I have wondered for a long time about the following, and just decided to ask. Since most EMDs have 900 rpm max's and GE has 1,050 rpm max's, when going to notch 8 say on a mixed dpu consist of SD 70ACes and ES 44ACs, during that time where the GE is at 900 rpm, the EMD has maxed out. Does that mean the EMD is in effect "pushing" the GE's until they reach 1,050?
The short answer is that at a given throttle notch, the locomotives will go at about the same speed.
Locomotive speed is controlled by the power to the traction motors, not prime mover speed. While EMDs and GEs have different prime mover RPMs at a certain throttle notch, the traction motors are receiving the amount of electricity required to go a similar speed. (EMD and GE traction motors are different.)
That said, some locomotives of both builders load faster than others.
Thanks; that's a simple explanation for me. :) I just presumed that the higher the prime mover RPM, the higher the current to the traction motors.
Well, yes and no. EMDs have larger cylinders than GEs, and so different alternators that are designed for more strength, as opposed to more speed. Modern EMDs produce slightly less horsepower, 4300 compared to GE's 4400.
Thank you again; it's all starting to make more sense. I appreciate the simple but very informative answers.
Given relatively similar speed ratings, the horsepower is a factor only in how much push the locomotive contributes to the "cause." That's why you can find a 2000 HP GP38 in a consist with a 4000+ HP SD70 (or ES44). Within it's capabilities, each will produce a similar result in a given notch.
Yes, if you need 8,000 HP to make the necessary HP/ton ratio, you'll need 2 GP38's to replace each SD70.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
VGN Jesswhen going to notch 8 say on a mixed dpu consist of SD 70ACes and ES 44ACs, during that time where the GE is at 900 rpm, the EMD has maxed out.
NorthWestEMDs have larger cylinders than GEs
ES44s only have 12 cylinders. The cylinders would need to be bigger to get to a similar engine size and similar horsepower rating.
Generally, each throttle notch corresponds to a horsepower rating. However fast the engine has to turn to get to that rating will vary among manufacturers. Computer controlled GEs do a few other things to get each notch.
I think Baldwins only turned 750 rpm at full speed, yet still put out 1600 hp, where a EMD of that vintage and rating might need 850-900 rpm.
Mike WSOR engineer | HO scale since 1988 | Visit our club www.WCGandyDancers.com
WSOR 3801I think Baldwins only turned 750 rpm at full speed, yet still put out 1600 hp, where a EMD of that vintage and rating might need 850-900 rpm.
The catch is that the Baldwin, maxed out with supercharging, produced that 1600 hp. The equivalent size EMD, with the advent of turbocharging, and at the same general rpm range it used when NA (with the Roots blowers only for scavenge air), could produce far more, and out of a lighter engine to boot.
I'd like to see Matthew Imbrogno comment on this, as he has said more horsepower could be developed from the later Baldwin engines, even turning at their relatively slow rate. He also noted that 'idle' on a Baldwin could easily produce enough power to accelerate the locomotive to something like 20mph, even with a short train...
WSOR 3801ES44s only have 12 cylinders. The cylinders would need to be bigger to get to a similar engine size and similar horsepower rating.
Or cycle faster, IIRC that being the solution GE used to lower emissions while retaining the same horsepower.
Will Davis, do you have anything on this?
Baldwins were noted for their incompatibility with others when ordered without MU equipment, having notchless air throttles, so retrofitting MU capability was hard. Those built with MU equipment IIRC had notches.
NorthWestBaldwins were noted for their incompatibility with others when ordered without MU equipment, having notchless air throttles, so retrofitting MU capability was hard. Those built with MU equipment IIRC had notches.
Most Baldwins did in fact have multiple-unit control capability -- just not the EMD electrical multipin-cable approach. IIRC Baldwin/BLH made something of a point out of how their version of MU was superior to EMD's 4-bit relay-logic approach. Will Davis, or some others, will have the specific references to discuss the technical differences in detail, and provide some of Baldwin's literature on the subject.
What you are discussing is that Baldwin would on request build units compatibie with electric, 27-pin-cable MU, and as I recall offered kits that would provide 'retrofit' capability. Interesting that so few roads that ran Baldwin power saw the need for this...
timzNot sure this is 100% true any more, but in the old days if the GE was in Notch 8 it was doing 1050 RPM and producing full power. The SD70 would be doing 900 RPM and producing full power. No reason for one to be "pushing" the other, in any notch (once power has stabilized, anyway).
It has been my experience that GE units do run at 1050 rpm normally in notch eight. They will run in the mid to high 900 rpm range making maximum HP, then when the train is lugging uphill and gets below about 15 mph +/- , the rpm's would increase to about 1050. However, there was no increase in HP associated with this higher RPM. My guess was that the extra rpm's were needed for traction motor cooling.
.
Thanks, the memory can be a bit fuzzy on occasion. Wasn't there some issues with compatibility of the air throttle with notched throttles, or am I confused again?
OvermodInteresting that so few roads that ran Baldwin power saw the need for this...
I suspect that all that thought they might need it purchased it when the locomotive was new. Baldwins also tended to be "troublemakers" in the eyes of maintenance staff, and were often repowered or kept close to the shops, in jobs that MU might not be required.
Most Baldwin diesels were built with a notchless air throttle while most other builders used the 8-notch electric throttle, so there's the incompatibility right at the outset.
Re-powering wasn't always a total solution, either. EJ&E's re-powered centercabs got two 12-567 engines but kept the Westinghouse main generator. The generators were designed for use with a De La Vergne engine which topped off at 625 RPM. 567 engines operated at higher RPM's and couldn't run that slowly and maintain oil pressure and the main generators couldn't survive operating at the higher RPM's.
For our original query: It's important to remember that engine and generator RPM isn't the only thing at play here - there is also the amount of field applied to the main generator, which is referred to as "excitation." Thinking about this, we might also note that there have been many diesel-electric locomotives built whose engines ran at a constant RPM all the time (think of the Amtrak F40PH units) or whose diesel engines ran on a modified speed schedule, as for example UP's U50C units wherein the engine ran at what one would think of as Notch 4 speed with the throttle in actual notches 1 through 4, and in what one would think of as Notch 8 speed with the throttle in Notches 5 through 8. I believe some of PC's U23B units were built like this as well, from information a former NYC/PC/CR engineer posted on another board.
So we see then that diesel engine speed really isn't the whole deal. The amount of current applied to the traction motors is -- and even this doesn't correlate exactly if the system voltage differs between units being compared. That's about as simple an introduction as I can make.
And we don't have to get really complicated either -- I can find for you load testing data which shows the horsepower output in each throttle notch for a number of locomotive models. You would see right there that the percentage of full load in each notch is a roughly corresponding percentage, comparing between different makes and models.
And we haven't even talked about traction motor gear ratios yet.
.....
Baldwins -- Looking at engine speeds it's instructive to see that these idled somewhere between 275-315 RPM depending on engine model and full speed was 625 RPM.
Baldwin throttles -- Baldwin had THREE throttle setups.
D-1 Controlair -- Standard on switchers and single unit road switchers. Air throttle; reverser operator is separate from the throttle unit and is electro-pneumatic. This is built into, concealed in the control stand. Think general Baldwin VO engine or 600 engine series switcher control stand. This can be for single units or for multiple units.
CE-100 -- Electro-pneumatic throttle for road units with dynamic brake. Incorporates both electric contacts for "off" and air reducer for throttle pipe, and controller contains the reverser operator. This is the familiar big cylindrical throttle with the large wooden handled lever coming out of a convex disc on top. On the RF-16 the controller was enclosed in a new control stand that looked more like that which you'd find in an ALCO road unit like an FA or PA, or like an EMD E-Unit. Usually multiple unit control.
XM-781: Westinghouse electric throttle. Available setups on locomotive allowed compatible MU operation with either ALCO-GE units (21 and 12 point jumpers) or EMD units (27 point jumpers.) This throttle was not what you'd call super rare, overall either... this was used in every US-built Fairbanks-Morse C-line unit, as well as every single Lima-Hamilton switcher, road switcher and transfer locomotive. I can tell you that the New York Central's RS-12 units had this throttle as well. I believe SAL's RS-12 units did too, and a good number of Baldwin road switchers on the Erie also did. This controller would have an added lever sticking up from the rear if a selector was needed, or dynamic brake. (Baldwins generally don't make transition and don't need selector levers, but might need selector levers if fitted with electric throttles and then put in the lead of ALCO-GE or EMD units which had manual transition.) Usually multiple unit control.
NONE of the three throttles I've described above was compatible with any of the others. The air pressure range developed by the two different air throttles was NOT the same. And, with the D-1, you had to have a piped-in air operated throttle switch to get a signal to shut the power contactors; with the CE-100 this was done by a contact right in the controller.
Baldwins with air throttles STILL had an electric jumper, to trainline reverse and air compressor synchronization and headlight control and whatever else. Also, if equipped with dynamic brake, the signal to change to dynamic brake was electric but the same throttle lever was used to control braking effort, and so the throttle pipe again was the controlling feature for dynamic brake effort as well as for motoring (pulling) effort.
For those unfamiliar.... with the air throttle, an air operator (cylinder) is used to position the speed control shaft on the diesel engine governor. On earlier Woodward UG8 governors this was a big outside cylinder with an adjustable linkage; Woodward also came up with a PG that had the air operator completely inside and the air pipe hooked right to the governor. So air is being piped from unit to unit to order the required engine speed; more air pressure, more ordered speed and load.
Electric throttles generally use four solenoids on the governor, which means there are four wires in the MU or Multiple Unit cables - one for each solenoid. Each of the throttle positions energizes a different combination of these four wires, like a code if that makes it easier to understand; this corresponds to a combination of the four solenoids each either on or off. This positions components in the governor to again order up the required speed and load, but there are exactly eight speeds instead of an infinite range of speeds from idle to full speed as you'd have with an air throttle. (Remember - Notch 1 is also the same actual engine speed as idle. Unless you're talking about something really new which has a special low idle feature.)
You can see now why air and electric throttle are not compatible. You can also begin to wonder why more roads didn't buy Baldwins with electric throttles, but that's hindsight. Most roads didn't mix and match units when they were first converting to diesel; thus, why not just buy the standard throttle, whatever that may be? After all, taking the PRR as an example - everything was bought in 6000 HP sets. Doesn't matter if it was EMD E-7 units for passenger service, or F-M "Erie" units for freight. Or Baldwin units either. The sets were intended to remain together, so therefore MU compatibility between, say, EMD and ALCO-GE units was not required or considered. Later, PRR began buying road units in less than 6000 HP sets, and began adding floods of road switchers, but by then it was too late. The full benefits - and requirements - of economic and flexible dieselization hadn't dawned on everyone early enough to prevent the giant mish-mash of non-compatible units they (and many other roads) ended up with.
To get specific for a moment, the standard throttle on Baldwin road switchers without dynamic brake was the D-1. On road units (think Sharks) it was the CE-100. If a railroad just bought the units with the standard throttle and then later, after splitting up sets and trying to assign by horsepower, was upset that the units couldn't MU, whose fault was that? Something to think about.
Finally... I have here a sales proposal from Baldwin to the Louisville & Nashville for AS-16 road switchers, dated October 1953. We all know they were never built, but had they been built, they were specified to have had electric throttles and MU compatible as desired with BLH, EMD or ALCO-GE units. This was an added cost per unit of $2262.00. Of course, had the road elected to have MU compatible with EMD or ALCO-GE units, the equipment would have included an electric instead of electro-pneumatic throttle.
Hope I addressed all the questions and comments!
-Will Davis
Railroad Locomotives - My Blog
Will DavisHope I addressed all the questions and comments!
Yes you did, with lots of detail and specific facts from primary source documents! A very big thank you!
Each engine (EMD or GE) has it's own rpm setting for each of the 8 throttle positions. The throttle position does not dictate the rpm, only the horse power for each throttle position. The control computers on the locomotives decide what rpm to provide to make the HP requested.
Buried in Will Davis' excellent post on Baldwin throttles was a description of the MU jumpers used between Alco-GE units (two jumpers, 21 and 12 pin) and EMD units (27-Pin). Some companies, like UP, standardised on one or the other (UP used the Alco-GE system on early units). It was possible to MU units with different receptacles using a "Y" cable, as the CB&Q and UP used on their early-1960s Grand Island run-throughs. Keep in mind that many first-generation cab units didn't have nose MU either.
Many first-generation road switchers, not only Baldwins, were built without MU. Roads bought them like steam locomotives, specifically for one assignment. The flexibility advantages took longer to be implemented.
NorthWest Many first-generation road switchers, not only Baldwins, were built without MU. Roads bought them like steam locomotives, specifically for one assignment. The flexibility advantages took longer to be implemented.
Soo Line was an example of this. The Soo's GP7's didn't get MU until after the GP9s arrived.
On VGN Jess' original post --
I'm surprised Don Oltmann hasn't weighed in on this, because he has a specific example of mixed loading of EMD and GE power on his blog.
This is the one where the GP38 had to be put in isolation until the GE loaded down. It defines a 'correct' context for the underlying question Jess was asking -- not so much 'were the engine speeds equal' as 'is there a problem with loading until the engines are developing maximum power into the load'.
BRC's GP7's and GP9's were also built without MU, the GP7's were also equipped with friction bearings.
I once got the opportunity to watch an Amtrak FL9 and GE P32DM pair up on a demonstration train, something that rarely if ever happened in regular service. The FL9 loaded quickly and stretched the drawbar, but the P32DM had the "kick" that really started the train moving.
The train was part of an Amtrak exhibit in White River Jct. VT. Consist included three brand-new Superliner IIs fresh from the Barre VT factory, a Viewliner sleeper, and a wooden ex-Rutland Green Mountain Railway combine with oil markers (sadly unlit...) that was ferried to Bellows Falls, where it was taken off by GMRC's ex-Rutland RS1 405.
Even among EMDs, each model loads differently. Because of the turbo, early GEs load slowly, to avoid the cloud of smoke given off by turbo lag. (This isn't always successful.)
IIRC GE used a turbo powered by the exhaust gasses, while EMD's were powered directly from the engine, leading to the slower loading.
EMD turbochargers had a clutch linking them to the crankshaft when the throttle was first opened as a way of reducing turbo lag. As the engine came up to speed, the clutch disengaged and the turbocharger was powered strictly by exhaust gases.
The clutch on the turbo was EMD's way of getting rid of the Roots blower for aspiration of the two cycle engine. At low throttle settings, the exhaust gas didn't have enough energy to spool up the turbo.
One benefit of this design was much better throttle response.
- Erik
Our community is FREE to join. To participate you must either login or register for an account.