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Banned on April 7, 2007 Registered Member #277
Joined: Fri Mar 03 2006, 10:15AM
Location: Florida
Posts: 157
Many of you have been kind enough to discuss with me on this board different ideas/concepts for stepping down the HV from a spark gap to LV. Thanks very much. So far, the simple 'Snubber' aka "Buck Converter" in the diagram below that I started out with a couple years ago provides the best results (the red transistor in the diagram is replaced by my randomly firing spark gap, typically 1-3 sparks every 5 seconds). The circuit works decently, however, I need to squeeze just a bit more efficiency out. According to articles listed below, higher efficiency is obtainable if the diode in the circuit is replaced with a suitable 'triggered' Mosfet or Transistor, thus creating a kind of Sychronous Rectifier. This is the part where I admittedly could spend the next six month tinkering/stumbling around trying to come up with the proper trigger circuit necessary to turn on/off a suitable Mostfet or transistor, it's just not my area of expertise, whereas considering the amazing talent present here on this board, some of you could do it in your sleep. I would be very appreciative for any assistance in this part of the circuit. I am even willing to pay a mutually agreeable consultation fee to whichever person helps me get this done (per a written agreement). Thanks in advance. CM
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Did you ever stop to think what inverse voltage rating the rectifier in that circuit needs? If you do think about it, you'll see that it needs to be the same as the breakdown voltage of your spark gap: several kV.
If you think some more, you'll hopefully come to the conclusion that this needs a series string of the highest voltage MOSFETs you can find, with snubber capacitors to equalize transient voltages.
Then you might sit down with the MOSFET datasheet and notice that the parasitic shunt capacitance of this assembly is going to be large compared with the capacitance that you're extracting energy from, hence it's going to end up LESS efficient than a string of low current HV diodes! (SMPS design manuals usually recommend not to bother using synchronous rectifiers for output voltages above 5V, let alone kV.)
In fact, if you thought about this long enough, you might come to the conclusion that your device would never harvest enough energy to pay back its bill of materials cost and its recurring maintenance costs. (Its insulators are going to have to be kept very clean, or the charge will leak away.)
I still think that the "Tesla coil in reverse" idea I proposed has the most chance of working, which is still not very much chance, though.
Banned on April 7, 2007 Registered Member #277
Joined: Fri Mar 03 2006, 10:15AM
Location: Florida
Posts: 157
Steve:
I appreciate the insights of your past posts. In reply to your recent post, yes indeed, I've stopped many times to think and reflect on my project over the last three or so years. One leason I've learned is that sometimes relying strictly on written specifications doesn't actually reflect real world performance. Case in point, I've successfully been using the above Snubber circuit for over a year to reduce KV sparks down to around 3 volts continuous, using one low voltage diode and one low voltage cap in combo with an inductor. The key is selecting the proper value inductor to make this work to keep the LV diode and LV cap from degrading over time. When connected to my novel HV source (patent applied for in Feb 2006, my 3rd patent) the overall system is efficient enough to operate multiple jumbo LEDS continuously, or small motor, and on it's best days, can operate a small fuel cell to produce Hydrogen/oxygen. My system is right on the 'hairy' threshold of being able to operate a fuel cell producing hydrogen round the clock, just a small increase in the snubber circuit efficency should reach the goal. Although what I've done may be counter-intuitive, it works. I continue to thank you and others that can offer helpful advice from time to time. CM
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Triggered Mosfet to increase efficiency?
