[PRCo] General description of DC Control

[Fred Schneider]

General description (as simply as I can make it) follows on direct current control
for traction motors) :

Discussion excludes earliest designs, and concentrates only on those systems that
started in the middle 1890s.  This diatribe also excludes foreign stock or generic
scheme nomenclature although many similar products were built overseas.

Platform controllers with directly controlled traction current to motors through
resistors came in four basic types:  The basic problems with drum controllers were
a) they were limited in the number of motors they could handle, and b) they were
easily abused by motormen with frost on the brain.  Because of amperage limitations
they were not suitable for train operation (although Pittsburgh did run six-motor
trains on K43 control).  Abuse by motorman includes, for example, operators who
slowly back off on a controller and pull am arc that fries the controller.

    1.  R stood for rheostatic control (as opposed to systems which also changed
motor connections).  It would have one or two or four motors permanently wired in
either series or parallel.  R control was most commonly used on mine locomotives.
I would imagine that some of the engines on the Chicago Tunnel used it too.   R
control simply cut out resistance as you moved the handle from point to point.

    2.  L control was a series / parallel scheme with open transition from one to
the other.  Go back to high school physics.  Series indicates that electricity
passes sequentially through all objects, in this case motors.  (Many Christmas tree
light strings were wired in series ... problem is that if one bulb (or one motor)
in the scheme burns out, the others cannot work.)  Parallel wiring is not
sequential ... each bulb (or motor) is connected from the positive to negative
wires independent of the other motor.  A motorman moves the L control from off in
one direction through series.  Then he backs off to the starting point (off) and
goes the other way in parallel.  Open transition means there is no power on the
motors in transition from series to parallel (because it goes through the off
position).  I understand that L controllers were most often used in locomotives.
The only one I ever saw was stored in a baggage car at OERM in Perris, CA.

    3.  K control used bridge or shunt transition to keep power on the motors as
they passed from series into parallel.

    4.  B control was simply a two drum controller.  Moving the handle in one
direction from off worked through the motoring or traction drum.  Moving it in the
opposite direction from off worked the braking drum to control dynamic braking.
There may have been some that incorporated both braking and motoring into one set
of cams and fingers but I have not seen it yet.  In the Coke Region, the B-50A was
very common because West Penn used it on the 286-297 and 700-739 cars.  The B-50A
was nothing more than a K-35 with a separate braking control drum.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

The need for multiple unit car control required some method of accelerating cars
from one control stand.   This would, in turn, call for some platform controller
that was operated by the motorman, and a separate motoring controller on each car
that handled the 600 volt motoring circuits.  Through several basic methods, the
platform controller told the motoring controllers on each car to notch up and to
transition from series to parallel, all in unison.  The platform controllers and
the circuits leading from it to the remote or motoring controllers were either
low-voltage or low-current 600 volts, and therefore there wasn't much that a sloppy
motorman could do to abuse them.  And they could be wired in such a way as to
prevent virtually any abuse.  Therefore, in addition to M. U. trains, remote
control schemes were often applied to single cars (including Muni #1 which started
this whole discussion.   (South Side Elevated #1 has been preserved by Chicago
Transit Authority)

Those who are conversationally familiar with New York have heard the term Lo-V and
Hi-V assigned to subway cars.  Lo-V = low-voltage control = Westinghouse and HiV =
High Voltage Control =- General Electric type M.  Remember, we are saying low or
high voltage control wiring from the master controller to the motoring controller
(generally under each car).

Sprague (who sold his patents to General Electric) started out  in 1898 using an
synchronous electric pilot motor on each of a more or less standard drum controller
mounted in the roof on each car as the motoring controller.  A small platform
controller was used to tell the pilot motor when to revolve to the next point.  In
1899, Westinghouse developed a scheme also using a drum controller, but it tended
to be somewhat more complicated.  Dave Garcia described it as a plumbers
nightmare.  On the earliest Westinghouse scheme, electrical wires from the platform
controller energized pneumatic magnet valves on the controller. The controller was
advanced by air with a most complicated array of pistons and paws and cams.  The
earliest Westinghouse Notching Head Control was sold to Brooklyn Elevated Railroad
and two of their cars survive at Branford.

General Electric next evolved into a solenoid-switch control scheme referred to as
Type M control, the letter obviously standing for the magnetic solenoids.  The
platform controller worked on 600 volts DC but at very low amperage ... just enough
to work the magnets under the car that closed the 600 volt motoring and
series/parallel transitioning circuits.   The original type M scheme was designed
for manual acceleration ... the motorman chose when to go from point 1 to 2 to 3
etc.  Prior to 1917-1918 GE also sold a type M form A for automatic acceleration,
which was nothing more than a relay interlock progression scheme operated through
an accelerating limit relay.

And now I'm blown most of your minds, I know.  Let's try to clarify:   When power
is first applied to a motor, amperage becomes briefly infinite.  As the motor picks
up speed, resistance to the movement of electricity (ohms) increases and thus the
flow of electricity (amps) decreases.  Some of you might now remember Ohm's Law
from physics.  We can use that flow of current to tell the car when to notch up on
its own ... and all of the automatic acceleration schemes used the same idea.  The
limit relay is nothing more than a two part coil with an armature that slides back
and forth in it.  Usually they are mounted vertically with down being the open
position so that it is fail-safe ... gravity always shuts off power.   OK ...
motorman turns on controller.  Up to this point there is no flow of current so the
limit relay says go to point one.   But as soon as power was applied, the current
instantly builds up and the limit relay opens again. As the motor picks up speed,
current drops and when it reaches the threshold setting, the limit relay closes
again, allowing the car  only to notch to the second point.  It is held in the
second point until speed again picks up and current drops.  The process is repeated
until it has reached the last point.  Same scheme applies to 1902 el cars or 1952
CPC cars.

Relay Interlock Progression ... a series of relays determine the sequence.  It
cannot move to point 2 until it has already been in point 1.  And so forth.  To my
mind, not simple.

A relay?  OK, it is just one switch telling another to do something, or relaying
info to another switch.  I've got one on my darkroom ceiling.  I use flood lights
to copy pictures.  No time can handle 1,000 watts.  So the timer controls one side
of the relay, and the other side of the relay controls the high amperage circuit
(in that case the lights).

Westinghouse continued its favoritism for pneumatics, and went from their abysmally
cumbersome notching head control to what they called unit switch control, but with
later (after improvements were made) was retroactively called turret control.
Westinghouse mounted an array of pneumatic switches around a central air drum or
tank.  Where GE had used 600 volt solenoid switches to close motoring contactors,
Westinghouse used magnetic-solenoid air switches to close pneumatic 600 volt
switches.  One can suspect that Westinghouse felt that there system was more
positive than the GE system.  Or maybe Sprague/GE got in their first with the
patents on the straight solenoid scheme.  Doesn't matter much.  Both worked and
worked well.  (Of course you couldn't move a Westinghouse car until the air was
pumped up.)  In time, a need developed for more control points than could be
mounted around a rotary drum, so Westinghouse arranged air unit switches very
simply in a rectangular frame and simply ran pipes for air to each one.  Here I'm
thinking of something like a North Shore interurban car with 6 series and 6
parallel points and field shunts.

In time  Westinghouse assigned letter designations to the basic schemes ... all
sorts of letters.  H stood for hand acceleration while A denoted automatic
acceleration.  B identified cars using batteries to provide the control voltage
whereas L stood for those that used line voltage (and in answer to Jim's question,
generally passed through a dropping resistor to get low-voltage DC for control).
The letter F was applied to cars having field control.  The letter V stood for
variable acceleration rate control ... always in conjunction with the automatic
designator, hence VA.  (I know of two VA cars in museums: LA 2601 or 2602 at Perris
and a Baltimore Peter Witt at Seashore).   The Chicago steel el cars from the 1920s
... the 4000s ... had Westinghouse ABLFM ... automatic ... could work on battery or
line ... field taps or field shunts ... and would train with cars having GE type M
control.    These were all generic terms and the actual hardware varied all over
the place as one would expect to happen over a half century interval.  Pittsburgh's
low floor MU cars supposedly had Westinghouse HL but they were really knockoffs of
GE type M with magnetic instead of air switches.  So that HL from 1903 and HL from
1948 could not be expected to have interchangeable parts but the concept was
essentially the same.

Along about 1917-1918 General Electric developed PC (or pneumatic cam) control
which thereafter was used in place of MA for almost all automatic acceleration
schemes.  It doesn't take a rocket scientist to understand that a rotating cam
shaft to sequence points from 1 to 9 is a lot easier or simpler than a tray full of
relays to interlock each motoring contactor.  The first installation of PC was on
four Steinway Tunnel cars of the IRT in New York.   But it became very common ...
the P&W Bullets, more than half of the C&LE Red Devils, most of the Oakland city
cars had PC (or PCM).  In order to get a greater number of control points, GE took
PC and added solenoid switches for the transition to parallel, and then ran the
same cam in reverse ... this way you could get up to 18 points out of 9 cams ...
called it PCM ... the 6119 at Baltimore Streetcar Museum and Red Arrow 78 at Arden
are good examples.

Westinghouse used relay progression schemes for AL and AB but they eventually
seemed to settle on a small wooden drum with copper strips on it and copper fingers
as a sequencing drum for AL and AB.  Remember my comment about PC for sequencing
points.  Nothing works better than a revolving drum.  Westinghouse called theirs
sequence switches.  If you can find a P&W Strafford car ... mounted on the
motorman's side of the bulkhead in one end is the sequence switch for AB and AL
control.  Westinghouse, however, couldn't seem to get away from their roots.  At
the same time GE was fitting four Steinway cars with PCM, Westinghouse fitted the
other 4 with PK control.  Russ Jackson described it as a poor-man's PCM.
Westinghouse simply took a K controller and mounted a pneumatic drive engine on it
(much more refined than in 1899), and mounted the shebang under the car ... and
used a small platform controller to drive it.  The actual designation followed what
motoring controller was used ... if you used a K-35 as the guts, the whole scheme
was called PK35.  Montreal ran a flock of PK control systems into the late 1950s,
and they can be found both at Branford and Seashore.  The Broadway Battleships in
New York City also used PK ... probably PK36.

On the automatic schemes, there was really no off position on the motor
controller.  You really only needed off under the motorman's hand.  Most remote
control schemes used a separate 600 volt line-breaker to turn the current on and
off.  This prevented arcing of the control tips when power was shut off ... any
arcing would be confined only to the limit relay.  The instand you back off on the
controller, the line breaker opens and then the motoring controller resets itself
to point one.  When the motorman goes from off to point one, the line breaker
closes ... the motor controller was already in point one.

The reverser drum was also mounted under the car, usually with a air-engine or a
pilot motor to move it from forward to reverse.  There is no off position here
either, again because the line-breaker being open is the off position.  The general
scheme here is that the remote reverser says where it was from the last usage until
the line switch is again closed.  At that point the remote reverser matches the
forward or reverse position of the controller key under the motorman's hand.

If you want to know about chopper (or thrystor), p-wire technology, AC  traction
motors and all that new stuff, better ask someone who knows it.

Enough male bovine defecation for one day?????




Jim Holland wrote:

> Good Morning!
>
>         Directed mostly to Fred but might have general interest.
>
>         Not savvy to controllers on TrolleyCars, but this was said about Muni's
> #1 with general comments about controllers, and I quote:::
>
>         """Better check No. 1's controller.    You'll find that it has 600 volt
> control.    The L in HL control stands for "line" meaning the controls
> are line voltage.    If it was 32 volts the control would have been
> called HB, B standing for "battery" meaning the controls are at battery
> voltage, usually 28 or 32 volts."""
>
>         Is this a good general description and if not, why not?
>
>         What about controllers on PRCo cars?    Low voltage?
>

fws