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Application notes for the N8101 & N8101B DC Power Source
in an analog (non-DCC) environment
Analog track power
Simply put, a variable DC voltage is applied to two tracks with one being +DC and the other, -DC. Increase the voltage and the electric motor in the locomotive spins faster making the train go faster. If the train is required to reverse, track polarity is reversed. Also, what defines "forward and reverse" is dependent on which way the locomotive is facing when it's put on the track. The bottom line is that track polarity is not fixed.
Discussion here is limited to an input voltage maximum of 16-volts because that is the design limit of our N8101. For model railroading this includes track voltages for Z, N, and some HO Scale. We strongly recommend maximum track voltages be limited to around 14.5 volts to provide a safety factor.
The N8101B can handle a maximum of 25-volts DC so it can support All HO track voltages and DC S & O Scale voltages. Some G scale applications may work depending on maximum track voltage. For AC applications see that link from the More Info table.
Our N8101 & N8101B converts analog track voltage (polarity not important) to a DC output voltage of known polarity via the on-board full-wave bridge rectifier. The N8101's big plus here is that this bridge rectifier uses a type of diodes known as Schottky diodes. These are very high speed diodes with much lower voltage losses than conventional silicon diodes used in most bridges. This is especially beneficial in analog operation because it is desirable to have lighting and special effects function at as low a voltage as possible. For example; it would be nice to have that roof beacon or Mars light working when to locomotive starts moving, rather than when it's up to road speed.
Analog power and special lighting effects
Coupled with the N8101 or N8101B, tests using analog track power show our Simulators function (with LED connected) as follows:
Analog and "always on" lighting
The N8101 is well suited to provide constant-polarity DC power for general lighting of model railroad rolling stock. This would include passenger car and caboose interior lighting, marker lights in general and locomotive cab, class, and number board lights. Its very-low loss schottky rectifiers will ensure that the majority of track power (regardless of polarity) is passed through allowing polarity sensitive devices like our LEDs to function as soon as their threshold voltage is reached. Having current carrying capacity of 200ma, the N8101 is powerful enough to support any typical rolling stock lighting requirement with room to spare. As noted above, the on-board 10μf filter capacitor is not intended to provide any meaningful flicker control. External capacitor(s) are required for that purpose. The diagram in Figure 1 covers the connection of capacitors to the N8101 & N8101B's output solder points.
When wiring passenger cars for interior lighting (in most cases, multiple LEDs), we always recommend wiring the LEDs in parallel with each having a protection resistor selected based on maximum expected track voltage. If you need to review parallel LED wiring, more information is available here.
Other power needs
While the vast majority of track powered applications for rolling stock (other than motors in locomotives) is lighting, there are certainly other cases where polarity sensitive devices might need power. Since the N8101 & N8101B will support up to 200ma of current, this could include tiny motors, solenoids or other DC actuators, or miniature circuitry to perform various functions. Its tiny size will allow it to be place just about anywhere.
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