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DRSSTC Tuning, UD2.7C

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orac12

Mon Apr 18 2016, 10:12AM

Registered Member #9879 Joined: Tue Jan 29 2013, 05:00AM
Location: New Zealand
Posts: 37

This is the first tesla coil I've built, taken a few ideas from others seen around here :)

It's basically completed and time for tuning, not sure what to expect or what is acceptable so some pointers in the right direction would be great.

CM600 Full bridge
680VDC ~ Bus
0.6uF MMC
10 turn primary, tapped at approx turn 6 for now
1100~ turn 24AWG secondry
Ring style toriod
Automatic precharge + discharge
JavaTC calculates the primary at approx 40kHz, and the secondry a little higher. (Don't have all the JavaTC stuff with me atm to post right now)

At the moment we are running a lower bus voltage, 360~VDC while testing.

A few questions for people with more experience than me that could point me in the right direction:

What sort of on time and BPS should we be expecting before getting any breakout?
When tuning the phase lead, what would be an acceptable voltage spike? When tuning phase lead, we arent really seeing any improvements.
What sort of primary currents do we want to be tuning phase lead at? At the moment I believe we are at 3-500 amps primary.

We havent yet had any breakout, but it is certainly buzzing quite loud and if I bring a earthed wire up to the toroid it will strike an arc from around 1ft away.

Here are some scope shots. Current transducer is 1V : 100amps

There is approx a 100v spike on the bridge output and cannot seem to get it any smaller, is that acceptable? Some of these shots have different bus voltages as we were experimenting.

Blackcurrant

Mon Apr 18 2016, 07:41PM

Registered Member #2989 Joined: Sun Jul 11 2010, 12:01AM
Location: UK
Posts: 94

Hi Orac, A few things I would do first before putting any real power in.

Tune your coils first with a signal generator and scope.
I would start by finding the secondary frequency, quite easy and should peak quite sharply on the scope. The scope will pick it up meters away just with a probe with a small wire attached. Also a fluorescent tube will light quite easy just leave it on top.
Then work out your needed tap point on the spiral coil and check this frequency to.
When your happy that it's more or less in tune, add a sharp breakout point on top then power it up slowly. you can always remove this later it just gives an easy way for testing.
Also in the dark you may see were this buzzing is coming from.
Above all keep your distance!

PS from your picture I would say it may flash over near the bottom part, remember to keep everything smooth. My first coil was rather crude and had all sorts of things (small fires/flash-overs) happen.

Uspring

Tue Apr 19 2016, 08:16AM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
Location:
Posts: 711

You should definitely add a breakout point to the top. It helps tuning especially if you're still much out of tune. Then play around with your primary tap, adding or subtracting quarter turns.

The breakout point is essential also for another reason: For best performance, the secondary must be tuned somewhat higher than the primary. When the arc begins to grow it will then add capacitance to the top and pull the coil into tune. That means also, that the coil will be initially somewhat out of tune, providing not very much voltage. A breakout point will help to start the arc in this condition.

orac12

Tue Apr 19 2016, 08:54AM

Registered Member #9879 Joined: Tue Jan 29 2013, 05:00AM
Location: New Zealand
Posts: 37

I did have a small breakout point, but that was just a piece of solder wrapped around and sticking out. I have completed a proper breakout point tonight and will check secondary frequency in the next few days.

Blackcurrant: What part are you referring to at the bottom that you suspect may flash over?

Blackcurrant

Tue Apr 19 2016, 12:52PM

Registered Member #2989 Joined: Sun Jul 11 2010, 12:01AM
Location: UK
Posts: 94

The closest part between the two coils, although I had this happening on a spark gap based coil. It might not be quite the same with a transistor driven one.

Graham Armitage

Tue Apr 19 2016, 03:40PM

Registered Member #6038 Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248

I had the same ringing/spikes with my UD2.7 driver, but the phase shifting helped. It does not remove the spikes, but I could shift the peak spikes within the beat envelope. LoneOceans suggestion was to adjust the phase so that the high spike occurred at the beginning of the pulse and and was smallest just before the end of the pulse. That way you don't get the spike on top of the peak of the envelope. Running like this I never had any problem and the IGBT ran very cool.

I did my testing at around 30-40 amps and it seemed ok for low power testing.

orac12

Wed Apr 20 2016, 02:48AM

Registered Member #9879 Joined: Tue Jan 29 2013, 05:00AM
Location: New Zealand
Posts: 37

Closer up picture of between the primary and secondary. There is no real sharp edges, but we will see what happens.
Measured the secondary frequency at 35.71 khz.

Just replacing a precharge resistor, then will check freq of primary and adjust.

1461120498 9879 FT176476 20160420 1445341

orac12

Fri Apr 22 2016, 11:45PM

Registered Member #9879 Joined: Tue Jan 29 2013, 05:00AM
Location: New Zealand
Posts: 37

Ok, so started having some flash over between primary and secondary.

Whats the best way of stopping this?
Options I see are:

Take some inner turns out of the primary to give more space between the two.

Lift the secondary higher so its further away.

What are other people doing to try and prevent flash over?

Antonio

Sat Apr 23 2016, 01:40AM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

You can keep the inner end of the primary coil grounded. Note that the currect tune of a DRSSTC is not with the primary and secondary exactly resonating at the same frequency, even ideally. The difference is small if the coupling coefficient is not too high, however. The waveforms show significant voltage drop at the driver, and strange spikes in the middle of the half cycles that should not be there. Verify if the connections used in the measurements are correct, with the oscilloscope correctly grounded.

Blackcurrant

Sat Apr 23 2016, 09:24PM

Registered Member #2989 Joined: Sun Jul 11 2010, 12:01AM
Location: UK
Posts: 94

I see you can easily put more space between pri and sec coils by just starting the pri coil further out, also you could put some insulating tubing on the first pri turn if needed after.

I would run the thing with a current limited power supply, say 30v on the Bus until you figure out whats happening with the wave forms etc this way even if somethings not quite right you will save things melting.

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