jrbernier wrote:
There have been 'upgrades' to older GP7/9 locomotives that replace the electrical controls with 'Dash 2' style modular equipment. The ex-BN 1400 series and ex-ICG GP11 programs did just that.
The 'high brow' on the GP30 was basically a GM styling feature. There was some additional electrical cabinet stuff up there due to the increased space it offered.
You are confusing calculated starting T/E vs Continuous T/E. That 65,000 vs 91,000 lbs of starting T/E is basically 25% of the weight on the drivers(The SD weighs about 50% more). The key number is the 'Continuous T/E' at the 'Minimum Continuous Speed'. The GP's have a MCS of about 12-13 mph(depending on gear ratio). The SD7 has a MCS of around 7-8 mph(at the same gear ratio). What this means is that the SD7 will be out of red zone(short time rating) faster than the GP7. The GP7 will outpull that SD7 above 50 mph. At that speed, the 6 traction motors in the SD7 are sucking up the output of the main generator. This is known as 'Amping Out'. That GP7 with only 4 traction motors sucking juice and will not 'Amp Out' the main generator until a higher speed and will maintain continuous T/E higher than the SD7 at those speeds.
The bottom line is that the SD7 will pull more tonnage all day long in the 25-40 mph range, but the GP7 will deliver more continuous T/E over 50 mph.
In the case of the GP50, there are some additional technologies that come into play. The '50' line of engines had the radar controlled 'SS' wheel slip/correction feature where a small amount of wheel slip was dialed in by the computer and this heated the 'contact patch' where the wheel/rail meet - Resulting in a large increase in Continuous T/E. Of course this system was not perfect and wild excursions in wheel slip can still happen. But with 3500 hp, the GP50 does not lose Continuous T/E as fast as that SD7 or GP7. Still, it is not a good choice for short line or regional trains that never get over 35-40 mph(but the used price may be just too good of a deal).
Jim
Jim or anybody,
At what HP level did the SD's stop "Amping Out" and truly become suitable for high speed work(50-70 MPH) w/o having a high speed gear ratio like 60:17 or 59:18????
It seemed that through the 70's and into the 80's and 90's that RR's by and large with a few exceptions entrusted their high speed hotshots to locos like the GP40-2, the B36-7, the GP50 and those slippery race horses the GP60 and B40-8's. Other than the SD45 and SD45-2 they seemed to only give the high speed nod to the SD40-2 usually when those units were geared high like UP's 8000 series and CNW's Falcon units.
What was the "tipping point" that RR's consider C-C's a true high speed locomotive as well as a lugger??
Was it the SD70 and C40-8???
Colin
GP40Jim or anybody, At what HP level did the SD's stop "Amping Out" and truly become suitable for high speed work(50-70 MPH) w/o having a high speed gear ratio like 60:17 or 59:18???? It seemed that through the 70's and into the 80's and 90's that RR's by and large with a few exceptions entrusted their high speed hotshots to locos like the GP40-2, the B36-7, the GP50 and those slippery race horses the GP60 and B40-8's. Other than the SD45 and SD45-2 they seemed to only give the high speed nod to the SD40-2 usually when those units were geared high like UP's 8000 series and CNW's Falcon units. What was the "tipping point" that RR's consider C-C's a true high speed locomotive as well as a lugger?? Was it the SD70 and C40-8??? Colin
With the arrival of the SD40 which had the AR-10 alternator and which at 600hp per axle was the same power level as the GP35.
The reason for some railroads ordering higher speed gearing was that 62:15 gearing was rated at 65 mph, at some point the railroads decided that it was good for 70 mph if you had D77 motors, once that happened most railroads changed to 62:15 gearing to get down to a more practical minimum continuous speed. Chessie System went with GP40-2s more because too many mining branches were restricted from 6 axle power, rather than because of a need for high speed intermodal power. The B&O didn't run that many Intermodal trains.
I remember reading that the UP had some high speed geared SD-40's, often referred to as the fast 40's. Prior to that, the GN had some SDP--40's, the SP had SDP-45's and the AT&SF had F-45's.
GP40The GP7 will outpull that SD7 above 50 mph. At that speed, the 6 traction motors in the SD7 are sucking up the output of the main generator. This is known as 'Amping Out'.
A 62:15 SD40-2 might slightly outpull a 62:15 GP40-2 at 70 mph, due to the GP reaching AR10 voltage limit-- in any case, it won't do worse. Of course, on any significant upgrade the SD40-2's greater weight will quickly overcome its advantage in rail horsepower.
The SD-7 did run in straight parellel . It started in Series Par , 2-3 steps of field shunting , parellel , 2-3 steps of shunting in Par . The SD -24 started in straight series, 3-4 steps of field shunting, series parellel transition, 3-4 steps of field shunting, parellel transition, 3-4 steps of field shunting in parellel.
The SD9 operators manual says it goes from two strings of three to three pair-- no parallel. Any reason to think the SD7 did different?
SD24 probably started with two strings of three, then to three pair, then to straight parallel? You didn't mean "straight series", did you?
Some basic math here: 6 X 600 = 3600 = SD45! The SD40 only had 500 horsepower per traction motor.
beaulieu With the arrival of the SD40 which had the AR-10 alternator and which at 600hp per axle was the same power level as the GP35.
SD24's that I worked on started in straight series. TM motor voltages were kept pretty low that way.
The SD-7 and 9s early on may have worked the way you describe but by the time I got to them they worked as I described, in your scenario , Tm voltages probably did not exceed 600 volts .. not a very fast locomotive at all , I would guess that max speed would have been 35-40 mph.
So you're saying your SD24s went from 6S to... 3S2P? Or 2S3P? Or both? And then to 6P?
Can anyone find a manual showing any road locomotive starting in straight series, as built? All the unit's motors in one series string? The SW1 did, but I didn't think road units were ever built that way.
SP's SD9 commute engines (the well-known Huff and Puff) could reach 65-70 in a reasonable amount of time-- think SP converted them to 6P?
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