Re: VTTC provisional results

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <FutureT-at-aol-dot-com>

In a message dated 3/17/01 2:44:11 PM Eastern Standard Time, tesla-at-pupman-dot-com 
writes:

> John Freau wrote:
>  
>  > My guess is that the coil is maxed out for filtered DC operation. 
>  
>  John,
>  
>  Neither the tube nor the tankcap nor the primary coil nor the 
>  secondary coil get extremely hot. There are no signs of secondary 
>  coil breakdowns. I have got plenty of power. Why do you think that 
>  there is no space for improvements? Where are the borders?

Herwig,

I sort of look at the issue as I would when hammering a nail into
a piece of wood.  If the friction and density of the wood is a certain
value, and the hammer is a certain weight, and is swung for a 
certain distance with a certain speed and force, then the nail
will sink into the wood a certain distance.  The only way the
nail can go deeper, is if we change something.  We can use
more force, a longer swing, a softer wood, etc.   In the case of
the Tesla coil, it takes a certain amount of power and energy
to raise the voltage high enough, and give enough current to
form the spark.  Forming the spark takes power and energy.
Basically, the only way to make the spark longer is to add
more power input, assuming the coil is reasonably efficient
at changing the 60 or 50Hz power into RF power at the proper
voltage and current.  As you improve the coil, you reach a 
point of diminishing returns.  Think of a car, they get maybe
30 miles per gallon here in the US.  Why don't they get
80 miles a gallon?  It takes a certain amount of energy to
push the car along, and it gets harder and harder to extract
the last ounce of efficiency.  There's a limit.  Even if the car
was 100% efficient, it may get only 100 miles per gallon.  
I'm just guessing at that figure, to make the point.  The same
thing with the Tesla coil.  If it was 100% efficient, you might
gain only 20% on the spark length.  You can of course do 
tricks such as lowering the pulse rate, but that's not a true
increase in efficiency.

>  
>  > mentioned that there are individual streamers.  This makes me
>  > think that the filtering is not very good.
>  - David Trimmell suspected the same. As soon as I have 
>  reassembled the parts of my system I shall parallel my 15µF/10 
>  kVdc filter cap by another one and check for improvements.

Better filtering will reduce the individual streamers, but make them
shorter overall.

>  
>  > I forget if you said you're using some sort of staccato or pulsing 
>  action?
>  - If there was any pulsed action other than driving the tube in C-
>  mode, it is not intended. I am a little bit afraid to check it by scope 
>  as I do not want to fry it in this environment. How do you perform 
>  your tests? Are there any special precautions to be considered?

I don't use any precautions.  I just set up the scope about 5 feet 
away from the coil, and use a piece of wire as an antenna to pick
up the RF.  I keep the antenna 5 feet away from the coil also.
You'll see the RF envelope on the scope.  Since you didn't build
any staccato feature into the coil, I'm sure it's running steady.

Since you're using 3 phase power, I'd say you hardly need much
filtering anyway, since 3 phase power is pretty smooth to start
with.  
>   
>  > The sparks from filtered DC VTTC's tend to be about half the length
>  > of raw AC VTTC sparks.
>  - These are clear words, John. Thank you. The "only" thing I have 
>  to manage still, is to find the power drawn from the wall (my 
>  system is operated from a 3 phase tranny).

I know the wattage of each phase is 1/3rd of the total.  I don't know 
if the current works the same way.  Three phase power confuses
me at times.  I just realized, if you want to get the typical long AC
type sparks I'm familiar with, you'll have to use just one of your
phases, instead of 3 phases.  My guess is that 3 phase will always
give shorter tube coil sparks for a given power input (unless you
use staccato).  Staccato would be hard to control with three
phase power since the power never goes to zero.

BTW,  regarding tank impedance, I use trial and error also.  The
reactive load of a TC, makes it hard to calculate well.  There's 
lots of weird stuff happening in a tube coil.

Cheers,
John

>  
>  Regards,
>  
>  Herwig