First Sparks - Holy Crap!

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First Sparks - Holy Crap!

Postby junktronix » Sat Sep 21, 2013 10:47 pm

Finally found the time to finish assembly and did my first test this evening. This thing is *way* more impressive than I was expecting! Time to get midi working.

http://youtu.be/e1iMQ358Ags
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Re: First Sparks - Holy Crap!

Postby Alex » Sat Sep 21, 2013 11:49 pm

Wow! Nice sparks!

Though you shouldn't let the sparks hit the IEC cable...
Point it in another direction
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Re: First Sparks - Holy Crap!

Postby DJKOR » Sun Sep 22, 2013 1:47 am

Holy crap alright. Looks like yours is giving quite some impressive sparks.

This is the type of coil I want to use for reference. If you are able to get your hands on an oscilloscope and frequency generator, then you may be the key to some further fine tuning :D
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My build thread: viewtopic.php?f=15&t=998 | 246kHz Primary / 267kHz Secondary
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Re: First Sparks - Holy Crap!

Postby stegu » Sun Sep 22, 2013 2:52 am

Wow! Congratulations! I would very much like to see some more data from that coil.

One simple question that is very important to many of us right now: what is the resistance of your secondary coil? Use a multimeter and tell us how many ohms you have between the toroid and ground. It would be most helpful.

Could you please make another video like that, but where you turn the toroid so the breakout point points away from the cables? I would like to include some stills from this video in my tuning guide to present a "success story", and I would prefer it if the reference images didn't have the sparks strike the cables, because that's generally not a good thing to do. (EDIT: No real need for another video. It was actually good for the presentation to show what happens when you point the breakout point in the wrong direction. Tuning guide updated with your images.)

Also, like DJKOR said, for those of us who are experiencing tuning problems, it would be really nice if we could get some measurement of your resonance frequencies. Do you have access to an oscilloscope? If not, no worries, the resistance measurement I asked for above will be a good hint in itself.
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Re: First Sparks - Holy Crap!

Postby junktronix » Sun Sep 22, 2013 11:27 am

Thanks. I measured the secondary resistance as 235 ohms. I thought it was supposed to be closer to 300, but it seems happy. I have a function generator and scope here. Point me at the tuning notes and I'll let you know what I see. FWIW, I didn't do any tuning at all - the video is about 5 minutes after I first applied AC power. Don't know if that makes me lucky or just good at following directions. And yes, I'll move the breakout to avoid striking the cables. Is there any reason not to angle the breakout up so that the arcs start higher off the ground?

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Re: First Sparks - Holy Crap!

Postby Alex » Sun Sep 22, 2013 11:31 am

junktronix wrote:Is there any reason not to angle the breakout up so that the arcs start higher off the ground?


No
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Re: First Sparks - Holy Crap!

Postby DJKOR » Sun Sep 22, 2013 5:07 pm

Hi Kevin. To hear you have a function generator and scope is such a good thing to hear. There are quite a few of us here that will find any input you have to be extremely valuable. Your resistance measurement is already about 10 ohms higher than those here that appear to be having issues. We all suspect we have dud secondary coils. In the meantime though, getting the secondary resonance can help us get ours in the right state of tune while we sort out this secondary issue. If you get a chance, the best starting point would b to get a measurement of the secondary coil's inductance.

If you have a multimeter that can measure inductance, could you remove your toroid (try to leave you breakout point as is or remember how far it is sticking out from the toroid) and measure the inductance of the secondary coil? You can do this between the top of the coil and the IEC ground but if you can stick the probe at the base of the coil, that would be even more accurate.

The next most valuable piece of information would be the secondary resonance. A good starting point is here:

Image
download/file.php?id=75

You then start your function generator at about 200kHz and start winding it up until you notice a strong peak in the waveform. Turn it too far and it will drop again. So then turn it back and forward when you reach that point until you get the largest peak.
This was from the site: http://www.hvtesla.com/tuning.html

There is also a video there demonstrating the method. Just a couple of notes though.

- Firstly, don't worry about that wire to represent a streamer. Just have the breakout point on the toroid and do the measurements when it is in that state.

- You may not get multiple frequencies where you notice a peak. That's what I observed anyway, but it makes finding the resonant frequency easier.

- For the connections that say to leave disconnected, connect them to ground/mains ground instead.

- Position your scope probe so it is pointing towards the breakout point. You may need to place it about 1-2 feet away if you can't see much on your scope.

We will be forever thankful for the data you can provide. If your coil has all the figures we are expecting, then some of us unfortunately got a bad batch.
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My build thread: viewtopic.php?f=15&t=998 | 246kHz Primary / 267kHz Secondary
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Re: First Sparks - Holy Crap!

Postby stegu » Sun Sep 22, 2013 9:18 pm

FYI, I got a replacement secondary in the mail a few days ago. It has a resistance of 234 ohms, which is slightly better than the 224 ohms I have for the first one, but the inductance is still only 23.6 mH (compared to 21.5 mH for the original one), so the replacement coil is also off tune by a fairly large amount. Instead of 330 kHz, the new secondary would resonate at 315 kHz. That's 25% higher than the 250 kHz primary, still 15% higher than the desired 275 kHz (10% higher than the primary). I know for sure that 30% detuning (330 kHz) blows the bridge on 50% power. I have tried that too many times already.

It will be very interesting to see your results for the resonance frequency test.

Concerning the inductance measurement: it's quite OK to leave the toroid on and measure the inductance between the breakout point and the ground prong in the IEC connector. The secondary coil has a fairly large inductance, so the stray inductance in the connections done not make a big difference.
Last edited by stegu on Mon Sep 23, 2013 7:07 am, edited 1 time in total.
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Re: First Sparks - Holy Crap!

Postby Bayley » Sun Sep 22, 2013 11:54 pm

Alex wrote:
junktronix wrote:Is there any reason not to angle the breakout up so that the arcs start higher off the ground?


No


Watch out for flashover while doing this, messing with the breakout point affects the distribution of the e-field.
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Re: First Sparks - Holy Crap!

Postby junktronix » Mon Sep 23, 2013 6:30 pm

Bayley wrote:
Alex wrote:
junktronix wrote:Is there any reason not to angle the breakout up so that the arcs start higher off the ground?


No


Watch out for flashover while doing this, messing with the breakout point affects the distribution of the e-field.


I found this out the hard way last night :( The fuse popped, but haven't had time to figure out what else is bad. Does anyone have a digikey link for the tiny fuses? Are people using 10A fuses or something smaller (on the 110V version)?
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