[PRCo] Motor clarification

[Fred Schneider]

This responds to a query from Holland about PCC motors.  If that doesn't interest
you, delete now rather than be bored!

To the contrary Jim.  Just because blown motors were a 1940 improvement doesn't
mean they lacked importance.  I find it significant that after merely four years
experience someone decided to force cool traction motors.  Probably Bill
Rossell.   The basic laws of physics didn't change in 1940 or 1945; rather
someone got tired of spending money rewinding traction motors and he saw an easy
out once there was no compressor to drive off the MG set.  .

Maybe I was not clear before.  The advantage of a series wound DC motor is
simple.  It creates the greatest torque at the slowest speeds. This gives the car
a lot of get up and go, and an ability to climb steep grades.   The disadvantage
is heat build up is also greatest under load at the slowest speeds.  And if the
fan is on the armature shaft, the heat dissipation is worst at the slowest speeds
because the fan is also turning slowly.   Now consider also that motor vehicle
traffic also increased in the late 1930s and drastically in the late 1940s.  As I
write this I'm looking at a color picture of PRC 4823 followed by four other cars
in front of the Cathedral of Learning on Fifth Avenue in Oakland.  It was a
traffic jam of streetcars and motorists.  I remember riding through there in the
late afternoon with my mother .. we moved inches at a time.  That sort of traffic
is deadly to internally vented traction motors.  They just sit and bake, and bake
some more.

With a 1600 or 1700, that wasn't a problem.  Air was forced through the
propulsion motors at a constant rate of flow.  Didn't matter if the car was
moving at 40 mph or lugging along on resistance, and stopping, and moving another
twenty feet, and stopping again.  The motors were constantly being cooled.

What happens if you don't cool them.  Remember the Lehigh Valley Transit's
Liberty Bell Route?  They were plagued for the life of the Ten-hundreds with
burnt out motors.  Why, because motorman on the HL cars notched up too rapidly
and the accelerating limit relays on the PC equipped cars were set too high just
to make them accelerate on hills (without locking up).  These cars were
engineered to run flat out across level western Ohio but not to run up and down 5
percent grades in eastern Pennsylvania with stops every half mile or so.  Out of
12 cars, I think about three or four were available for service on the last day.
The Indiana car (1030) was in the shop for motor work (it came out on the
abandonment afternoon).  So what happened to all those "junk" motors?   Red Arrow
bought all of the GE 706 motors for spares for the Bullet cars.  And once they
were no longer abused, they worked fine.

fws


Jim Holland wrote:

> Good Morning!
>
> > Fred Schneider wrote:
>
> > I went back to the equipment chart in the PCC book ...
> > the easiest way to determine blown motors is on
> > GE cars because that apparatus supplier changed the
> > motor number.  Their 1198 motors were internally fan
> > vented, while the 1220 weries were blown motors.
> > The first cars in Pittsburgh with GE 1220 motors were
> > 1675-1699.  .
> > If you have the first edition of PCC From Coast to Coast,
> > there was a fold-out chart in the rear.  It did not appear
> > in second edition (I think Mac was trying to save money).
>
>         Actually in  *PCC The Car That Fought Back.*
>
> > ...You'll find that the 1600 had 1432J, cars 1601-1975 had
> > 1432HE and 1700-1775 had 1432K........
> > How were the motors on the 1600s ventilated.......
> > I apparently found evidence that the 1600s had a
> > PC2 compressor,  which had to be driven off a pulley
> > on the MG set.    This suggests that the other end
> > drove a single fan to cool both the resistors and
> > the motors, and to heat the car.
>
>         VERY  Interesting.    Apparently associated the move from Truck-Level
> air-intakes to Roof-Level air-intakes to Also mean Forced-Air (Blown)
> Ventilation   ---   but after reviewing the charts as you suggested, I
> Now see that All That Changed was the source of the air!
> Truck-Level air source allowed for dirt stirred up by car movement to
> be drawn into the motors so Air-Source was changed to roof level!
>
>         So the 1600--1799 cars were the Only PRCo Cars with Forced-Air
> (Blown) Motor Ventilation  --  all other cars used Motor-Mounted Fans
> for ventilation.
>
>         Cooling of motors must not have been a real problem since
> Forced-Ventilation came along so late in the game.    Maybe this
> development was held up by the war as well.
>
>         Thank You for taking the time to clarify this Information.
>
> > Please note that all-electric cars do not
> > require standee windows.
>
>         Good Heavens   ---   A Given!    How did Windows get introduced into
> Electrical specifications?!?!(:->)
>
> A reminder (how often do you need the Reminders?!)
>
> Assignment__For__FWS3:::::::
>
>         Next time at PTM, please check the spare PCC trucks.
> B2Bs have an obvious cradle welded to the tube frame for
> holding the Rubber--Spring  bolster.
>         **-PCC The Car That Fought Back-**  pg.128 shows
> 3-photos of the  *Demonstration__B2B*   ---   with clear
> photo of cradle.    If there are any spares with the
> WAB drum actuator, a check of the bolster mount will
> be revealing.
>

fws