Forums

[Anonymous]

I'm trying to work my way through figuring out the nuances of MU operation of locomotives. I gather they allow the running of a group of locos from one set of controls. That I get. However, I have noticed several locos running together, set out as nose to tail rather than all heading the same direction. How does the control unit know that some units are facing backwards? Wouldn't that mean that they would be working against each other when they moved off? Or are they not connected?

[David_Telesha]

Reverser. Unit backwards, set it to reverse.

Locomotives have equal pulling power both directions. It means absolutely nothing which direction they are facing.

MU's are all electric now-a-days. It takes care of everything - modern units don't have to worry about transition like old RS-3's and the like.

Fairbanks-Morse had electro-pneumatic in the 1950's.

[Saxman]

It's all in the MU cable and the way the locomotive is wired. Belive it or not, the wiring for direction control is reversed, by design, at the rear of the locomotive to allow the trailing locomotives to operate in the same direction as the lead locomotive regardless which direction the trail locomotive(s) is facing.

Saxman

[Anonymous]

Thanks for the info guys. I appreciate it.

[chad thomas]

Randy Stahl provided me with this info a couple years ago. Thought some of you might be interested.
==================================================================
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
most of these pins are allocated by the AAR but the ones that are not can and are used for many different things, for example the Santa Fe used the pin 19 as an extra control negative, the Milwaukee road used it for a positive to ring the locomotive bells, guess what happens when you MU them?
Randy

[chad thomas]

From the above note that pins 8 & 9 are reversed. This automaticaly makes the loco run in the right direction.

[CSSHEGEWISCH]

Baldwin locomotives and early FM's were equipped with pneumatic throttles and MU controls and could only MU with their own kind as a result. Pneumatic MU could only control up to four units with any reliability. Most FM's were later rebuilt with electric throttles and MU.

Union Pacific used a two-cable MU system with 12 and 21 pins on the cables. When CB&Q and UP began their run-through operations in the mid-1960's, UP devised a V-type MU cable for this power pool since Burlington used conventional 27-pin MU cables.