[TCML] The truth about LTR, STR, and resonant modes
Mddeming at aol.com
Mddeming at aol.com
Wed May 28 12:34:10 MDT 2008
Exceptional clarity and conciseness. You definitely learned your writing
skills in the era before text-messaging. ;^)
In a message dated 5/28/08 2:21:00 A.M. Eastern Daylight Time,
FutureT at aol.com writes:
In a message dated 5/27/08 6:21:03 PM Eastern Daylight Time, FutureT at aol.com
> >If a pig or PT coil is run with a small
> >cap at high bps, then the ballast L has to be reduced to let in
> >more power (if long sparks are desired). Then the coil is truly
> >running in STR mode.
Correcting my post above here. Such a coil as above
(small cap, high bps), is not necessarily STR mode.
This can be resonant or LTR mode also. It all depends on
the ballast setting (explained below). My other recent posts
mostly spoke of 120 bps operation but the comments
in those posts
apply to higher bps operation also, except the power
factor might not be as good at the higher bps.
Deano is most likely correct that most folks are
probably running in resonant mode with their pig and
PT systems. Resonant mode is not solely dependent
on the cap value for a given non-shunted transformer.
Any cap value can be run in LTR, STR, or resonant
mode by adjusting the ballast as needed to give the
respective mode. This is mostly independent of
the transformer size (within reason of course). A
too large cap will not be able to be charged to
a reasonable voltage, etc.
NST's (and OBITS), i.e. shunted, transformers are a
special case. For a given NST, a given cap value is
either LTR, STR, or resonant. This is not true for
unshunted transformers such as pigs and PT's. These
transformers are always run with a ballast. The
setting of the ballast will determine, along with the
cap value, whether the system is running in LTR,
STR, or resonant mode. The transformer doesn't
really enter into the equation except for impedance
transformation which determines how much ballast
L is needed for a particular mode, and also the
transformer must be able to handle the power, etc.
It's not correct to say, "this pig has an LTR
value cap" or something similar. The cap itself
doesn't determine if the system is running in LTR
mode. This will be determined by the setting of
the ballast also. Of course the spark length has to
be considered. Longest sparks may be produced
in resonant mode, or slightly LTR. In resonant
mode, the reactance of the ballast "cancels" the
reactance of the cap, and this lets the maximum
power enter the system. This should give longest
sparks. LTR may work somewhat similarly up to
a point. There are issues such as inductive kick
to consider. As the ballast is increased in
inductance, this will create an LTR mode in
high bps systems, but it will also tend to
throttle back the power and reduce the spark
Coilers should select their cap value based on
the needed spark length, and the capabilities of
the transformer. If the transformer is extra powerful,
they can select a smaller cap, and adjust the
ballast for resonance or LTR and still get rather
short sparks if that's what they want. If they
want longer sparks, then just use a larger cap,
and again adjust for resonance or slight LTR. If one wants
super long sparks, then use an even larger
capacitor and again adjust for resonance or
slight LTR. This may force the pig to provide
double its rated power, but pigs can handle that.
Folks used to talk a lot about each coil having
its own personality so to speak. I believe one
cause of that was the relative cap value versus
the transformer power versus the ballast setting,
thereby making the coil run either LTR, STR, or
resonant. I used to often talk about how
important it is to use the proper value cap for
120 bps coils, but the proper value cap is
important for high bps coils too, so that the
spark lengths will be correct, when the ballast
is set (tuned) correctly. This is what Bill Wysock
talks about when he talks about tuning the ballast.
This is probably creating a resonant or slight LTR
condition for maximum efficiency and best power
factor. I'm not sure exactly what adjustment
(LTR, STR, or resonant) will give best power factor
with high bps, but surely one of them will be best
in that regard.
In some cases folks may use a capacitor that
is larger than optimal for the desired spark length.
This may make it necessary to misadjust the
ballast and introduce inefficiency or a bad power
factor into the system to deliberately reduce the
Some may say that fixed LTR, STR, and resonant
cap values are valid for pigs and PT's. This
may be true if the transformer is run at its
rated power. But if it's not run at it's rated power,
if it's run at either higher or lower power, then
the LTR, STR, and resonant values change.
This is why it's best to look at it from both
and cap value *and* ballast inductance value
perspective. Otherwise the situation can be very
I hope the above is written clearly enough.
I kind of jumped around with the thoughts.
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