John: Did you happen to try feeding the motor with 140V from a step up type
variac?
Dan: WOW! The 140VAC trick seemed to fix the sync issue! Thank you for the
suggestion! Any long term damage risk of doing this?
John: 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.
Dan: Yes I have 4 flats on the rotor. Rotor diameter is 3.480" and my
flats are .728" (or 20.9% of diameter). 25% would be .970". Is 25% the new
standard? Back around 2001 when I had it machined, it seemed like the
proper way to determine flat size was to measure the distance between the
run winding poles.
John: 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.
Dan: I understand the sync operation and low break rate would necessitate
a larger cap, but what I can't understand is why all the standard/old
school capacitor calculations don't calculate the full charging of the
capacitor. The TeslaMap gives you 3 capacitor values: the resonant cap, LTR
cap (which is resonant cap x 1.61), and SRSG cap (which is LTR cap x 1.61).
Side question: I understand that as the sine wave goes up, the capacitor
charges. Then at the peak of the sine wave the SRSG breaks, releasing the
peak charge. However, what happens at the zero line crossing? Assuming the
capacitor begins re-charging right after peak, as the sine wave drops,
wouldn't the charge also bleed off? So at the zero line crossing no
spark/break would occur?
Thank you!
~Dan
Kansas City area
On Sun, Feb 25, 2018 at 9:52 AM, Futuret via Tesla <tesla@xxxxxxxxxx> wrote:
> 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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