Diesel Loco question from new member
 

Hello,

I'm new to these forums and must confess to knowing very little about trains in general despite holding a strong interest in them, however I do have one question that i'm sure can be easily answered.

Last night whilst waiting for my train to pull out, we were sitting next to a set of carriages with a diesel locomotive at each end. I've often wondered, how are the two diesels connected so as the control inputs from the front loco is repeated in the second?

Fraser.

Hello fraser and welcome, I have no idea but You will get an answer soon.

Hi Fraser.

I think that the control is effected using circuits through each coach of the train. Connected one to the other until the second loco is reached.

As far as I am aware this is called something like multiplex control using standard inter coach connections. I wonder if in this particular event both locos were working. I think has been known for a loco to be returned to a remote depot "dead" in/on a train. Of course this operation is standard practice with HST 125s.

In push/pull trains there is a system called TDM (Time Division Multiplexing) which enables the control signal between the remote driving trailer and the actual locomotive to be passed through the lighting circuit cables of the intermediate coaches.
I don't know if this also applies to locos at either end of a train.
John.

That's what I was trying to think of.....honest! :D

TDM certainly is used in push pull, but I am not sure whether it is the system used in HSTs - I think that TDM post-dates the HST. ON the old push pull sets used for Glasgow Edinburgh (with Class 27s - anyone remember?) the wiring was bespoke. Not sure how it is done these days - most use lead loco under power with the trailing loco providing other sources such as ETS or additional braking power...

Hope that helps

on a HST there is usualy a set coach set to go with the power cars, and basiclay when the coach set is coupled with the power car, there is a wire that transmits info from one power car to the other so that if one setting is changed in one power car, the trailig power cars speed or brake apliance so on changes to

most of the time with 1st generation diesels the rear loco is hauled as an additional vehicle the driver, depending on type, has to isolate the DSD on the rear etc.... 'top and tailing' is done nowadays to save money on running round the train or maybe the train traverses a branch with no run round facilities.....TDM was/is used on the overhead electric hauled services and is a little different to remotely controlling a loco from another loco....

Yes, I remember them very well indeed. In fact, the only bespoke parts of the trains were the uprated disc brakes fitted to the 27/1s and 27/2s, and the ETH (ETS/HEP) fitted to the 27/2 subclass. <edit - disc brakes on the Mark 2 coaches too>

Most people are surprised when they find out the the coaches were fitted with standard blue star multiple working cables throughout so the locos thought they were next to each other and were working in multiple. I don't know if there are any photos existing but if there weren't enough 27/1 or 27/2s available then 37s used to deputise and you would often see a standard class 37 at one end although I can't recall seeing the service ever with a 37 at both ends