Direction of wheel power

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Direction of wheel power
Posted by kenny dorham on Saturday, August 05, 2017 11:22 PM

When you have 5 locos all hooked up, how do they know which way to go.? Maybe i am asking about AC Phase? Do the Locos have a Front and Back or Forward and Reverse as far as the Motor/Electronics are concerned. When you have the "Front" of one engine coupled to the "Back" of another engine, they do not fight each other.?  I hope you understand what i am asking. Do they all, somehow, phase up with the lead engine.?

Thank You

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Posted by SD70M-2Dude on Sunday, August 06, 2017 12:33 AM

Yes, every locomotive has a front and back end, and it is normally lettered on the exterior of the locomotive.  Forward/front is usually the direction the Engineer's control stand faces inside the cab.

Others on here can explain in better detail exactly how this works, but the control system within each trailing locomotive automatically senses which way it is facing in relation to the controlling one and reacts accordingly.  Unless something is wrong with the control system (or the MU cable between the locomotives) trailing units will all act the same as the lead unit, and apply power in the same direction while in the same throttle notch. 

Distributed Power (remote locomotives in the middle or on the rear of a train) is a bit different.  When setting up the system and linking the lead and remote locomotives the Engineer must manually enter the direction the remote is facing (same or opposite) in relation to the lead.  If you get it wrong the the two will indeed work against each other.

Greetings from Alberta

-an Articulate Malcontent

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Posted by RME on Sunday, August 06, 2017 1:48 PM

To add a smidge:  The direction of wheel rotation on an AC locomotive is indeed determined by AC phase, but at the traction motor that's determined by the inverter drive, just as the frequency and waveform to give best power at a given rotational speed are.  The signals over the relevant wires of the MU system that "set direction" go to appropriate control circuitry in the drive that determines the phase timing that will rotate the wheels.

If I remember correctly, connections to pins 8 and 9 in the MU cable connection determine forward/reverse, and the connections at the "F" end for these two pins are reversed from those at the rear, which automatically 'hands' the locomotive for running no matter which way it is facing in a consist. 

I suspect that if one locomotive is 'fighting' the others, it has either been wired incorrectly 'by mistake' or someone has not properly set it to 'trail' when the consist was sent out.

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Posted by DSchmitt on Sunday, August 06, 2017 2:06 PM

I remember a post by a railroader (I think retired SP) about about strugging with a train and later finding out one of the locomotives was running the opposite direction from the others in the consist. 

I tried to sell my two cents worth, but no one would give me a plug nickel for it.

I don't have a leg to stand on.

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Posted by kenny dorham on Sunday, August 06, 2017 7:05 PM

Aahhh...OK. So there IS a little bit to this. Smile

 Thanks Again

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Posted by 1019x on Sunday, August 06, 2017 7:52 PM

I can add a second to the comment regarding distributed power. Back in the 70s when I was with Southern Railway we ran Distributed Power, (we called them Radio Units in those days) on a number of trains into and through the terminal I worked at. Sometime the lead unit on a through train had to come off and go to the shop and would have to be replaced with another Lococontrol equipped unit. This meant that someone would have to go to the radio control car and reset the code to match the new lead locomotive. One of the things we had to do was find out which way the lead unit was headed and set up the radio units accordingly. Once that was done we would tell the engineer to load up in #1 throttle with the brakes still applied to see if the connection was working and the radio units responded. We would also tell the engineer to apply forward sand when doing the test load, that way we could see if the radio units were indeed operating in the same direction as the lead units. 

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Posted by BigJim on Monday, August 07, 2017 6:38 AM

I suspect that if one locomotive is 'fighting' the others, it has either been wired incorrectly 'by mistake' or someone has not properly set it to 'trail' when the consist was sent out.

Wired incorrectly would be correct. I had a unit one time that had the 8 & 9 pins wired wrong on one end. The consist was put together at the away from home terminal with the afflicked unit near the rear of the consist. It took me little while to figure out why the train didn't want to move as easily as it should. The fact that it had a computer screen to tell which way it was loading helped a bunch.

"Trail" has absolutely nothing to do with the running of the locomotive. It only effects which headlight turns on.


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