Dash 9 vs AC4400

[Anonymous]

Hi, I'm sure this has come up before, but what is the difference between the two? Are they fairly similar ? I've also heard talk of AC or DC traction motors and was curious what the difference was or advantages/ disadvantages of each?
Thanks

[BaltACD]

The engines are visually similar.

The Dash-8's and Dash-9's are DC traction motors, The AC 4400's are AC traction motors.

The AC traction system has much better wheel slip controls and as such can haul more tonnage than DC traction motored engine. AC traction motors and their associated control systems are more expensive that DC traction motors and their control systems.

My road used to use 2 Dash-8's or Dash 9's on 90 car unit coal trains that would stall on several hills with the least suggestion of dampness on the rail....a heavy dew would stall the train. Since the switch to have 2 AC's the stalling problem is a thing of the past.

[M636C]

higssy,

The Dash9 and AC4400 are basically similar apart from the traction motors and associated control system. In addition to BaltACD's comments, the AC traction motors are not affected as much by heating, and can work for longer under ver heavy load, making them really useful for big coal trains, and similar bulk haulage, where the number of units can be reduced by using AC traction.

The recognition point for the AC4400 is the large AC inverter compartment behind the cab on the left hand side of the unit. The Dash 9 normally has a much smaller box in that location, and the air conditioner is usually fitted above the box. In the Dash 9, the electrical equipment is mounted below the cab floor, and this space is vacant in the AC4400, so they move the air conditioner to there instead.

Otherwise, the units look much the same, and are the same length, and can use the same trucks, although some AC units have steering trucks (but Dash 9s could have steering trucks if the road specified them).

Peter