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Registered Member #3824
Joined: Sun Apr 10 2011, 08:29PM
Location: Edmonton, Alberta, Canada
Posts: 54
Hello there, So I lit up my coil for the first time today and it did a whole lot of nothing. My setup: power supply: 2 MOTs in series 12kV full wave rectifier 1.5uF electrolytic cap in parallel.
The rest: 5 MOT secondaries in series w/ primary shorted. 30kV de-q-ing diode. 17nF tank crappy rotary spark gap
So I have measured the voltage at the output of the rectifier with the electrolytic cap in parallel connected and it is the proper output voltage (~5.5kV). BUt, when I connect the rest of the circuit (the MOT inductors, diode and cap), the voltage drastically decreases at the output of the rectifier to a couple hundred volts at 120V input, and nothing happens.
I haven't a clue what could be wrong. Please shed some light if you have any, 4hv detectives.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Ed -
How about providing some more info, and some photos?
1. "1.5uF electrolytic cap in parallel" In parallel with what? The output of the bridge rectifier? Specifically, what kind of capacitor is this? What is its voltage rating? Assuming that your MOTS are each putting out at least 2.5KV RMS, your filter/reservoir cap should be charging to the peak voltage (~7KV). Are you sure that you have these transformers phased correctly? How did you measure the 5.5KV output?
2. "17nF tank" I assume this is your tank capacitor. Again, what type of capacitor is this? What's the voltage rating?
3. "30KV de-quing diode" Describe this diode. Voltage and current ratings? Commercial diode, of home-made MMD?
4. What's happening at your RSG when you apply power to the MOTS? What's the TOTAL spark gap length in the RSG?
Registered Member #3824
Joined: Sun Apr 10 2011, 08:29PM
Location: Edmonton, Alberta, Canada
Posts: 54
Hey, sorry I cannot provide photos I don't have a camera and my cell phone doesnt connect to my computer.
But by any means I will try to explain this as best as possible:
So, my setup is DC resonant charging.
Rectifier: 12 x 1n4007 diodes in series with 1mohm resistors across each one.
"ripple reducing" electrolytic cap: 14 x 450V 0.22uF with 1mohm resistors across each one. I tested the output votlage with a multimeter at 10V in and got about 390V. Yes, the MOTs seem to be phased correctly as this setup gives me the highest output.
Inductor: 5 MOT secondaries with a total series resistance of 450 ohms. primaries are shorted but I do not know how much inductance.
Diode: 30 x 1n4007 diodes with 1mohm resistors across each one. When I measure the diodes with a multimeter for continuity I get an open circuit? but the same with my rectifier and that I know works for sure, so ??
Tank: 2 series stacks of: 20 x 940C 0.1uF 2000VDC caps 1 series stack of: 20 x 940C 0.15uF 2000VDC caps. These are all in parallel for a total of 0.0175uF at 24kVDC.
Spark gap: what I have done is used a microwave fan motor and attached a thin piece of aluminum stock to the shaft. Then, I have a plate with 12 stationary electrodes. Instead of a gap, I use some very thin copper strands as brushes that contact each electrode when it goes around. Although, I should be seeing at least some arcing from this, and I am not.
The electrolytic cap is in parallel across the rectifier. The inductor and diode are in series. At this point I have my spark gap in parallel then my tank circuit in series.
So, when I disconnect everything after the ripple cap the voltage across the ripple cap is ~5.5kV. But, when i connect everything else, the voltage takes a dive and nothing happens. I tested my rotary by putting it across the cap but there were no sparks. Not sure why, maybe the voltage is too low to spark over without the inductor doubling the voltage.
But regardless, I cannot seem to find the problem and have been troubleshooting for hours.
Registered Member #3885
Joined: Sun May 15 2011, 12:47AM
Location: Newton, Massachusetts, United States
Posts: 94
Can you post a schematic as well as some pictures of your setup? I think it would be easier for us to understand your problem if we saw exactly what you are working with.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Ed -
If one of your diodes was open (or you had a defective solder joint at a diode), you might see symptoms similar to those you describe. The reservoir cap would charge to a voltage somewhat less than expected through the 1 meg resistor across the open diode. However, the power supply would not be able to provide any useful current to the tank circuit.
If you are using quality diodes, there is no need for the "equalizing" resistors. Get rid of them, and it will make it easier to troubleshoot your diode strings. I think your 1A diodes are marginal for a MOT-powered system; I'd recomend using 3A or even 6A parts.
Registered Member #3824
Joined: Sun Apr 10 2011, 08:29PM
Location: Edmonton, Alberta, Canada
Posts: 54
Update: Got it working! Will post video soon. Got about 1 1/2 - 2' sparks from it.
Now, I will be running this coil at my work soon with a very valuable server located in the next room. What kind of protection devices would I require?
I am thinking a solid, separate RF ground to my secondary. Would a Faraday cage be necessary?
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DC resonant troubles
