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"Inazuma" Mk.1 DRSSTC

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thedatastream
Fri May 04 2007, 10:02PM Print
thedatastream Registered Member #505 Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329
"Inazuma" Mk. 1 (from the Japanese for "lightning") is going to be a mid sized DRSSTC running with a full bridge of TO-247 IGBTs.

Progress so far:

I've constructed the basic full bridge assembly, with CPU heatsinks, fans and bulk decoupling on a piece of pine shelf

Full Bridge Early Stages Small

This uses short sections of aluminium U-channel to clamp the IGBTs to the heatsink for reduced thermal impedance

IGBT Heatsink Clamp Small

Controller is Steve Conner's PLL controller, essentially unmodified. This is split across two boards connected via ribbon cable and mounted in a diecast aluminium box. Building is still in progress, this is it's current status.

Controller Parts Small

Controller Early Stages Small

Holes in the top of the lid are to enable me to adjust the pots when the circuit boards are built into the case.

Controller Lid Small

Current transformer is a ferite toroid with 47 turns of Furakawa triple insulated wire and mounted on a bit of copper clad board with hot-melt. The bolts are just for mounting to the controller case top.

Current Trasformer Small

I've also built an interrupter based on a couple of 555 timers and housed it in a plastic case.

Interrupter1 Small

This uses a TOSLINK / SPDIF fibre optic emitter with a receiver on the coil controller for electrical isolation

Interrupter2 Small

The internals are a bit crammed but it all fits and works pretty well.

Interrupter Internals Small

To do:
Complete building the controller circuitry including fan speed controller, LED indicators and test that it all works OK
Build into the metal box
Complete base assembly
Finish winding secondary
Decide on primary geometry + tank cap

Onwards!

EDIT: I've also put up a new page on my website which gives more details about the construction.
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Sparrow338
Fri May 04 2007, 10:14PM
Sparrow338 Registered Member #661 Joined: Sat Apr 21 2007, 03:17AM
Location: Ventura, CA
Posts: 41
Nice job! Looks great so far. Did you make the entire interupter on your own? Looks like something you'd buy. :) Keep up the good work.

BTW: Did you use some IGBTs as spacers for the longer sections of AL U-channel? ;)
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Brett Miller
Sat May 05 2007, 03:16AM
Brett Miller Registered Member #593 Joined: Tue Mar 20 2007, 12:32AM
Location:
Posts: 50
James,

Very excellent and neat work indeed. I too am working on my first DRSSTC, which will feature a half bridge of TO-264 IGBTs. Great idea for heatsink mounting. I spent some time earlier tonight, going through my box of heatsinks trying to decide how I was going to meet this thermal challenge with those IGBTs. I'm basically still collecting heatsinks and looking.

My coil will probably be a project that I will have to stretch over most of the summer. I hope to have first light sometime by late summer to early fall. I'll probably start a thread when I have more accomplished. Mine will be based around a 12.5" x 4.5" AWG 31 secondary, which I recently wound and coated.

-Brett
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Bennem
Sat May 05 2007, 06:33AM
Bennem Registered Member #154 Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260
Hi James,

Great construction!!
I'm looking forward to following this thread in
all its construction,testing and its sparks!

Allthough i have only constructed small DRSSTC's,
it makes me wanna build a bigger coil.

All the best James.
See you at the Derby thon?
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thedatastream
Wed Jun 06 2007, 01:20PM
thedatastream Registered Member #505 Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329
*** Updates ***

Ran up and tested the controller and it all works OK. It's really crammed in there, I've fallen into the trap of underestimating how big my box needed to be so everything is really crammed in!

1181134250 505 FT24811 Controller Lid Underside Sm
1181134269 505 FT24811 Controller Main Box Sm


In soldering the heavy current connections, one of the GDT wires came unsoldered. I took the opportunity to take a photo of the GDT on the underside. Good labelling of the connections is key!



1181134190 505 FT24811 Full Bridge Pcb Sm



The bridge is a _lot_ busier now, with mains input for both controller and bridge supplies, mains transformer for the controller being added onto the board.

1181134385 505 FT24811 Prototype Bridge Overview Sm

I've also finished my MMC, two parallel strings of 9 caps to give me 100nF @ 9kV. These were connected using two parallel strips of single sided copper clad board with bits cut out. M4 bolts form the connection points.


1181134844 505 FT24811 Mmc Mounted Sm

1181134860 505 FT24811 Mmc Detail Sm


Measured the gate drive signal with the deadtime control turned up to maximum and I get nice burts on the gate with very little ringing using a 4R7 resistor
1181135637 505 FT24811 Gate Burst 360us


So what's left to do?
  • Run up bridge and controller to fully test system

  • Finish the primary supports
  • Wind the primary
  • Wind the strike ring

  • Clean up the secondary coilform (5" HDPE gaspipe)
  • Make secondary endcaps
  • Wind secondary
  • Varnish

  • Assemble and test


Onwards!
James
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Sulaiman
Wed Jun 06 2007, 05:42PM
Sulaiman Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Looking good and compact.
Nice work.

I just have a couple of questions I'd like to ask;
Have you found balancing resistors for MMC are not required?
Are that many fans required?
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Steve Ward
Wed Jun 06 2007, 06:50PM
Steve Ward Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
Have you found balancing resistors for MMC are not required?


I never use them. They function fine without them, but i cant say i recommend handling the MMC afterward (since i have found voltage on the caps individally, yet the bank itself is discharged). This was when using caps of various histories and abuse, so they were all out of capacitance spec. The situation is far less severe when you use all fresh caps and they are all seeing the same use.
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thedatastream
Thu Jun 07 2007, 06:53AM
thedatastream Registered Member #505 Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329
Sulaiman wrote ...
Looking good and compact.
Nice work.

I just have a couple of questions I'd like to ask;
Have you found balancing resistors for MMC are not required?
Are that many fans required?

Hi Sulaiman, thanks for the comments.

I've got some 9M1 resistors that I was going to add to the MMC when I have time. Even if they aren't strictly necessary they'll serve to discharge the bank when it's not operating.

As to the fans, I've got a PWM control circuit built into the controller so I can vary the voltage between off and way too much. I'm only using TO-247s which have a higher thermal impedance from j-c than ISOTOP bricks. So I'd prefer to run some fans just to keep everything cool and increase reliability. I'll probably need it when it comes to pushing the peak current envelope a little.

James
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thedatastream
Mon Jul 02 2007, 03:20PM
thedatastream Registered Member #505 Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329
I've completed the primary now, so I should be able to do some initial low voltage tests just using the primary. I still have to clean, make the endcaps, build a winding jig and wind the secondary which is the last major job remaining.

1183389592 505 FT24811 Img 2627

James
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thedatastream
Wed Jul 11 2007, 01:28PM
thedatastream Registered Member #505 Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329
Progress.

Secondary winding is going well, I'm about 60% done and it's only taken a couple of hours so far. I gave up trying to motorise the jig because the gear I had attached to the motor shaft keeps coming unstuck and slipping.

I'm doing some initial testing on the controller and I've got some results. Here is a plot of the primary current waveform in series with the cap, no secondary just the primary circuit. Frequency is 116kHz, pretty much spot on what was predicted.

1184160445 505 FT24811 Primary Current Ringup No Sec


The current is measured using a second CT + burden (47 turns and a 0.47 ohm resistor to give 10mV/A) and the peak is 228A running from a 22V power supply. This seems high, but then there is no secondary to load the tank so it could be reasonable. Comments?

Looking at the half bridge voltage with a 10:1 probe, it's not pretty (top trace in below plot). You can see that ZCS occurs during the period of deadtime but the actual voltage is all over the shop. Any comments on this?

1184160464 505 FT24811 Hb Voltage N Primary Current


My tuning LEDs don't appear to light and the PLL doesn't appear to track the frequency. If my phasing was incorrect, the PLL wouldn't track - correct? Also, I wouldn't expect the PLL to track if the input signal was low, or would the diodes in series with the burden resistor help here?

Still plenty to do!
James
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