"Splain it to me, Lucy!
Many thanks, Jimmy
Hi,
The biggest difference I see is that the DC units do not have the big openings below the radiator on the sides of the nose. They also look to have 4 louvered doors just ahead of the cab. I was using the 2008 ‘Diesel Spotters Guide’ as a reference. As you may already know the traction motors are different as in the name designation.
Lucy (ha,hah!)
MP15DC - 1,500 HP - 1974 thru 1980 - 351 examples built. Used an V12 EMD 645-series powerplant with a DC generator, riding on Bloomberg Trucks. Originally named MP15, renamed when MP15AC introduced.
MP15AC - 1,500 HP - 1975 thru 1984 - 246 examples built. Used an V12 EMD 645-series powerplant with an AC alternator and a DC rectifier, riding on Bloomberg Trucks. The AC model is 1.5 ft longer than an DC model.
Easiest way to tell them apart - MP15DC has a forward facing radiator grill - the MP15AC has side radiator grills mounted lower on the body.
These logically are a follow on to the SW1500 series switches, but a considered more a road unit lurking in a switcher body.
Info is available on http://wikipedia.org and at http://yardlimit.railfan.net - unit production number differ between these sites.
Gil, known as Bill somedays … [8D]
Chad,
There is NO difference in the traction motors. Both have D77 traction motors. There is an AC main alternator that produces AC, but it is converted to DC before it gets to the traction motors. This is similar to the ‘Dash-2’ line of engines at the time. That ‘compartment’ just forward of the cab is where the ‘toilet’ was installed. There was a ‘cube’ in the cab with the electrical gear.
Jim
Jim
Jim,
Thanks for teaching me something new (to me) , I appreciate the knowledge & correction.
Just FTR, the EMD trucks are Blomberg (one O); Bloomberg is the news service.
Martin
Spinning of of Jim’s post, it is more efficient to produce AC power and convert to DC (traction motors are DC) than to produce straight DC current. EMD also had some pre -2 models that did this, but were not as popular for the simple fact -2 models were made AC/DC (sorry had to).
EMD started kicking around with AC generators with the introduction of 2nd generation locomotives. GP38AC (1971), GP39 series (1969-70. also had a DC model), and of course the 40 series (1965-71).
Don’t forget the 8-cylinder turbo-charged MP15T. A miniscule model when compared to the rest, but never the less it was there. Also, when the AC designation is used on modern loco’s, like the GEAC4400W or EMD SD70ACe, it is actually referring to AC drive traction motors.
After all that though, I will still take my Century series Alco’s.
Spinning of of Jim’s post, it is more efficient to produce AC power and convert to DC (traction motors are DC) than to produce straight DC current. EMD also had some pre -2 models that did this, but were not as popular for the simple fact -2 models were made AC/DC (sorry had to).
EMD started kicking around with AC generators with the introduction of 2nd generation locomotives. GP38AC (1971), GP39 series (1969-70. also had a DC model), and of course the 40 series (1965-71).
Don’t forget the 8-cylinder turbo-charged MP15T. A miniscule model when compared to the rest, but never the less it was there. Also, when the AC designation is used on modern loco’s, like the GEAC4400W or EMD SD70ACe, it is actually referring to AC drive traction motors.
After all that though, I will still take my Century series Alco’s.
It became more efficient to do the AC to DC conversion when large capacity diodes became available. Prior to that, AC driving a motor-generator(GG1) or selenium rectifiers(E44C) were used. There was a significant ‘loss’, but PRR had to convert the AC delivered by the overhead to DC for the traction motors. Mid-life in the E44C’s they got a conversion to the new solid state diodes, which resulted in an increase on available power.
The diesel builders were rapidly approaching the physical limit of a main generator(DC) that would fit in a 6’ wide car body. Someplace between 2500 & 2800 hp was the limit. When EMD offered the ‘40’ line of locomotives in 1966, the models at 3000 hp or greater were offered with AC/DC ‘standard’. As costs of the new solid state gear dropped, EMD offered ‘AC’ models of the 38/39 line, and eventually made it ‘standard’ with the release of the ‘Dash-2’ line(except for switchers). The MP15AC broke that barrier a few years later
Even though the solid state conversion did result in some losses, the alternator delivered higher power output - So the actual power delivered to the traction motors was greater.
Jim
The GG1 did not have a motor-generator arrangement; it had AC traction motors with a step-down transformer to reduce the 11KV to 600V for the motors. (Various other electrics did have motor-generator systems, but the GG1 was not one of them.)
Martin
For Berkshire Steam, the first alternator equipped US locomotive was the Alco C630, one of your favoured Century series. The big question is: “why did GE sell an alternator to Alco before installing it in one of their own locomotives?”
For jrbernier, I think selenium rectifiers do count as solid state. The last valve type rectifiers were the ignitron type which were used in the NH rectifier units and possibly in the earliest E44s.
M636C