Re: Problem with common leads in dual channel scopings?

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

Original poster: davep <davep-at-quik-dot-com> 

(We may be getting a tad remote from Tesla systems, as such???)

>The stator voltage and consequent amperage that
>developes in the alternator output is governed by a
>variable DC input to the field of the alternator,
>which is a rotating DC electromagnet connected by slip
>rings. This regulation is actually a AC variac stepped
>down four fold by transformer, and then given a full
>wave DC rectification, and finally a 15 uf cap to
>smooth out the DC ripple.

         Does it?
         How much 'DC' is drawn?
         15 microfarad is Way Small for most 12Vish
         (?) DC work.  a few hundred uFd is more typical,
         with Much Larger if drawing significant current.


>I shortened all this with
>the words "DC variac." The volume of amperage rise was
>reffering to the process of gradually increasing the
>amperage in the circuit via said variac control. There
>are two primaries in parallel in this set up,

         'Tesla' primaries?
         With spark gap, or 'resonant' with the
         Alternator output?
         What is the alternator output (loaded or
         otherwise?)

>and it
>was initially observed that one primary was recieving
>more current on its branch than a perfect split would
>enable, and these primaries were not fine tuned, they
>were just given the approximate capacity needed for
>resonance on each branching, and evidently one branch
>was better tuned then another branch. After a certain
>volume of amperage was reached by this variac
>regulation of field, suddenly the least effective
>branch no longer recieves its proportion of amperage
>in the circuit that was initially noted, and the more
>"resonant" branch then seems to take up most all of
>the amperage delivery.

         How Seems?
         Current measurement?
         Are the multiple 'primaries' connected IN PARALLEL
         or each to its own phase?

>Balance problems with
>alternator branchings can be shown in other things,
>such as procurring 3 resonant rises of voltage from
>three phases, all 3 phases of voltage rise being of
>sufficient voltage to be able to light florescent
>bulbs.

         Bulbs connected to the circuit, in free air?
         While a common automotive alternator will run
         to 110VAC ish, it can start acting strange, due
         to saturation.

>We can light two of the bulbs in delta, but
>lighting all three is almost impossible. The other two
>branches will seem to suck up all the available
>current.

         OK.  I infer the bulbs are wire connected to the
         circuitry.  An automotive alternator will easily
         go to 110vac with no added 'resonance' if pushed
         hard enough.  fluorescents will stay lit down to
         40ish volts, tho more is needed to strike them.
         Are ballasts used with the fluorescents?  They
         get unpredictable without them.

>We are also aware of the balance problems
>that exist with lighting two neons in parallel, which
>again is practically impossible, the one ionization
>branch will seem to always take up all the current.

         Yep.  Neon, as fluorescent, has a lower voltage
         once struck.  Characteristic of ionized gas.


>Here a similar balance problem seems evidenced that
>two phases of resonance that are obtained as 180
>phased series resonances, involving a branching
>pathway derived from a single phase: and at a certain
>volume of amperage delivery,

         The outputs of the alternator are at 120 degrees.
         Whence the 120?

>one phase wants to take up most of all of the available

>current. This might
>also be that its  secondary coil in reaction as the
>secondary is acting far more efficiently, or that even
>the same branching amperage problems might be occuring
>on the secondaries, which are also wired in parallel.

         What load is on the 'secondaries'?
         If gas tubes (fluroescent/neon) low impedance of
         the firing tube will 'reflect' back to the
         primary, drawing more current.


>These problems seemed to be effectively solved by
>changing the coupling to secondary on one of the
>primaries. Perhaps those building bipolar tesla coils
>have experienced a similar problem, in that tuning for
>bipolar systems is more problematic then given for the
>single tuning case. In this case here the secondaries
>are also a common circuit to both primaries inductive
>influence, as those secondaries are wired in parallel.
.....
>  > >to field, all of a sudden the primary being
>  > monitiored simply stops resonating. Could it be possible that
>  > the internal impedance of the scope might act
>  > differently when observing a 480 hz signal?
>  >          Unlikely.
>  > >probe connections I thought...
>  > >In any case a solution to these monitorings was
>  > found, by making the dual channel leads connected to the
>  > >voltage rise of the circuit, WITHOUT any of those
>  > >probe leads having a common connection point.
         There is a common connection at the 'scope.


>  >   Are the probes being used 'differential mode' NO, each probe is used 
> to monitor a different voltage
>point in the circuit, one probe for the outside stator
>input, and the other probe for the inside series
>resonant voltage rise that is BETWEEN each series LC
>circuit in the branchway. My Tek scope simply has a
>switch setting between channel 1 and 2 that says BOTH,
>and this gives a dual channel scoping.

         How is the alternator output (and associated
         circuitry) referenced to 'ground'?

....
>  > How is it known that the indication drops
>  > 'on the scope monitoring'?
>Both a voltage meter AND the scope are used to monitor
>the voltage rise on the circuit. Without the scope
>measurement being done, the voltage is double on the
>digital meter. Adding the scoping measurement drops
>the former voltage measurement found by meter down to
>50% of the fornmer readings.

         Curious.  The few pF of the scope probe should
         not affect anything at 460 Hz (???)
         One possibility is that the meter is misreading,
         due to stray rf (if present), which is 'filtered'
         by the added probe tip, tho this seems unlikely.


>  > >so for this case example anyways, it is definite to
>  > >conclude that the action of scope monitoring the
>  > >primaries resonance, acts to significantly drop the
>  > >possible amount of resonance obtainable given a
>  > fixed
>  > >stator voltage input. This scope has a 30 pf
>  > internal capacity.

>  >          Calculate the impedance of 30 pf at 480 Hz.
>  >          It is large.
>  >          is 30 pF the scope or the _probe_
>30 pf is written on the scope itself beside the probe
>connections impedance?

         Arghhh.  I'm getting phuzzy.  I think that is the
         capacitance associated with the scope input
         impedance.


>>          Is a probe being used?
>Pardon my terminology, I thought a probe is always
>used with a scope,

         Sometimes not.

>and is just a thingy that has a 10X switch, so that the

>full range of voltage differentials made for the scope

>ranges can be used.

         Sort of.  It also decreases circuit loading, in
         10X mode.

>Scope specifies also 1 M ohm impedance, so I imagine
>it should have 8 M ohm impedance at 8 times the
>typical 60 hz frequency.

         It's more complex than that.
         fer on thing the 10x probe (or 10x mode of switchable
         probe) raises the impedance.


>  >          What cap resonates the load?
>The primaries are each roughly 11 mh and 10 uf used
>for resonance at 480 hz. A special problem exists here
>however. The ratio of the internal resistance of the
>source of emf found as the actual stator wiring
>resistance, and the actual resistance of the load to
>be resonated is not a large ratio, which is a typical
>requirement for efficient power delivery for most
>power applications. The maximum power transfer theorem
>states that the maximum power that can be delivered is
>when the external load equals the internal resistance
>of the source driving that load.

         Uhuh.  Thats MAXIMUM power transfer.
         Mostly, for power work, the interest is in
         MAXIMUM Power EFFICIENCY, which is a very different
         matter.
         (The 'matched impedance' case is much misunderstood
         and sometimes, misapplied...)

>The equivalent
>resistance of just the wire on the primaries is about
>.6 ohms.

         ...and what is the 480 Hz _impedance_ of the
         primaries?  Or, rather, of each primary plus
         resonant cap?

>If I WAS operating BELOW that maximum power
>transfer level by having such a high internal
>resistance/load ratio, we might find some strange
>things happening. In this case here adding the high
>impedance of the scope probes attachment seems to
>greatly influence the entire process, so that somehow
>the scope's measurements actually degrade the
>measurement.

         Leave me close with two cases, if i understand:
         Scope does not (appear to) degrade measurement
         (resonance?) when no explicit ground at probe
         tip is used.
         Scope does appear to degrade resonance when
         explicit ground at tip is used.
         Correct?

         How is circuitry on alternator output grounded?
         IF it is ONLY grounded thru the scope tip ground,
         then all sorts of curious effects are EXPECTED.

         When reference is made to 'primaries in parallel':
                 Are they Literally IN Parallel?
                 Or is each connected to a separate phase of
                 the alternator output?
         Further:
         When the alternator current is increased, several
         other things change also: notably the output
         voltage from the alternator, the load current to
         the connected load (resonant primary?), the
         output voltage from the associated secondary, the
         load current from that secondary to any connected load.
         This WILL affect conditions on the primary side.
         If the primary be driven from a specific phase
         of a polyphase alternator, some effects WILL be
         seen on the other phases, and on any connected
         loads.

         This is a rather complex 'system' to describe/understand.

-- 
         best
         dwp

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