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Registered Member #1807
Joined: Tue Nov 11 2008, 07:36AM
Location: San Luis Obispo, California
Posts: 19
*Thanks MadsKaizer for the help!
I've been wondering if a regulated Mazzilli-based capacitor charger would be practical...and curiosity finally had the better of me. The charger is supplied by a 740maH 7.4V Lithium Polymer battery and regulates the output to 350V w/ about 10V hysteresis. Regulation is accomplished with a Linear Technology LT6703 comparator turning a PFET/Schottky on/off prior to the Mazzilli circuit (simplicity itself!).
The charger isn't as compact as I would have liked but, hey, it worked the first time. When does that ever happen? Charger Circuit
Here's a close-up of the resonant components. The transformer (1:1:17) is on an ETD29 core. The parallel resonant inductor is 6 turns of 0.7in Litz on an RM7 core. Cores are 3C90. Mazzilli Resonant Circuit
I crunched some simulations in LTSpice IV that proved extremely helpful in the charger development. The screen shot shows a typical simulated drain waveform. Since the resonant characteristics of the Mazzilli appear to change as the capacitor voltage increases, it's tricky to judge how close sims and real life match up...here they are anyway. Simulated Drain Waveform Hardware Drain Waveform
The test capacitor is 400V, 470uF (verified by an impedance bridge). Test Capacitor
Scary battery! The battery is only 9.5 x 33 x 55 mm. Yet it's spec'd at a devastating 29.2A peak discharge current. You can see a fuse holder in series w/ the battery. Funny to think that a 20A fuse is kinda small for a battery smaller than a pack of gum! Scary Battery!
Next scope shot is the cap voltage. At nominal input voltage, it takes about 500ms to charge the test cap. If the cap is fully charged, it's holding about 29J. 29J/500ms is about 60W out. Not too shabby.... Capacitor Charging Waveform
And the mess of alligator clips and test leads is the test setup. Test Setup
Next step is to carve out some time for a coilgun/ETG/...etc!!!
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Mazzilli Capacitor Charger
