[PRCo] Re: PCC Control

[Fred Schneider]

Bob and anyone else crazy enough to tune in to this station:

There was an two or three old old issues of Modern Tramway with a  
pieces by W. J. (Jack) Wyse that explained all this.   They covered  
both the high voltage and the low voltage (32 volt) wiring on a pre- 
war PCC and it was probably the best explanation that appeared in  
print anywhere.   But it takes a whole bunch of evenings looking at  
the wiring diagrams before it all sinks in.    It explains the  
sequence of all the motoring, braking and field shunting contactors  
and what they do.  It was very wordy but that is necessary for a very  
complex subject.    It was almost essential that you have a prior  
course in physics or electronics before you read the articles.   Jack  
never wrote a subsequent dissertation that covered the changes needed  
for extended dynamic braking.

I don't remember when it was published but perhaps Mike Taplin can  
come back to us with a citation.    It was sometime back in the 1960s.



F3

On May 15, 2007, at 6:58 PM, Bob Dietrich wrote:

> Holy cow Boris!  This is like listening in to a conversation  
> between Dr.
> Fred and Dr. Allman.  I understand all the words; it is the  
> combinations
> that throw me.
>
>
>
> -----Original Message-----
> From: pittsburgh-railways-bounce at lists.dementia.org
> [mailto:pittsburgh-railways-bounce at lists.dementia.org] On Behalf Of  
> Boris
> Cefer
> Sent: Tuesday, May 15, 2007 12:48 PM
> To: pittsburgh-railways at dementia.org
> Subject: [PRCo] Re: PCC Control
>
> 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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>
>
>
>
>