i see on various forums talk about ‘issues’ when DC-motored locomotives lead an AC one yet there are train operators who use either in lead with no restrictions. I am yet to understand (in basic terms) as to what really is the ‘issue’.
Is it something that was prevalent in older times when motor controls were basic and didn’t protect the DC motors in trail-mode. Specifically, can a SD70ACe (high Tractive Effort /HP) lead something like a GPL38 (lower TE/HP with DC motors)? What ‘issues’ if any, it would cause?
Back in the “olden” days of diesel locomotives, it often was the practice to have the weaker locomotives leading to avoid overheating of the traction motors. With AC traction motors being more rugged than DC traction motors, it would make sense to have the DC locomotives lead to protect the traction motors.
In practice, on the UP, that isn’t what happens. The DC SD70Ms can be found anywhere in consist with the SD70ACes C44AC/ACCTE/45ACCTE/whatever they are calling them now. I suspect that the electronics that are no part of the locomotive do a better job of protecting the DC motors in these kinds of situations.
Could that be more to do with UP preferring more modern locomotives in the lead, due to the newer safety electronics, etc (I don’t know how extensivly the SD70Ms have been modernized lately)?
Didn’t UP buy 1K of the SD70M’s that is a significant part of any carriers power roster, even UP’s.
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UP had 1,454 SD70Ms (incuding 25 ex-SP units after the merger). A number have been wrecked or retired, so I dont know the current number on the roster.
There’s 1365 left out of the 1454 they had at one point but more and more are being laid up bad order as well. The UP isn’t totally happy with them and hasn’t decided if they’re going to do what the NS is doing with all their power that had an AC option and rebuild them into AC locomotives at this time.
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CSX bought several orders of GEVO DC engines. They are routinely operated both in lead and trail with the AC cousins.
I don’t know if there are any special action necessary when they are used with the AC’s.