GP 38-3AC

[IRB Souther Engineer]

I saw this video on the Maryland Midland and saw the locomotive at 3:20 had a GP 38-3AC designation: http://www.youtube.com/watch?v=HNhbDkGH488

Anyone have any info on that?

[MJChittick]

The locomotive you're referring to (#304) was rebuilt from Denver & Rio Grande Western GP-40 #3090.  Don't know the details of the rebuild, but obviously the turbo was removed and I'm guessing it included a significant electrical upgrade.  The "AC" refers to the locomotive having an AC main alternator as opposed to a DC main generator.

[bubbajustin]

So answer me this:

 

Do the GP38AC's have that traction controll system like the newer AC's where if one axel looses traction it will cut the power to that axel untill it regains traction? Or are they not that advanced on the GP AC's?

-Justin 

[YoHo1975]

No,

The AC in GP38AC refers to the fact that the locomotive uses and Alternator instead of a generator to produce electricity from the diesel engine.

In older locomotives, a DC generator produced electricity that then supplied the DC traction motors. 

 

In GP38ACs and all of the Dash2 and newer engines, an AC alternator produces AC current. This is then sent to a rectifier (same as a model railroad uses to convert wall electricity to DC track current, though obviously bigger) to turn it back into DC current.

This conversion allows the locomotive to develop higher amounts of electricity and provide better control.

A modern AC locomotive has the Alternator, then it recitifies it to DC, then it sends it through inverters which convert it back into AC and on to the AC traction motors. Again, all this conversion provides a level of power and conditioning unavailable straight out of the engine.

[cx500]

Doubt it.  I'm sure the traction motors are still DC.  You are being confused by equating 1970's designations with modern terminology.

When the GP38 came out, two models were offered.  The straight GP38 had a DC main generator, while the GP38AC had an alternator instead to generate power.  In the latter case the AC current was converted to DC before going to the traction motors.  The same option was offered for EMD's switcher (SW and MP) models of the time. A DC version of the GP40/SD40/SD45 was not offered because the much higher power was beyond the practical limits of a generator.  But development of a control system for AC traction motors robust enough to meet North American freight duties still lay in the future.

The clear advantage of using an alternator instead of a generator meant that the DC option was dropped with the introduction of the -2 line.  As a result the suffix was unnecessary and discontinued.  When it reappeared a decade or so later it had an entirely different meaning. 

John

[WSOR 3801]

The same option was offered for EMD's switcher (SW and MP) models of the time.

John

The first (and only) EMD switchers built with AR10s (AC main gens) were the MP15ACs.  These also got rid of the front mount, belt drive radiator fan in favor of a tunnel-motor style radiator, with electric fan.  The lower maintenance of the AC main gen and electric rad fan made it worth the extra cost of purchase.  This also accounts for UP snapping up 32 former MILW MP15ACs when the lease expired.