Clearly the digital modules that give you individual control of one or more engines on your layout provide a significant advantage that can not be minimized. However, there is no free lunch in this world. The intention of this examination is to identify the impact that DCC & constant DC digital modules have on the performance of HO model railroad engines.
This impact is compared to running the engine on conventional DC with no pulse wave modulation.
The process used in this series is to run the standard engine only and grade & train length tests using the three different power supply options on the same engine.
These supply options are:
- DC with no digital module in the engine
In this case a lab DC supply is used. The Supply is adjustable from 0 to 25 volts in one tenth increments. For these tests, the NMRA maximum of 16 volts is used as the upper limit for the DC portion of the tests.
2. Rail Pro constant DC with an Rail Pro LM-3 digital module installed. No sound system included for these tests. Factory settings are retained on the module. One module was used for the entire testing.
3. DCC using a NCE Power Pro system with a DCC module in the engine. Factory settings are retained on the modules. Individual modules were used in the testing. The unit was sold with the DCC module after the tests.
This process was used on several engines. These are all Athearn blue box test bed engines with upgraded motors. The engines and motors tested are as follows:
- SP F7A- Kato #3 motor
2. NP F7A – Kato #4 motor
3. SP Trainmaster – P1K #3 motor
4. SF Trainmaster – P2K motor #4 motor
5. NWP Trainmaster – Atlas China #1 motor
6. SF GP38-2- Athearn HP #1 motor
7. Seaboard GP40-2- Mashima 1824 #3 motor
8. SF U30B- Kato #5 motor
9. P1K UP F3A- stock P1K motor
10. NP F7A – Alco Helix Humper motor#5 (same engine picture as #2)
11. B&O (Tyco shell) F7A- MRC-24 motor
To calibrate the Rail pro & DCC test settings, the track voltage when the supply is set at 12 volts. This is shown here:
The same track voltage for the rail pro system is shown here for the maximum power setting. Note the current reading on this meter is in error.
Finally the track voltage for the NCE DCC system is shown here for the 28 speed step setting.
The DC establishes the track at the power supply of 16 volts, which is 100 percent. DC. To compare the three systems, on an equal basis, a DC supply voltage needs to be assigned to the speed steps for the DCC system and the percent power for the Rail pro system.
Based on the track voltage values shown above, 12 volts DC supply voltage is equalivent to a DCC speed step of 25 to a Rail Pro percent power 82.4:
The low speed velocity differences are shown in the figure below. This is engine only sustained velocity. The blue bar is the average of all tests for each power supply. The red bar is the maximum measured and the green is the minimum measured
Both of the digital modules are producing a pulse wave modulation that should allow the engine to creep at very low scale speeds.
Based on the results shown in the figure:
- The digital modules run slower on the minimum measured with the Rail Pro being the slowest.
- Both digital modules show a larger variation than the DC results.
- The DCC has the fastest average and maximum
- The DC results are much more consistent.
Moving up in speed, the 12 volt velocity results are shown in the following figure:
This compares the resulting speeds for the engine only on a level grade, engine only on a 2.5% grade & the nominal train on a 2.5% grade. The nominal train is made up of 2 times the engine drive axles number of four ounce cars. This is either eight or twelve depending on the engine.. Once again, the red is the maximum measured. The blue is the average of all engines and the free is the minimum measured. These results are show as a percentage variation from the DC average in the following figure:
Based on these results:
- For the engine only at both grades the DC displays the highest speed at both grades. This includes all conditions(max, average & min)
- The Rail Pro is second with the DCC running slowest.
- When the nominal train is added at the 2.5% grade the result relation ship changes
- The all show a significant loss in speed at all of the points. The DC shows the largest loss.
- The DC minimum measured at 2.5% is now the slowest of all.
- The Rail pro results are slightly better at all points.
- The differences at this grade a not good for any of the options.
Examining the train length impact, the results are shown in the figure below:
Here the digital modules are showing an advantage over the DC only option.
The following figure shows these results as a percentage from the DC average result
These results are summarized as follows:
- Best puller on average and the maximum measured is the Rail pro module
- While second on average, the DCC results show the least variation from minimum to maximum, where the Rail pro has the most variation
- In general all of the versions nearly met or exceeded the nominal train car number requirements.
Looking at the overall performance criteria the results are shown in the following figure:
Using this the study results can be summarized as follows:
- The Rail pro shows the highest results at all comparison points.
- While the DC shows the poorest result, it has the least variation from min to max.
- The DCC had the highest Maximum measured case, but its average of all engines fell to second.
- The negative value of the min measured DC case is due to the lack of nominal train length for that case.
- The min measured DCC case is also disappointedly low.
- This highlights how the variation in the engines an make a particular result seem exceptional while others are quite disappointing.
- When adding load requirements, the digital module cases draw even. It will be interesting to see how they would do with a nominal train length on a level grade.
Additional results will be added to this analysis as they become available. The last point will be included in any further testing.
