[PRCo] Re: PCC Accelerator, WH Version

[robert simpson]

Thanks Jim!
   
  I have a lot to learn.  Please bear with me on some of my questions which, to you and other list subscribers, may seem trivial.  I am slowly going through the archives.  Regret I have nothing to offer to enrich the archives.
   
  Robert Simpson
  from Krazy California
  
Jim Holland <PRCoPCC at P-R-Co.com> wrote:
  >.Robert Simpson (Rockwell?) wrote:::
.
>.How did they control speed on a Direct Current system? I remember 
watching the operators on PRCo pressing the "accelerator" (sorry, I 
don't know the appropriate lingo) to the floor when starting and the 
wheels didn't spin. Was there some kind of regulator which limited the 
amount of power going to the motors? A simple rheostat would seem to be 
very inefficient.
>.Did the Direct Current cars use resistive braking on long downhill 
grades?

>.So, in the case of a complete power failure on an ALL electric car, 
which is the last resort ? A motor drum brake spring loaded (reduction 
type brake), or a magnetic track brake fed from 32 v batteries?
.
I may have confused Robert Rockwell and Robert Simpson on the quote - My 
Apologies!~!
.
the photos sent to the list are in Noah's ArkIves at this URL::
.
http://lists.dementia.org/files/pittsburgh-railways/
.
but I have been unable to find a photo of a PCC accelerator where many 
of the photos are not appropriately identified is worse than the needle 
in the haystack -- I am certain there is one on the list somewhere. 
(And while this has been disgusted onlist before, someone new trying 
to find such a discussion in the archives is horrific since we are 
anything but good about subject line adherence!!!) Attached is a 
Westinghouse accelerator which is also used for dynamic braking. A 
pilot motor *-reportedly-* moves the accelerator through about 
180-degrees to cut out resistance to the motors for acceleration and 
automatically spots the accelerator for dynamic braking when the power 
pedal is released. I say the pilot reportedly advances the 
accelerator because this accelerator was inverted and placed in a glass 
top case in PCC 100 renumbered as M11 Instruction Car and I watched it 
revolve corresponding to how far the motorman depressed the power pedal 
-- half way on pedal and accelerator immediately went up half way. 
Every movement of pedal was followed by immediate movement of 
accelerator -- one would expect the pilot motor to lag somewhat.
.
There are 99-points of resistance on this accelerator which is what 
makes the PCC so smooth. The accelerator usually doesn't remain in 
one place so resistance ribbons are relatively light and would burn out 
easily if the accelerator did stick in one position. Boris could 
give excellent description of operation if so inclined.
.
On Most but Not All PCCs the motorman had 3-pedals:::
.
.......Right - Power Pedal
.
.......Center - Brake.
.
.......Left - Deadman Pedal.
.
With the brake depressed about halfway the motorman can remove his foot 
from the deadman pedal which will hold the brake half-way - This Is Park!~!
.
To move the PCC, the motorman places his foot over the brake, depresses 
the deadman which releases the brake, then moves his foot to the power 
pedal for acceleration. Foot is always on deadman unless the car is 
placed in Park.
.
The maximum acceleration on the PCC was 4.75-mph/ps and this was a 
variable rate depending upon how far the power pedal is depressed - 
pilot motor mentioned above drives accelerator.
.
Maximum """Service__Brake""" is also 4.75-mph/ps variable to that 
point. Pushing the brake further into emergency would provide up to 
9.0-mph/ps braking.
.
The primary brake on a PCC is dynamic which is operable at all times 
regardless of state of 600-volts overhead (but in an ImPerfect World, 
dynamics can fail for a variety of reasons) And Which faded at about 
3.0-mph for Air-Electric PCCs (friction brake, doors, windshield 
wipers, sanders operated by air pressure). The dynamic was extended 
to 0.75-mph for All-Electric PCCs sans Air (and a few Air-Electrics 
when built (PRCo 1601s) and not a few retrofitted for same) after which 
a lockout relay allowed automatic application of the friction brake to 
complete the stop and hold the car once stopped. While this friction 
brake was designed so the car could be stopped with Only The Friction 
Brake """A_Few_Times""" (when All Else Fails,) this is Not the 
Intended purpose of the friction brake and using it as the sole brake 
will completely wear the brakes Very Fast - much less than a trip - 
witness the runaway of 1727 in Mt.Wash tunnel (also disgusted here 
innumerable times!~!~!) Magnetic Track brake came into play when 
emergency braking is engaged!
.
You might enjoy going through the photos at the archive - just copy and 
paste the url into an email if you have any questions. Someone here 
will have some answers!~!~!
.
.
.
Jim__Holland



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