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*To*: Tesla Coil Mailing List <tesla@xxxxxxxxxx>*Subject*: [TCML] QCW sparks*From*: Steve Ward <steve.ward@xxxxxxxxx>*Date*: Sat, 28 May 2011 21:36:37 -0500*Delivered-to*: teslaarchive@xxxxxxxxxx*Delivered-to*: tesla@xxxxxxxxxx*Dkim-signature*: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:date:message-id:subject:from:to :content-type; bh=ebJcHYnpo7JvF9HA0IpP+YLv7SPGQNW81aclNO6IRIA=; b=i4Bb4gc6QMihfnxWyCIPmYz+IbzgMlJJp8Z7Kz1pBCsoeE4a8dXubWlogFwHGg4GN3 32pWAvyrn4B73jEdR8bOKkb4EPb7xNW6aq8mtgp2p5BUizbP4ZacCzSK5dah5NIb1Lyg E2FJqF1isZmRae75vl6ukWVRxyPe4KTKEC6us=*Domainkey-signature*: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:date:message-id:subject:from:to:content-type; b=ZVLbDRHfPFAk4X7gqlOmtYZs1O0sHBW8QDXln1z9TmmrtI0vmqEohjOiTGlTgykrho H6rPyuCjm2Z2bKTS8Rv3dqSMr/JMl8jQrhbWLQnZw3JU7vaMPm0U9h4s/iu/hGJNTGfS a7Ym++rFf5GcDJRCcrDR7FB/4busKrqeDP64o=*List-archive*: <http://www.pupman.com/pipermail/tesla>*List-help*: <mailto:tesla-request@pupman.com?subject=help>*List-id*: Tesla Coil Mailing List <tesla.pupman.com>*List-post*: <mailto:tesla@pupman.com>*List-subscribe*: <http://www.pupman.com/mailman/listinfo/tesla>, <mailto:tesla-request@pupman.com?subject=subscribe>*List-unsubscribe*: <http://www.pupman.com/mailman/listinfo/tesla>, <mailto:tesla-request@pupman.com?subject=unsubscribe>*Reply-to*: Tesla Coil Mailing List <tesla@xxxxxxxxxx>*Sender*: tesla-bounces@xxxxxxxxxx

Greetings, First, a bit of rambling: I recently obtained a Jennings vacuum capacitor voltage divider. While i could not find a manual for it, i did see mention of it on the Jennings site as being rated for 50kV peak and 60hz to 30MHz. I did my own calibration with a 40khz AC source up to 5kVpk or so, and found the division ratio to be right at 800:1 for this unit, i may look for more ways to verify this later as its important, but for now i at least have relative data to compare. The Jennings website mentioned ~600:1 for this unit, so i have some uncertainty. I'll go with 800:1 since it gives what should be "worst-case" voltages. So what have i done? Well ive been working on this "QCW" (quasi-continuous-wave) DRSSTC. The power supply is unique in that it can ramp the bus voltage to the DRSSTC from ~30V (enough to reliably start oscillation of the tesla coil) to 300V, basically a high power arbitrary wave-form generator feeding the H-bridge drive of the tesla coil. I discovered that keeping the Fres of the system suitably high (> 300khz), and providing a linear ramp in supply voltage over 10-15mS could grow extremely long, straight, sparks compared to the size of the coil (best is 65" sparks from a 9.25" length winding of 30awg). The top voltage was suspected to be low because of the lack of flash-over between primary and secondary, and because of the small 2" minor diameter of the toroid. http://www.flickr.com/photos/kickermagnet/4386617170/in/photostream So finally i made some measurements! So far what i see is the top voltage ramps quickly to about 45kV, at which point the breakdown process begins. The secondary base current is about 1.76A pk at this point. From here it takes relatively little extra voltage to grow sparks up to 4 feet long, i measure just 56kV! The base current is just over 3A at this point, which means the secondary current is growing faster than the voltage, so the spark impedance is going down over the 12mS pulse. Waveform can be seen here: http://www.flickr.com/photos/kickermagnet/5770183734/in/photostream Further pictures of the setup can be browsed from my home page: http://www.flickr.com/photos/kickermagnet/ Im not 100% sure what to make of it yet. The explanation i like to give is that its a "self-stretching arc". If you consider the arc length you can stretch from a 15kV transformer (many feet if there is enough current... say 2A), then the fact that this tesla coil functions at relatively low voltage, yet still producing long sparks, makes sense. The spark just takes a loooooong time to get to that length. Another interesting point is that the top voltage is a lot lower than V = IZ would suggest for a lumped model of my secondary coil. Basically, the secondary is ~25mH, and with 3Apk current through 25mH at 325khz, id expect a peak voltage of 153kV. The only way i can account for this large discrepancy in apparent impedance of the coil is that there must be significant capacitance from the secondary to primary, so the base current looks much larger compared to say, the toroid current. I'd like to next work on measuring the current between secondary and toroid and see if it is consistent with my voltage measurement claims. The fact that the 50kV probe hasnt shown any signs of stress makes me think that the voltage really isnt 150kV, but really is more like the 56kV i claim. The next step will be to measure the ramp voltage and work on a spice model to determine the streamer impedance. Thoughts? Steve _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla

**Follow-Ups**:**Re: [TCML] QCW sparks***From:*Aron Koscho

**Re: [TCML] QCW sparks***From:*Bert Hickman

**Re: [TCML] QCW sparks***From:*Jim Lux

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