High efficiency for half bridge MiniSSTC?

Brett Miller, Sat May 05 2007, 07:19PM

Hello, I took some measurements yesterday of my half bridge SSTC and was somewhat surprised at the results. I am currently getting 10-11 inch air streamers and 12-13" arcs to ground from this system. The coil is basically Steve Ward's MiniSSTC using a half bridge of IRFP260N mosfets, a pair of UCC's and a remote interrupter.

I started getting much longer sparks after I used this driver to test and get some Fo measurements for the secondary I recently wound for my first DRSSTC. The resonator is 12.5" winding length, by 4.5" long, wound with AWG 31. The primary is 4 turns 10 gauge stranded close wound directly over the Envirotex secondary coating, about 1 inch up from the bottom turn. On top, I have a 6" x 1.75" John Freau toroid, with the old ACR from my 6" distruptive coil as the main toroid. This toroid is 11.75 x 2.75. With this stacked topload configuration, I measured the frequency (by looking at the efield of the running coil on my scope) to be 178Khz.

Here's a video of the coil making the above described sparks via a PRF of around 30hz and an on-time of 2ms:

http://www.hot-streamer.com/brett/misc/12_inch_sparks.avi

With the coil operating in this manner I used a Fluke 30 clamp meter to measure a current draw of 0.7A from the wall at 120V (which is the max voltage I have dared with these 200v mosfets). I thought 84 watts for 1 foot sparks seemed more efficient than the average conventional antenna feedback SSTC. I did notice that increasing the on time produced the expected increase in power draw.

Anyone have any power measurements from their antenna feedback half bridge systems running at low PRF and short On-times? Perhaps I should get a Kill-A-Watt, or equivalent power meter. With my VTTC work, and SSTC work up until this point I have just measured current with an amp clamp and then multiplied...however, I know this doesn't take certain things into account, such as power factor. Now that I have started on the design of my first DRSSTC I will need to hone my quantification skills.

Opinions? I can provide numbers for other interrupter settings if anyone is interested.

-Brett

Re: High efficiency for half bridge MiniSSTC?
Steve Ward, Sat May 05 2007, 08:11PM

The efficiency numbers start to lose perspective unless you give the duty cycle for the coil's operation. In any case .7A is pretty low.
Re: High efficiency for half bridge MiniSSTC?
Brett Miller, Sat May 05 2007, 08:26PM

Steve,

I gave the PRF plus Pulse width...30 and 2ms respectively. I figured everyone would derive the duty cycle from that. In fact, wouldn't that be a 6% duty cycle?

But yeah, 84 watts seems close to the numbers you show in your DRSSTC 0.5 page...however, I am sure if we substituted my 12.5" winding length 4.5" diameter secondary into your .5 driver, it would give much longer sparks at 84 watts.

-Brett