A look at the performance of a Rapido Amtrak F40PH plus three others

This post compares the performance of the Rapido Amtrak F40PH with the three other recently released engines and the data base of engines. The data base spans release dates from the 1950’s to the present day. The four focused engines are all 2014 or later releases.

The engines test compared here are as follows:

1. Rapido Amtrak F40PH #200

2. Kato Amtrak P42 #145

3. Bowser SP&S C-636 #341- fuel tank and trucks updated to the best configuration

4. Intermountain Santa Fe SD40-2 #5085

All of these engines were new out of the box for these tests. The Rapido, Kato and Bowser engines are DC ready without any significant electronic module in the power circuit. The Intermountain engine is a no sound version with an EMU pilot DCC decoder installed. This module on board makes this engine stand out from the others, as can be seen in the data presented. More about, the impact of modules on engine performance in general is being examined and will be discussed in subsequent posts.

These engines have been randomly acquired from different sellers. There has been no prior examination to bias the selection. Except for the Kato engine there have been no other products by these manufactures examined in this test environment. Because of this no statement on how these engines compare to the average of their individual product line can bme made or implied. The comparisons can only be drawn between these particular engines.

At this time it assumed that these are representative of the product types, but no further tests will be intentionally performed to verify that to be the case.

The Rapido Amtrak F40PH engine is shown in the following figures:






The other three engines are shown in the following photos:

First the Kato Amtrak P42 running on rollers:

Second The Bowser SP&S C-636:

And Finally the Intermountain Santa Fe SD40-2:

This discussion will focus on the performance measurements of the unit. The basic test requirements are as follows:

1.) Powered with DC voltage with no pulse wave modulation from the power supply.

2.) Running on a level surface (that is measured and adjusted as required weekly.

3.) The same 8-foot segment of track is used for all the basic tests.

4.) the track is cleaned before each test.

5.) All engines are run on rollers at 10 volts for 30 minutes before any data is taken.

6.) the unit is run without external load for all but the max draw bar force tests.

7.) Each track running data point is the average of three measurements.

These discussions do not deal with accuracy of the shell, the location and nature of the details or the lettering. In fact, several add-on details have been left off because the engines are new and will likely be sold after the testing is completed.

To appreciate the results, the question of relative to what always comes to mind. For this reason, the data is compared with the results from the full set of nearly 250 engines tested in the data base.

Basic function results are presented in the following charts. The data in each category is compared to the total set of engines. Note, the voltage function curves do not show the minimum voltage data. That data is shown on the weight function charts.

1- Scale velocity vs voltage of the engine running alone on straight and level track. There is no external load.
This data is shown from 4 to 16 volts. The actual minimum values are compared on another chart. The color code is maintained throughout these charts. The grey lines are from the data base of engines tested in this manner. These include all the engines in the data base with no attempt to segregate by some feature or era.

In this chart a reference line is shown (in black dashed) that is intended to represent the ideal best speed voltage function. Basically, the desire is for the unit to crawl as slow as possible at low voltage and be able to replicate the full size unit at high-speed. For this purpose, 80 smph at 12 volts was chosen as the value. One could argue that it should be higher. True, but without any external load, why would it be lower? Notice a significant number from the data base and two of the recent engines run slower than this ideal level.

Of the four specific engines, only the Rapido F40PH replicated to ideal over the voltage span. It is running a little slow at low voltage. The Kato P42 is consistently fast over the entire range. This is likely due to the two motors in the trucks. As will be discussed, this is the only questionable result for this model.

The C-636 and the SD40 both run slow relative to the goal. These are believed to have the same motor type in the drive. Neither do very well in speed. The SD40-2 has a DCC decoder in the circuit and that is effecting this result. Electronics may be also impacting the C-636. The motor is a voltage driven device. It converts electrical energy to mechanical energy in the form of speed(rpm) and torque. The voltage that drives these is the potential at the motor connections. A module in the circuit impacts the motor voltage to power supply voltage ratio. At 12 volts, that ratio is 0.975 measured at the track on the test facility. It appears that electronic modules reduce that ratio. This will be discussed in a later post on that topic.

2- current draw vs voltage for the engine only operating on straight and level track.

Here, all four of the engines are showing to be excellent current machines. All are falling near the low-end of the data base.

The lowest is the Kato P42, even with the two motors. The next best is the Rapido F40PH engine. It seems to draw more current at the low-end, then running almost flat over the range. This is maximizing the power in the low voltage end. The C-636 and the SD40-2 really look like twins in this parameter. The slope is steeper, focusing more power at the high voltage side.

Keep in mind that the input voltage times this current is the input power to the system. If the efficiency of the engines were the same, this would indicate how the output power would look. They do not have the same operating efficiency. That was indicated in the velocity chart and will show in other parameters as well.

3- Starting velocity. This is the minimum velocity that will sustain movement. This occurs at a discreet input voltage. This voltage varies from motor to motor and drive to drive. It seems to be a function of engine weight and motor capacity. For these charts it is shown as a function of weight.

The back ground data on this chart has been segregated by era, pre 2000 and post 2000 approximated release date.

The starting velocity for the SD40-2 is very low. This is due to the Pulse wave modulation created by the decoder in the circuit. This is likely not the actual minimum sustainable speed. The voltage supply can only be varied by 0.1 volt increments. With a finer setting, a lower velocity may have been sustained. The pulse impact on the engine was noticeable in this range of testing. At higher voltage settings, the pulsing disappears.

The other three engines are near the post 2000 starting velocity expectation. The Rapido F40PH tends to be a little high and the C-636 and the P42 tend to be at or lower than the expectation for a recent engine.

4- The voltage that is required for the sustained velocity is shown in the following chart:

Here the Bowser C-636 appears to be the lowest(best). Particularly when comparing to the expected function with weight. The F40PH and P42 are better than the data base with the F40PH being the better of the two.

Again the SD40-2 is different from the others. The DCC module is impacting the starting voltage by the electronic function and losses involved with it in the circuit. Here the engine runs at 6.9 volts, but not at 6.8. This is near the highest level measured in any test so far. I suspect all of the high post 2000 engines had modules of some sort in the circuit. The potential impact has only recently been understood by the author.

5- Starting velocity variation, implied torque wobble

In every case the data is repeated three times. Running over the same distance. The velocity and current levels are measured digitally. Differences in these readings are an implication of the potential torque wobble of the motor.
Even with the visible pulsing, the SD40-2 had no variation in the measured velocity. The Rapido seems to have the most variation, nearly on the pre 2000 engine average. The P42 and C-636 are both comfortably lower than the recent expectation curve.

6- starting current draw:

The starting current draw for all four of these engines is better than the pre 2000 technology average. The lowest is the Rapido F40PH.
Even with it high starting voltage, the current draw on the SD40-2 is in the range of these other recent units. This is more evidence that the module is impacting the motor voltage to power supply ratio on this unit.

7- The maximum pull force of the engine is shown in the following figure. These data are taken at 12 volts, when the engine will no longer pull the weight off the floor. Thus it is zero velocity. This may actually be just above the maximum pull force.
This data is for the as received engine weight.

These results show the Rapido engine is the best puller technology per pound than the other three recent engines. It clearly exceeds the recent engine expectation. It is very close to the Post 2000 average for its weight.

Here the impact of base weight shows its benefit. While the technology of the P42 is less than the F40PH, the actual heavier base weight allows it to pull more train than the F40PH. Both are good choices for this function.

Interesting ly the SD40-2 seems to hold its own relative to the expectation where the C-636 falls short of the expectation.

8- Maximum Pull force weight function is shown in the following chart. Here four weights increments have tested for each motor configuration. This is a relatively new test in the series, so the data base does not include as much history. The weight increments are roughly 150 grams. Totaling just over a pound of added weight. The base engine configuration from the previous chart is the left end of the curve.
As was indicated in the previous Rapido F40PH is the best pulling technology of the four recent engines in this test series as configured. However when weight is added, the torque capacity starts to diminish relative to the P42 configuration. When the full weight is added, the P42 is the best technology. This is likely due to two motors adding the extra torque on the P42, compared to one on the F40PH.

The C-636 appears to do well with increased weight, where the SD40-2 looks to be nearly out of capacity. Again that may be due to the impact of the module on that engine.

9- The current draw at this maximum pull force condition is shown in the following figure. This is the current when the motor can no longer lift the weight off the floor. This data is taken with wheels spinning. So there is some current relief because of that. This is representative of the operating current draw of these motors pulling a loaded train. More the actual case.

All of these engines are clearly on the low side of this parameter. The best is the Rapido F40PH engine, The highest is the C-636 engine. The P42 may be showing the impact of two motors relative to one for the F40PH.

The SD40-2 again looks to be of a different character. Clearly comfortably low, but a different shape.

10- Based on the work of others, this maximum pull force can be translated into the number of 4 ounce cars that can be pulled up a 2.5 percent grade. This assumes that the entire train is seeing an integral grade of 2.5 percent. This is a fairly sever assumption.
In this case the force curve is mimicked by the translation constant. The beauty of this is that one can see how many cars are implied by the differences in pull force. Depending on the weight, the Rapido F40PH engine will pull 10-15 cars more than the poorest engine. Keep in mind, all of the engines can pull the required cars up the grade. The real engines would be expected to pull 2 times the number of drive axles, or 2 X 4 = 8 cars or 2 X 6 = 12 cars.

The four axle engines seem to do better than the six axle engines in this sample.

The P42 is clearly a beast when it comes to this function. Adding the extra weight, it can pull 43 cars up the hill.

11- Taking all of these results into account through the second performance criteria that I have defined in another post, these engines are compared in the following figure. As a gage, a PC2 value of 10 or more is considered acceptable. Greater than 50 would be very good to excellent.

This criteria, the P42 is off the chart. The engine has been discussed separately and was shown to have a value of 1100 in this parameter.

The Rapido F40PH also shows to be excellent based on this assessment. The other two recent releases do not fair as well in this parameter. They get knocked down because their speed is so much lower than the ideal at 12 volts. These then could not pull a loaded train with any significant speed and consisting will still yield a speed that is likely lower than the real engine could pull a similar train.

In Summary:

This examination has shown the Rapido F40PH engine to be a very desirable selection. It seems to be well-balanced in its capabilities. As such it shows to be a real good performer all across the operating range.

As has been discussed in earlier posts, the Kato P42 engine seems to be in a class by its self over all. In most areas it does better than the F40PH.

Kato Amtrak P42 engine

Bowser PC C636 engine

Intermountain SF SD40-2 engine

The Bowser C-636 and the Intermountain SD40-2 are very nice engines. They are both very current friendly. Because of the way they are balanced, the overall performance criteria leaves them as acceptable but not outstanding performers.

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