Magazines » Model Railroading - May 2001 » Page 39

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May 2001 - Page 39

Check your locomotives pulling power Check your locomotives pulling power


w ith a deadweight car (flatcar with w eights to equal freight or passenger cars) Check your locomotives current draw under load conditions with locomotive alone; this requires a power pack with volt and amp meters or separate meters wired to the terminal block Check your locomotives current draw under load conditions with locomotive and deadweight car; this requires a power pack with volt and amp meters or separate meters wired to the terminal block Use as an electrical conversion tool when converting from HO to HOn3 one power truck at a time Use as a test track for your locomotives Use to check motor performance (alone). THIS WOULD BE FOR ADVANCED M ODELERS and would require a jig to hold the motor, and pulleys to transfer the load to the scale; there would be play in this setup and would only give a rough approximation on the output of the motor. Information contained in this article is for individual use and may not be used for commercial purposes. For comments, commercial applications, or if you would like me to build one for you, write to: R. T. Whiting, PO Box 134, Wauneta, NE 69045-0134.

To Power Supply

Instructions on Use
To use, simply hook up the dynamometer to the DC variable side of your power pack and set direction away from scale. With the throttle off, set your locomotive on the test track and engage the coupler on the scale slide. Turn on your power pack and increase the voltage incrementally. If you would like to plot drawbar pull for your locomotives at various voltages, you can graph the results at settings of your choice. For example, if your power pack has speed or similar markings, you could plot your results at 10, 20, 30, etc., for each locomotive to see how they compare to each other. Readings at each setting should be taken when forward motion ceases and motor stalls or wheels slip. Be sure that the scale is set at 0 before each test. Be sure you dont exceed the voltage rating of your locomotive or allow the motor to overheat or serious damage could result. (Optional) If you have a power pack with volt and ammeters or meters attached to the terminal block you can also check and/or
* CAUTION This portable dynamometer i s designed to test HO/HOn3 locomo tives with less than 9 oz. of pull. To test a locomotive or locomotive set with a higher drawbar pull, use a deadweight car loaded with oz. per inch of train length minus 5 oz.). For info on testing motors see June 1979 Model Railroader, pp. 93-97.

The use of a terminal block or dual-gauge track is not essential, but is recommended. By soldering the connecting wires to the top of the rails, your connections can also serve as wheel stops while the terminal block acts as a bumper. The length of your track is not critical; just make sure it is longer than the longest locomotive or locomotive set you ever plan to test. record current draw at various settings. Converting drawbar pull readings to the number of cars that can be pulled on your l ayout is dependent on a number of factors, so there is no single, definitive answer. Track radius, gauge and code, as well as how well your track is laid will affect this ratio, but even more important is how your cars are weighted and how free rolling your trucks are. Model railroad magazines use anywhere from about 13.75 to 23.37 cars per ounce of drawbar pull for their ratings; Model Railroading uses 18.5 cars. Once you know the drawbar pull figures of some of your locomotives, you can determine how it correlates to number of cars by old-fashioned experimentation. Just keep adding cars until a particular loco stalls, then divide the number of cars by the locos drawbar pull reading in ounces. For example, if your drawbar pull reading was 3 oz. and you could pull 60 cars, your ratio would be 20 cars per ounce. Try several other locos to see how they compare. After testing several locomotives you will end up with a range which can then be averaged to give you a reasonable approximation using your equipment.

By mounting couplers to the top and bottom of the scale slide, both HO and HOn3 locomotives can be accommodated. To use this Ohaus scale for larger scales either put a spacer between the scale and baseboard or add spacer washers between the coupler and scale slide. For N scale, the easiest way to modify it would be to use spacer washers under the slide.

MAY 2001


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