[PRCo] Re: Air Brakes - CERA Trolley Sparks 85

[Fred Schneider]

Bob:

I've never seen a wiring diagram.   I have been told that West Penn  
used the B-50 controller for dynamic braking and used some of the  
energy created by the motors used as generators to feed the track  
brakes.   I was also told that there was a mechanical linkage  
connecting the track brakes to the wheel brake shoes.

Lets get a basic understand of dynamic braking ... motors will  
optimally generate current at a certain speed with a certain  
resistance in series with it.    The amount of resistance is  
determined by how fast the car is going.   The slower the car, the  
more resistance you need to get the same braking rate.

The rate of dynamic braking is determined by how fast you insert the  
resistance.

On a PCC car this is simply automatic.   As soon as the motorman took  
his foot off the power pedal, the motoring contacts opened, and the  
first braking contacts closed setting up a brake loop.   The car was  
in braking mode then.   A spotting coil moved the accelerator drum on  
a Westinghouse car backwards (or the KM unit on a GE car) as the car  
slowed down so that the drum was in the precise position for maximum  
braking whenever the operator put his foot on the brake pedal.     
Then the same limit relay that was used in acceleration determined  
how fast the car stopped depending on how far down he pushed the  
pedal ... it stretched the relay calibration spring and the pilot  
motor spun the drum back faster the farther he pushed the pedal down,  
thereby inserting resistance faster.

Now on a hand control car, like a West Penn car with a B-50  
controller (or any of the European equipment at National Capital or  
the equipment in Crich England), the motorman has to instinctively  
know ... I'm doing 15 miles per hour therefore it would be best if I  
start braking in the 5th notch.   Or I'm doing 40 miles an hour so I  
can start braking in the first notch.   It becomes an experience  
thing.   And how fast the car stops then depends on how fast the  
operator cranks up that controller.

On the PCC, as soon as the dynamic current faded, the air brakes came  
on (at about 8 to 10 mph) or drum brakes on an all-electric (at 1 to  
2 mph).    On a West Penn car, again this was something the motorman  
had to do.   When the dynamic current faded, there was no lockout  
relay to do the thinking for him.   He had to wind up the hand brake  
on his own.

Now if the dynamic brakes were connected to the track brakes (as has  
been alluded) and they were in turn connected by linkage to the wheel  
tread brakes, then simply snugging up the hand brake while you are  
winding up the controller and holding it should work.   It should be  
very easy to wind it up when you are already in dynamic mode.   On  
the other hand, in the yards at 5 mph, then you would be using hand  
brakes only to stop those cars.

But what I really need is a wiring diagram and a mechanical plan for  
the trucks to be sure.

Clear as mud?

Fred Schneider





On Dec 8, 2007, at 3:34 PM, ROBERT R ROCKWELL wrote:

> Briefly, how did the West Penn track brake work ?
> Robert Rockwell
> w3syt1 at msn.com<mailto:w3syt1 at msn.com>
>   ----- Original Message -----
>   From: Mark McGuire<mailto:macmarka at netzero.net>
>   To: pittsburgh-railways at dementia.org<mailto:pittsburgh- 
> railways at dementia.org>
>   Sent: Friday, December 07, 2007 10:12 PM
>   Subject: [PRCo] Re: Air Brakes - CERA Trolley Sparks 85
>
>
>