, i started soldering a pcb and this is what it looks like :



Here's the schematic and the link to where I found it :



https://highvoltageforum.net/index.php?topic=493.msg3068#msg3068

What I don't understand is why not choosing a classic gate drive circuit (diode and resistor).
Why is there an extra diode and resistor ?
Also, putting two 5.6ohm resistors in parallel gives a value of 2.8ohm, it seems small to me but maybe I'm wrong.

If someone or Hydron himself could explain this to me, that would be great.

EDIT : I forgot to put the link to my Mouser cart, it took me so long to do it so if it helps anyone, here is the link :

https://www.mouser.fr/ProjectManager/ProjectDetail.aspx?AccessID=9bfd2b6a8c

[Mike]

The design gives the maximum flexibility. You have independent control of the gate charge resistor and discharge resistor allowing you to tune each to get the rising and falling edges as fast as possible with acceptable ringing.

With the classic single resistor and diode circuit you can't adjust the turnoff speed, it will always be as fast as possible which, depending on your layout and IGBT package inductance may cause excessive ringing during turn off. Under most circumstances this ringing doesn't do any harm but it could result in an EMI issue as it will likely be at quite a high frequency. You can still replicate this by setting the turn off resistors to 0R, which brings us to your other point about the low resistance.

The schematic notes that the 5R6 resistors are placeholders only. You are meant to set these correctly for your IGBTs and driver. In particular having the charge and discharge resistors equal negates the advantages of the diodes.

[Mathieu thm]

The design gives the maximum flexibility. You have independent control of the gate charge resistor and discharge resistor allowing you to tune each to get the rising and falling edges as fast as possible with acceptable ringing.

With the classic single resistor and diode circuit you can't adjust the turnoff speed, it will always be as fast as possible which, depending on your layout and IGBT package inductance may cause excessive ringing during turn off. Under most circumstances this ringing doesn't do any harm but it could result in an EMI issue as it will likely be at quite a high frequency. You can still replicate this by setting the turn off resistors to 0R, which brings us to your other point about the low resistance.

The schematic notes that the 5R6 resistors are placeholders only. You are meant to set these correctly for your IGBTs and driver. In particular having the charge and discharge resistors equal negates the advantages of the diodes.

Ok, I understand thank you



I made progress on the build, I finished putting the driver in an aluminum box and I put polycarbonate on the frame, here are some pictures and one that shows what it will look like :
I also added a signal led like the original ud 2.7c.





I don't know if I put too many pictures, but when I look at other people's builds, I like when there are lots of pictures, so I think other people must also like when there are lots pictures

[Manz]

I really appreciate all the details and pictures as I'm currently working on a similar sized coil
Did you buy the drivers aluminum box ?

[Mathieu thm]

I really appreciate all the details and pictures as I'm currently working on a similar sized coil

I'm glad it could help 

Did you buy the drivers aluminum box ?

I bought the aluminum box on amazon, here is the link :
https://www.amazon.fr/dp/B08QMGTLLZ/ref=sspa_dk_detail_6?psc=1&pd_rd_i=B08QMGTLLZ&pd_rd_w=KTm7I&content-id=amzn1.sym.a30983a5-b2e2-49b6-b674-0e622b88d06d&pf_rd_p=a30983a5-b2e2-49b6-b674-0e622b88d06d&pf_rd_r=XDV0Z03YX32QSGJRJ9CR&pd_rd_wg=yq5VN&pd_rd_r=657a4804-48c8-4164-873c-b7265ae7c832&s=industrial&sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWw&smid=A30I4SWEQ03TXF

[Manz]

Thanks.
Did you figure out the new mmc values as it was a bit too small for such a big coil?

[Mathieu thm]

Did you figure out the new mmc values as it was a bit too small for such a big coil?

Sure, at first I wanted to make a mmc with 10 Eurofarad SP2550 3.75uF 580Vrms in series but impossible to find and I think it would have been a bit expensive.
So I'm probably going to do a mmc with FKP1T031007E00, 4s15p or 5s20p

[Hydron]

Aha, glad to see someone is using some of the stuff I put on Github Really need to do some updates and add some new stuff there!

Mike is correct - this was designed for maximum flexibility, I've dug up a photo (attached) and I used 2*2R2 in parallel for turn off, and 2*10R in parallel for turn on. Those values were somewhat guesswork though, but they seem to work OK with the CM300s I was driving.

BTW I'd avoid using any of the other boards on my Github other than the "Big_DRSSTC..." ones (of which this is one of them), and I'd check the compatibility with the terminals on your brick before using either of them. The others have known issues or could be improved, but I have a coil running using the "Big_DRSSTC..." ones (with the bridge ones using a stack of thin boards as noted in the README.md on github.