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Re: Odd numbers
Hi Sundog,
Tesla list wrote:
>
> Original poster: "sundog" <sundog-at-timeship-dot-net>
>
> Hi All!,
>
> I had myself an idea (Quick! Run and hide!), and plugged same #'s into
> Wintesla.
>
> I was looking at the J per bang figure, and since the more J you push, the
> bigger the bang. J=.5*C*V^2 Right?
Right, (V^2 should be Vp^2).
>
> Good. That formula itself tells me
> that if you maintain the same current (30mA in the case of my example
> NST's), the higher voltage units have a better watts/joule 'rating'. IE, the
> 15/30 charges it's reso cap to ~4.9J (did I do that right? sounds
> reasonable, but it it *iss* wrong, it's consistantly wrong).
Reso cap size is 53nF or 1 / 2piZF = 1 / (6.28 * 500,000 * 60) = 53nF.
Joules = 0.5 * 53nF * 21,210 = 1.19 joules.
I assume your talking about a cap size other than a reso cap.
>
> The same size bang, for a 4kv tranny takes ~115mA (aroung 450 watts) to do
> the same thing, as it's charging a 76nf cap.
A 15/30 NST using a 76nF cap is 1.71 joules. A 4kV tranny and 76nF cap is 0.12
joules. If you set the gap to fire at say 21KV, then the joules on the cap will
increase due to the voltage (how fast you get there is determined by the
current). The cap energy is determined by the "cap" voltage, "not" the charging
voltage from the tranny. It is likely the 4KV tranny will never get there, but
it is possible to reach this potential even using a 4kv tranny if the current
is huge and the cap size is really small. Therefore, the cap voltage "by
itself" is the true value to use to determine energy (in a lot of situations,
the cap voltage is very near the transformer peak voltage so equations using Vp
work, but there are situations where tranny Vp is WAY off base).
>
> There's the basis. Now,
> let's say I want a bigger bang, say, 1J bigger. I'll just increase the
> current.
Nope. You'll increase cap voltage by way of the gap distance which determines
the break over voltage and you might be able to increase current to get there,
but typically you'll need to actually increase the transformer voltage due to
the cap size range we all use in comparison with the tranformers used to charge
the caps.
>
> The 15kv'er will see less of an increase, and the 4kv will see a fairly
> chunky increase just to meet the same J per bang. But each is still ~ the
> same wattage.
Well, yes in a way. Assuming the break is 21KV gap distance: The 15/30 will get
there at some point in time. The 4kv could get there as well. If the 4kv has a
high enough current, then it can get there just as fast (if the 4kv tranny
doesn't die trying - the windings may not be capable of the cap voltage). The
watts would be about the same but in order for this to occur, the cap would
have to be small. 76nF is just way too big. You would probably be around 6 or 7
kv max with this (a 10kva pig transformer would boost cap voltage, but I'm not
sure if it could reach the breakover voltage implied if set for 4kv out). ** I
just simulated 10nF with a 10kva pig at 4kv input and it reached 12KV with a
15mH ballast and 55kv at 14.4kv applied with a 84kv spike (ouch!) - (full
system schematic). Increasing the cap to 100nF brought it down to 28kv. This of
course was without a gap conducting which would set the voltage to a specific
level if used. But, it shows this action for the purpose here.
Bang of the cap is determined by cap voltage and capacitance. Increase either
one and you increase the bang (as long as the cap can be charged to arc across
the gap distance).
>
> For TC's, it's been said that a higher primary voltage is better. i'm
> guessing it's because a 5J bang at 4KV will sink a lot of current, but a 5J
> bang at 15kv will have less current (I see the correlation of
> voltage&capacitance of the tank cap there), for the same size bang. Less
> current=less heat=less losses in the gap.
Sure, a higher primary voltage is better, but the cap voltage and energy will
be the same for either tranny as set by the breakover voltage "if" the lower
voltage tranny has enough current capability with the cap size used to cause
capacitor voltage rise I've hinted to. With a higher voltage at the cap there
will be more bang energy (if the gap distance is increased to allow a higher
voltage) otherwise, if the gap is the same, the bps will increase because the
charge time is faster due to RC time constant. I'm talking about a static gap,
not a rotary (that's based on gap distance and timing - an added variable).
>
> Okay, it's beginning to click. Now, when the gap fires, you get a healthy
> dose of voltage/current into the primary. What makes a stronger magnetic
> field?
Current by way of the voltage value and impedance of the solenoid. A higher
voltage at the primary will cause a higher current and therefore, a stronger
magnetic field.
>
> A higher voltage or current, or is it just a combination of both (IE,
> is a 12kv30ma energizing a selenoid of wire just as strong as a 100v/3.6A?)
> Both are 360 watts.
The 12/30 will have a stronger magentic field assuming the solenoid doesn't
totally load it down. It's the voltage over the solenoid impedance that
determines the magnetizing current, not the current rating of the tranny's. The
current rating identifies only the tranny watts. The solenoid itself will
determine actual watts - the load.
>
> Okay, if it's the voltage, I can see a 28kv1.5kva PT being worthwhile. If
> it's the current, I can see MOT's or a 7.2kv20-50kva PT being a solution.
> On either end of the examples, quenching is a problem. The 28kv system can
> ignite a long arc just by it's potential. The 7.2kv'er will try to powerarc
> just by sheer current (several hundred MA at least)
Both are worthwhile. In TC setups, the cap size and gap distance determines the
bang and cap voltage. Have you ever wondered how a gap distance that is suppose
to arc at 40KV can actually arc across that gap with a tranny spitting out only
12,000V? Because the cap voltage climbed until it arc'd. The 40KV potential and
the capacitance will instantly let you know the bang size by 1/2C*Vp^2 (so will
your ears) and vise-versa - the gap distance will identify the cap voltage if
you were sure about the arc potential required to arc across the gap being
used. To do this right, you would need to set up a test ficture with known
ROC's and sizes for arc distance to voltage, then place in your gap and test at
that voltage (most likely, the distance would be increased a bit to match since
typical spark gap tables use sphere's and we typically use something else like
copper piping or whatever). Jim Lux is real good with stuff.
Capitor voltage rise can occur with high current tranny's and small cap values.
I'm not saying the cap voltage continues to climb to infinity or that it climbs
in every case. But, if conditions are right, it can climb very high until the
cap or tranny dies. If the tranny doesn't have enough current capability, then
the cap may never arc across a 40KV gap, but if the tranny in comparison with
the cap size is capable of causing this action, then yes.
But regardless if this action occurs or not, the gap distance and cap will
ultimately determine the bang even if you have to decrease the gap distance for
the gap to conduct (which may actually match tranny Vp). In small tranny's
(NST's, MOT's, etc..) the tranny's just don't have the capability to cause this
action unless the cap is really small. But a 10KVA pig with say a 10nF cap size
will definately see this action - the pig can probalby take it, but doubt the
cap could - then again, if conditions were right, the pig could be harmed as
well.
>
> A side-question: The low voltage/high current approach would need a cap
> with a good DT/VT, as it's got a *lot* of juice to move very quickly,
> whereas the HV caps (smaller in capacitance by far), could be a bit "slower"
> i guess. ?
dv/dt (rate of change in voltage)
By "good", do you mean a high rate of change when the RC time constant is fast?
Then yes, the low voltage approach must have a fast time constant to reach the
bang size for an equal bang size using a higher voltage approach (but again,
only when the transformer is capable with the capacitance being used -
otherwise, the cap voltage will never get there and the joules will be less
because Vp is less - bottom line).
>
> Soo, it all boils down to : more intense magnetic field by current or
> voltage (if the total wattage is the same)?
It all boils down to a more intense magnetic field when the voltage is larger -
causing more current to flow through the primary - causing a denser magnetic
field - causing higher current to be felt in the secondary - causing a higher
voltage in the secondary - causing increased watts in the secondary.
>
> Hmm..re-read it all, and It all looks to boil down to the total input
> wattage. Only real variable I can see is the V & I. I'll be researching
> this on my own, but freely welcome comments :)
>
> now my head hurts...
> Sundog
Yep, it all boils down to watts (sort of). Actually, it all boils down to watts
in the secondary system. When watts in the secondary are small in comparison to
watts before the secondary, efficiency is poor. If it takes 10KW in to get 5KW
out, there's a problem (5KW of losses). But, the more efficient the coil, the
secondary watts will come closer and closer to the input watts. If we were
capable of achieving 100% efficiency then we could put 10KW in and get 10KW out
and the spark length will not necessarily double, but will increase
dramatically. Of course, 100% effientcy isn't possible, but the closer we get,
the longer the spark lengths get for the power input.
Ok, now my head hurts.
Take care,
Bart