I have searched in the archives for an answer to my question, but either I am not searching with the right keywords or something, but can’t seem to find an answer. The question is when multiple engines are coupled together (MU’d) and the they are facing opposite directions (one engine facing forward and the other engines facing either forward or backwards-say 3 or more MU’d) how does the lead engine control the direction of other engines? If said engines were using servos, then both engines would be applying power in opposite directions, as the engineer would have the direction control in the forward direction, the trailing engine would also be in forward (but in reality would be physically be reversed.) I don’t know if I stated this clearly but I always wondered how one engine going forward could control an engine facing the opposite direction. With todays technology a computer would probably be the logical answer, but how about back in the early days of diesel? Hope this isn’t too much of an un-intelegent of a question.
Thanks,
Jim
There are two wires in the MU cable which control direction, one or the other is energized. I don’t remember which wire is which but let’s call them wire #1 and wire #2. When the lead locomotive wants to go forward and the trailing locomotives are at the rear, wire #1 is energized, nothing is plugged in at the front, but at the rear the second locomotive is facing forward and its #1 wire is energized by power flowing from the lead loco which lifts a relay causing it to go in the same direction as the lead loco. Now turn the second loco if facing the opposite direction to the lead locomotive, again the lead loco is set to go forward #1 wire is energized but at the rear MU plug of the second loco the #1 and #2 wires are reversed so when the #1 wire of the lead loco is energized it powers the #2 wire of the second loco again lead loco goes forward and the second moves backward, but both in the same direction. It is this reversal of the wiring that makes the whole consist go in the same direction. The second loco passes through the forward signal on the #1 wire but doesn’t act upon it that way since the signal enters the locomotives own control system over its #2 wire.
The locomotives all respond to the controls being operated in the lead unit, or whichever unit is set up as the controlling unit. Think of the prewar FT units, usually an A-B-B-A consist. The booster units wouldn’t have known which way to pull! The presence or absence of a cab on trailing units has no influence on which way they pull–only the reverser in the controlling cab does. So a trailing unit won’t sense “forward” or “reverse”, it will just sense “thataway”, whichever way the controlling reverser is set. No computerization necesry.
I see Mr. Beaulieu beat me to it, with a more technical explanation.
The answer lies in the MU socket at the front and rear of the engine. The two connections that control direction are reversed.
And you guys beat ME to it despite my brief summary compared to your in depth detailed explanations. [:P] Boy…I sure type slow.[#oops]
Thanks for the explanation. It’s clearer now. One other question and I will quit asking these questions. When different engines are used together is there a way to control each engine so the power is applied equally? My reference is two different HP engines (such as 3000HP and and say a 4000HP.) Notch 1 on one engine would not equal notch one on the other. I appreciate your bearing with me on this.
Jim
The energy supplied to every traction motor in the locomotive consist is a result of the combined output of all alternators/generators that are running. The current is ‘pooled’ and each traction motor draws from that pool, not just from the power supply of its respective locomotive.
A good example is that of CSX’s road slugs/mates. The mother unit provides all the current but the traction motors from both locomotives draw from that current.
Also, onboard microprocessors ensure that each traction motor puts down equal amounts of tractive effort.
Thanks you Ted and others. Last question now is does it matter whether engines are AC or DC? Guess I should have thought this out better and listed them all at the same time. I promise there will be no more on this. Just a fan wondering about the inner working of the trade.
Jim
Not quite. Slug sets have one prime mover turning the main alternator which supplies the energy for all of the traction motors on both the slug mother and the slug. There are additional jumper cables which carry the electricity from the slug mother to the slug.
When locomotives are run in multiple, each locomotive’s prime mover turns the main alternator which supplies the energy for the traction motors on that locomotive only.
I have no problem at all answering questions that I know the answer to , no matter how many. There are those here however (you know who you are) who do have a problem with repetitive questions being posed.
They will actually type a longer reply stating the importance of digging through old threads for the answer than they would if they’d just actually answered the darned question.
As for your last question regarding AC/DC consists, not sure, but I did stay at a Holiday Inn Express. [(-D]. Seriously…don’t know, but I have seen them hooked up together before.
Perhaps in some applications, but certainly not in all. Power pooling is real. Either way the onboard microprocessors enure that all traction motors in the consist applies equal t.e. to the rails based on the engineer’s input.
I know of no common locomotive ever manufactured that pool main generator outputs between locomotives, with the unique exception of slug-mother combinations. There might have been some one-offs way back when, but not any ordinary EMD or GE or Alco.
RWM
Ditto. None of our vintage locomotives have the capability.
I’ve seen it stated that you can hook up an SW1500 to an SD45 and have an effective “locomotive.”
Current generation locomotives have enough smarts to keep their feet under them in most cases, so horsepower mismatches aren’t going to be a major factor. There were cases with first (and second) generation locomotives where that wasn’t the case - you might end up with a wheel or truck spinning away merrily while it’s mates ground along like they were supposed to.
No, it is not pooled, each engine supplies only the traction motors of its own engine. The 27 pin jumper cables wires are not anywhere big enough to supply 1000 amps to traction motors. A slug is different as it is getting its power from another unit and has large cables between them for the traction motor current.
As for mixing AC and DC locomotives in a consist: not a problem. I see it now and again, in spite of the fact that they’re usually used in different types of service.
A/C or D/C makes no difference as each locomotive provided the power for its own traction motors.
In the case of slugs, there is a power cable between the mother and the slug.
With the exception of first generation diesel electric locomotives, they all have alternators; the term generator is left over from the old lexicon.
The term A/C and D/C is used to describe the type of traction motors the unit has…even those with D/C traction motors have alternators, the alternating current produced is run through a thrysistor or bridge rectifier, just like your automobile, and converted to D/C or left as is if the unit has A/C traction motors.
Think about it this way…your automobile has an alternator, but the electrical system is a 12/15 volt D/C system.
The alternator produces 15 volts A/C at somewhere around 450 amps…the bridge rectifier converts that to 15 volts D/C…and the voltage regulator maintains it at 12 volts D/C to run your cars electrical systems…and about 15 volts to charge the battery.
Locomotives do the same thing, only on a larger scale…if I remember correctly it is around 600 volts A/C at the alternator.
As for different HP ratings…the 4500 or the 1500 HP rating is the maximum diesel engine horsepower available, that is not a constant rating through all the throttle notches…the “notches” on the throttle are simply detents in a revolution control…the notches equate to alternator out put to the traction motors, so notch 1 on a big SD70 produces the same engine revolutions/alternator output as notch 1 on a GP38… if you had these MUed…the SD70 wouldn’t run off with the GP, nor would the GP drag the SD down…the hp rating described the maximum HP output of the diesel, which, when run through a alternator, equates to a give amount of amperage to the traction motors…it has nothing to do with the speed, in notch 8, each unit would contribute it’s maximum pulling power to the entire train.
T
[insert men carrying log similie here]
Seems like this topic has become popular, since we are asking questions, I got one: I have noticed that every other month or so BNSF hauls a local SW1500 off, I would say for a PM check up and probally oil change. When they haul it away, 95% of the time it is added into a coal hauling consist. Would this bring limit the over all output of the 3 big units down? Say it was cut in between 3 SD70MACs.
Only if it was on line. If it was hauled off line, in consist, then it would have no effect on the consist (other than being 100 tons or so to haul around). The only consequence might be on the speed restriction on the switcher (which would depend on what type of trucks it has, some AAR B switcher trucks are speed restricted by railroads).
Dave H.
Locomotive pull is additive so if you were to pull the coupling pin between locos while it was pulling a train ( yes I know the pressure will prevent that) the front locomotives would race away and the train and those locomotives still connected to it would slow down.
For those people interested in facts and figures about locomotives such as power in various throttle positions, fuel consumption there is no better place than Al Krug’s website here;
And especially this section of that website RR Facts & Figures
Click on the Dash9 and SD70MAC links for power ratings and the various throttle positions.
Another problem with “mis-matched” locomotives mu’ed together is the short-time ratings. If the locomotive with the shorter of the short-time ratings is not the lead unit, then an engineer could easily forget that the poor old GP7 is burning up while at the same time the nice new SD70 he was on was merely chugging away.
Er, ah, been there, done that…oops!