Run 8 and Only 5-10 MPH?

I have read about the highest-powered EMD and GE units (AC traction motors) being run in full power and only crawling. I would imagine the noise is tremendous, but cool I'd think that kind of use would be hard on the equipment.

Is that the case? In that situation do they only run them for short amounts of time?

Thanks.

It doesn't hurt them to run them in Run 8. The engine has multiple protective systems built into them to prevent damage.

What you DO have to be careful with is the traction motors. If you have a DC loco, the ammeter will be marked into zones with short time ratings given for the amount of time you can spend while drawing large amounts of amps. Too long at full amperage will cook traction motors.

AC drive units can withstand this treatment better than DC units. AC units will have, in place of an ammeter, an indicator for amount of tractive effort produced.To run at low speeds in high throttle settings requires great adhesion. Otherwise, you will get wheel slip. This is why you seldom see this situation. You have to turn on the sand and back off the throttle until you get traction. You won't be pulling many amps if you are slipping.

A unit geared for pulling can handle low speeds under heavy load better than most others because the traction motors can run at a higher rpm.

Les

I read a while back that when testing GE AC4400 units they could get down to less than 1/2 MPH at full power and the AC traction motors could take it. Amazing.

As far as wheel slip, I thought that the on-board computer would automatically cut power to the traction motors when the wheels began slipping. Is that not the case?

Is is common to run 'em in run 8 and only get up to 10 MPH or so because of weight, grade, or both?

Denver,

That's right, the new units will do this. But the idea is to prevent the slippage in the first place, before the power reduction occurs. Manual engagement of the sanders is a pre-emptive step.

The AC units are great luggers. Apparently, the AC traction motors lack brushes that can bounce, arc, or overheat.

It is not unusual to run all-out at 10mph if you have a limited length of heavy grade (ruling grade). However, I think most railroads would try to avoid that situation by assigning adequate power to get over 19mph. Fuel consumption is very high in Run Eight, and track occupancy/time factors reduce operational efficiency by tying up a main line with a 10mph train. Consider that, on a 40-mile segment of track, a 10mph train requires 4hrs. to cross it, vs. 2hrs. at 20mph. This sort of thing can build up operating costs in a hurry!

Also, there can be harmonic rock issues caused by operating between 13 and 19mph, so that speed range should be avoided.

Les

Denver Dude wrote:I read a while back that when testing GE AC4400 units they could get down to less than 1/2 MPH at full power and the AC traction motors could take it.

Full power at 1/2 mph would mean something over 2,000,000 lb of tractive effort.

Desertdweller wrote:there can be harmonic rock issues caused by operating between 13 and 19mph, so that speed range should be avoided.

Dunno if it should be avoided, but it isn't. 13-19 mph is very common for freights on western hills.

timz wrote:

Denver Dude wrote:I read a while back that when testing GE AC4400 units they could get down to less than 1/2 MPH at full power and the AC traction motors could take it.

Full power at 1/2 mph would mean something over 2,000,000 lb of tractive effort.

Really??? I'll look for the article.

AC induction motors are different than DC motors. An induction motor is basically a rotary transformer. You lock the rotor and not overheat. The stator field simply just "sweeps" and rotates around the stationary rotor. No commutator to burn up. You can set indep brake, lock the wheels and thottle up with out melting the motors. You can start a coal train, on an uphill grade, at thottle 8. The consist will crawl with no damage.

P.S.
A 4000 HP MAC AC does not put 4000 HP to the rails at slow speed. The loco is adhesion limited at slow speed (30 - 40%) and putting out less than 4000 Hp even though your at thottle 8. It's counter intuitive.

timz wrote:

Denver Dude wrote:I read a while back that when testing GE AC4400 units they could get down to less than 1/2 MPH at full power and the AC traction motors could take it.

Full power at 1/2 mph would mean something over 2,000,000 lb of tractive effort.

Ummm.....not a chance. Knuckles on cars are rated I believe around 550-600,000lbs before they break.

So let's clear some things up. I've run coal trains with GE's on the verge of stalling. First of all, on AC motors you DO NOT modulate the throttle to control slippage. The computer does that and remember it allows a small % of slippage on purpose in the attempt for each axle to gain adhesion. The units go into what is often called "earthquake mode". What that is comes from the difference that each TM is exerting on the truck. It literally causes the engine to buck and jump and down. Those desktops aren't fully attached to the floor and they will hop up and down too....its quite a ride.

IN full throttle at those speeds, those GE's managed 200,000lbs a piece....I had two.

Harmonic rocking, as mentioned earlier, is usually to be avoided. But it usually only pertains to high cube load cars like grain cars.

We all agree that no one unit can exert 2,000,000 lb TE at 1/2 mph-- but "full power" from an AC44 would be that much or more.