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4" DRSSTC build thread

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Aragorn

Thu May 08 2014, 08:48PM

Registered Member #18516 Joined: Sat May 18 2013, 09:09AM
Location: Lancashire, UK
Posts: 38

Started building my first coil, progress is slow, but i figured i would stick some photos up here and make a bit of a build thread.

Started with a 4" PVC drain pipe and a lump of nylon, and turned a couple of end caps up on the lathe:

Work has a coil winding jig, typically used for much smaller solenoids and things, but it turned up an adaptor and mounted the secondary in it. I'm not sure if it'll be suitable yet, as the motor seriously lacks torque when run slowly. So far i've painted and sealed the coil form with many coats of Anti Corona laquer from RS:

Once i'm happy the laquer as fully cured i'll have a go winding the secondary!

Meanwhile i also attempted to sort out a toroid. I didnt really want to spend the money on a spun toroid, but being from an automotive background i found a source of 4" 180degree aluminium bends for not much money (Â£17 each).

I picked up two, and set about making them into a toroid:

I've taken the two halves to a local shop to get them welded together, once i get them back i'll have to grind the welds smooth and cut an alloy plate for the middle and have that welded in too.

For the electronics/control circuitry i've had some PCB's made to the tried and tested UD2.5 design.

The board is more or less finished now, i dont seem to have an uptodate photo of it yet, i need to solder in the missing resistor as unfortunately these are Rev.0 boards and then do some testing to ensure its all working correctly.

I've also bought a Midi controller from Phil Slawinski, which i've just finished building up into an enclosure

The wirings all done and its been powered up and seems to flash its LED's as expected!

I still need to sort the power electronics, i'm planning a full bridge of IXYS IXGN72N60C3H1's with the usual Cornell 942 0.15uf tank caps, probably in a 4x4 series-parallel arrangement.

I want to get the secondary and primary coils sorted out before i start spending Â£Â£Â£ on the expensive IGBT's and caps though.

I've also procured 6 1000uf 400v electrolytics from a busted inverter, so hopefully i'll be able to use four of those in parallel for the DC bus to give 4000uf at 400v. The Bus will be rectified 240v AC, so around 340v DC.

Aragorn

Thu May 08 2014, 09:08PM

Registered Member #18516 Joined: Sat May 18 2013, 09:09AM
Location: Lancashire, UK
Posts: 38

[Moderator edit]: Posts were merged together. Please do not double post, refer to site rules Part 2:G

Mads Barnkob

Fri May 09 2014, 06:07AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Anti corona varnish, I am not too sure you gain any advantage if you do not wind the wire onto it while still wet, else you will still have some air behind the windings and that is plenty of room for corona or possible flash over.

I really like your toroid, what are these pipes called and where should one look for those?

You have plenty of DC bus filtering for a coil you properly can not push much beyond 500Apeak, I think you should aim for double mmc capacitance.

The smaller the capacitance, the higher voltage rating is needed for it, if you went for 2 in series, 4 parallel, you can make it cheaper and run it just on the brink of voltage rating or 4 in series, 8 parallel for double voltage rating. If you want to play around with the number to get an idea, choose the right cap and medium drsstc:

Aragorn

Fri May 09 2014, 09:14AM

Registered Member #18516 Joined: Sat May 18 2013, 09:09AM
Location: Lancashire, UK
Posts: 38

Thanks for the pointers.

The varnish was cheap, 4 quid a tin, so the same price as normal acrylic lacquer and has a high dielectric strength (50kv/mm IIRC). Everyone says to lacquer the form to seal it before winding, so i figured the anti-corona stuff with its higher insulation value would be better. If its no better, i dont think its going to make anything worse?

The pipe bends i got from a company that sells automotive silicone hoses and connections. They're usually used for custom turbocharger/induction pipework on engines. Not really sure what engine would use something as large as those 4" pipes, but they were available and cheap.

DC bus caps were free so i figured i might as well use them. I could always use two or three instead but i dont think having four will be a problem?

The cheapest place around for the 942 caps has a minimum order quantity which means i'll end up having to buy probably 25 of them (and buying 25 will be cheaper than buying 16 from the next cheapest place!), so plenty of scope to use different arrangements. 3x6 would give 6kv and .3uf for instance but only use two more caps. I was going to use them as snubbers across the IGBT's too.

I'm not quite sure i fully understand the advantages that the increased capacitance gives though?

I've used this as a basic design guide/outline:

Obviously there are differences, I anticipate my Fres will be closer to 150khz looking at javaTC, due to a slightly smaller toroid (4x17) and 30awg wire rather than 32. I'm also using a full bridge of smaller IGBT's for cost and availability reasons.

Cheers
Kev

Ash Small

Fri May 09 2014, 12:41PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Mads Barnkob wrote ...

I really like your toroid, what are these pipes called and where should one look for those?

My guess is turbocharger intercooler pipes:

Hydron

Fri May 09 2014, 04:25PM

Registered Member #30656 Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208

If MMC capacitor costs are an issue, you may be able to get away with something other than the 942Cs, as the stresses in a DRSSTC are different to that in a spark gap coil (less peak current for one).

I'm not really qualified to say what caps are good options, but others here may have suggestions. My own coil uses a big pile of aerovox snubbers, with no issues so far.

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob