Author Topic: Is this going to work very well  (Read 260 times)

Offline thedoc298

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Is this going to work very well
« on: September 29, 2019, 06:43:34 PM »
Both tesla programs recommend a 27nf cap for srsg. How is that to work using 15000/60 or 15000/120 as it is not enough to charge the capacitor fully. 33.75 ms

would it be better to use a smaller cap that can be charged fully in 120 bps time frame

Why use a cap that can only be charged to 70 percent using 15000/60, don't this kill proformance...? Or you get what you get...

Mabe just need to get a pig.

Offline MRMILSTAR

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Re: Is this going to work very well
« Reply #1 on: September 29, 2019, 10:37:20 PM »
The SRSG will fire regardless of the capacitor size and charge due to the transformer output being shorted across the gap as the SRSG electrodes align. This will establish a plasma path for the capacitor to discharge through if it doesn't fire on its own charge voltage. This assumes of coarse that your transformer has a sufficiently high voltage to bridge the spark gap. 3 KV/mm is a good rule-of-thumb.

Perhaps you are referring to this parameter in JAVATC: "SRSG LTR Cap Size". If so, this is NOT a required capacitor size for primary circuit resonance. You can use any capacitor value that is convenient for that. LTR stands for "Larger Than Resonant". Due to their fragile construction, NSTs can be destroyed by a resonant condition (not the same as the primary circuit resonance frequency) between the NST secondary coil and the capacitor. I can't see your JAVATC design but the 27 nF that you refer to is probably the LTR capacitor size for a SRSG. This is an ideal size to avoid that NST-capacitor resonance condition and to yield maximum output. Its just a guide line. You can use other values. You can read a detailed explanation of LTR on Richie Burnett's web site or elsewhere (pupman.com).

You will get an output, though maybe no streamers without a break-out point, even if your capacitor is not fully charged. It is better, but not necessary, to have your capacitor sized so that ideally it would be charged close to 100% at the beginning of each bang. This is because streamer length is based on energy per bang. The energy in the capacitor is determined by the following equation:

E = 0.5 * C * (V**2)

Since the energy is related to the square of the voltage but only linearly with the capacitance, it is better to trade off slightly smaller capacitance if a larger charged voltage can be accomplished. In other words, a slightly higher voltage has a much bigger effect on energy than a slightly larger capacitor. You can experiment with this relationship in JAVATC.

FYI, I have my capacitors sized (45 nF) to charge to 95% at the start of each bang at 240 PPS. My power supply is a 14.4 KV pole pig current-limited to 27 amps. I don't have to worry so much about LTR size because pole pigs are much more robustly built than NSTs.

Your NST should be fine. Use a 60 ma one if you have it. It will charge the capacitor faster.
« Last Edit: September 29, 2019, 11:37:45 PM by MRMILSTAR »
Steve White
Cedar Rapids, Iowa
Retired electrical engineer

Offline thedoc298

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Re: Is this going to work very well
« Reply #2 on: September 29, 2019, 11:49:18 PM »
The SRSG will fire regardless of the capacitor size and charge due to the transformer output being shorted across the gap as the SRSG electrodes align. This will establish a plasma path for the capacitor to discharge through if it doesn't fire on its own charge voltage. This assumes of coarse that your transformer has a sufficiently high voltage to bridge the spark gap. 3 KV/mm is a good rule-of-thumb.

Perhaps you are referring to this parameter in JAVATC: "SRSG LTR Cap Size". If so, this is NOT a required capacitor size for primary circuit resonance. You can use any capacitor value that is convenient for that. LTR stands for "Larger Than Resonant". Due to their fragile construction, NSTs can be destroyed by a resonant condition (not the same as the primary circuit resonance frequency) between the NST secondary coil and the capacitor. I can't see your JAVATC design but the 27 nF that you refer to is probably the LTR capacitor size for a SRSG. This is an ideal size to avoid that NST-capacitor resonance condition and to yield maximum output. Its just a guide line. You can use other values. You can read a detailed explanation of LTR on Richie Burnett's web site or elsewhere (pupman.com).

You will get an output, though maybe no streamers without a break-out point, even if your capacitor is not fully charged. It is better, but not necessary, to have your capacitor sized so that ideally it would be charged close to 100% at the beginning of each bang. This is because streamer length is based on energy per bang. The energy in the capacitor is determined by the following equation:

E = 0.5 * C * (V**2)

Since the energy is related to the square of the voltage but only linearly with the capacitance, it is better to trade off slightly smaller capacitance if a larger charged voltage can be accomplished. In other words, a slightly higher voltage has a much bigger effect on energy than a slightly larger capacitor. You can experiment with this relationship in JAVATC.

FYI, I have my capacitors sized (45 nF) to charge to 95% at the start of each bang at 240 PPS. My power supply is a 14.4 KV pole pig current-limited to 27 amps. I don't have to worry so much about LTR size because pole pigs are much more robustly built than NSTs.

Your NST should be fine. Use a 60 ma one if you have it. It will charge the capacitor faster.

I just have never noticed the charge voltage not at 100 percent, I thought in my mind I had seen that my cap had time to multi charge to full in in the 4 ms period but the math showes different. Thanks again for the reaffirm. I need about 200ma to get to 100 percent. will buy a pig soon, found several. Need to buy some pole climbing gear.

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Re: Is this going to work very well
« Reply #2 on: September 29, 2019, 11:49:18 PM »

 


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