Andrew,
I am not sure what your source of information is, but IDAC had little to do
with loading coal or ore trains at very slow speeds. IDAC stand for
Instantaneous Detection And Correction. It was one of the earlier and very
successful solid state wheel slip control systems. Prior to that, most wheel
slip control systems, including EMD's, were hard wired low tech rate of change
systems that looked for imbalances between traction motors. Then, through a
series of relay controls, adjusted generator output to reduce or correct the
slip, often not anywhere nearly fast enough. Later, systems, such as EMD's
Super Series, were developed around the concept that allowing a small amount of
controlled slip provided even greater tractive effort that is found on RRs
today.
As for slow speed loading operations, that was accomplished through another
system known as slow speed control which basically allows the engineer to fine
tune the power output between throttle positions. Most loading operations are
level or nearly level although a few, such as that at Craig, CO on the former
D&RGW, are downhill. In those operations, the DC locomotives are allowed to
roll forward with the reverser in the reverse position and a small amount of
throttle provided. The motors act as a retarding force and maintain speed very
well. I don't know if the same procedure works with an AC locomotive, but it
may as long as the locomotive is placed in reverse before the brakes are
released and it starts to roll.
Concerning mixed consists with SD45s and older SD7s and 9s, I am sure that they
weren't popular and probably weren't good a operating practice. However, I am
sure it was done from time to time. As I recall, an SD45 only had one step of
transition, while the SD7s and 9s had three. Early SD45s also had shunting
steps as did all of the earlier SDs. I think that the SD7s had manual
transition that the engineer had to control. If the SD7 wasn't in the lead, it
would be difficult to know when to make transition. If a locomotive doesn't
make transition, it simply can't accelerate any more and drags the consist
down. It is like a automobile stuck in 2nd gear. Those early SDs were fine
locomotives and were great in heavy drag service, but they were not race
horses. The SD45, on the other hand, with more than twice the horsepower of
either the SD7s or 9s, was intended to be a compromise between the slower, but
higher tractive effort SD40 and the higher speed / lower tractive effort GP40.
In that function, it served well, particularly for those RRs that had a
combination of higher speed operation and heavy grades in the same operating
area.
Bill Barber
Gravois Mills, MO
On Feb 16, 2014, at 4:51 AM, CBQ@yahoogroups.com wrote:
> Re: compatibility of engines
> Sat Feb 15, 2014 10:42 am (PST) . Posted by:"Andrew Koetz" andrewkoetzI have
> seen the term "Bozo Consists" when describing a consist that had
> SD45s in it mixed with older SD7 & SD9s, this was due to the IDAC slow
> crawl feature the SD45s and later EMDs were built with. The IDAC system
> active, coal trains, ore/taconite trains could be loaded uniformly with
> pretty much equal tonnage of cargo in each hopper. I think I saw the term
> "Bozo Consists" used in a story on the Erie Lackawanna RR back when TRAINS
> magazine had their "Locomotive of the month" thing that they were doing,
> they would dedicate about three or four articles in the magazine to the
> L.O.T.M. and look at how the locomotive was developed, numbers built,
> variants thereof, etc.
> Andrew Koetz
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