Dan
CNW 6000 wrote:By that reason the locos couldn't talk to each other, makes sense. What else is carried in MU cables or are they for loco cpu-loco cpu communication only? Could/did that ever get tried with a vacuum system? Why is it purported in some threads to be a big deal to break up a MU?
I believe M.U. cables only carry the electrical connections needed to M.U. two or more engines together. It goes back to the late thirties so pre-dates computers in engines.
I suspect the threads you've read are talking about model railroad situations, using Digital Command Control you can M.U. two or more engines together (steam, diesel or electric) and operate them from one throttle. Sometimes setting up and breaking down the "consists" can be a little sticky, your command station is basically a computer and like all computers can be a little difficult from time to time.
a13398 wrote:In the Nov issue of Trains, a story on the Montana Rail Link gas local confused me. It stated the trian stalled on a grade. The crew decided to unhook the MU cables between the units to operate tehm independently, and were able to restart the train on the grade and proceed. This seems counter-intuitive. Can anyone enlighten me as to why the units working independently would, apparently, provide more traction or power to accoplish this? Thanks!
Thread was "Double Heading Diesels"
JonathanS wrote:IIRC only the 1st unit in an MUed set sands the rail. So by separating the units they could get both to sand.
Nope
Randy Stahl wrote: JonathanS wrote:IIRC only the 1st unit in an MUed set sands the rail. So by separating the units they could get both to sand.Nope
Isn't sanding a function of wheelslip control and automated per unit by its computer?
broncoman wrote: Randy Stahl wrote: JonathanS wrote:IIRC only the 1st unit in an MUed set sands the rail. So by separating the units they could get both to sand.Nope Isn't sanding a function of wheelslip control and automated per unit by its computer?
as stated older engines dont have computers....and sanding is controled thru the MU cable.....my guess would be either a weak connection as stated or.....individual throttle control on each unit assuming they were older without computer wheelslip.....3rd possiblity and this happened to me once...trailing unit was tripping a ground fault...unhooking the MU and running the trailing unit at a lower thottle setting might stop the ground fault and maintian power enough to crest the grade.....that was fun for me as a conductor it was my first time at the throttle....and not to sound what is IIRC??
thx
I wish I could have explained it better in the article, but to be totally honest, I wasn't 100% sure myself, and I had some space considerations. I assumed the answer was since the locomotives in question had their m.u. cables unplugged, they could be ran separately, and therefore the throttle settings could be different. That way the if one of the locomotives started to slip at a lower throttle setting, the other might be able to run at a higher throttle setting, and in turn, the two could maximize their tractive output. And since I'm no expert, I asked an MRL engineer for input. He said I was pretty close. He added that when the lead unit backs off the amps account slipping, it might cause the trailing units to do the same. Pretty soon the whole outfit snowballs to a slow walk, and maybe a stall because they keep slipping. So pulling the cable between units can help and one unit might stay loaded longer. Especially the second unit, since the lead unit may have had a chance to sand the rails better.
He also went on to say that it is also possible the MU cable had a loose connection or wasn't plugged very well into the receptacles. When the crew plugged it back in, they may have got it to seat better than before. Lots of curves on MRL, those things can work loose somehow, and especially if they are in the same consist week after week and no one checks the cables to reseat them. We'll never know if that was the case, since the crew of the train I rode, didn't try wrangling with the cables before they decided to remove them completely.
I want to thank the MRL engineer that helped to get the answer straight. He and arbfe (who responded to the earlier thread about this same subject http://www.trains.com/trccs/forums/1230185/ShowPost.aspxobviously know their stuff. Especially when it comes to MRL operations. Thanks guys!
Tom
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