"Early diesel-electric locomotives in the United States used direct current (DC) traction motors, but alternating current (AC) motors came into widespread use in the 1990s, starting with the Electro-Motive SD70MAC in 1993 and followed by the General Electric's AC4400CW in 1994 and AC6000CW in 1995." Taken from Wiki, you know how they say everthing on the internet is true, right ? If so this is good for us to know. _______________________________________________________________________________________________________________________________________ We decided in 2003 not to take the leap to DCC and have held to that with no problem. I guess we're just lucky to enjoy the old DC Block System. Actually DCC has helped our DC operation choices and in other areas. I love to watch several other engineers running remote DCC, all at the same time. That's entertainment. Are we (Wife & I) the few remaining DC Modelers ? Cliff & Sam
True and False Way back when in my college days, the word was to watch the word "always" on tests, which means it was not true. Your observation is also mine, but from experience I am suspecting there was some obscure AC diesel in the formation days. But until your observation is proven wrong, I am on your side of the fence. Ken "FloridaBoy" Willaman (and freezing tonight)
No , your both right . A/C traction motors were not viable on diesel locomotives until inverters were practical (1993) . Some electric railroads did use A/C traction motors and some of them were VERY early. The Baltimore and Annapolis comes to mind . A/C motors were removed from B&A equipment and D/C equipment installed at some point. The PRR GG1 was A/C powered. Randy
If the question about DC modelers I am still a DC guy. I think DCC is cool but for the investment I have in DC I have no plans to convert. Not that big a deal to me. Maybe its time for a new poll. I know its been done before.
EMD made some AC engines before the MACs started production in the early 1990's. I think GT/CV ordered several GP38AC engines in the early 70's. I'm not sure about other railroads. Those GP38ACs looked just like the regular DC counterparts. EMD also sold the MP15AC switcher in the late 70's. The main advantage to an AC motor is that they do not overload and burn out like DC motors. This is a major danger when the motors rotate slowly under a heavy load - think moving long cuts of cars in a yard. The disadvantage was that they were less efficient than the DC motors and I believe they were harder to repair. The efficiency issue was addressed by the MAC generation's use of microprocessors to chop direct current into percise alternating cirrent waves.
None of these engines were A/C locomotives. They are referring to the fact that instead of a D-32 main generator (with 60 damn brushes on a commutator) EMD used the nicer AR-10 alternator (with 8 brushes on a nice slip ring) and a different SCR control system. They all still had the EMD D-77 DC traction motors.
I would pretty much agree with the wiki. My understanding was that advances in computers/ micro processors, were the key to using ac. I know that as of a couple of years ago, Norfolk Southern still preferred dc locomotives, but I don't know if thats still true. I guess it was a maintenance, reliability, or initial cost vs. benefit decision.
Slightly off Topic but Very Nostalgic for me: While I don't have the answer this conversation brings back bits and pieces of conversations with my father whose specialty was Analog to Digital and Power Conversion. At the time I was in high school, (I graduated HS in '73), and he was working at Analog Devices. I can remember asking why bother converting A/D and what power conversion was all about. I don't remember much but his basic answer was "in the long run" it would be faster, more accurate and more interchangeable. Guess he was right.
I can't comment on the traction motors but I can answer the DC/DCC question: DC and staying that way! Regards, Pete Davies
CP Rail's lone M640 was converted in early '85 to an experimental AC unit. It was given 4 Brown Boveri traction motors, thus making it an A1A-A1A type loco. Here it is before conversion, http://www.rrpicturearchives.net/showPicture.aspx?id=501405 and here it is after, http://www.rrpicturearchives.net/showPicture.aspx?id=1891814. This unit might have been why CP decided to go with AC4400s. It was great seeing these back in the early '90s. Trevor D.
A couple years ago, I was trying to learn about early AC locomotives. They arrived in Europe before North America. https://en.wikipedia.org/wiki/Henschel-BBC_DE2500 http://mitglied.multimania.de/steamy/baureihen/de2500/de2500.html First AC traction diesel, 1971. https://en.wikipedia.org/wiki/NSB_Di_4 First production AC diesel, 1980. And, as I had expected/hoped given the Henschel/GM connection at the time, EMD 16-645 engine. https://en.wikipedia.org/wiki/DSB_Class_ME http://www.jernbanen.dk/motor_solo.php?s=8&lokid=186
For those curious enough, the advantages of AC motors over the DC are numerous. Primarily that a well cooled AC motor can run all day at slow rpm's without burning up, which adds a lot to operational usefulness. The DC motor has a time limit at slow speed/high amperage running, exceed that and the brushes overheat, melt and destroy the commutator and brushes and brushholder. It's not pretty. The AC motor has no brushes, which is also a second advantage. There is no need for an electrician to go under the unit every quarter and inspect and change out brushes, a dirty, time consuming and expensive job when added up over the life of the unit. The AC motors disadvantage USED to be a lack of adequate speed control, which is frequency based on a straight AC motor. That means it would require a variable rpm control an the diesel with an infinite number of settings from minimum rpm to maximum. The controls for that were bulky and unreliable in analog days, more operational headaches and maintenance issues. The advent of the chopped DC digitally controlled system used now made the units reliable and easily operable. The biggest headache is making sure that the HUGE capacitors are properly discharged and grounded before starting maintenance work. That is definitely a safety issue, but easily done. Hope this clears up a little of the history and theory.
