Re: Question

Subject:        Re: Question
       Date:    Fri, 11 Apr 1997 08:28:43 -0700
       From:    Bert Hickman <bert.hickman-at-aquila-dot-com>
Organization:   Stoneridge Engineering
         To:    Tesla List <tesla-at-pupman-dot-com>

> I noticed a post about the strike rail.  Should the strike rail be a
> continious circle with the ends connected together?  Or should the ends
> be
> close together but not connected?  Or does it make any difference?

It should be an incomplete circle - leave at least a 1/2+" gap between
the ends. Otherwise you'll have a shorted turn very close to the primary
that will rob LOTS of power from your system.

> I have been told not to use a rotor on a neon transformer because it
> will
> destroy the neon.  That must not be true from the posts I have seen this
> week.
Depends on if you use chokes, safety gaps, the speed of the rotary and
the value of the caps. If the transformer is "sized" to match the cap
(like many Tesla Coil design programs suggest), the open-circuit voltage
peaks on the transformer and tank cap can easily reach 5X (or more) the
regular peak voltage put out by the transformer. This usually "takes
out" the weakest link - the tank cap or the neon. Because the rotary can
have such a wide variations in breakdown voltage, the odds are much
greater that you'll see these peaks than if you use a series of static
gaps. A safety gap can help, as well as a static "clamping" gap placed
across the rotary. However, it's also not at all clear that rotaries
offer any significant performance benefits when used with a neon
transformer power source (see below).  

> What is the best design for a rotor?

Depends upon what you want to do. A simple two-coil system can often run
very well with a very simple hot or cold rotor design. A rotary gap
constructed so that there are a number of gaps connected in series will
always quench better than simpler style single or double-gap rotaries.
The rotor needs to be constructed from high-strength materials if you
intend to make a large diameter rotor or spin it at high speeds. For
high tensile strength, G-10 is about 5X better than aluminum, and is
fairly heat-resistant. Stay away from thermoplastic rotors.

> It seems like if the rotor is turning too fast or has too many contacts
> it
> will discharge the capacitor before it can reach a full charge.  Is the
> rotor
> RPM and number of contacts critical?

Yes. However, many coilers run at 400 - 600 BPS (and some even higher).
The trick is to have the right balance of recharging current, break
rate, and dwelltimes. Ideally, you'd like to "hit" on every firing
opportunity, dwell long enough to fully transfer the most of the
primary's RF power to the secondary, and then openning the primary
circuit ("quenching" the arc), recharging the tank capacitor until the
next electrode presentation, and doing it all over again. Once you have
determined the number of electrodes and their configuration versus the
stationary electrodes, you can easily figure out the break-rate as a
function of rotor speed. Dwell-time is a lot trickier, since it's not
just the mechanical overlap time of the electrodes, but is also a
complex function of the power source's dynamic characteristics, and you
coil's coupling coefficient, operating frequency, and output loading
(streamers). Here's where lots of trial and error comes into play to
achieve the best performance. Getting all these in balance is sometimes
called "synergistic" operation. 

> How do you know if you have the timing right on the rotor?  Should the
> rotor
> discharge the capacitor on the 60 HZ peak when the capacitor is at full
> maximum voltage charge?  

Only if you want to run synchronously at 120 BPS. Proper adjustment of
phasing on a synchronous rotary will permit you to get consistently
maximum energy per bang. You won't, necessarily, get the best
sparklength and performance out of your system.

> Should the stationary part of the rotor be
> adjustable like the distributor on a car for timing adjustments?

For a synchronous gap, you need to be able to "lock in" to the phasing
of the AC line via a synchronous motor (See Brent Turner's Home Page for
excellent details on modifications to induction motors to make them
synchronous. Assuming you have a motor which can "lock in" proprely, you
also need to properly adjust the rotor position relative to the motor so
that you're consistently fring near the maximum voltage peaks of the
incoming AC mains. Once properly phased and secured, no further phasing
adjustments are necessary.

> What is 1st notch quenching, 2nd notch quenching, 3nd notch quenching?
> What
> does this mean?

When the primary gap first fires, RF energy transfers from the primary
to the secondary until no more can be transferred. The rate at which
this transfer occurs is a function of how tightly the primary and
secondary are coupled (k). For a typical 2-coil system, this energy
transfer will take 2.5 - 4 "cycles" at the resonant frequency of your
coil - the tighter the coupling, the shorter the time. Once all the
energy is transferred to the secondary it will then want to try coupling
back into the primary by re-igniting the gap. If your gap reignites
(i.e., does not quench) the secondary's energy will then transfer back
into the primary, and the cycle repeats again. 

The first "notch" is the FIRST point where all the primary's energy has
transferred to the secondary - its at this point that you'd like to
quench, "trapping" the energy in the secondary. This first "notch", is
the first point where the primary energy (voltage/current) is at a
minimum, and the secondary energy is at a maximum. If you could
consistently quench at this point, you'd obtain maximum performance.

Quenching at later times (such as the second, third, or later notches)
means that you're now "wasting" energy by transferring secondary energy
back into the primary, where it simply heats up your gap electrodes. If
your system is quenching at the third notch, you'll see significant
performance improvement by improving the quench to the 2nd or (best
case) the 1st notch.

> I have a Richard Quick type spark gap.  Above 1500 watts it operates
> fine for
> a few seconds then stops working.  If I let it cool a few seconds then
> it
> works again for a few seconds.  The problem is too much power makes it
> over
> heat and not work. Is it the HEAT that is the real problem?

Yes - indirectly. The real problem is that the electrodes are heating up
to the point where the gap is richly ionized by hot air ions and metal
vapor ions from the electrodes. The gap fails to quench as well as it
did when cool - you may be going from the 2nd or 3rd notch to much
later, and your performance drops. Going to a static vacuum gap or an
air-blast gap can often give you the best overall performance if you're
using neons without any need for the expense and complexity of a rotary
> Gary Weaver

Hope this helps, and safe coilin' to you, Gary!

-- Bert H --