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Uspring

Fri May 17 2013, 09:35AM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
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Posts: 711

Dex wrote:

assuming ~15ms ramp,and 60 kW peak power with linear rise of input power that would give:

W ~ 60kWÃ—15ms/2 = 450 J

If zrg ramps up voltage linearly, power consumption would rise much more steeply, more like V^4. So the total energy would be much less. If he'd use shorter bursts, the bang energy would be even less, probably at the cost of having the nice swordlike sparks.

generating 7' long sparks in normal atmosfere with less than 100 kV top voltage is an amazing.

Interesting info. Where did you get that from, I couldn't find a source?

Steve Conner

Fri May 17 2013, 10:06AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Bang energies of several hundred joules are the norm for QCWs.

Steve Ward measured the topload voltage of his QCW with a high voltage probe, and got an answer of about 50kV.

Due to nonlinear streamer loading, the inverter looks somewhat like a constant current sink to the DC bus. So a linear ramp in voltage implies a linear ramp in power too.

dex

Fri May 17 2013, 10:27AM

Registered Member #2566 Joined: Wed Dec 23 2009, 05:52PM
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Posts: 147

Uspring wrote ...

Dex wrote:

assuming ~15ms ramp,and 60 kW peak power with linear rise of input power that would give:

W ~ 60kWÃ—15ms/2 = 450 J

generating 7' long sparks in normal atmosfere with less than 100 kV top voltage is an amazing.

Interesting info. Where did you get that from, I couldn't find a source?

ok,maybe less but not much less.

for excersise,let's assume both current and voltage rise in a linear fashion (and this isn't very true for current i guess).
we would have:
i(t)~Im*t/Tr
u(t)=Um*t/Tr

P(t)=u(t)*i(t) *tÂ²/TrÂ²=Pm*tÂ²/TrÂ²

W=âˆ«Pm*tÂ²/TrÂ² dt=(Pm/TrÂ²)âˆ«tÂ²dt

since we integrate from t=0 to t=Tm ,the result would be:

W=Pm*Tr/3=60*15/3= 300J

Steve Conner wrote ...

Bang energies of several hundred joules are the norm for QCWs.

Steve Ward measured the topload voltage of his QCW with a high voltage probe, and got an answer of about 50kV.

Due to nonlinear streamer loading, the inverter looks somewhat like a constant current sink to the DC bus. So a linear ramp in voltage implies a linear ramp in power too.

if i remember correctly ,he has reported something like 60 kV for 5' spark?

teravolt

Fri May 17 2013, 08:01PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

Steve said he grows the spark. If the voltage is only 50 to 60kv then the spark has to be all current to get that long. It is reasonable to asume the spark length is reflective of how much energy storage, ie capacitance, there is in the ramp driver.

Uspring

Sat May 18 2013, 07:57AM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
Location:
Posts: 711

Steve Conner wrote:

Steve Ward measured the topload voltage of his QCW with a high voltage probe, and got an answer of about 50kV.

Ok, I thought, the 100kV quote about zrg's sparks was based on some measurement of his.

Due to nonlinear streamer loading, the inverter looks somewhat like a constant current sink to the DC bus. So a linear ramp in voltage implies a linear ramp in power too.

I confused the toroids voltage with the bus voltage. The bus voltage is the one with the linear ramp.

@dex:
I agree with your calculation of bang energy. What I meant to say is, that if you are looking for the longest sparks for a given bang energy, QCW isn't the way to go.

PhilGood

Sun May 19 2013, 03:17AM

Registered Member #3806 Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259

Awesome Coil !

Never seen such an impressive Arc lenght / secondary lenght ratio, great job

What is the max rep rate you can run the coil at for long time without overheating ? Is there any way to increase it ?

dex

Sun May 19 2013, 08:18AM

Registered Member #2566 Joined: Wed Dec 23 2009, 05:52PM
Location:
Posts: 147

Uspring wrote ...

What I meant to say is, that if you are looking for the longest sparks for a given bang energy, QCW isn't the way to go.

agreed, qcw is more like "the longest spark for given voltage"

but,for the sake of qcw construction one should be aware of energy requirements as well .

Steve Ward

Tue May 21 2013, 09:51PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

The last time i measured my Tesla Gun after just calibrating my HV probe, i measured the initiation voltage for corona at 39kV and the voltage required to create a spark to bridge a 56" gap to be 55kV. The data suggested a fairly linear increase in top voltage for a linear increase in spark length. So another 16kV should be required for 112" sparks is what id predict for a first order estimate. This means even super high power QCW coils shouldnt have problems with voltage standoff, other than maybe their sparks terminate to ground too easily.

I only measured the "straight spark" ramp setting, so i need to see what voltage it gets to when i ramp much faster, but id guess its only 60kV or so.

ZRG, Do you know the coupling coefficient of your tesla coil? I found this to make a big difference in the ability to make straight sparks. The coupling on my latest design is ~.26, and i think this is too low for making the sword sparks, instead i get the straight segmented sparks.

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