Intro and Test Loads

DCC brings the ability to control many different parts of your layout through a single control system.  A stationary decoder is similar to the decoder used in your locomotive except that it is optimized to control items that are usually fixed in position on your layout such as switch machines, signals, crossing gates, turntable motors, etc.  While locomotive decoders typically have a single address, stationary decoders will allow you to individually address up to four separate items at four separate addresses through the same decoder.  For example, section one of the decoder might control a switch machine, while section two controls an overhead signal.  Section three could start and stop an action accessory such as some of the motorized carnival rides, while section four could provide all of the functions needed to animate a grade crossing. The possibilities are limited only by your imagination.

Test Loads

In order to compare the various decoder functions, I selected an assortment of loads that would be representative of the kinds of functions that would be used on a typical layout. The first selection was a Circuitron Tortoise™ slow motion switch machine.  This unit is designed to operate normally with the motor stalled at the end of the switch point movement in order to apply a positive holding force on the switch points.  When running, the unit draws about 3 ma, and when stalled, it will draw a maximum of 25 ma.  The Tortoise™ requires a continuous output whose polarity reverses direction in order to control it properly.

The second test load was a latching switch machine from Nick & Jack International.  This is a particularly nasty load to drive because the coil resistance is only 1.9 ohms.  At the normal track voltage for DCC, there could be a momentary current demand of over 6 amperes.  Since the machine is a latching type, there is hysterisis in the mechanism that requires a significant force from the coil in order to kick the machine through its cycle.  There are also auxiliary contacts that must be moved with the rest of the mechanism.

The third test load was a dual coil switch machine from Peco.  This machine is typical of the type used on snap action switches.  The coil resistance is 10.9 ohms, almost a factor of 10 large than the NJI switch machine.  There is no auxiliary mechanism to move, so this machine draws about 1 ampere when activated.

The fourth load was a pair of grain-of-wheat lamps. These lamps are Model Power part number 252 and are rated at 14 volts.  They draw about 30 ma at their rated voltage.  I did not include light emitting diodes as part of my test since they draw about the same current as the grain-of-wheat lamps.  In general, if a decoder works with the grain-of-wheat lamps, it will also work with an LED.  Except in special cases, the LED will require a series resistor of about 470 ohms, and may require a series diode for cases where the decoder reverses the output polarity.  (Note: although an LED is a diode, its reverse breakdown voltage is often on the order of only 5 volts.  This means that if the reverse voltage is more than 5 volts, you also need a series diode to ensure that the LED does not conduct in the reverse direction.  One way to solve this problem is to put two diodes in reverse parallel; this ensures that the reverse voltage on one is no more than the forward voltage of the other.)

The last test load that I used was a small DC motor. This motor is typical of the type that is found in motorized accessories. In fact, this particular one came from an IHC carousel motorizing kit.  The motor has a DC resistance of 4.5 ohms, and draws 430 ma at 10.7 volts.

The table provides a quick overview of the test results. It is good for reference, but I strongly encourage you to read the detailed results.  There are a number of subtleties that the table cannot cover.

Stationary Decoder	Performance Rating with Test Loads
	Tortoise™	NJI Switch Machine	Peco Switch Machine	GOW Bulbs	Accessory Motor
Digitrax DS54 Quad Stationary Decoder	Very Slow	No	Yes	Yes	No
Digitrax DS44 Quad Stationary Decoder	Recommend	No	No	Very Dim	No
EasyDCC AD4KA Accessory Decoder	Recommend	No	No	Yes	No
EasyDCC AD4HA Accessory Decoder	No	Recommend	Yes	No	Pulse Only
Lenz LS100 Digital Plus	LA010 required	Recommend	Yes	Yes	LA010 required
NCE Corporation Switch-It	Recommend	No	No	Very Dim	No
Wangrow SM-104 Stationary Decoder for 4 Switches	Yes	No	Yes	Yes	Recommend

My baseline layout system is the NCE Corporation Powerhouse with the NCE ProCab.  It is capable of supplying 5 amps to the rails, and is powered by the XFR 8 DCC Power Supply available through Tony’s Train Xchange.  Where required, I also used an MRC Tech II 2800 to supply AC or DC auxiliary power.  Once programmed, all of the decoders operated on this system with no problems, a testament to NMRA standardization.  Decoder programming, however, was a little more problematic.  There are some incompatibilities, so read the programming remarks carefully.  Enough background, let’s bring in the contestants.