Sunday, January 9, 2011

Check it out: I'm not making progress!!

I've made an obvious mistake. I assumed that I'd just need to downsize the caps and the pulse of power would be shorter. I failed to consider the obvious problem that inductance controls the rise time. I'm simply not rising the amperage fast enough. Even smaller caps won't speed things up.

Of course, I discovered this after installing smaller and smaller caps. It'll do about 55m/s but no faster.

You can see the waveforms in the attached pictures. The red one is where the cap is at 600uF. The blue is when I put 2 600s in series to cut their capacitance. Clearly we go from 1ms to 500us as expected.

There are a couple options at this point.
* Lead the munition - Fire well in advance of it's arrival. When it does get there, it'll change the inductance of the coil and hopefully absorb most of the energy in it, cutting the flow of current from the cap.
* Force the SCRs down - Lead the munition but then fire a dump scr to drain the energy when the munition arrives.
* Rebuild the barrel with lower inductance on the later stages - With lower inductance, we'll reach peak amperage faster and I'll still be able to use small caps and fire at the time.

Of course, doing #1 and #2 don't require rebuilding a big portion of the machine so I'll do those first.

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