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Rollingblackout

Mon Jul 21 2008, 03:16AM

Registered Member #1524 Joined: Sun Jun 08 2008, 05:25PM
Location: Grand Junction, Colorado
Posts: 38

I found that my grounded strike rail was getting hot during my testing and tuning. I happened to look at the book and there is a section missing in the original builds strike rail. after removing this 3 inches of 3/8 tubing the output of my coil gained 3 inches in arc. Can anyone explain the effect on output that the solid loop strike rail had?

Andyman

Mon Jul 21 2008, 03:25AM

Registered Member #1083 Joined: Mon Oct 29 2007, 06:16PM
Location: Upland, California
Posts: 256

In a coil, if the strike ring is continuous, the coil "sees" it as a shorted turn and performance drastically decreases.

ragnar

Mon Jul 21 2008, 09:10AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Dr. GigaVolt wrote ...

Rollingblackout wrote ...

Im not very skilled with an O scope yet maybe I was zoomed in to fare.

Here is a shot of a sample take with channel 1 on the pos igbt gate terminal and channel 2 on the neg igbt gate terminal.

The polarity is definitely correct. The waveforms look a bit funky, but that could be just an artifact of the oscilloscope - not sure.

Unlikely to be artefacts on the scope; looks like a Fluke PM3092 or PM3094.

Rollingblackout

Tue Jul 22 2008, 12:05AM

Registered Member #1524 Joined: Sun Jun 08 2008, 05:25PM
Location: Grand Junction, Colorado
Posts: 38

Here are 4 scope shots:
1. corona just starting to form at full bridge voltage and PW at min.
2. max spark length same power level not sure about the PW about 250us I expect
3. no change in spark output more power through the primary PW about 300-325us
4. no change in spark output even more power at the primary, PW 400us

Is there any direction in tuning that can be gathered from this information?

HV Enthusiast

Tue Jul 22 2008, 01:21AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

What exactly am i looking at here?

Is this primary current?

If it is, then it looks like what i would expect to see.

Tuning will be a compromise between longest arc and maximum current.

If you have my book, read the section on advanced tuning and pay special attention to the tuning graphs. You'll see the graph of arc vs. current in which you want to shoot for.

Basically, you sort of detune it at low power (i.e. it requires much more current to begin arcing), but as you increase power (increased arc length), the system becomes "more" tuned and you get more output with little current increase.

If you tune where current is lowest when arcs first initiate, thats basically a tuned system at no load and what will happen, the arc will detune the system and limit output.

Of course, the trade-off is that you don't want too much current or you'll blow the system.

Rollingblackout

Tue Jul 22 2008, 05:14AM

Registered Member #1524 Joined: Sun Jun 08 2008, 05:25PM
Location: Grand Junction, Colorado
Posts: 38

The samples are taken with one probe leads ground connected to a large metal table under the tesla coil and the probe not connected to anything.

HV Enthusiast

Tue Jul 22 2008, 11:58AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Okay, that still looks like the profile you would get.

Rollingblackout

Tue Jul 22 2008, 11:51PM

Registered Member #1524 Joined: Sun Jun 08 2008, 05:25PM
Location: Grand Junction, Colorado
Posts: 38

looks like all the tuning is within one turn, so some place in this turn should be a taping point where spark length will double and I will need to limit duty cycle and even voltage to keep the current under control in the 350-400 amp range.

I just want thank you all for answering my noob questions.

Rollingblackout

Fri Aug 08 2008, 05:44AM

Registered Member #1524 Joined: Sun Jun 08 2008, 05:25PM
Location: Grand Junction, Colorado
Posts: 38

My variable transformer does not out put over input, but it has 2 transformers on one shaft. My house voltage is only 119 and so I get about 300vdc on the buss.

Would it be ok to use my 240 connection and pass each leg through its own variable transformer to get the dc buss voltage to 400 vdc?

Secondly, should the capacitor board be connected directly to the top turn of the primary or to the bottom turn of the primary and tapping with the neutral jumper. Does it even make any difference in polarity and/or primary to secondary relationship physically.
Link

HV Enthusiast

Fri Aug 08 2008, 11:53AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Not sure about the variable transformer. Not something i would personally recommend.

The capacitor board can be on either side - doesn't really matter. I would tap with the upper jumper though. Also, once you find an optimum tapping point and are confident you won't be changing it, you can simply cut off the extra primary at the top. This will help reduce arcs as the voltage there will exceed what is present at the upper tap point.

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