RE: John Freau's SRSG Dwell Controller

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "sundog by way of Terry Fritz <twftesla-at-uswest-dot-net>" <sundog-at-timeship-dot-net>

Hi all,

  Just a thought, but to those whom are running polepigs and always changing
their current limiting, this is a godsent!  I *HATE* having to adjust my
SRSG on my NST system everytime I add (or blow) a tranny, and a pig system
will do the same thing (only less hassle to add/remove current).
    Now you can dial it in remotely! WOOHOO!!
												Shad

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Monday, December 18, 2000 9:04 PM
To: tesla-at-pupman-dot-com
Subject: John Freau's SRSG Dwell Controller


Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi All,

I have been studying John Freau's remote gap phase controller at:

http://hometown.aol-dot-com/futuret/page3.html

This wonderful Idea is full of great promise and I have been running some
computer models today.  The MicroSim model is at:

http://hot-streamer-dot-com/TeslaCoils/Misc/srsgVI.sch

A GIF diagram is at:

http://hot-streamer-dot-com/TeslaCoils/Misc/srsgVI.gif

There are three cautions I should give right off:

1.	There is a danger that if the motor were disconnected, and with some
combinations of capacitors and inductors, that the LC circuit could go
resonant at 60Hz.  This could cause the voltage and current across the cap
and variac to shoot way up which could cause the cap to explode or the
variac to arc over.  One simple way to guard against this fairly well is to
add a 3amp fast blow fuse to the circuit John shows in series with the cap.
 Then if the voltage and current goes high the fuse will blow and disable
the resonance.

2.	The work I have done so far is only a computer model with not too great
inputs.  The circuits I give have never been tested to insure that they
work at all.  So "highly experimental and unknown!" applies :-))  Nor does
the circuit take into account and dynamic effects like loss of sync or
startup.  However, it does "kind of" suggest those cases are tame.

3.	The models suggest that component values are fairly critical (like
+-20%).  If the values go to far off, the voltages and currents can get too
high.

Ok, so I don't know if this is right :-))  but let me tell you where I am
at...

Using the data I got from measuring the input voltage and current of my
sync motors is at:

http://hot-streamer-dot-com/TeslaCoils/Misc/SRSG-VI.gif

I roughly modeled the motors as a 0.315H inductor in series with a 63 ohm
resistor.  These are L2 and R1 in the diagram.  L4 is the variac that the
model says should go from between 0 and 225mH.  R4 is simple a safety drain
resistor across the cap if the fuse blows.

C1 is a standard AC motor run PFC style capacitor.  This seems like it
should have a high voltage rating to withstand the stress from the circuit.
 The circuit really likes to resonant the voltage up and having this cap
being able to withstand high voltages is a real plus.  R3 is a damping
resistor.  It allows the variac to have a wide range but still be able to
maintain a reasonably constant output voltage.

The problem seems to be that the voltage across the motor likes to either
rise or fall dramatically as the inductance of the variac is changed.  Of
course, we want a steady voltage but lots of phase shift.  By adding R3 I
was able to get a pretty steady voltage output.  You want C1 to be a fairly
low value otherwise the currents get too high.  I was surprised 40uF would
do it but I needed a lot of inductance from L4 (the variac) to get a good
shift.  R3 should probably be a little lower value but I wanted a common
part and didn't want to waste current or make a lot of heat.  So here is
what the model says:

Variac Inductance	Voltage to Motor	Line Current	Phase delay
25mH			120.7 V			1.9 A		0.4mS
50			127.5			2.0		0.8
75			131.48			2.1		1.2
100			131.64			2.1		1.7
125			128.0			2.0		2.2
150			121.4			1.8		2.6
175			113.0			1.8		3.0
200			104.2			1.7		3.3
225			95.6			1.5		3.5
250			87.6			1.4		3.64

The input voltage was 114 VAC and the motor's normal current is 0.835 amps.
 Thus, the circuit doubles the input current.

Of course, I need to really test all this to see if it is at all accurate
or not.  However, the computer model gives me a good idea of what is going
on and what to look and watch out for.  I will now find the components and
give it a try in the next few days.

Cheers,

	Terry