8-10-15 Eureka

The recent activity has included a study pertaining to the Bowser C-636 and an Intermountain SD40-2. This topic was discussed on the Atlas Rescue forum. It will also be posted here in a few days.

What prompted this discussion is the feeling that these two models have a “new” motor that stems from the Atlas recent releases and their apparent poor pulling capacity. The first look at the C-636 did not flag it as a poor performer. In this assessment the engines were compared to the pre and post 2000 engines like the Kato P42 post.

Going in it was thought that these were both DCC ready models. Reviewing the facts, the realization that the SD40-2 has the ESU Pilot decoder on board. This does help explain some of the short comings that were seen the results of the SD40-2’s performance. In particular, the high voltage engine only velocity is low and the draw bar force has a very slight gain with engine weight.

This was the result that caused some additional examination of the differences. The decoder in place definitely helps for low-speed performance. However, any electronic module will introduce some voltage loss. Voltage is the primary power driver for electric motors. Based on voltage potential and the load, the motor will draw a current. When the forces balance, that is the speed which it will run. The maximum pull will be highly influenced by the voltage to the motor. for this testing this voltage for this measurement has been set at 12 volts. Experience has shown that the maximum draw bar force has been measured close the 12 volt result on almost all engines. So to save time and enhance consistency, the MDF has been measured at 12 volts in recent tests. That is also near the resulting maximum equivalent voltage for a DCC system.

Comparing the results for the C-636 and the SD40-2, it appears that it is possible that the motor is seeing 10 volts when the supply is set at 12 volts. This is judged by the speed to voltage function curves would be similar if there was 2 volts less feeding the SD40-2. To test this theory, the C-636 MDF test versus engine weight was reexamined at 10 volts.

Eureka, it follows a similar trend to the SD40-2. In that is actually falls between the third and fourth weights. This confirms that the decoder is adversely impacting the maximum power that the motor can develop, even in DC. Because of the transient nature of DCC the situation will likely be worse.

To further explore these results, the C-636 MDF to engine weight curves will be defined at 9, 10 and 11 volts adding to the previously defined 12 volt curves. Additionally, the SD40-2 curves will be expanded to include 11, 13 and 14 volts.

Clearly the decoder power loss is larger than previously understood. One has to ask how much variation exists over the potential decoders? Are Electronic modules for DC systems, like Rail Pro any more efficient? Do they allow the motor to see a higher voltage level? How much?

This activity has brought to question the current motor variation series that is process. It will be restructured including the SD40-2 motor and others.

The more you test, the more you need to test. Time for DOE.

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