Re: Beating Solved

To: tesla-at-pupman-dot-com
Subject: Re: Beating Solved
From: open_minded <bturner-at-apc-dot-net>
Date: Fri, 27 Sep 1996 03:47:34 -0700
Tesla List wrote:
> <<SNIP>>

> 
> Brent
> Several questions which I hope don't bore you and others
> 
> 1. Have you ever tried to use only 1 break per half cycle?
> 
> 2. Do you phase the break points with the AC, ie., do you adjust the
> break rotor with respect to the rotor shaft to place the break points at
> a particular point in the AC cycle?
> 
> I have found at the 1 and 2 kva levels that I run that a single break
> per half cycle at synchronous speed placed just before the peak is
> extremely efficient. At my lower powers dwell time is not an issue since
> the capacitor is pretty well discharged during its one chance. I have
> tried 1, 2, 3, and 4 breaks per half cycle and have achieved the best
> efficiency at 1 break per half cycle. I have varied the dwell time by
> using smaller and larger contacts and both 1800 and 3600 rpm motors with
> little change when set up as above.
> 
> Please publish your results at reduced dwell times and larger number of
> breaks. It should help to better define the problems of runnung at
> synchronous motor speeds.
> 
> Thanks
> 
> Skip


Answers:

1) Yep. What you have is a 4-pole, 1800-RPM sync. gap. The reason
why it *appears* to work the best is that the gap is firing at the
peak voltage across the primary cap. In other words, where maximum
energy level is reached.

2) Again, yep. In my gap, I use a motor which rests in a standard
NEMA clamp-type mount. To adjust the firing angle, I loosen the
clamps and rotate the whole motor a bit. BTW - there are two types
of sync motors: one type locks into the line frequency, and the other
is called a 'salient-pole' motor. Only the salient-pole will lock into
the exact same firing angle each time it is turned on. This is called
*indexing*, and has to do with the location of the magnetic poles in
the stator. (The poles in the armature then lock into those poles.)

The reason why it appears to be efficient is that you are commutating
power into the primary tank only once per AC peak. Hence, you get the
spark length, but at a much-reduced actual ouput power level. Have
you ever noticed the spark activity at low gap rates? It tends to be
more mellow, slowly ebbing and flowing. At faster gap rates, it will
become more energetic and really start to dance around. Also, at faster
gap rates, the output discharge will start to get a 'singing' quality
to it's sound. I think Tesla referred to that when he mentions that
the tuning was 'sharp'.

One thing I did notice - at 1 break per 1/2 cycle, I was only able to
light a 15-watt bulb doing the 'human conductor' demonstration. When
we switched over to a gap that fired twice each 1/2 cycle, we could
light a 40-watt bulb simply because we were commutating more energy
into the system. The sparks didn't get any longer, but they sure got
brighter.

I will post more data as it becomes available:

coil ring-down (Fr):       270KHz
freq. shift    (delta-F) : 5.4KHz

as measured per the grid-dip-the-secondary-while-in-place technique.

Turns out that I screwed up my math a bit, and discovered (to my horror)
that my current gap has a dwell time of 600uS! Whooooeeeeeee. 1800-RPM
with 3/8" electrodes on a 6" diameter. Yuck. I plan to spend this
weekend re-fitting the gap with 1/8" solid-tungsten rods, and putting
a 3600-RPM motor on it. This will get me down to about 130uS or so.
Makes me wonder how Richard H. can get the dwell down near 10uS...gotta
be using counter-rotating disks or something.)

- Brent