Model 82D

Specs

  • Secondary: 8.4” x 45” winding length, 26AWG wire
  • Resonant frequency: 41.3kHz
  • Topload: 10” x 47” ring type
  • Primary: ~9T of 3/8” soft copper tubing, 3/8” edge-edge spacing, water cooled
  • Primary Capacitor: 5s16p CDE942C20P15K MMC, 0.48uF @10KVDC, 216A RMS, 6912A peak
  • Bridge
    • Layout: H-bridge with voltage doubler for 680VDC with 240VAC input
    • IGBT: 2x Mitsubishi CM300DY-24H
    • Bus capacitor: 5500uF @ 900VDC. 2x CDE 520C 11000uF, 450VDC inverter-grade electrolytic in series. 15kOhm / 10W bleeder/balance resistors
    • Bus: Laminated, 1/16” aluminum, 1/16” G10/FR4 insulating layer
    • Snubber: 2x Aerovox RBPS direct-mount, 2uF 1000VDC each
  • Power Supply: Remote single-phase 240VAC voltage doubler with precharge/discharge. 680VDC @ 20A output
  • Driver: UD2.7C
  • Feedback/OCD: 50:20:1 current transformers, Fair-rite Type 77 (5977003801 and 5977006401)
  • Interrupter: Dual Channel MIDI Interrupter
  • OCD: 1200A minimum
  • Arc length: ~7ft with ~200VAC input running ~45uS on-time while playing music.

Introduction

After the success of model 81D, I decided to design a new 8” coil with more optimal physical parameters to give a much lower resonant frequency, which would allow a much higher OCD setting.

This new system would revolve around another 8” secondary, but wound with thinner wire and for 11” more than 81D. All other components are sized to match the secondary and planned arc length.

Design

Power Supply

Remote 680VDC voltage doubling rectifier with builtin EMI protection.

Bridge

Same as 81D, but without the onboard rectifier/doubler configuration. In addition, new PCBs were used for the gate connections.

A second version of the CM300 Gate boards was later designed, but v0.1.0 worked well enough with minimal shoot-through and ringing that this is what is on the bridge today. 820mOhm resistors were added in series with the anti-parallel Schottkey diodes to slow down the turn-off just slightly, and a lower voltage TVS diode was used to clamp the over/undershoots. The result is better than the original configuration which proved effective, so I’m running with it.

KiCad files are available on github. PRs welcome: github.com/acobaugh/cm300dy-24h-gate-drive-board


Driver

Same as 81D


Primary

9 turns 3/8” copper with water cooling.

Secondary

The secondary is a piece of 8” SDR-35 drain pipe that has been sanded, sealed with polyurethane, wound, then coated with Envirotex Lite 2-part epoxy for a protective, glass-like finish. The ends are finished the same as 81D, with 1/2” pieces of HDPE secured with nylon screws along the edge. The mount is a 1/2-13 nut captured in machined blocks of HDPE on the inside.

Ground connection is a piece of 5/8"x1/16” copper bent to follow the curvature of the pipe and a piece of brass soldered to it, which is then drilled and tapped for a screw.


Tuning

Videos