Diesel Mismatched Lash-ups

Dan Padova posted:

I can almost understand, though not fully, how one manufacturers different locos can work.  

However, with the combination I mentioned in my first paragraph, how do the units coordinate as far as speed and pulling power ?   

Dan, there are eight throttle positions.  When the throttle of the controlling locomotive of a consist is in, say, Run-5, then each locomotive of that consist does what it is programmed to do any time it is in Run-5, regardless of where it is in the consist, or what other locomotives are in the consist.  

Therefore, in a consist of EMD F7's and Alco-GE FA2's which are sitting at idle, when the Engineer places the throttle in Run-1, the F7's begin a slow process of amperage buildup, while the FA2's immediately produce about 200 amps of traction power, because that is what they are respectively designed to do.  As speed increases, the Alcos will make transition at pre-programmed speeds measured by an axle generator, while the EMD's will make transition based on the amount of amperage being used by the traction motors.  Each does what it was designed to do when given the same throttle command.

When engines are in Multi Unit (MU) control, there are control cables which are connected between the units.  Many control braking.  However one line is a 27 wire electrical cable.  This cable sends signals to all the locomotives commands from the lead unit concerning throttle and dynamic brake commands.  Now the details of which hose and pin does what is beyond my pay grade....

90:

Your post brings up an intetesting point.  If EMD, GE and ALCO load differently, did that cause the units from different makers to buck each other with throttle changes?

Dominic Mazoch posted:

90:

Your post brings up an intetesting point.  If EMD, GE and ALCO load differently, did that cause the units from different makers to buck each other with throttle changes?

Yes, when starting.  That's why a little bit of locomotive air brake is used when initiating movement.  It smooths out any fighting among locomotive units, and, of course, enables very gentle stretching of slack in the train, if the locomotive is coupled to cars.

Once the consist is moving and all are loading, the locomotive couplers are stretched tight and there is no more bucking, in spite of different loading characteristics or methods of making transition.  Unless -- there's always that one exception -- the front locomotive is an Alco, in which case, when that unit makes transition, its whole world drops out and then the unit rapidly loads up again at higher amperage.  The whole thing only takes about two seconds, but creates a bit of slack adjustment between the first and second unit.  Nothing severe, but definitely noticeable.  Fortunately, differences in wheel size due to wheel wear prevent all Alcos from making their speed-driven transition at exactly the same moment.  On very -- I mean very -- rare occasions, and strictly by coincidence, a solid consist of Alcos with identical wheel sizes was created, and then the whole consist bucked during transition.  Extremely uncommon, but it has happened.

Dominic Mazoch posted:

90:

Your post brings up an intetesting point.  If EMD, GE and ALCO load differently, did that cause the units from different makers to buck each other with throttle changes?

Yes, however, it is not something to worry about or depending on speed, maybe even notice. In the case of a GE leading an EMD, you might feel a very slight bump because the EMD loads up faster. In other words, it is a non-issue!

Thanks guys.  There's something to be learned every day.  

Dominic Mazoch posted:

When engines are in Multi Unit (MU) control, there are control cables which are connected between the units.  Many control braking.  However one line is a 27 wire electrical cable.  This cable sends signals to all the locomotives commands from the lead unit concerning throttle and dynamic brake commands.  Now the details of which hose and pin does what is beyond my pay grade....

As far as the pins go, you’d have to talk to a electrical guys, don’t know about that.

As far as the hoses, you have (from outside) A&R...apply and release of independent brakes.

ACT...Basically the bail off for the independent 

MR...Main reservoir, to use the both or multiple air tanks as one large one.

Now, last night, I had a GP38-2 and a ES40DC(not my favorite my any means to spot) and they’re was a decent bang when the Gevo was trailing 

We need not go so deep into this that we identify each of the 27 pins and wires by number.  But . . .

the m-u jumper connects locomotives by low voltage electrical signals to control the following:

• Generator field (the "ignition key" - without it there is no traction power)
• Direction of movement
• Throttle Position
• Forward sanding, reverse sanding
• Rear headlight Off/Dim/Bright
• Dynamic braking control
• Fuel pump
• Low voltage control (contactors, relays. etc.)

All locomotives in the consist receive the same signal via the 27 pin jumper cables.  How they actually use it varies, especially between older locomotives and microprocessor controlled locomotives.

Strangest motive power combo I’ve ever seen was an SD40E, GP40-2 and two DIT ES44ACs today in Conway. Wish I took a picture of it...