Western Railroad Discussion > Hump control?

"Hump controls" were referenced in an earlier thread. Please elaborate on what this is and how it's used. Why is using the hump control better than using the throttle at low speeds, as implied below. Thanks, Steve

Date: 07-02-03 09:14
tricks and tips when stuck
Author: danderson

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Sometimes when i am having problems on the grade with wet and slippery rails and getting slower and slower to a stall is to apply a small amount of independant brake/[engine brake for those who do not know] or try using hump/manual power control and gradually reduce or increase the amperes to the motors to stop the wheels spinning

Abstinance, my friend, abstinence.

Hump Control or Low Speed Control (Pacesetter) allows the Engineer to make power adjustments in much smaller increments than the main locomotive throttle which has only 8 powered positions. The Pacesetter allows the Enigneer to adjust the speed in increments of one one-hundreth of a mile-per-hour up to 3 mph, and in increments of one-tenth of a mile-per-hour up to 10 mph. Let's say the train is making 8 mph up a grade and but the wheels are slipping and the speed is falling, the engineer reduces throttle to Run 7 which stops the slip but speed keeps falling. So the Engineer engages the Pacesetter and sets the speed for about 7 mph, he then puts the throttle in Run 8
giving the Pacesetter full control, the Pacesetter will then be able to make fractional adjustments that the trottle doesn't allow the Engineer to make, effectively like being able to set Run 7.6 etc. What the Pacesetter does is adjust the Field Strength in the Alternator thereby controlling the power output of the Locomotive.

The hump control is also extremely convenient when loading coal-trains & continuous slow speeds are desirable. It's a pain in the arse to keep your speed at 0.7 mph with throttle adjustments.

The primary intent of hump control is to make it easier to control the speed of hump engines as they shove cuts over the hump. Once the cut is moving over the hump, they usually want to maintain a speed of around 1 mph so the pinpuller can keep up with the process, and cars can clear the hump throat in time to throw switches for the next car.

If you try to use the throttle, the engineer would have to constantly move it back and forth between throttle settings to keep the speed constant. It gets more and more difficult to do as the train gets shorter, since being lighter it reacts more quickly to any throttle changes.

The way hump control works is that the throttle is set to something like throttle 4, then the hump control can be dialed back to infinitely select a power level below that of throttle 4. He can then make minor adjustments as the weight of the train lessens with progressive humping. No more fighting with the throttle.

Hump control was the original way it was done. Now most hump locomotives use a slow speed control. As a previous post suggests, the engineer just dials in the speed he wants and lets the control do the rest.

Hump control was also useful for other low speed applications, like when picking up or dropping rail, weed spray trains, and rail grinding trains.

Some engineers find it effective when a locomotive is having wheel slip problems. For example, when the throttle is reduced from 8 to 7, locomotive loses about 20 percent of its tractive effort. With hump control, and engineer can set the power between 80 and 100 percent, and perhaps reduce wheel slip while maintaining a relatively higher tractive effort than by selecting throttle 7.

It doesn't do that much good with a full consist, since as the speed of the train drops, the tractive effort will rise, and the same problem will start all over again, but at a lower speed. It can help if the power on only the lead locomotive is reduced, since it sees poorer rail conditions than the trailing locomotives. Thus the lead locomotive might operate in the equivalent of throttle 6 or 7 to avoid heavy wheel slippage, while the trailing locomotives stay at full throttle. Newer adhesion control systems make this less of a requirement.

I'm going to give some more detail regarding pacesetters since they were mentioned and I know them well. I'm a train operator at a coal mine so I've seen the different kinds of systems that are out there. Older locomotives require a separate computer device called a "Pacesetter box" to be connected to the locomotive for constant slow speed control. These are not normally on the locomotives, they are only placed on them when needed. Of course, the locomotive has to be wired for this device, which was an option the original buyer of the locomotive chose. I've heard of units with a built-in manual "Power reduction" control but having no pacesetter box connections. I've seen units with both on them, such as CSXT 7818. Power reduction leaves the speed control to the operator, you just dial down the percentage of the amount of amps a certain throttle notch will give you. You have to gauge your own speed based on the speedometer (which on some units is useless below 2MPH) One the other hand, the pacesetter box will display your speed down to two decimal points and allow changes in hundredths increments below .8MPH (depending on the type of box you have) and it will reduce the power automatically to maintain your set speed. They may take a minute or two to settle down to your set speed but once they do they hold it very well. Also, pacesetting is a MU function, all units that are equipped for slow speed control "should" try to mimic the pacesetting effect of the leading loco.

After 1993-1994 and computerized screens came to locomotives, they permanently built the pacesetter right into the systems, eliminating the need for a separate box. On EMD units the speed is adjusted in .02MPH increments. As for GE locos, well, I'm not sure if these dates are the same for other roads, but on UP locomotives I've observed these systems: C44AC units built in 1994-1996 - the pacesetter only had tenths (.1MPH) increments. (many of these older units have subsequently upgraded to one of the two newer systems) In 1997 the slow speed computer would allow changes in .01 increments, but the design was poor (Below 5MPH,you could only change in .01 increments, meaning you'd have to push the button 100 times to get another MPH, although they have a "current speed" button that can help speed up the process) Later in 1997 they came out with a much improved system, simplying a similar system that GE used on the C60AC and C4460AC's. This new system, a "set speed" system, allows you to pre-enter a new target speed, making larger changes in speed much much easier to effect. This system is what they use to this day. All the slow speed computers on GE units (except the C60 family) have a "load" setting of light,medium or heavy which basicaly just speeds up the response time of the computer. Each variety of these slow speed modes would have a manual mode (older ones), or hump mode(newer). These modes are just like the manual power reduction in the older units, only instead of turning a dial for more or less power, you select a different percentage. I've also seen a "Plug Load" button but I have no idea what that one does.

Loading coal doesn't require any of this manual stuff so I don't use it. Sometimes we'll have to follow a loading train up to the silos, so you're matching their current loading speed but maintaining it exactly isn't necessary. In these instances I'll sometimes play with the manual mode to see how hard it is to do it yourself. The computer does a much better job. Occasionally we'll get a train that has a defective pacesetter, and will have to be "hand loaded" - and that can be pretty nerve wracking and difficult. I have the best luck with only one unit pulling (I'll isolate the trailing units), throttle notch 3 and varying my speed with the independant (locomotive) brake. DPU trains are the worst to hand-load, because there is a time delay before the DPU's independant brake "mimics" what you have on the lead. So you'll just get it balanced for the speed you want, when the rear BC pressure will change, which will speed you up or slow you down and you'll have to correct for it. By the time you correct, the rear's changed again, starting everything over again.

andy

Android wrote:

> I've also seen a "Plug Load" button but I have no idea what
> that one does.

Plugging an electric motor is where the motor is rotating in one direction, and power is being applied to get it to rotate in the opposite direction.

An example would be where a locomotive is operating in the forward direction, and the engineer moved the reverser to reverse, and opened the throttle. Plugging a motor at more than one or two mph results in fireworks in the electrical cabinet, locking of the traction motors, the stalling of the diesel engine, and is generally frowned upon by railroad management.

Plugging can be used at very low speeds, and some engineers will use the technique to hold a train while the brakes recharge if the independent won't do it alone. It's typically again railroad rules, since there is a great risk of damaging the motors by overheating the commutators on DC motors. Some AC locomotives can't be plugged, since the system won't allow it, while some of the newer ones will allow it up to a couple of mph.

Therefore, the "plug load" button is probably to set up for cases where trains are loaded downhill, and the system is used to control the speed of the train by applying power in the opposite direction to the locomotive's movement.

Thanks to all for the insightful replies.

- Steve

Some AC
> locomotives can't be plugged, since the system won't allow it,
> while some of the newer ones will allow it up to a couple of
> mph.

Thanks for the info on plug loading. I seem to recall something about it now that you described it. As for units with the Plug load button, I think the only AC units I've seen them on are the oldest AC4400CWs, the ones still set up with their original 1/10'ths-only pacesetters. I was on one today, CNW8832 (and had CNW8831 as the 2nd unit, hows that for a rare combo!) The only other units I seem to recall seeing plug loading is on the BNSF 8200-series SD75M's.

One other pacesetting note, newer EMD MAC units have a slow speed mode that you can use downhill, but it's not plug loading. It uses the dynamic brakes instead.

andy