Futurist's DRSSTC 0.5

[futurist]

Hi everyone

welcome to my latest project thread - a relatively small 75 mm TO-247 half-bridge DRSSTC
This coil started together with my medium sized DRSSTC in 2017, back then I acquired almost all the components and the driver, however I only assembled it last year

Everything is laser cut from wood or 3D printed and the coil should be easy to replicate. Overall the project turned out nice
Few minor details are missing, like a proper enclosure for electronics


JAVATC


Overview of the coil specs
- (for now) Chinese 40N60 TO-247 double halfbridge IGBT inverter, set to 300 A over-current protection
- 2x 250 V 1 uF snubber capacitors (KEMET R75LN41004000K)
- Bus capacitors 2x 1000 uF 400 V caps with KBPC5010 1000 V 50 A bridge rectifier, for 240 V AC in (no voltage doubler)
- 99.9 nF 6 kV MMC 13.5 Arms (3 in series 2 strings in parallel CDE 942C20P15K-F)
- UD+ driver with Universal bus precharge & fan speed controller
- Flat spiral primary 85 mm inner diameter, 4 mm copper tubing with 4 mm spacing, 8 turns tapped at ~xx turn
- Secondary 75 mm diameter on PVC drain pipe, ~2000 turns (300 mm long), 0.15 mm double enamelled copper wire - coated 3x with 2K polyurethane varnish for wood flooring
- Spun aluminium toroid 62 x 250 mm from highvoltageshop.com
- Controlled over 10 m ST-ST 125/62.5 um optical cable
- Maximum 40 cm sparks!


Universal bus precharge & fan speed controller board

The coil uses my universal bus precharge & fan speed controller board mounted bellow UD+. This is the first test of the board and it has proven it's useful
It has built in DC-DC step down to 12V to power the fan/relays (selectable) and STM32 MCU to control bus precharge relay and fan speed. More info here.
There is an option to turn off the UD2 driver in the event of fault (pull down P1 of 74HC74), or while bus caps are precharging.
Precharge resistor is 150 ohm 10W, and discharge resistor is 1 kohm 10W. Relays I'm using are 6-1419102-3 TE Connectivity 24 V for BUS precharge and 5-1419102-2 TE Connectivity 24 V for BUS discharge.


Original MMC


New MMC testing


New MMC 3D printed holder

Originally I planned to use 2x 942C20P15K-F 0.15 uF caps for MMC, however the resonant freq turned out lower than predicted on javatc and I ran out of primary turns.
New MMC is 3 in series 2 strings in parallel CDE 942C20P15K-F giving 99.9nF, and it barely fits in the coil MMC capacitors are fitted with vishay HV 10Mohm balancing resistors.

GDT is 10 turns on TN25/15/10-3E25 FERROXCUBE toroidal ferrite
Current transformers are wound on TN16/9.6/6.3-3E25 FERROXCUBE toroidal ferrites (1:xxx) using UTP cable



Mini double-halfbridge board


Inverter is double-halfbridge of 40N60 TO-247 IGBTs. This bridge was meant to be temporary because I wanted to test some chinese 40N60 IGBTs I bought from ebay, but they won't die even at 300 Apk OCD
0.1uF 2000VDC film capacitor is connected a la Steve Ward - from negative rail to ground to protect the bridge


Inverter and driver

I don't remember exactly why I went with double-halfbridge configuration instead of full H-bridge. I think I wanted to have only half-bridge of TO-247 IGBTs, but at some point decided that I'll need more current
Gate resistors are 10 ohm, schottky diodes are STPS340U and TVS diodes protecting the gates are SM6T30CA
The coil maybe needs a bit more robust IGBT brick halfbridge. But so far TO-247 half-bridge works OK so I won't change it




Primary supports were laser cut from 3 mm plywood and glued, two pieces are glued together to make 6 mm thick part







Secondary is wound on 75 mm diameter drain pipe, endcaps are 3D printed








This time I invested in a beautiful 62 x 250 mm spun aluminium toroid from highvoltageshop.com

3D printed parts (secondary endcaps, relay, MMC, IEC connector, BUS capacitors stands)
drsstc05_3dparts.zip

Laser cut parts
drsstc0.5_4mm_primary.zip

PCB for the double-halfbridge
to247hb.zip

[Mads Barnkob]

A really clean build and similar to one that I have planned to do a video about as well

Time flies, so its also about a year ago that I bought secondary coil and toploads from highvoltageshop.com, so thanks for sharing the 3D parts, I can properly use those aswell! I am not an expert on laser cutters and 3D printers, but can the files for laser cutter be converted easily to 3D print?

I did however order the Dan/prof9dc double TO-247 full-bridge boards and drivers instead, so still have to populate those and I think I will scavenge IGBTs out of old equipment.

I might as well make it with a bigger MMC the first time, I dont want to run out of primary turns.

[futurist]

I used tinkercad to design 3D printed parts, laser cut parts are designed in librecad
I think it should be straightforward to add third dimension to laser cut parts to make them 3D printable

If the secondary is wound on 75 mm diameter drain pipe you could 3D print endcaps and toroid stand-off
prof9dc double TO-247 full-bridge would be really nice for my coil also, allowing more primary current