MU'd Locomotive question

[dwil89]

This thought popped into my head this morning. When a consist of locomotives is MU'd together and all on line on the head end of a train, how do units facing different directions work in unison? For example, the lead unit is facing the direction of travel, and the second unit is facing the opposite direction. When the engineer applies throttle, the 2nd unit has to run in reverse while the lead unit runs in forward....How does the engine that is running backwards know to apply motion in reverse so that the engines are not pulling against each other? It would be like 2 cars connected rear bumper to rear bumper. One vehicle would need to run forward in "D", while the other would have to be in "R" Otherwise the two cars would be pulling in opposite directions. Dave Williams http://groups.yahoo.com/group/nsaltoonajohnstown

[dehusman]

When the crew MU's the engines they set a switch that tells the engine which way its facing.

Dave H.

[Anonymous]

Is there a true reverse on loco? They do have use of all speeds in reverse, Yes, unlike a car?

[Anonymous]

QUOTE: Originally posted by dehusman

When the crew MU's the engines they set a switch that tells the engine which way its facing.

Dave H.

Can all locos in the consist be set reverser from the lead unit or the engineer has to manually set them one by one?

Karn[:)]

[dwil89]

QUOTE: Originally posted by dehusman

When the crew MU's the engines they set a switch that tells the engine which way its facing.

Dave H.

Oh.. okay....so when the engineer throttles up, a 'backwards facing' engine will throttle up in reverse...The switch is on the control stand of each engine? Dave Williams http://groups.yahoo.com/group/nsaltoonajohnstown

[SteelMonsters]

The easy answer is they flip a switch and the direction changes but the way the motor runs is exactly the same.

There are two general types of Diesel-electric locomotive traction motors, AC or DC. AC uses a wire wound 3 phase AC motor.

DC motors have a field and a rotating armature. The field produces a static magnetic field that the armature sits in. When the generater feeds DC current to the motor the armature reacts with the field and rotates. The faster a DC turns, the more counter EMF (CEMF) the motor produces canceling out part of the source voltage. The faster the armature rotates, the more the motor counters the source voltage and the lower the current flow is. When a DC loco is moving slow, they put it in series so the current goes through all the motors and the CEMF adds up to counter source voltage. They do this so the motors can run slower for extended periods without burning out the motors. They put it into parrelell when the train is moving fast because the motors are producing enough voltage to counter the source voltage. This allows more current to flow at medium speed and faster increasing power and top speed.
The way to reverse the motors is switch the leads to the motor's armature or field. Switching both at the same time will result in a double direction change. (you will got the same direction as before)

The more efficient, more power per size, and better contorlable motors are AC motors. They use a variable speed drive that controls each traction motor. To keep it simple, the motors's speed is controlled by the frequency of the AC. There are three wires going to the motor, switch two and the motors reverses. Again it works exactly the same forward and reverse.

Cars transmissions are designed for forward operation and have an extra gear set for reverse. They could have used an independent reverse gear, though driving 70 MPH in reverse is extremely dangerous because of the steering.

I went a little in depth with DC motors because they are easier to understand. I gave you a very watered down version of AC motors because there is so much to them.

[chad thomas]

Correct me if I'm wrong here, but this is how it was explained to me.

The actual reversing of the electric motors is done with air.
there is one hose for forward and one hose for reverse(MU hoses). They are on oposite sides of the coupler so that if a unit is "backwards" so are the air lines, thus
establishing forward to mean reverse for that unit. The air acts on a cylinder that is linked to a big electrical switch and this switch is what reverses the unit(s).

[jimrice4449]

I"m not an engr but a retired brakeman but maybe I can state the situation simply.
First there's no connection between the air hoses and the motors. The air hose are part of the brake system. All MU functions are controlled by the MU cable.
Let,s say we,re talking about a three unit power consist heading west with the first two units heading forward and the rear unit heading east. In the cab of each unit, on the wall behind the engineer is a control panel with a number of switches. The one we're concerned with is a large rotary switch with a number of positions to set the mode of that particular engine. If memory serves they are for a unit running alone, a lead unit with units coupled at the rear, lead unit with units coupled at the front, trailing unit coupled front and rear and trailing unit coupled at rear and trailing unit coupled at front. In our hypothetical case the first unit would have the switch set at "lead unit coupled at rear" the second at "trailing unit coupled at front and rear" and the last unit at "traling unit coupled at rear". With the switches so configured the engineer in the lead unit would set the reverse lever on his control stand to forward and all three units would go west. If he set the headlight switch on the lead unit to "on forward the headlight on the lead unit only would go on. If he wanted to make a back-up move, he'd change his control stand reverser to reverse and all three units would go east. If he changed the headlight switch on the lead unit to "on reverse" the headlight on the rear unit only would go on.
As for the automotive speed/reverse analogy, the reverser controls only the direction, the throttle controls the speed.

[csxengineer98]

QUOTE: Originally posted by dehusman

When the crew MU's the engines they set a switch that tells the engine which way its facing.

Dave H.

no..we dont...no such switch
csx engineer

[dehusman]

Air reversers died with Baldwin diesels in the 1950's.

You MU a consist once. The engineer sets a switch on each locomotive to indicate its direction once. The MU is all electrical.

Once consisted the reverser switch/handle/control stand in the lead engine controls all the locomotives in the consist at the same time.

Since reversing is electrical, an engine has the same throttle or dynamic brake positions available regardless of which way the engine is pointed.

Dave H.

[csxengineer98]

QUOTE: Originally posted by jimrice4449

I"m not an engr but a retired brakeman but maybe I can state the situation simply.
First there's no connection between the air hoses and the motors. The air hose are part of the brake system. All MU functions are controlled by the MU cable.
Let,s say we,re talking about a three unit power consist heading west with the first two units heading forward and the rear unit heading east. In the cab of each unit, on the wall behind the engineer is a control panel with a number of switches. The one we're concerned with is a large rotary switch with a number of positions to set the mode of that particular engine. If memory serves they are for a unit running alone, a lead unit with units coupled at the rear, lead unit with units coupled at the front, trailing unit coupled front and rear and trailing unit coupled at rear and trailing unit coupled at front. In our hypothetical case the first unit would have the switch set at "lead unit coupled at rear" the second at "trailing unit coupled at front and rear" and the last unit at "traling unit coupled at rear". With the switches so configured the engineer in the lead unit would set the reverse lever on his control stand to forward and all three units would go west. If he set the headlight switch on the lead unit to "on forward the headlight on the lead unit only would go on. If he wanted to make a back-up move, he'd change his control stand reverser to reverse and all three units would go east. If he changed the headlight switch on the lead unit to "on reverse" the headlight on the rear unit only would go on.
As for the automotive speed/reverse analogy, the reverser controls only the direction, the throttle controls the speed.

that switch your talking about is the head light controll switch..i has nothing to do with the electrical system as far as power to the traction motors...and the headlight is controlled from the controll stand of the engin that is set up as the lead unit... the headlight wont come on by itself for any direction..you have to turn it on by a switch for what ever direction you want to move in...
csx engineer

[dehusman]

Ok, "direction switch" may be over simplified, as described previously it indicates position in the consist.

Dave H.

[chad thomas]

My bad.

I went back in the forums to a conversation I had with Randy Stahl and I see now that pins #8 & #9 on the electrical MU cable controll the direction.

From Randy:
This is a general pinout on EMD locomotives, some RRs have added trainline ground reset, slowspeed control,etc.
Pin#1 not normally used, some RRs are using this for slow speed control.
Pin#2 train line alarm, rings the bell in all the units.
Pin#3 governer D valve, for trainline shut down and engine rpm
Pin#4 control negative
Pin#5 emergency sanding
Pin#6 generator field
Pin#7 governer C valve, engine rpm
Pin#8 foreward, pin out pin 9 on the front pin 8 on the rear
Pin#9 reverse. pin out pin 8 on the front pin 9 on the rear
Pin#10 train line wheel slip light
Pin#11 not used,,
Pin#12 governer B valve
Pin # 13 control positive
Pin #14 not used
Pin#15 governer A valve
Pin#16 engine run relay
Pin#17 dynamic brake setup,( if equipped )
Pin#18 not used
Pin#19 not used
Pin#20 trainline brake warning light
Pin#21 dynamic brake setup controls rpm in dynamics
Pin#22 compressor syncronisation(if equipped)
Pin#23 trainline manuel sand
Pin#24 dynamic brake train line potential, 0-72 volt
Pin#25 MU headlights
Pin#26 some times used for mu ground relay reset
Pin#27 not used
=========================================================

Note they are reversed on the rear end. This implies that there is no need for a switch.
It is automatic, just like how model trains work (pre d.c.c.)

[csxengineer98]

QUOTE: Originally posted by dehusman

Ok, "direction switch" may be over simplified, as described previously it indicates position in the consist.

Dave H.

the direction switch only.......only applies to the headlight.....nothing else... it only lets the headlight light up on the end of the consiste..if the switches are set up in the proper order...if you have it set up wrong on 1 unit in the consiste..the headlight wont come on on the last unit of the consiste..it will come on on the unit befor where the switch is not in the proper postion....
csx engineer

[edblysard]

Ok,
lets try this..
The rotary switch described is for the headlight controls.
On the side of the control stand is a valve for trail or lead,,,it along with the big air hose and the smaller air hoses are for the train brake and the independent brake(locomotive only), sanders and such.
On trailing units, the reverser is centered(netural) and the throttle is set at idle.
When you hook up the MU cables, in essence they by pass the control electrical control surfaces on the stands on the trailing units.
Because of the way the locomotives are wired, when you move the reverser or throttle in the lead unit, the relays in the trailing units respond and follow suit.

Note that locomotives have two mu plugs per end, one on each side.
Also note that when you MU units, the cable crosses to the opposite side, instead of on the same side.

Diesel electric locomotive work just as well in either direction, so which way they face has no bearing on their performance.

Ed

[ValleyX]

I'm sorry, I'm FOFL. Setting a switch? Laugh. Sir, with all due respect, if you are a retired brakeman, you must have rode the rear end for years and years.

MU stands for multiple unit and MU'ing power permits the engineer to operate all locomotives in his consist from the controlling unit.

[csxengineer98]

QUOTE: Originally posted by edblysard

Ok,
lets try this..
The rotary switch described is for the headlight controls.
On the side of the control stand is a valve for trail or lead,,,it along with the big air hose and the smaller air hoses are for the train brake and the independent brake(locomotive only), sanders and such.
On trailing units, the reverser is centered(netural) and the throttle is set at idle.
When you hook up the MU cables, in essence they by pass the control electrical control surfaces on the stands on the trailing units.
Because of the way the locomotives are wired, when you move the reverser or throttle in the lead unit, the relays in the trailing units respond and follow suit.

Note that locomotives have two mu plugs per end, one on each side.
Also note that when you MU units, the cable crosses to the opposite side, instead of on the same side.

Diesel electric locomotive work just as well in either direction, so which way they face has no bearing on their performance.

Ed

locomotives have 2 to 3 MU respetical sockets on each end of the locomtove....they have 1 hot MU reseptical RED cover plate)...and one or 2 DUMMY rreseptical (GREEN coverplate)... and to get any 2 or more units to work as one by MUing...you have to have both ends of 1 jumper cable in the hot reseptical sockets on both locomotives....the green sockets are dummys...just a place to plug in an unused cable to keep it from dragging on the ground..or fowling the drawhead and coupler...and keeping the holes free of dirt..and in the winter time..ice and snow......
the jumper cable is just 1 part of MUing locomotives...thier is also air hoses that have to be made... air brake controlls have to be set up proprly..as well as other things in the cab..such as the head light controll switch.....and the safty chains and drop steps...
csx engineer

[Randy Stahl]

QUOTE: Originally posted by csxengineer98

QUOTE: Originally posted by edblysard

Ok,
lets try this..
The rotary switch described is for the headlight controls.
On the side of the control stand is a valve for trail or lead,,,it along with the big air hose and the smaller air hoses are for the train brake and the independent brake(locomotive only), sanders and such.
On trailing units, the reverser is centered(netural) and the throttle is set at idle.
When you hook up the MU cables, in essence they by pass the control electrical control surfaces on the stands on the trailing units.
Because of the way the locomotives are wired, when you move the reverser or throttle in the lead unit, the relays in the trailing units respond and follow suit.

Note that locomotives have two mu plugs per end, one on each side.
Also note that when you MU units, the cable crosses to the opposite side, instead of on the same side.

Diesel electric locomotive work just as well in either direction, so which way they face has no bearing on their performance.

Ed

locomotives have 2 to 3 MU respetical sockets on each end of the locomtove....they have 1 hot MU reseptical RED cover plate)...and one or 2 DUMMY rreseptical (GREEN coverplate)... and to get any 2 or more units to work as one by MUing...you have to have both ends of 1 jumper cable in the hot reseptical sockets on both locomotives....the green sockets are dummys...just a place to plug in an unused cable to keep it from dragging on the ground..or fowling the drawhead and coupler...and keeping the holes free of dirt..and in the winter time..ice and snow......
the jumper cable is just 1 part of MUing locomotives...thier is also air hoses that have to be made... air brake controlls have to be set up proprly..as well as other things in the cab..such as the head light controll switch.....and the safty chains and drop steps...
csx engineer

Not always true however, on locomotives equipped to run with slugs, often times there are multiple MU receptcles. I have seen many arrangements with 17 pin 21 pin and even a 9 pin MU jumper. The real secret to MU or multiple unit operation is the electrical jumper itself, the 27 pin jumper that is. I recall the older locomotives that had air over electric or all air MU sanders, what a mess of hoses.
Randy

[Anonymous]

Locomotive direction is determined by which end of the locomotive the controlling
unit is coupled to it. On the rear of engines, the circuitry of pins #8 and #9 are reversed
from the front MU receptacle, completing the electrical circuit in directional order. As
a rule, GE locomotives usually load slower than EMD units of any model, so in a mixed consist from the two builders, an engineer has to be careful when starting a train due to the push-pull slack action between them. The selector switch others were referring
to is the headlight selector switch which has five positions: 1. Short Hood Lead
2. Long Hood Lead 3. Single or Middle Unit 4. Long Hood Trail 5. Short Hood Trail,
the position of the switch determined by the unit's standing in the consist and the direction it is facing. The MU2A valve was used with the 26 type brake systems when
units with other type brakes such as the 24RL or #6 brake were still in common usage
on many roads years ago when different type brake systems were often found in multiple unit lashups. Like the headlight switch, the MU2A valve position was set according to the type brake system on the lead locomotive. As 26 type brake systems came into more common usage, a simple IN/OUT air selector valve became the common instrument to cut the independent brake in or out of it's controlling mode.

In MU operation, logically the more locomotives you have in a consist, the more problems you will have getting them all to cooperate in the starting and running of a train. It's tricky, especially with power braking where you bail off the independent brake application that builds up after making a reduction with the automatic brake. More than
6 units in an MU'ed consist will usually make for a slow bail-off release of the rear unit's
brakes and if insufficient power is being used, often times unwanted buff-force slack action results.

I had this problem once back in the mid-1970s with a train of something in the neighborhood of 157 empty TTX flatcars and 8 units for power, everything from
an SD-40 as a lead unit, Penn Cental's lone Century 415, several GE U25Bs,
plus an F-7 and a GP-9B buried in the middle of it all. And the trip was from Harrisburg, PA to Kearny, NJ, via the Northeast Corridor. If you can picture this train in your mind, you can probably understand the train dynamics that came along with it. Needless to say, the conductor and rear-brakemen were not happy campers back in the cabin car almost three miles away.

As an aside, while on the subject of 27 point jumper cables...An E-44 electric had two of them in use when the units were MUed. We had some interesting happenings if the cables were accidentally reversed. But I won't get into that, as sometimes the results
were quite astounding.

John A. (Captain Jack) Neiss,
retired locomotive engineer, Penn Central/Conrail/Amtrak

[csxengineer98]

QUOTE: Originally posted by Randy Stahl

QUOTE: Originally posted by csxengineer98

QUOTE: Originally posted by edblysard

Ok,
lets try this..
The rotary switch described is for the headlight controls.
On the side of the control stand is a valve for trail or lead,,,it along with the big air hose and the smaller air hoses are for the train brake and the independent brake(locomotive only), sanders and such.
On trailing units, the reverser is centered(netural) and the throttle is set at idle.
When you hook up the MU cables, in essence they by pass the control electrical control surfaces on the stands on the trailing units.
Because of the way the locomotives are wired, when you move the reverser or throttle in the lead unit, the relays in the trailing units respond and follow suit.

Note that locomotives have two mu plugs per end, one on each side.
Also note that when you MU units, the cable crosses to the opposite side, instead of on the same side.

Diesel electric locomotive work just as well in either direction, so which way they face has no bearing on their performance.

Ed

locomotives have 2 to 3 MU respetical sockets on each end of the locomtove....they have 1 hot MU reseptical RED cover plate)...and one or 2 DUMMY rreseptical (GREEN coverplate)... and to get any 2 or more units to work as one by MUing...you have to have both ends of 1 jumper cable in the hot reseptical sockets on both locomotives....the green sockets are dummys...just a place to plug in an unused cable to keep it from dragging on the ground..or fowling the drawhead and coupler...and keeping the holes free of dirt..and in the winter time..ice and snow......
the jumper cable is just 1 part of MUing locomotives...thier is also air hoses that have to be made... air brake controlls have to be set up proprly..as well as other things in the cab..such as the head light controll switch.....and the safty chains and drop steps...
csx engineer

Not always true however, on locomotives equipped to run with slugs, often times there are multiple MU receptcles. I have seen many arrangements with 17 pin 21 pin and even a 9 pin MU jumper. The real secret to MU or multiple unit operation is the electrical jumper itself, the 27 pin jumper that is. I recall the older locomotives that had air over electric or all air MU sanders, what a mess of hoses.
Randy

a slug/mother combo dont count..becouse we (atleast on csx) are not alowed to cut them apart...only mechanical personel are alowed to seperate them... they may count as 2 units on paper..but in fact they are just 1 unit when MUing other units is involved...
csx engineer

[daveklepper]

The main answer the question, if you have not figured it out, is the wiring of Pin 9 on the front to pin 8 on the rear and visa versa. This means if you had three locomotives all heading front east and running east, and then while the train was stopped some huge giant picked up the center unit and reversed it and put it back in the consist heading in the other direction, all units would still run east, the center unit backwards, as if nothing happened.

[K. P. Harrier]

For simplification’s sake, don’t MU’ed units sense WHICH WAY a direct current signal initially travels through a unit, and, irregardless of which way any unit is physically facing, will automatically move in directional unison with the other units in the consist? Wouldn’t the only way to get a trailing unit to work opposite other units would be to have a 100-foot MU cable and connect it to the opposite far end of a unit?

[arbfbe]

Quite simply, all units in the consist will move in the direction the reverser in the lead unit is placed. Trailing units behave as if the lead reverser was installed in that unit. There are NO switches specifying the trailing unit orientation to the lead unit EXCEPT for RCU consists.

Most of the answers posted here are just absolutely wrong.

[Randy Stahl]

QUOTE: Originally posted by arbfbe

Quite simply, all units in the consist will move in the direction the reverser in the lead unit is placed. Trailing units behave as if the lead reverser was installed in that unit. There are NO switches specifying the trailing unit orientation to the lead unit EXCEPT for RCU consists.

Most of the answers posted here are just absolutely wrong.

Perhaps I can simplify it a bit, seems like alot of people are over complicating things. A locomotive isn't that smart, it is A very simple machine. Each locomotive has a RER (reverse) relay and an FOR (forward) relay. If you have a single unit and you throw the reverse handle in forward, the FOR relay will energize and pick up. When this relay picks up the reversers will move to the correct position, the power contactors will pickup,and the locomotive will begin to load. At the same time a parellell wire . 8T will also become positve 74 VDC. remember that the pinouts are different from front to rear. Pin 9 will be positve on the front, pin 8 on the rear. You will see that no matter which direction the locomotives are facing the correct relay will pickup .
Randy

[Anonymous]

On my MRC throttle, I pu***he switch to Rev and the engines move backwards. Regardless of the way they are facing in the consist or whether they are Atlas, Athearn, or Kato.

With the AHM's its different. But then again, they are european.

[daveklepper]

Again, this works because pin 9 on the front is pin 8 on the rear and visa versa.

[chad thomas]

Didn't I say that already ???[:D][8D][:D][8D][:D][8D][;)]

[zardoz]

QUOTE: Originally posted by Randy Stahl

QUOTE: Originally posted by arbfbe

Quite simply, all units in the consist will move in the direction the reverser in the lead unit is placed. Trailing units behave as if the lead reverser was installed in that unit. There are NO switches specifying the trailing unit orientation to the lead unit EXCEPT for RCU consists.

Most of the answers posted here are just absolutely wrong.

Perhaps I can simplify it a bit, seems like alot of people are over complicating things. A locomotive isn't that smart, it is A very simple machine. Each locomotive has a RER (reverse) relay and an FOR (forward) relay. If you have a single unit and you throw the reverse handle in forward, the FOR relay will energize and pick up. When this relay picks up the reversers will move to the correct position, the power contactors will pickup,and the locomotive will begin to load. At the same time a parellell wire . 8T will also become positve 74 VDC. remember that the pinouts are different from front to rear. Pin 9 will be positve on the front, pin 8 on the rear. You will see that no matter which direction the locomotives are facing the correct relay will pickup .
Randy

Unless, of course, you happen to be using a 27-point jumper that had got pinched somewhere and had a few wired crunched together; then one unit might want to go a different direction than the other unit(s). Quite exciting when it happens. Sometimes the units want to seperate, sometimes the want to collide.

[Randy Stahl]

QUOTE: Originally posted by zardoz

QUOTE: Originally posted by Randy Stahl

QUOTE: Originally posted by arbfbe

Quite simply, all units in the consist will move in the direction the reverser in the lead unit is placed. Trailing units behave as if the lead reverser was installed in that unit. There are NO switches specifying the trailing unit orientation to the lead unit EXCEPT for RCU consists.

Most of the answers posted here are just absolutely wrong.

Perhaps I can simplify it a bit, seems like alot of people are over complicating things. A locomotive isn't that smart, it is A very simple machine. Each locomotive has a RER (reverse) relay and an FOR (forward) relay. If you have a single unit and you throw the reverse handle in forward, the FOR relay will energize and pick up. When this relay picks up the reversers will move to the correct position, the power contactors will pickup,and the locomotive will begin to load. At the same time a parellell wire . 8T will also become positve 74 VDC. remember that the pinouts are different from front to rear. Pin 9 will be positve on the front, pin 8 on the rear. You will see that no matter which direction the locomotives are facing the correct relay will pickup .
Randy

Unless, of course, you happen to be using a 27-point jumper that had got pinched somewhere and had a few wired crunched together; then one unit might want to go a different direction than the other unit(s). Quite exciting when it happens. Sometimes the units want to seperate, sometimes the want to collide.

Yea, lost a good friend at Western Ave. that way. Myself, I have seen the MU recepticle cover come apart and short out pins. Really scary when locomotives get a mind of thier own.
Randy

[wccobb]

They was a persistant rumor that the guys at ALCO didn't figure out the "pin #8 & pin #9" automatic directional reversing on the early SR-1s. They HAD to be coupled "elephant style" to go in the same direction.