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Re: Problem with common leads in dual channel scopings?
Original poster: davep <davep-at-quik-dot-com>
> > (We may be getting a tad remote from Tesla systems,
> > as such???)
> The reactance current that a 15 uf cap might draw at
> 60 hz might be deemed small, and too small to use as a
> typical DC pulse filter. However recall that I am
> working at 480 hz, where the same cap would have 8
> times the reactive draw at AC, so the ability of the
> 15 uf cap to smooth out the ripple of the AC would be
> equivalent to a 15*8= 120 uf cap acting at 60 hz,
> which is 1/8th the the frequency I am obtaining at the
> alternator.
How much current is the alternator field
drawing? Measured with what?
How is the field supply rectifier rigged:
three phase?
Single phase?
Half wave?
> Yesterday I did a DC cap experiment, to
> see how much capacity that needs to be added to smooth
> out the DC pulsing through a large induction coil.
Why not measure the ripple on the running test bed?
How is the electrical side grounded, exclusive of
scope?
> Here the scope problems are becoming very evident, as
> the measuring instruments stated 1 mgOhm internal
> capacity, should be 8 times less at 8 times the
> standard frequency and not more as I had formerly
> mistakenly reasoned. The coil that the probes are
> hooked to sees a pulsing DC of 480 *2 DC pulses per
> second. Without doing the calculation, I am assuming
> that the stated 30 pf internal capacity would be
> equivalent to the stated 1 meg ohmat 60 hz. However
> that same 1 megohm would become only 125,000 ohms
> reactance if measured at 8 times the 60 hz frequency,
> (which I am assuming is a sort of scope standard of
> measuring the scopes internal capacity ohmic value.)
Without knowing the voltage/current supplied
to the field, hard to judge the significance.
Assuming 12Vish with 1voltish ripple.
thats 1v/125,000 ohms or a few MICROamps
of current into the scope. Microamps
should not affect anything.
> Now the coil I was measuring already has a reactance
> of over 200,000 ohms. So the thing being measured and
> the internal resistance of the instrument being used
> are actually very similar.
Is the coil being measured anything like the
operational load (Alternator field?)
If not: its adding an unknown.
> The net result of making
> the pulsed DC scoping, is that yes I get a signal of
> Inverted AC peaks all in one direction fron the
> rectification system, BUT the signal is not above the
> zero reference potential line as DC pulses would be
> interpreted,
Direction depends on the polarity of the rectifier.
> and instead I see the correct waveform
> shifted downwards below that zero reference voltage
> sweep, so that this waveform appears as a AC signal!
If its all below the zero reference, its DC, in inverted
polarity. Does the scope have an invert switch?
How is it set?
> The internal capacity of the scope is actually storing
> a charge and giving it back to the circuit, making a
> DC pulse measurement appear as a strange AC signal!
Unlikely. !
the 30 pF gives back MICRO amps roughly.
See above.
> 3 uf needed to be added to the coil in parallel to
> smooth out the DC ripple. When the smoothed out DC
> pulsing is then scope monitored, it is a ripple near
> the zero point voltage reference sweep, while an
> ordinary analogue needle voltage meter will record the
> true action which is an actual real voltage above the
> zero voltage margin that the scope reads.
With the analog meter set to AC or DC?
(The analog meter, in fact, will sort of average
in any waveform present on the DC.)
> So some well
> reasoned scope artifacts are indeed taking place here,
Maybe.
> this is involving only a single channel sweeping and
> not two of them. I also see that some bipolar primary
> wiring mistakes were made on the circuit, so repeat
> monitoring of the other idiosyncrasies noted needs to
> be made.
> In regard to the question of how much amperage does
> the DC field get from its source at various voltage
> output levels, here is a chart from past records, with
> commentary included;
> I have a Delco Remy Car Alternator that
> I have converted to three phase AC, with pulley
> arrangements made to procure 480 hz I just put this
> thing through some grueling tests, not a wise thing to
> do since the amount of internal heat generated at the
> end of these tests was probably enough to start
> melting the insulation, and I could smell that
> starting to happen. At the end of these tests I was
> making 46.7 volts with some 9 amps. (which might be
> considered about 420 watts output!)
Such a unit, used in spec s/b good for
30 A minimum, to 60A for larger units.
call that 360 to 720W. (which means it needs
1/2 to 1 HP drive motor.)
> unevenly
> distributed on three phases to three ~ 12.5 ohm
> inductive loads in resonance. For the DC field I use
> an AC variac to 4 fold step down transformer,
Driven by what?
The output of the alternator, i gather?
> then a
> set of 4 diodes for rectification, and then a 15 uf
> cap for DC filter. Here is a chart showing Variac
> Input volts, dc field amps, and voltage measured
> between two of the stator lines.
> Parametric effect
Whatever that means.
> before field turn on was a 2.08 volt stator output.
It will take a volt or so to turn on the
diodes, depending on how wired.
> Note the the nonlinear effect of
> the voltage out vs the DC amps in, and also the
> apparent saturation effect near the top end.
>
> Variac Volts/DC field Amps/ Stator Volts
>
> 10 .04 A 2.55 Volts
> 15 .21 A 5.28 Volts
Anything above 15 or so field volts is over
driving the field. Damage, while not immediate,
may result. (this is an auto alternator, with
nominal output of 14.mumble volts.
above that is overworking it. Anything above that
on the field risks overheating it.)
Something is weird if full voltage (DC) on the
field does not yield 14.mumble on the stator.
Load on stator may be high enough that it is
overloading. Be interesting to know, by
measurement, what current is flowing from stator
to load.
> 20 .41 A 9.11 Volts
> 25 .60 A 13.4 Volts
> 30 1.04 A 21.6 Volts
> 35 1.32 A 26.5 Volts
> 40 1.63 A 30.3 Volts
> 45 1.94 A 34.7 Volts
> 50 2.28 A 38 Volts
> 55 2.58 A 40.6 Volts
> 60 2.92 A 42.8 Volts
> 65 3.2 A 44.2 Volts
> 70 3.52 A 45.3 Volts
> 75 3.8 A 46 Volts
> 80 4.05 A 46.7 Volts
> Note that at the top end there is a corresponding
> diminishing law of returns due to saturation.
Or to something else.
> A reverse aspect of this saturation also exists on the
> low end, where the spin itself establishes a magnetic
> field along with the parametric effect of the stator
> seeing a changing inductance in its core in the
> unenergized field condition. As Such until the
> magnetization made by the amp turns of the field rotor
> actually exceeds the pre-existant magnetic field, the
> input of amperage to the field has little efect of
> increasing the stator output voltage until the level
> of 200 ma DC field current is reached.
Why not reverse the applied polarity, so the two
aid?
> Even when this
> is doubled to 400 ma, as the first chart entry shows,
> the stator voltage has not doubled, it has merely gone
> from 2 volt to 2.55 volts. There is also a "Correct"
> polarity to be used when applying the DC current to
> the field, because of this pre-existant magnetic field
> effect.
The why is it bucking out, as noted above?
> > 'Tesla' primaries or 'resonant' with the
> > Alternator output?
> > What is the alternator output (loaded or
> > otherwise?)
> The bipolar primaries do not use the typical arc gap
> found in tesla coils, instead they are source
> frequency resonant circuits, either arranged in
> parallel resonance or series resonance. The
> practicality of this becomes possible by the higher
> frequency output of the alternator, and trying to make
> this same set up using 60 hz wall frequency would be
> very problematic. The high induction coils can be
> resonated at 60 hz easily, but the low inductance
> components,(the primaries) would require a massive
> capacity to resonate. As it is I am using multiturned
> hardware store bought 14 gauge coil spools of 500 ft
> of wire for the primaries, which then only require ~
> 10 uf to "source frequency" resonate at 480 hz. The
> inductance of these primaries measures about 11 mh.
> A test of these primary coils in parallel resonance
> yesterday showed a good Q factor, for a .03 Amp input,
> I was obtaining 1.05 amps inside the primary circuit's
> midpoint pathway. Doing things this way might
> represent a "power factor corrected" air core
> transformer, since parallel resonance is used to make
> the primary system appear as a maximum impedance,
> obtaining the "resonant rise of amperage" on the
> primaries that text books refer to. This high q factor
> however is considerably reduced when they are brought
> into the closest coupling with the secondaries
> however. It was here where scoping idiosyncrasies
> began to be noted...
if moving 1 A into the primary, then 30 MICROamps
into the scope stray capacitance have no effect.
Something Else is going on.
How is the 'stator/primary' circuit grounded?
> The air core transformer operated in this fashion is
> VERY efficient.
Which is why they are used for power delivery?
> The same currents inputed into the
> primary appear on the ending secondary line coupled
> tank resonant circuits which are 20 coils of this same
> 14 gauge wire spools. This would ~ 10 times the
> resistance of the two primaries itself, yet no
> reduction of INPUT VS OUTPUT currents are noted. This
> is why I say it resembles a sort of magnifier effect.
Or a series circuit:
current in equals current out
> This is due to the incredible fact that compared to
> the action of just hooking the ending tank circuit
> directly to the alternator, and the effect of instead
> introducing those currents by the primary /secondary
> air core transformer connections, the air core
> transformer delivers better currents on the ending
> component, then would exist if instead those ending
> components were directly hooked to the same inputs the
> primary uses!
If i wire 11 spools of wire in series, with no
ground leaks, I will get the same current out
as in.
> If this isnt a reason for calling it a
> magnifier effect, I dont know what is!
cf as above.
> > How Seems?
> > Current measurement?
> Yes a current measurement of differences between the
> branches of the primaries showed that it was not well
> balanced, and changing the coupling of one of the
> primaries equalized this out.
> > Are the multiple 'primaries' connected IN
> > PARALLEL or each to its own phase?
> Everything is derived from only one stator phase
> output, yes they are in parallel.
> > >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.
How are they 'in delta' from a single phase?
> > OK. I infer the bulbs are wire connected
> > to the
> > circuitry.
> Yes, as I may have mentioned a group of ten 14 gauge
> coils in series resonance to the alternator can
> provide a good voltage rise. However procurring three
> phases of these voltage rises, and then drawing
> voltage and current by florescents on the three phases
> of voltage rise is problematic.
There is as a matter of course, some variation in
the strike and sustaining voltages of the lamps:
Once one or two strike, yes, that leg will
draw more/all current.
> There may be an issue
> of how much current limiting is occuring here, and
> voltage without the availability of amperage to
> accompany it. In any case the procurring of three
> simultaneous arcs from the three phases was also
> impossible.
A minute ago there was one phase, with two primaries
on it. Now there are three phases?
> Apparently voltages should have to be very
> high for this to occur, and eventually with a second
> rise of voltage component installed, (A delta series
> resonance, placed inside another delta series
> resonance as an inside midpoint triangle, as a two
> fold resonant voltage rise circuit, that eventually it
> was found that balance could be maintained with neon
> discharges, so that either a 3 bulb DELTA or WYE neon
> assembly could be lit from alternator inputs, all
> without using any transformers. It is here in these
> higher voltage regimens that I feel an alternator
> tesla coil could be made, again without having to use
> a transformer to maintain the necessary voltages, but
> instead using voltage rise available in source
> frequency series resonance. I have been half heartedly
> working on these problems for several years now, but
> still haven't delivered a resultant alternator powered
> tesla coil. I need to make a better secondary to
> explore these options. With the existant secondary,
> all I have got is voltage that will light a neon from
> the top terminal.
What sort of neon?
> > Are ballasts used with the fluorescents?
> No, the current limiting that takes place is found
> when the delta series resonances are shorted across
> their voltage rises. This is the maximum current that
> should exist on those branchways. Thus the branchway
> is current limited by the impedances of the outside
> components found on the delta series resonances in
> reactive condition.
> > They get unpredictable without them.
> This shows why the balance problem can exist. If we
> are measuring the current limitation to the inside
> branches on two shorts of resonant voltage rises, and
> then add the third short, obviously the former current
> found with just two shorts will be decreased when
> three are applied. The same issue applies when
> measuring the current limitations involved with the
> alternator operating without the energized field.
> Since we have no field being energized, it is safe to
> short out the stator input and measure the current.
> For one phase at this rpm to make 480 hz; this
> measures just over 1.5 amps, for two phases just under
> 1.5 amps, but when all three phases are shorted we
> obtain .75 A on all the branches. The alternator
> itself should be viewed as a current limited device.
Indeed. One of the characteristics of an alternator.
However whether its the 'correct' current limit
of a given fluorescent (or neon?) is a matter
of chance.
> Hence if we were to try running a tesla coil off one
> of the phases, using the conventional pole pig
> approach, we would not need to worry about current
> limiting the pole pig. We can determine beforehand how
> much the alternator itself is current limited, by
> making such short measurements for a breif instant of
> time. We CANNOT however light an unballasted neon from
> such a alternator/pole pig scenario. Neons have a
> funny issue involved with a sort of negative
> resistance that appears upon firing.
As does any gas discharge device.
> Trying this with
> a pole pig, and having an amperage meter on the
> stator, resulted in the fuse of the amperage meter
> going out. This should be interpreted as a tremendous
> surge upon firing, repesenting a short on the
> secondary.
Any transformer can and will draw a roughly
10x, worst case, first half cycle surge.
Even with no load. In 'usual' size transformers
(say 100W and down) this is low enough to be
'ignored' Much above that, this can confuse
people, and pop breakers.
> A tesla arc gap however usually does not
> represent such a short on the secondary, because the
> arcing normally occurs at the zero crossing point of
> the applied AC signal, since it is consideraed a
> capacitive reactance to the supply. An Alernator/NST
> arrangement will not work, I could make an arc gap
> with the pole pig, but not with the NST. Again there
> is the frequency issue. A NST that is current limited
> to 30 ma, becomes current limited to 30/8 ma at 8
> times the input frequency. In contrast however if we
> can get a tesla coil to function at these higher
> frequencies, both the arc gap firing voltage and the
> performance of the coil should be enhanced, compared
> to 60 hz operation.
I'd be surprised.
> This is because with the same
> capacities being employed on the primaries, we now
> have 8 times the energy transfer, at 8 times the
> frequency.
...and higher losses as the NST is outside
its designed freq range...
> I feel that with the existant garage set-up, having
> the AC alternator and the pole pig, it should be
> possible to run a small conventional tesla coil with
> the traditional method. Any regional NE Ohio coilers
> having such a small coil is welcome to come here and
> try this out. Meanwhile I will soon be doing some work
> with a larger bifilar primary set up, and to get my
> own alternator tesla coil set up trials running again.
> In this category any one with a large secondary could
> bring this over for trials, but this would take much
> longer for a trial. My secondary is inherently
> innefficient, which is part of the problem... I also
> have a much larger AC alternator 6 phase system that
> runs at 360 hz if a power issue becomes the problem.
> This is actually two bus alternators coupled to a
> common axle, where the phasing of each three phase
> system has been matched in the variable phase options
> available so that one can either parallel or series
> these two alternators together for better power
> outputs. But first I would like to see what can be
> done with the smaller model alternator, to serve as a
> guideline for what is possible.
> > The outputs of the alternator are at 120
> > degrees. Whence the 120?
> Standard three phase dictates that each phase going
> around the circle will be 120 degrees apart for a
> total of 360 degrees in the circle: this is elementary
> stuff...
Uhuh. However previously things were
described as 'in parallel' on a single phase.
That 30 uA of current into a scope input impedance
will not derange a system operating with an amp
or so of load current is also 'elementary stuff'.
best
dwp