Yes, I concur with John's assessment of the sync vs. async debate. I
experienced the very thing that John referred to where my output spark
length deminished after converting my sync SG over to sync. Just as he
mentioned, I left the original STR (0.1 uFd) primary cap unchanged.
Since
we are talking about a pole pig fired beast, it has proven far more
practial (and economical) for me to remain async with my system, as big
bright sparks were my goal, anyway. A truly LTR cap, whose voltage
standoff
and capacitance can match up with a 14,400 volt,10 or 15 kVA rated pole
pig
in sync operation would have to be a real monster (> 0.3 or 0.4 uFd @ 25
kVAC or 60 kVDC) and a real drain to the typical hobbiest's budget!
Probably the only type of TC drive sytem that could possibly complete
with
or possible beat the asnc rotary gap for pole pig fired coil systems of
equivalent power levels, whose endgame is the biggest and brightest
sparks
possible, would be the DC resonant system. Of course, the required giant
storage cap(s) - (up to several 10's of uFds @ >20 kVDC) and ultra fast
recovery, high voltage diodes also render this approach considerably more
pricey that the standard async system, too.
Sync RSG with LTR primary caps is the best way to coax maximum spark
length from the limited available power, while at the same time going
easier on the fragile HV side windings of (an) NST(s), though.
David
----- Original Message ----- From: "Futuret via Tesla" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Sunday, February 25, 2018 9:52 AM
Subject: Re: [TCML] Best Spark Gap for NSTs?
The answer is not simple or direct. There are advantages and
disadvantages for sync or non-sync.
Did you happen to try
feeding the motor with 140V from a step up type variac?
Often this will keep it in sync. If you created flats on
the rotor that are at least 1/4 the width of the full rotor diameter,
that is enough metal to remove. Some small motors
are very wimpy and don't work well such as small
shaded pole fan motors. And of course you should
have 4 flats on your motor.
Yes the preferred break rate has a lot to do with it.
Sync operation is most beneficial at low break rate
of 120 bps. However it's absolutely necessary to
use a large enough capacitor to take advantage of
this. Back in the "day", a lot of people were installing
a sync gap onto their TC and getting worse results
because they were using a small capacitor with
a static gap previously. They left the small
capacitor in place and therefore saw a reduction
in spark length when they installed the sync rotary
gap.
For anything over 120 bps, sync doesn't really
help, you might as well use non-sync or a static
gap. Gary Lau posted some information about
the best capacitor sizes for sync or non-sync, etc,
in the past and I guess this is at his website. Also
JavaTC might give some information about the
best capacitor values for sync or non-sync, for
NST powered coils.
120 bps sparks will not be quite as bright as
higher breakrate sparks. Also they tend not
to create the kind of long tendrils that can
form at higher breakrates. Certain coils
tend to show these long thick tendril
type sparks.
John
-----Original Message-----
From: Daniel Kunkel <dankunkel@xxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Sent: Sun, Feb 25, 2018 9:45 am
Subject: [TCML] Best Spark Gap for NSTs?
I modified a 1725 rpm motor to run in salient pole operation years ago.
It
will seek and then lock into phase and then break out again. I think I
recall reading that if you don't remove enough rotor material it will
seek.
If you remove too much it will over heat.
So before to I take this back to machining, is it even worth it? What is
the best gap for NSTs? Is SRSG is the answer what is the preferred break
rate?
~Dan
To synch or not to synch
Kansas City area
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