In regards to units 690,621,643, maybe Ive missed something in reading various posts. When some one refers to a unit having loading problems or dropping its load, what mechanically goes a fray and how would this be remedied? I have some mechanical knowledge so specifics would be nice if possible.
Railroad Forums
Loading problems?
- Discussion of Electro-Motive locomotive products and technology, past and present. Official web site can be found here: http://www.emdiesels.com/.
Moderator: GOLDEN-ARM
The short answer is that most locomotives in North America use a diesel- electric drive system rather than a mechanical transmission like most road or off-road vehicles. That means that the diesel prime mover turns an alternator (or a generator in older units) which generates current that then energizes electric traction motors geared to each of the axles. "Slow to load" refers to the lag between the engine reving up (responding to the throttle) and the traction motors responding via the electrical system. It's obv. a lot more complicated than that when you factor in AC vs. DC drive, ect..
So im assuming now that if a locomotive "drops" its load over a certain speed it simply doens't produce any power at the axles. Ive head several terms or phrases in reqards to loading problems. Maybe im just getting hung up on wording. Thanks you for the answer.
The locomotives in question are not slow to load. There issue is the fact they often do not load over 10mph. The Prime Mover (The Diesel Engine itself) responds to the throttle just fine, the issue lies in the electrical system. The Offical, unoffical word is there is an issue with the transition system on the SD26's PAR owns and in many instances when they reach the speed they are supposed to make transition, the simply drop the load altogether. I have ran those three units many times back when they used to run through out of Rotterdam. I have had the issue more then once on all of them. And many of my buddies over there say not much has changed with them.
Slow loading is not always in direct relation to traction power at the axle coming on slower then the prime mover. Many locomotives such as F40PH's and GE P40/42 units have the prime mover already at near full RPM at all times. But they can still load slowly in that instance too.
An example of Slow Loading is pretty much any GE locomotive. From the early models to the newest models, GE's are MUCH slower then EMD's when it comes to loading. Once they do load, they pull great.
Slow loading is not always in direct relation to traction power at the axle coming on slower then the prime mover. Many locomotives such as F40PH's and GE P40/42 units have the prime mover already at near full RPM at all times. But they can still load slowly in that instance too.
An example of Slow Loading is pretty much any GE locomotive. From the early models to the newest models, GE's are MUCH slower then EMD's when it comes to loading. Once they do load, they pull great.
The Offical, unoffical word is there is an issue with the transition system on the SD26's PAR owns and in many instances when they reach the speed they are supposed to make transition, the simply drop the load altogether.When you say transition speed, are you talking about the engine speed of the prime mover, or of the train itself moving over the tracks? I would think that such a transition would be related to throttle position/engine RPM rather than train speed (after all, you need pulling power no matter how fast or slow the train is moving), but I really have no idea. What do you mean by transition speed? Thanks.
If 10 mph is about the max on these units then they should fit the bill up by where I live, when they cross at depot road in gray(maine), the train generally crawls by for what seems like 15 or 20 minutes.
Hi
Transition speed refers to the speed at which the current to DC traction motors shifts from series to series/parallel finally to parallel operation. At low speeds to start moving the current to the tractions motors is fed in series to each motor for maxium tractive effort on all trucks. At a speed between 20 and 25 mph this method maxis out and transition occurs that changes the current fed to series/parallel mode In this mode current is fed in series to the traction motors in each truck and in parallel to the trucks. At high speeds it is more efficent to fed current to all the traction motors in parallel. On older unit the relays can be VERY noisely and the unit can jurk abit. Newer units have solid state relays so transition is a lot smoother.
Transition speed refers to the speed at which the current to DC traction motors shifts from series to series/parallel finally to parallel operation. At low speeds to start moving the current to the tractions motors is fed in series to each motor for maxium tractive effort on all trucks. At a speed between 20 and 25 mph this method maxis out and transition occurs that changes the current fed to series/parallel mode In this mode current is fed in series to the traction motors in each truck and in parallel to the trucks. At high speeds it is more efficent to fed current to all the traction motors in parallel. On older unit the relays can be VERY noisely and the unit can jurk abit. Newer units have solid state relays so transition is a lot smoother.
To go along with what NV said, I have also been inside each of the SD26's on more than one occasion and witnessed this. As well as not loading at anything over 10 MPH, I have also seen them not load more than 1500 amps or so, no matter what speed they are at. We used to consider them half a locomotive when calculating the train's tonnage profile. They need to be scrapped and/or sold to a museum.
Years ago engines with transition circuits often had problems taking transition when different models were MU'd. I recall
GP-35's were terrible when in a mixed consist but a few times I had a solid GP-35 consist, they would run like the wind
and the entire trip without any problems. Sometimes cutting out a traction motor would help in the transition because then
the remaining motors were in parrallel but this did not always solve the problem. Then again, not all locomotives even had
traction motor cutout switches on them.
As for the GE's I remember the old U-33b's which were about the worst road engine that I worked on. Advance the throttle
one notch and the load would drop to zero for a period. When the engine decided to load back up it would pull so much
amperage that the wheels would slip and then all hell broke loose. Sometimes the manufacturer just tried to load too much
horsepower in a locomotive and especially the electrical system would not handle the HP. GP-35's, U-30b's and U-33b's were
noted for this problem and it happened often especially when these engines were part of a mixed consist. Often this made
a stinker of a job handling a train especially a long freight train of mixed freight cars.
Noel Weaver
GP-35's were terrible when in a mixed consist but a few times I had a solid GP-35 consist, they would run like the wind
and the entire trip without any problems. Sometimes cutting out a traction motor would help in the transition because then
the remaining motors were in parrallel but this did not always solve the problem. Then again, not all locomotives even had
traction motor cutout switches on them.
As for the GE's I remember the old U-33b's which were about the worst road engine that I worked on. Advance the throttle
one notch and the load would drop to zero for a period. When the engine decided to load back up it would pull so much
amperage that the wheels would slip and then all hell broke loose. Sometimes the manufacturer just tried to load too much
horsepower in a locomotive and especially the electrical system would not handle the HP. GP-35's, U-30b's and U-33b's were
noted for this problem and it happened often especially when these engines were part of a mixed consist. Often this made
a stinker of a job handling a train especially a long freight train of mixed freight cars.
Noel Weaver
There is an engineer who used to work with SD-26's on another railroad (guess which RR). He would fool around with something inside the electrical cabinet when the engines would drop their load. Maybe he was cutting out a traction motor, but whatever he did, he got them to run better. They are pretty beat though. The 619 used to have some switches on the back wall that were labelled "unknown". They were probably for the old mid-train helper operation.
So basically they are glorified slugs with a prime mover and not connected to another locomotive?
I believe "dead weight" is the answer the judges were looking for. 
MEC407
Moderator:
Pan Am Railways — Boston & Maine/Maine Central — Delaware & Hudson
Central Maine & Quebec/Montreal, Maine & Atlantic/Bangor & Aroostook
Providence & Worcester — New England — GE Locomotives
Moderator:
Pan Am Railways — Boston & Maine/Maine Central — Delaware & Hudson
Central Maine & Quebec/Montreal, Maine & Atlantic/Bangor & Aroostook
Providence & Worcester — New England — GE Locomotives
MEC407 wrote:I believe "dead weight" is the answer the judges were looking for.Ouch, but lol
What models and makes go from series to series/parallel to full parallel? Haven't run into any of those yet, and I've had my head in a few cabinets, rewired several, and studied many a wiring diagram.
The Alco and EMD switchers start in series, go to S/P and then S/P reduced field (or field shunt). At least the Alco 539s did; the S/P reduced field was an option on EMD switchers.
Bigger Alcos and EMDS, first gen at least, start in S/P, then S/P reduced field, followed by parallel and then parallel reduced field. (The GP-7 was a bit different; as EMD's first real road switcher, it only had S/P and full P, with no field shunting. The excitation was different as well.) Some of the second gen units (C-424 and GP-30, 35 as examples) had the same transition, S/P to P, but with many stages of field shunting.
I'd hate to even think of all the contactors necessary for S to S/P to full P operation; I don't think anyone did it, at least in production units.
The Alco and EMD switchers start in series, go to S/P and then S/P reduced field (or field shunt). At least the Alco 539s did; the S/P reduced field was an option on EMD switchers.
Bigger Alcos and EMDS, first gen at least, start in S/P, then S/P reduced field, followed by parallel and then parallel reduced field. (The GP-7 was a bit different; as EMD's first real road switcher, it only had S/P and full P, with no field shunting. The excitation was different as well.) Some of the second gen units (C-424 and GP-30, 35 as examples) had the same transition, S/P to P, but with many stages of field shunting.
I'd hate to even think of all the contactors necessary for S to S/P to full P operation; I don't think anyone did it, at least in production units.