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Multi-kVA systems: SRSG vs DC-ARSG

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Kizmo

Sun Jul 13 2008, 08:33PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

Finally i got time to build larger spark gap device. What sort of sparkgap design i should choose when my tank capacitor is now 75nF and it will be updated to +150nF soon and i will be using power levels between 3 to 8kVA. I can easily build any kind of rotary gap but what would you do?

Shaun

Sun Jul 13 2008, 08:53PM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

Well if you can easily build any type of rotary gap I would say go SRSG, since then you dont have to mess with huge inductors and large HV diodes, you just build a regular SGTC, connect the rotary gap, and go.

An SRSG, from what I understand, is much tougher to build because you have to FIND a synchronous motor that big, and get the phasing right, but since that aspect doesn't matter to you, SRSG will enable the rest of the system to be simpler.

But DC-RSG does let you easily vary power levels via break rate...

Kizmo

Sun Jul 13 2008, 09:13PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

Regular SRSG has been in my mind for a while. AFAIK running @ 100bps (50Hz system..) can be tricky but it will give nice results when working correctly. How do you tune these things to match phase?

Shaun

Sun Jul 13 2008, 10:59PM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

IIRC they are tuned into phase with the 50Hz mains by rotating the body of the actual motor! I guess its easier than repositioning the electrodes...

Marko

Sun Jul 13 2008, 11:38PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hi guys, to my current understanding...

Kizmo wrote ...

Regular SRSG has been in my mind for a while. AFAIK running @ 100bps (50Hz system..) can be tricky but it will give nice results when working correctly. How do you tune these things to match phase?

A mains triggered stroboscope is required to see and accurately adjust phasing of SRSG rotor.

IIRC some people have used iron-ballast fluorescent lights, which can produce stroboscopic effect due to their 100Hz modulated output, but due to sine envelope of the waveform view is blurred, and there is a phase shift caused by ballast inductance so output isn't really in phase with mains voltage.

Stroboscope probably shouldn't be too hard to build though (you can even go with LED's instead of xenon flash lamps, especially if you have some of those flash-led's from cell phones).

tesla500

Mon Jul 14 2008, 06:53AM

Registered Member #347 Joined: Sat Mar 25 2006, 08:26AM
Location: Vancouver, Canada
Posts: 106

I've adjusted phasing on a RSGs by scoping the primary of the pole pig powering the coil (after the ballast). The voltage on the primary is a good reproduction of the capacitor voltage, and allows you to see when the gap fires. You can adjust the phasing to get it to fire at the peaks of the waveform, or to make a 240/200bps gap fire with the same peak voltage on each firing.

If you have a stroboscope, that only tells you what your phasing is. You still need to determine what it should be, and it's not something simple like 0 or 90 degrees. The ideal phasing changes with ballast inductance and tank capacitance, so if you vary power to the coil with a variable inductor (like the current control on an arc welder), you may need to come up with a compromise. I found that setting phasing to be optimum at maximum power works OK over the whole power range when using a variable inductance ballast.

Using a variac to vary the coil's power gets around this, as the inductance and capacitance don't change with voltage.

David

GeordieBoy

Mon Jul 14 2008, 02:22PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

Tesla 500 wrote:

I've adjusted phasing on a RSGs by scoping the primary of the pole pig powering the coil (after the ballast). The voltage on the primary is a good reproduction of the capacitor voltage, and allows you to see when the gap fires. You can adjust the phasing to get it to fire at the peaks of the waveform, or to make a 240/200bps gap fire with the same peak voltage on each firing.

I have also done this with good results. It is an excellent method to look at the HV waveform across the RSG and adjust phasing without having to connect directly to the HV circuit. It also gives you a good insight into the voltages that your tank cap, pole pig and RSG are actually seeing with resonant charging.

-Richie,

Kizmo

Fri Jul 18 2008, 04:21PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

So.. it will be SRSG

Now i need to make 100, 200 and 400bps discs :)

GeordieBoy

Fri Jul 18 2008, 04:36PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

Wow! you've removed quite a lot of material off that rotor!!! I hope it doesn't run too hot or loose too much torque.

Kizmo

Fri Jul 18 2008, 04:56PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

It has been running for few hours now and no problems so far :)

It was 3/4hp 1450r/min motor with quite many 'dead poles' and now its beatifully synchronizing @ 50Hz @ 1500r/min (runs VERY smoothly)

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