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Bennem

Tue Jul 03 2007, 11:22PM

Registered Member #154 Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260

Hi Folks,
Due to this years wet summer we're having here in the UK,
I decided to use some time on making another DRSSTC.
About two years ago, i purchased one of Dan McCauleys
Advanced controller boards, allthough i populated it with
components, i never got round to using it.
As it was designed for secondary feedback, i decided to
upgrade it to primary feedback and added sync shut off,
over current detection, a bargraph peak current readout
and 'set current' bar graph readout.
I have a quick question,
I read that some guys have used caps from their bus lines
to ground on their coils,
what is the reason for this?
Is it something to do with draining RF currents when subjected
to primary to secondary sparks?

Sorry about the poor quality pics....they were taken with a phone
camera.

cheers,
Mel.

Part Scavenger

Tue Jul 03 2007, 11:34PM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

Looking good as usual Mel!!!

Bennem

Thu Jul 05 2007, 06:03AM

Registered Member #154 Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260

Cheers GB !

It may look ok....but i still have to test it on a coil....

Any ideas as to the cap question?
I read somewhere about Firkrags DRSSTC and him having
sparks appearing on his bridge, and by putting caps from
his bus lines to ground cured this.
Is this the reason folks put caps from their bus lines to ground?

Steve Conner

Thu Jul 05 2007, 03:23PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Yes, the caps are to drain away any dangerous common-mode RF voltages, that might otherwise make your gate drive transformer break down and let the smoke out big-time.

I use a single ceramic disc cap between the DC bus negative, and the mains earth. I also connect the ground rail of the driver circuitry to that same mains earth.

Marko

Thu Jul 05 2007, 03:56PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

God, I've just laughed out my ass after reading steve's signature.

I read somewhere about Firkrags DRSSTC and him having
sparks appearing on his bridge, and by putting caps from
his bus lines to ground cured this.
Is this the reason folks put caps from their bus lines to ground?

The caps *did not* completely stop the arcing on my bridge. Much less than before, but it still occurs at ground strikes at only 60V input. I mothballed the coil for a while because of that.

This is crazy considering low RF impedance I created between two points, it still arcs over.

I now believe my single-point grounding is bad. Since I have nothing else available the secondary ground ends stuck on neutral wire wich has quite high RF impedance. Still, it doesn't explain the problem too well.

(this is all with isolation transformer. I don't know how will it behave if ran directly from mains).

Bennem

Thu Jul 05 2007, 05:10PM

Registered Member #154 Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260

Thanks for the replies!

I'll add something like a 1000pf cap from my neg bus rail
to mains earth.....

Bennem

Sun Jul 08 2007, 03:53PM

Registered Member #154 Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260

Today i made my primary coil and strike ring.
I have another question....if thats ok?
What do you guys use to connect to your primary coil?
on my last mini DRSSTC i used an ordinary fuse clip
from a mains plug and it got very hot!

1183910000 154 FT27741 Added Primary Coil

Tom540

Mon Jul 09 2007, 02:12AM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617

Wow that looks awesome. very clean.

thedatastream

Mon Jul 09 2007, 07:27AM

Registered Member #505 Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329

Mel,

I used some copper earthing straps from B+Q designed for 15mm pipe. I hammered them flat and then re-bent them around an M8 rod so that they would clamp to the 8mm microbore pipe that I used for my primary.

James

ArcLight

Mon Jul 09 2007, 07:36PM

Registered Member #341 Joined: Thu Mar 23 2006, 07:41PM
Location: Northern Illinois, USA
Posts: 69

I couldn't get a fuse holder to work properly either. And a clamp that I fashioned with a set-screw either didn't connect well or crushed the tubing.

For general coil use (MMC, gap, etc.) I purchased a 6â€ by 10' roll of copper flashing (USD $23) at a home improvement store. Using heavy-duty scissors I cut a strip about 5/8â€ wide by 1 3/4" long. Then drilled two holes (whatever size that's appropriate for a #10 screw) 1 3/16â€ apart. The piece was then wrapped around a form that was slightly smaller in diameter than the primary tubing and the screw installed. I then used needle-nose pliers to make the copper perfectly fit the form. After forming, the piece was finished on a belt sander to remove burrs, sharp corners, etc. The piece was then installed on the primary and secured with a couple of washers and a 1/2â€ #10 brass screw. It's not as convenient to move when tuning, but it has never failed to function properly.

After I wrote my response, I actually read thedatastream's post. Basically, I'm saying the same thing, but with more words.

Regards, ArcLight

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