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Uspring

Fri Oct 03 2014, 03:17PM

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

So my question is - How do you calculate the poles of a system with differing primary and secondary frequencies (not sure if I missed out some first order equation somewhere otherwise I'll just model it), and why would there be a tendency for the system to go to the higher pole?

fuppperpole=sqrt( (fpÂ²+fsÂ²+sqrt( (fpÂ²-fsÂ²)Â² + 4*kÂ²*fpÂ²*fsÂ² )) / (2*(1-kÂ²) )
flowerpole=sqrt( (fpÂ²+fsÂ²-sqrt( (fpÂ²-fsÂ²)Â² + 4*kÂ²*fpÂ²*fsÂ² )) / (2*(1-kÂ²) )

Arc loading will make the secondary fres drop from the above the primary fres to below it. Probably that won't make the system switch poles. But it does make a difference when you start ramping up. You usually ramp up on the pole that is closer to the primary. When fp and fs are close during rampup there will be some beating as both poles are excited.

zzz_julian_zzz

Sat Oct 04 2014, 03:10AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

hi loneoceans, can you give us the specs of your coil ? :) such as dimensions, impedance of Sec and Pri, igbt used? and why you don't run it on bigger Vin? Thanks!

zzz_julian_zzz

Tue Oct 07 2014, 10:49AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

Goodchild wrote ...

Your primary current waveshape is very intriguing. With a linear ramp on the input, my geuss is that your system impedance is low enough to start showing it's true nature. Normally you see a "close to linear" response of the primary current envelop with a linear change in modules voltage. This exponential growth of the envelop I bet is alway why you are seeing more branching than normal than with most other QCWs.

To Eric, What is the "advisable" level of primary impedance that will make these primary current envelop to be a more linear looking waveforms?
how do you compute for this impedance? Z=sq(L/C) ?

because I've set my QCW to about 70-80 ohms primary impedance and still getting branch sparks/drastic primary current waveform (please see my video)

My coupling here is about 0.4 , primary tank of 5-9nf (the bigger the capacitance the larger the current)

I saw your QCW videos, and yes I admire your results, very straight sparks indeed! just wondering if you could share some thoughts to make QCW sparks limited to only 1 straight spark.

Thanks in advance

Happy coiling to everyone :)

loneoceans

Tue Oct 07 2014, 05:14PM

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

Goodchild wrote ...

Very nice QCW build, I also love your photography.

Your primary current waveshape is very intriguing. With a linear ramp on the input, my geuss is that your system impedance is low enough to start showing it's true nature. Normally you see a "close to linear" response of the primary current envelop with a linear change in modules voltage. This exponential growth of the envelop I bet is alway why you are seeing more branching than normal than with most other QCWs.

Great build can't wait to see more.

Thanks for the comments :) I've been a bit busy recently so I haven't had time to play with the setup a bit more, but looks like lot of new things to investigate. Just a short post here to answer some questions.

zzz_julian_zzz wrote ...

hi loneoceans, can you give us the specs of your coil ? :) such as dimensions, impedance of Sec and Pri, igbt used? and why you don't run it on bigger Vin? Thanks!

My current secondary coil is 3.5 x 5.5 inch wound with AWG 32 wire with a 8 x 2 inch toroid for a frequency of about 400kHz. One of the reasons why I suspect that my coil is making those perpendicular branched sparks might be because of the frequency (runs at the upper pole so it's around 450khz at the moment). I recall Steve ward doing a test at about 500kHz and the spark with perpendicular branches looks very similar. I plan to wind a new secondary with a lower frequency of about 300kHz to test out what effect frequency has on spark appearance, though looks like going even lower frequency to say 280 or less leads to less straight sparks. Another reason is probably because of my small toroid as well as the high non-linear current ramp.

I'm using the IRGP50B60 Warp2 IGBTs from IR. They seem to hold up very well. MMC is 12.8nF Mica, primary has inductance of 11.7uH. The reason why I didn't use a higher voltage was mostly because I'm using full-wave rectified 120V giving me about 170V on the bus. I did test my buck originally with a voltage doubler through a resistor at about 300V or so, but I can't run that in QCW mode because I run out of capacitance, so I just changed to FWR. But I just got a 240V transformer. :) Also great job getting it to work zzz_julian_zzz! I think we need more information to help you out there.

Also to Eric - I recall you were working on a big QCW? I think you called it the 'HOG' or something like that. Is that still in progress? I think everyone would like to see that going :)

Finally, after a lot of writing, I've a draft of my QCW 1 page written up here:

Hope you guys find it useful, and I'll be continuning to add more information. Please feel free to drop me a note if you find any mistakes I might have, and let me know if you thought the page was useful. :)

Uspring

Tue Oct 07 2014, 07:08PM

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

zzz_julian_zzz wrote:

current waveform (please see my video)

Hard to see from the video: Is the drop of primary current at the end of the burst due to a loneoceans like bus voltage ramp down? Or does it drop from e.g. arc loading?

zzz_julian_zzz

Wed Oct 08 2014, 10:51AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

loneoceans wrote ...

Finally, after a lot of writing, I've a draft of my QCW 1 page written up here:

Wow! Thanks to this! for me, you've saved a lot of work to do.. haha, i was planning to also share my QCW build too (i dont have website, maybe by just posting here only ) :) mine is a poor man's QCW and easy approach too just like yours.

Your page will help a lot to people like us :)

We have similar setup of the ff:

1. buck converter controller , i borrowed the design from CJK (thanks to him!) although i made some modifications to this.
2. Async buck converter (without the diode of the high side IGBT)
3. we are both learning :D
4. I'm from Philippines so I'm South East Asian too! hahaha

Differences:

1. didn't use a double bridge of IRGP50B60PD1
2. didn't use a fiber optic for ramp isolation
3. didn't use micro-controller for ramp generation (just 555(s) and LM741) - but can modulate PPS, length, peak in real time
-(please see schem below(old), this is not very good design, but enough for my application, producing very linear ramp)

4. didn't use mica caps (just regular cheap MKP - no heating noticed @ 5pps for 3 min run)
5. I used single full-bridge fgh40n60smd (140 amp limit)
6. very high impedance of Primary of 80 ohms due to IGBT limitation
7. did use Eric's design buck control to produce ON interrupter pulse (going to UD) via comparator

I would like to mention some other sources i found over the net, maybe you could check their works too.
barmaley, bsvi, zrg, eric goodchild, cjk, & hvman. thanks to these guys though I was not able to talk with them even via mail :)

happy coiling! again thanks to your page! ;)

1412765498 3964 FT166191 1357002943 51 Ft0 Qcw Buck 1

teravolt

Wed Oct 08 2014, 01:34PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

hi loneoceans thanks for your work, I like your idea about a lower frequency secondary. how low in frequency can we go and still make sword sparks with a QCW

Steve Ward

Fri Oct 10 2014, 09:22PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Its funny, i thought i used to know the recipe for making straight sparks, but it often eludes me on some designs.

In some cases i find the ramp needs to be very slow (long) for a coil to respond well. My newer tesla-gun designs seem to like 20+mS ramps for 5-6 foot straight sparks to form, but even then, MOST of the sparks are not without branches and bends. Ive had other designs that would make sparks in the 5-6 foot long range, with less ramp time (18mS or so), and had a much higher probability of growing without branches or bends. These setups always had bigger toroids.

Here i tried a bigger toroid (and removed the MMC from my secondary) on my gun V2 with good results. Not branchless, but really long and mostly straight:

However, nothing has compared to this experiment/result:

I suspect that the impedances and tuning of the coils plays a role in how much power is transfered to the spark as it grows over time and alters the tuning and losses of the system. My best results have always been achieved using larger 13-16" diameter toroids, and still keeping a high pole frequency of 400-450khz. These coils would shoot branchless sparks most reliably.

zzz_julian_zzz

Sat Oct 11 2014, 12:57AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

Steve,

I am so wondering HOW you guys manage to get a low peak current on the primary given on that output length of about 6 ft?
my coil shoots a meter but having a 120+ Amps on the primary, i doubt that even when my Ipk reach 160 it will produce the same result as yours.
I've researched some russian QCW coils, and as expected, they need about 250-300 Amps to reach 6" sparks.
So what's your Magic steve? :)

May we know that coil's coupling?
Is it phase shifted shared bridge or DC modulated supply?
what's your Bridge's Voltage in?

That vid of yours freaks me out! :D

Uspring

Sat Oct 11 2014, 09:00AM

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

Steve Ward wrote:

I suspect that the impedances and tuning of the coils plays a role in how much power is transfered to the spark as it grows over time and alters the tuning and losses of the system.

Did you compare secondary voltage envelopes? The might differ from primary current shapes. My guess is, that arc style depends only on that and frequency.

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