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redruM69

Tue Jan 27 2015, 05:28AM

Registered Member #31557 Joined: Tue Aug 06 2013, 02:38AM
Location:
Posts: 58

skyler wrote ...

I have gotten the primary and secondary to resonate at the same frequency, first the primary was a bit high in frequency, but we added some extra coil, and they are both somewhere around 100khz.

4" coil, 4' high, 10" topload, 24awg ~154khz
With a 24nf cap, you'll need about 9-12 turns on your primary.
2 beer bottles is not 24nf. Each bottle will give about .5-1nf. So you're not even close. You'll need to build about 24 of em if your goal is 24nf
How many electrodes are on your RSG rotor?
Again with 4 MOT's?? We keep saying that is TOTAL overkill for a 4" coil but you keep ignoring us. 2 is MORE than plenty for that coil

Sigurthr

Tue Jan 27 2015, 12:11PM

Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597

Without seeing clear, focused, shots of the build in question all I can offer is general causes of issues.

1) Losses.

You need to minimize wire lengths between all points. Having heavy gauge wire isn't enough by itself. Reducing an extra ten inches of wire can have a tremendous impact in efficiency.

2) Ground effectiveness.

Lots online about good RF grounding, it isn't hard to find either since Hams (amateur radio) are well versed in it.

3) Environmental factors.
I recently had a student build a SGTC only to have disappointing results. It turns out his run environment was way too small and conductive for his coil. As a result it artificially detuned the secondary resonator and robbed it of most of the incoming power. Upon relocating to the driveway with a proper RF ground he found he was ~90KHz too high on the secondary. Fixed it and doubled the output.

skyler

Wed Jan 28 2015, 12:07AM

Registered Member #42712 Joined: Fri Jan 10 2014, 01:21AM
Location:
Posts: 21

Thanks. First, here is a shot of the coil in operation:

Kolas

Wed Jan 28 2015, 12:50AM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

Don't loose hope! My first coil was ugly but it did work. And as long as you don't have carbon racing through your secondary, your losses wont add up to your power input.
Your biggest issue is probably within your resonant charging technique.
8900 or whatever volts is plenty to fire through a spark gap. Especially a rotary style gap. Also short output is probably indicative of tuning to a
Fo that is too high in the primary. once spark outbreak occurs, the capacitance of the streamer becomes quite sizable. Be sure to tune (theoretically) about 5-10% below the resonant frequency of the secondary and topload to cause the secondary to be most effective under load.
Bottle caps are definitely terrible. Fact
The dissipation of glass at your frequency is high. any yet it will still work!
Take pictures of what you have currently and I'm sure that ppl will be able to offer specific advice.

skyler

Wed Jan 28 2015, 02:36AM

Registered Member #42712 Joined: Fri Jan 10 2014, 01:21AM
Location:
Posts: 21

Here is a video of how we found the resonant frequency of the primary. We used an oscilloscope and a square wave generator and found that the resonant frequency with the extra wire we just added to the primary was at 80-90khz ish.

Here is a video of the general setup we had going on. Notice how much chicken wire we put for ground. For the power supply, we are using a 5th MOT as a ballast.

In this video, I am testing the resonant frequency of the secondary using a sine wave input on the bottom and using a probe at a distance to watch the voltage climb on resonant frequency.

Here is a picture of the rotary spark gap with the tungsten rods

Wcd2c7

Hazmatt_(The Underdog)

Wed Jan 28 2015, 04:46AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

You guys are doing a great job! I bet you're learning a lot too!

For the Primary, 10 turns should be fine, I realize that's going to throw everything off, but 10 turns spaced equally will work out for you better then 40 turns closely spaced.

That will raise the frequency of course, but you can some capacitence to the top of the coil and primary and get back in tune, or close enough to tap it.

Also, good solid connections with heavy wire really is key here. any loose connection = loss. Thin wires = loss, and long wires = loss.

Remember that every inch if wire in your primary circuit, IS inductance, that means it literally is the tank circuit, not just your primary coil. That also means that every inch of wire that is not part of the primary is radiating energy that is being lost to space, and not your primary tank circuit, so it's not feeding the coil.

Also, if you're close to the coil, your proximity to it will de-tune the coil, so when making precision measurements, try to be at least 4 feet away.
If you get it tuned sharply enough, you can actually see the effect of proximity on the scope. Tune it for resonance and get your hand near, and you will see the amplitude diminish, it's pretty neat.

Keep up the good work!

Kolas

Wed Jan 28 2015, 07:09AM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

indeed, to get a lower primary resonant frequency, you will need a larger tank capacitor. you've got too many turns.

skyler

Wed Jan 28 2015, 05:07PM

Registered Member #42712 Joined: Fri Jan 10 2014, 01:21AM
Location:
Posts: 21

Can you guys tell us anything we need to test to give you more data on troubleshooting? We can test a bunch of stuff, and try to troubleshoot.

loneoceans

Wed Jan 28 2015, 06:39PM

Registered Member #4098 Joined: Fri Sept 16 2011, 09:26PM
Location:
Posts: 236

skyler wrote ...

Can you guys tell us anything we need to test to give you more data on troubleshooting? We can test a bunch of stuff, and try to troubleshoot.

I looked through your videos. Here are some comments.

It looks like the way you measured the secondary frequency is correct (i.e. signal generator fed in the bottom of the secondary coil, and use a wire on the scope probe placed near the coil to pick up the radiated signal, and adjust the signal gen until you get max output).

I'm not very sure what you're doing to measure the primary circuit. To measure that, short your spark gap. This will make your primary coil and capacitor connected together at both ends. Scope across the two ends of the primary coil. For the signal generator, attenuate the signal by putting a ~5 to 50k resistor on the output of the signal generator, and place that also across the primary coil. Adjust the frequency until you see the largest amplitude. You should set this to be about 5 to 10% lower than your secondary frequency.

It looks like you really need to work on your wiring. Everything looks like it's connected with crocodile clips (these usually have very very thin wire), and are very long. Please put some effort in getting some good wire (I use 8 AWG for my 4 MOT coil for all primary connections and even that's not really good enough). So the wire that connects the capacitor to the primary coil and the coil / capacitor to the spark gap needs to be not only short, but thick, and terminated properly with proper crimp terminals. You can't cheap out and just use 18AWG wire here. I'd recommend putting these components right underneath the coil. Same goes for your spark gap - you've just wrapped thin, bare, wire around the tungsten rods with no positive contact. That's not going work at all.

You should align the two stationary electrodes of your spark gap differently. The current configuration will cause the rotor to be near the electrodes for a significant amount of time, which can lead to the MOT simply shorting out and not sending power to charge the capacitor bank. (i.e. poor quenching).

Your primary coil looks a bit.. dangerous. I'd try to adjust it to make it nice and rounder so it doesn't have pieces of tape separating turns. Ideally you should make more supports for them as well. 8kV from the MOT stack can short through the wooden primary table if it has any sort of moisture in it. You also cannot simply use crocodile clips for your primary connections. It needs to be a solid, beefy connection. Please put some effort into this.

How is your capacitor bank made? Are they filled with glass bottles inside? Or are they simply made of the big plastic buckets? Did you make sure that all the connections inside are proper (electrically speaking?). I actually disagree with Kolas - glass capacitors actually work really well. You just need to build them properly. Can we have a closer look with photos of your capacitor? You might need to make a better one.

Feel free to see how I made my 4-MOT coil here:

Finally, I think a bigger toroid will also work, and look better. :) To conclude - you can't just slap together some wires and expect the coil to work. Put some care and thought into making the coil, otherwise you'll only reap the results of what you sow.

Hazmatt_(The Underdog)

Thu Jan 29 2015, 02:14AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

For my latest build I'm using very heavy connections, hahah 3/8" copper!

And it goes underneath the coil, and all the connections are very short.

I realize that it will be hard with your bucket configuration to keep the leads short, and get the buckets close, but try.
You might need some 8AWG "welding" cable or something heavy to make good connections, or if possible, get a large
tub to put the required cap bank in rather than the buckets, and get everything in one place.

Don't worry if your coil doesn't look perfect, they evolve over time and with experience.

My first coil was a horrendous mess, and wasn't even close to being correct. My secondary had like 50 turns of 18 AWG wire,
and it was not even close. So keep up the good work guys! and keep learning.

Here's a pic of a coil I'm building for a customer

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