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Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
That energy from the inductor gets forced into the capacitor after it is already charged to the supply voltage and that characteristic is what makes the system "DC resonant charging" and the diode just prevents that energy from sloshing back as it would naturally in an LC network (the L being the choke and the C being the tank capacitor; and since the filtering capacitor is so large, it is considered a short for the current in this network).
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
10uf is plenty. I would even say it is overkill. I used 3uf for the first doubler stage, and 1.5uf for the second, like this:
Your tank cap is fine, i used 20nf for mine: I could run high breakrate but the sparks where not too long. You should theoretically have longer sparks but limited breakrate. The 940 series should work fine. However, im not so sure you could run 600BPS with this setup while keeping the voltage on the tank cap at it's nominal voltage before firing.
Registered Member #3824
Joined: Sun Apr 10 2011, 08:29PM
Location: Edmonton, Alberta, Canada
Posts: 54
Excellent, thanks for all the input!
Arcstarter wrote ...
10uf is plenty. I would even say it is overkill. I used 3uf for the first doubler stage, and 1.5uf for the second, like this:
Your tank cap is fine, i used 20nf for mine: I could run high breakrate but the sparks where not too long. You should theoretically have longer sparks but limited breakrate. The 940 series should work fine. However, im not so sure you could run 600BPS with this setup while keeping the voltage on the tank cap at it's nominal voltage before firing.
As you mentioned I might be undercharging my 10nF tank cap with a higher break rate, is there a way to calculate the charging time of my tank cap? I have tried before but my derivation became far too complicated (I'm an EE so I might be over thinking things a little bit).
Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
The time it takes to charge your capacitor bank depends on the inductance of your choke and the capacitance of your bank. You have to find the resonant frequency, and then the time it takes to charge the capacitor is half the period of that frequency.
Registered Member #3824
Joined: Sun Apr 10 2011, 08:29PM
Location: Edmonton, Alberta, Canada
Posts: 54
I figured I might as well stay on this thread for this question. I've searched the forums for decent calculations on primary inductor current and I have had no luck. I'm assuming that the current that the tank cap can dump into the primary coil depends on the dv/dt rating of each individual cap. Is this true? As in does the basic equation i = C*dv/dt hold for this circuit? If this is the case, then this is what I have found. Each cap has a rating of 1142 V/uS. Thus, with a capacitance of 17.5nF, my primary tank current should be: i = (17.5E-9 [F])(1142E6 [V/s]) = 20 amps
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DC Resonant charging
