[PRCo] Re: PCC Control

[Boris Cefer]

Yes, I am a bee...

Well, what actually happened to you i do not know, but the car is expected 
to work this way:

When you release power, one of the field shunting contactors (F2) 
immediately picks up to secure low-amp spotting of the motors and the 
accelerator. At higher speeds when the accelerator as at positions close to 
the 99th finger, also other field shunting contactors are picked up (the 
usual arrangement is such that F1 picks up at 85th and F3 at 90th 
accelerator finger) to keep the spotting current at a reasonable value. The 
overall accelerator resistance is something around 3.3 ohm and without those 
field shunts applied above 85th the resistance would be absolutely 
insufficient and the spotting retardation would be pretty perceptible.
By depressing brake pedal (just only to obtain brake) you remove part of 
these field shunts which builds up the dynamic braking current rapidly, 
practically without any movement of the accelerator rollers.

The problem you are experiencing is very hard to judge - I need to get under 
the car and see certain components to make a conclusion. I believe it might 
be a limit relay problem. I think the limit relay of 1711 was modified to 
suit the back up controller.

B

----- Original Message ----- 
From: "Fred Schneider" <fwschneider at comcast.net>
To: <pittsburgh-railways at dementia.org>
Cc: "Orient Bernie" <bernieo22 at verizon.net>
Sent: Tuesday, May 15, 2007 6:22 PM
Subject: [PRCo] PCC Control


> Boris:
>
> You bees the expert on this ...
>
> When I was running 1711 this weekend, I was bothered by an inability
> to get the put my foot on the brake pedal lightly enough at almost
> any speed to keep the dynamic brakes from coming on with a real
> jolt.    It was especially rough at low speeds.   I know it isn't a
> characteristic of all PCCs because I've never had the problem with
> Baltimore Transit 7407; that car is much smoother.   Herb Brannon
> commented that some PAT cars were that way and some were not, so it
> must be either an adjustment or set up issue with the master
> controller or a failure.   Are field shunts supposed to come in very
> briefly in braking to cushion the initial application and then drop out?
>
> Fred
>
>
>
>
>
>
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