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Registered Member #2416
Joined: Sun Oct 04 2009, 04:23AM
Location: Oceanside, CA
Posts: 91
Hello all. I hope you'll humor me and answer a few of my surly trivial questions. Personal research has only go me so far. All help is greatly appreciated.
I'm currently planning out my next TC project and I would like to use a Synchronous Rotary spark gap. I've planned it all out in Java TC and I noticed that the LTR capacitor size for the rotary spark gap is larger than the LTR cap size for a static gap. Why is that? Why would the capacitor size be dependent on the spark gap configuration? Most of the sources I've read on the subject agree that LTR caps (resonant size * 1.6) is the way to go for NSTs to avoid resonant rise. So how is JavaTC calculating this larger LTR value for a SRSG? Is it important to adhere to that value or is just LTR okay? Should the rotary spark gap come into presentation at the end of each half cycle, or at the peak of each half cycle? How do I calibrate the electrodes relative to the poles in the motor? In other words, how can I be sure the electrodes come into presentation at the correct time? I hope that makes sense.
Secondly, I'm struggling to find an appropriate Synchronous motor with salient poles. I found this one on eBay but I'm not sure if it has fixed poles.
Registered Member #2416
Joined: Sun Oct 04 2009, 04:23AM
Location: Oceanside, CA
Posts: 91
Okay, thanks for the information. But why then is that LTR value larger still for sync gaps?
Kevin Wilson's guide has this formula for the primary LTR sync cap size: C = .83*((I/2f)/V) Which is essentially ~2.6 times the resonant cap size after you rearrange it a bit.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
A static gap fires any time its breakdown voltage is exceeded, but a rotary gap only fires when the electrodes come together. So a rotary gap can fire stably at twice the line frequency, but a static gap ends up firing somewhat chaotically. I think Terry Fritz found that it worked best at an average firing rate of around 200Hz, which implies a smaller capacitor value for the power source to charge it at the higher rate.
Electrode presentation is usually tuned by trial and error, using some combination of a rotatable motor mount and/or John Freau's phase shifter.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
I stick with 1.4. I've smoked enough NST's at this point that I trust my own calculations.
I wanted to ensure that terminal current was maximized for a given amount of power, which is to say loaded at the rated current and not exceed that by too much, or else the voltage will droop substantially. The power throughput is essentially an inverted parabola, so you want to maximize the power per unit capacitence.
If you can extract the parameters of your transformer you can figure out its equivalent circuit and go from there.
Normal power factor is usually about 0.86 or so, so that should help you a bit in your calculations, and the wiki has an article on transformer calculations.
Registered Member #2416
Joined: Sun Oct 04 2009, 04:23AM
Location: Oceanside, CA
Posts: 91
Thank you for the advice guys. I'm currently studying transformers and power systems in my undergraduate course so these topics are on the boarderline of my understanding. But I think I follow what you're saying.
As far as my design goes should I stick with JavaTC for determining the size of the synchronous SG capacitor?
Does anyone know if those Oriental motors have fixed poles?
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LTR Cap for SRSG Tesla coil size?
