FIRST DRSSTC SKM400GB128D OCD SETTING

[Alex_1996]

For mmc I'm a fan of dawncaps, they're a little sketchy but seem to work great and cost per amp is really good. I have a coil similarly sized to yours and I use 1 of these:

https://www.aliexpress.us/item/3256805356938958.html?spm=a2g0n.search-store.0.0.1006U8UDU8UDfU&browser_id=da6abc91876a4a029b5fb1f177997a7e&aff_trace_key=0cd93ca4228c45d6aef78be0b2713457-1720896888586-02113-UneMJZVf&aff_platform=msite&m_page_id=zyuhtulhccaridup190e57e42cc199fec31715751a&gclid=&pdp_npi=4%40dis%21USD%2117.77%2117.77%21%21%21128.75%21128.75%21%402101fb1917218371754772657e3894%2112000033476967120%21sea%21US%213080507328%21X&algo_pvid=9dabed1b-ddf4-4753-b7cd-92d455c73c16&_gl=1*y7yjkg*_gcl_au*NjI0NTM4MjkuMTcyMTgzNzE4MQ..*_ga*MTc1MTAwMjA5NzE0MzE0NC4xNzIwMTMwMjcyMjc5*_ga_VED1YSGNC7*MTcyMTgzNzE4MS4xLjEuMTcyMTgzNzQwNi42MC4wLjA.

If you want more current, you can put a few 20-40nF caps in parallel.

Copper tube is definitely the way to go for the primary, in the US you'd want to use either 1/4in or 3/8in tube.

Thank you very much

I keep this information for the construction of my next DRSSTC.

Best regards

[radbloke]

Hello everyone. After having built two successful DRSSTC's with a full bridge of TO247 FGA60N65SMD IGBT's, I have built a new model with a full bridge of SKM400GB128D. Here I share some data:

•Secondary 36cm high and 10cm wide with 0.2mm diameter enameled copper wire. The whole secondary coated with epoxy resin.

•Toroid 35,5cm x 10,5cm made with aluminum rings. The discharge wire is 47cm long. I think it may be too long.

•Resonant frequency of the secondary with the toroid is about 155kHz.

•7-turn primary and 66nF/12kV MMC bank for a primary frequency of 142kHz at the tuning point, which is a detuning of about 8.38%.

•2 DC bus capacitors connected in voltage doubler with a total of 900V/1650uF (each 450V/3300uF).

•2 snubber capacitors of 1kV DC and 2.2uF each.

•1.5ke400CA bi-directional protection TVS diodes (two in series).

•Feedback CT ratio is 1/625 (25 turns x 25 turns)

Driver 2.7.The phase advance adjustment was performed correctly and successfully.

Here comes my doubt. The discharges, in my opinion, are a bit small. Understand me. I achieve some 80cm discharges when they hit a target on the ground with a voltage input on the full bridge of 362VDC (150VAC from my variac) and the OCD is set to 350A. The tip of the discharge needle is 90cm high (maybe a little high). My question is:

Can I raise the OCD value to 400A or higher? I don't know if this model of IGBT's can support 400A or higher running at a primary frequency of 142kHz. They are placed on a good heat sink. The power consumption with the normal interrupter operating mode (70-100uS / 560 bps) and in MIDI mode is between 600W and 800W, respectively. My goal is that the discharges can reach the ground without having to place an object that shortens the distance to help the lightning to reach the ground more easily.

I had thought about raising the OCD limit to 400A and maybe 400V DC bus power supply in order to achieve higher discharges that can reach the ground without any problem.

I attach photos and if any data is missing do not hesitate to tell me about it. I also attach a video of the operation.

Video: https://youtube.com/shorts/fBSI0B8LMx4?feature=share

Best regards and thanks for your help

Here is the one that I built a few years back. It’s got exactly the same switches as yours i.e. the SKM 400 switches in a full bridge configuration. The OCD is set at 1000Apk.  I have dawncaps 375 nF bank - these get a little warm after long runs but work great. Using freewheeling with UD+
Fres is 52kHz with 31 inch x 6.5 inch secondary.

Here is a link to the coil running with 3/8”  copper tube breakout and 31 inch diam topload at 1000A OCD for the freewheel. The video files were too large to upload directly to this forum.

So you have plenty of room to increase your OCD to well above 350 A!!!

[Alex_1996]

Hello everyone. After having built two successful DRSSTC's with a full bridge of TO247 FGA60N65SMD IGBT's, I have built a new model with a full bridge of SKM400GB128D. Here I share some data:

•Secondary 36cm high and 10cm wide with 0.2mm diameter enameled copper wire. The whole secondary coated with epoxy resin.

•Toroid 35,5cm x 10,5cm made with aluminum rings. The discharge wire is 47cm long. I think it may be too long.

•Resonant frequency of the secondary with the toroid is about 155kHz.

•7-turn primary and 66nF/12kV MMC bank for a primary frequency of 142kHz at the tuning point, which is a detuning of about 8.38%.

•2 DC bus capacitors connected in voltage doubler with a total of 900V/1650uF (each 450V/3300uF).

•2 snubber capacitors of 1kV DC and 2.2uF each.

•1.5ke400CA bi-directional protection TVS diodes (two in series).

•Feedback CT ratio is 1/625 (25 turns x 25 turns)

Driver 2.7.The phase advance adjustment was performed correctly and successfully.

Here comes my doubt. The discharges, in my opinion, are a bit small. Understand me. I achieve some 80cm discharges when they hit a target on the ground with a voltage input on the full bridge of 362VDC (150VAC from my variac) and the OCD is set to 350A. The tip of the discharge needle is 90cm high (maybe a little high). My question is:

Can I raise the OCD value to 400A or higher? I don't know if this model of IGBT's can support 400A or higher running at a primary frequency of 142kHz. They are placed on a good heat sink. The power consumption with the normal interrupter operating mode (70-100uS / 560 bps) and in MIDI mode is between 600W and 800W, respectively. My goal is that the discharges can reach the ground without having to place an object that shortens the distance to help the lightning to reach the ground more easily.

I had thought about raising the OCD limit to 400A and maybe 400V DC bus power supply in order to achieve higher discharges that can reach the ground without any problem.

I attach photos and if any data is missing do not hesitate to tell me about it. I also attach a video of the operation.

Video: https://youtube.com/shorts/fBSI0B8LMx4?feature=share

Best regards and thanks for your help

Here is the one that I built a few years back. It’s got exactly the same switches as yours i.e. the SKM 400 switches in a full bridge configuration. The OCD is set at 1000Apk.  I have dawncaps 375 nF bank - these get a little warm after long runs but work great. Using freewheeling with UD+
Fres is 52kHz with 31 inch x 6.5 inch secondary.

Here is a link to the coil running with 3/8”  copper tube breakout and 31 inch diam topload at 1000A OCD for the freewheel. The video files were too large to upload directly to this forum.

So you have plenty of room to increase your OCD to well above 350 A!!!

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This DRSSTC presents an incredible result. The electrical discharges are impressive.

After what has been exposed in this forum thread, I am sure I can set the OCD above 350A. The only drawback I see is the resonant frequency of the primary, which is set at 142kHz. I don't know if that's too high a frequency for the SKM400's.

Also, maybe my small secondary won't handle the excess voltage from the increased current and could break.

However, for future models, I will build coils of a larger size to lower the resonance frequency and I will use higher quality MMC bank capacitors and copper tubing for the primary winding.

[Jj]

Very nice build!

you have already been given the good advice here,  but you could measure the switching time occurrence to check the performance. If you are staying close to zero current all is good. Switching losses are much less of an issue for low duty cycle operation.

Not sure how much more you can get from that secondary coil. Problems usually start when spark length is at 3x the secondary length for my DRSSTCs. Improvements can often be made, though it takes more effort and the returns get smaller.