[TCML] Phase tuning gadgets and when to set the gap to discharge.
futuret at aol.com
futuret at aol.com
Wed Jul 2 17:09:48 MDT 2008
The issue with the small oriental motors is that they're so
weak that they need a?light-weight rotor to permit them to
go into sync.?
The proper phase setting depends on both the particular NST used,
and the cap value used.? It would be hard to predict or calculate this.
Best to just adjust for longest sparks.? For a 120 bps sync system,
an LTR value cap must be used for the Tesla tank cap, for best
The proper cap value for the phase shifter circuit is around
3 or 4uF if I remember correctly for the small oriental motor.
The proper value will give a 5volt resonant (above line voltage)
rise across the
motor terminals (max) at some point along the phase
variac's travel.? A 10volt rise is acceptable also.? The proper
value phase cap is selected by trial and error by measuring
this resonant rise across the motor terminals.
240 bps will generally give shorter sparks, and would require that
additional electrodes be added to the rotary gap.
From: Jeremy Scott <supertux1 at yahoo.com>
To: tesla at pupman.com
Sent: Wed, 2 Jul 2008 5:52 pm
Subject: [TCML] Phase tuning gadgets and when to set the gap to discharge.
I designed and built a simple circuit to help adjust the phase of SRSG's.
It's a timing light (white LED .. fancy) that pulses at 120 pps at each AC zero
crossing. The pulse width is less than a millisecond or so with
half of it before and the other half after the zero crossing. Kind of like
an inverted rectified full wave if you can imagine that.
It uses a 120VAC to 9VAC power adapter/transformer that I found in my junk box
for the signal and power. It's a fairly simple two-transistor circuit.
Turn the lights out, shine it at a rotary spark gap, and you can see if the
electrodes line up like they should and if your motor is truly synchronous.
So I used it on the propeller gap of my first coil which was tuned right but
never worked very well. Hah. Way out of sync. Not at the zero crossing and not
at a peak, but somewhere in between.
I tried it with the SRSG phase adjust variac thing as discussed previously on
this list and turns out the adjuster isn't doing anything. (Anyone know the
proper size capacitor for one of those small square oriental motors?)
So now I know why my first coil sucked and I can fix it!
So I guess I got a few questions, now that I can visually see at which point in
the AC cycle the gap is firing at.
1. So now that I can actually see and adjust the timing, when is the best time
to have the gap fire, theoretically? (I know practically, it's 'whatever' ...
adjust it while running until the streamers get bigger.)
Is it at the zero crossing when the capacitor has had a full 8.3 ms to charge OR
is it 90 degrees (4.16ms) sooner/later when AC cycle has peaked
For any given input current (say 60ma NST), would it be better to pick a larger
capacitor size that takes a full 8.3 ms to charge then discharge it into the
tank before the current reverses (at the zero crossing)
OR would it be best to have a smaller capacitor and discharge it at the peak
input voltage but potentially wasting the rest of the current available in the
half cycle? (eg. step up the break rate to 240bps and fire the smaller capacitor
2. Is the timing light even accurate? The signal I'm using comes from a step
down AC wall adapter. Is the secondary phase angle from this small transformer
the same as the phase angle of the high voltage 15K secondary of the coil's
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