AC-DC mix

[wayne]

Can AC locomotives and DC locomotives be run in the same lashup and if so is it common practice? What problems or nuances must be overcome?

[BaltACD]

It is done every day. In fact CSX just issued a bulletin limiting trailing tonnage on all bulk commodity train (coal, ore, grain etc) to the tonnage rating of 2 CW44AC's + 1 Dash-8. The Dash-8's are all DC locomotive.

The problems in the lash up are that the DC locomotives must observe short time ratings with their traction motors to prevent overheating. The AC's don't have short time ratings as their control systems permit them the lug all day and all night with overheating (at least that is the theory....in practice ????)

[Overmod]

There are at least two "halves" to this question.

If you're asking 'can an AC unit be run in MU with DC' the answer should be 'yes'. Part of the 'programming' of the AC inverter circuitry will be to translate the signals coming through the MU cable and control traction power accordingly.

If you're asking if it's a good idea, the answer is far less robust. First, AC units as you know are more expensive than DC, and are often in limited supply (as on KCS). Even one DC-motored unit in an otherwise AC consist prevents the use of many AC advantages (as the DC traction motors become 'the weak link in the chain' and limit slow-speed power, etc.)

There is little advantage in running fancy AC locomotives as if they were cheaper DC equivalents, aside from the convenience of allowing their inclusion in 'normal' road-power lashups, or in balancing movements, etc.

I await comments from actual engine crews on this subject!

[Mookie]

Again - they do it all the time on BNSF coal trains. Doesn't seem to be a problem.

[corwinda]

Also done routinely on UP. In fact I've seen AC4400CTE/SD70M remote helper sets here in Oregon.

[adrianspeeder]

Man, i thought we were going to talk about "highway to hell" and "shook me all night long" hmmm that sounds like a GE.

Adrianspeeder

[Train Guy 3]

QUOTE: Originally posted by adrianspeeder

Man, i thought we were going to talk about "highway to hell" and "shook me all night long" hmmm that sounds like a GE.

Adrianspeeder

I really like hearing "hells bells" ring on those locos.

[Randy Stahl]

No short time rating on AC motors, in fact the traction motor cables are about half the size of DC engines, not alot of heat generated in AC motors, no commutators.
Mix and match, no problem, if you can't run em with existing engines they are worthless.
Randy

[mvlandsw]

The newer DC units that are equipped with computer control are programmed to reduce their output when the traction motors get too hot. They can be run with AC's without worrying about short time ratings. However when they they reduce their output it almost always means the train will stall. Older DC units do not do this and their motors will burn up if run over their short time ratings. This can happen if they run as trailing units with AC's leading and the engineer does not pay attention to the rating of the trailing units. CSX at one time required the older units to be in the lead for this reason. The crews did not like to ride an old clunker with the new air conditioned units trailing. In practice the AC's can run all day even if standing still without damage. They can even be reversed to hold a train on a hill.