More AC loco questions

I posted a question regarding seeing a BNSF AC4400 in unit Grain service in the BNSF forum which lead me to reading the march Issue of trains which lead me back here.

I want to make sure I have this Iced down in my mind (as my father says)
So, AC provides more tractive effort/HP then DC yes? At a higher up front cost.
Does this also lead to improved fuel efficency?


Do the efficencies of AC disappear when used with DC? For example clearly a set of two AC4400s is the most efficent and two Dash 9 44CWs the east, but what about an AC an a Dash 9? I assume the tractive effort of the lashup is higher, What about the fuel economy?
What about the AC unit in particular? Does it's individule effort retain the efficencies it would have in an all AC set?

 

I have to admit.... I think I have read about this, but don't remember,,,,,,

Harold

 

I'm trying to set up realistic locomotive pairings in my freelanced Model Railroad. The backstory has them having a lot of used power even some Alco as well as a lot of rebuilt power and they have very recently bought new power and I want the AC stuff to fit into the equation in a logical prototypical way. AND, I want to know why.

 

It really doesn't have anything to do with tractive effort. It has to do with "adhesion" or how well the wheels grip the rail. You can have all the tractive effort in the world, but if the wheels slip or just won't turn. then it does you no good. AC traction uses "Creep Control". It transfers more power to the other wheels as one begins to slip. It maximizes adhesion to the rail between all the wheels.

Although a much simpler system, DC traction merely puts down sand when one wheel begins to slip, there is no transfer of power to the other wheels. "Creep Control" does not work with DC traction. DC traction has a greater tendancy to overheat under exteme loads and traction motors are susceptible to "stall burns" if stationary for too long a time with power applied, as opposed to the AC system.

A pure AC consist is better than a pure DC consist not because there is more tractive effort, but because the tractive effort that is produced is better utilized by greater adhesion between the wheel and rail. A set of three C 44-9Ws may have a higher horsepower rating than a three unit set of SD-70 MACs, but the SD-70 MACs will do a better job of getting a heavy train over the road than the C-44-9Ws because the MACs have a greater "Coefficient of Adhesion".

The efficiencies of AC do not degrade with the mixture of DC power in the consist. Once again, it all comes down to adhesion. The DC units just don't have as much adhesion as the ACs. So instead of going by the horsepower rating, you need to go the the "Coefficient of Adhesion".

Fuel efficiecy is only one of the selling points of AC traction. Wear and tear on the physical plant of the railroad as a whole is the saving grace of AC. Along with the ability to haul more with less.

As far as fuel efficiency, it simply depends on how many locomotives it takes to get the train over the road. Once again, "Adhesion" comes into play. The greater the adhesion, the more tonnage can be moved.

I hope this clears thing up a bit!

 

Read it, answered no questions. it could just as easily been a sales brochure from GE.


Thanks err....Doofus. That explains exactly what I needed to know.

 

Going off on a slight tangent, I am curious that BNSF picked GE power for DC (Dash 9) and GM for AC (SD70 MAC).

UP, on the other hand, bought lots of SD70 DC's and AC4400 (GE) for AC.

I would have expected either road to have picked one vendor overall, or both to have gone to one for DC and the other for AC.

Like I said, it just looks curious to the uninitiated eye...

 

BN initially ordered SD-70 MACs bn9400- BN 9838. The BN-SF merger happened in between deliveries of these units, henceforth the change to BNSF on the later units. BNSF was in a power shortage in the Powder River Basin and went back to EMD and placed more orders of SD-70-MACs. BNSF 9839-BNSF 9999, and BNSF 8800- BNSF 8989. These orders swamped EMD.

UP, also in need of power either had to wait for EMD to fill the BNSF order, or go to GE to get the needed locomotives. They chose the latter. Initially, UP had to take delivery of C 44-9Ws because GE hadn't finished development of AC technology. As the orders progressed, AC technology came to GE.

A while after the BNSF orders were filled by EMD, UP ordered AC power from EMD and more DC power in the form of SD-70-Ms. (AC power wasn't deemed necessary on lighter freight trains.) And again, EMD is swamped!

At about the same time, BNSF finds itself once again in need of power. Since EMD is booked up, they turn to GE to supply the needed locomotives. They opted for C-44-9Ws and a three unit test set of AC 4400-CWs.(same story, AC power wasn't needed in the freight pool) The C-44-9Ws are placed into general freight service. The AC 4400-CWs roam the system for testing and eventually end up in the Powder River Basin.

BNSF desperately needs more AC power in the Powder River Basin. Since EMD was still overwhelmed with the UP orders, BNSF had to wait their turn, or go with GE and the ACs to fill the void in the Powder River Basin. They chose GE.

A side note: As BNSF began ordering AC power from GE, GE began buying large sums of BNSF stock.

 

Doofus - great information!! Thanks for sharing!

 

Oh, and next time I see one of those loooong mixed manifest freights rolling by, I will remember what Doofus said, this is the "lighter" side of freight operations!

 

Doofus,

On a slightly more serious note, does this mean GM has regained the lead in the locomotive market away from GE?

 

Ah yes, that 8,200' train of empty stack wells and trailer flats is much longer than the 3,900' ballast train!

After ther BN-SF merger ,EMD had significantly scaled back operations. Some MACs were assembled in London Ontario, while others were assembled in Shahagun Mexico. The La Grange Illinois plant was amost shut down. There were serious "quality control" issues on the Shahagun units and thus EMD's output was slowed even further. GE on the other hand was cranking out C-44-9's in record numbers. The railroads were grabbing anything they could get their hands on for power. GE was winning the numbers game.

GE finally developed their own AC system and entered the market behind EMD. Upon finishing the BNSF orders, EMD's answer to GE's entering the AC market was a 6,000 horsepower rating for the SD-90-43. The problem was that EMD's 710G prime mover was already at maximum output and couldn't handle the 6,000 HP rating, so the've contracted with a European firm to develop a prime mover that could handle the load. To my knowlege, no such prime mover has been introduced yet. GE, playing "catch up" again introduces the AC 6,000. But the same problem that plagues EMD, also haunts GE. A prime mover that can handle the load of a 6,000 horsepower rating.

EMD has for now, won the technology race. But because of EMD's production issues, GE simply out numbered them in the locomotive production game.

The new twist is the "Green Technology" or enviornmentally friendly locomotives. (SD-70-i versus GEVO) It will most likely play an important part of the sales game in the future. But for now the 6,000 HP rating is still elusive.

 

Yes, Iheard there was an ugly lawsuit between GE and the German company that promised to deliver the 6,000 HP.

 

Actually, the H-Engine is in some units. I've seen a couple UP 90 H-MACs in the past few months. True 6000HP units (angled roof different engine sound)


Didn't EMD reopen the LaGrange plant to suppliment the huge orders.


Also, what about SD-80MACs are those too much of a gas guzzler?


Fnally, I know that CSX has orders in for a sorta mixed breed SD-70MAC/ACe, but what about the actual new ACes? Any feelers on how they are bein received?

 

EMD's original plan was to completely shut down the La Grange plant. Then it was decided to keep in open and assemble a few components. As production levels fell behind, more and more work was being done at La Grange. I am not for sure how much or what work is being done at this time, (full assembly?) but it is much more than had been planned for the shop.

 

CSX was delivered C60AC's ( as they were called on CSX, otherwise known as AC6000's) many of them have been "derated" and reclassed as C44-6's (I don't know the whole story there)'

The ex-CR SD80's are all classified as 5000 hp, as far as I know.

The SD9043MAC are actually 4300 hp prime movers in SD90 bodies... the original premise was that the 6000 hp prime mover was not ready for use, so they would swap out the lower hp units for the 6000 hp units once they were "ready".

Harold