Abstract:
A model railroad train control system for supplying power to at least one DCC two-rail operated train engine and/or at least one AC three-rail operated train engine. The train control system used for operating the engines simultaneously and independently on the same railroad track or separate train section blocks making up the track. The control system includes one or more current limited voltage source modules connected to the track for providing modulated voltage to each engine. Each module has two identical channels composed of power transistors for a left track power output and two identical channels composed of power transistors for a right track power output. The outputs rapidly switch, alternately, between ground potential (zero volts) and as high as 48 volts. The transistors provide a return current path for the DCC two-rail engine and the AC three-rail engine. The power transistors are individually current limited and have a response time in a range of 1 to 5 microseconds. The fast response time means trains with shorting wheelsets will not cause excessive current from the power supply, since the average current is very low. The action of the current is limited in one phase and does not effect the operation of the other phase.

Description:
RELATED PATENT APPLICATION  
       [0001]    This application claims benefit of priority to a provisional application, serial No. 60/252,957, filed Nov. 25, 2000, which is hereby incorporated by reference to the same extent as though fully disclosed herein. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    (a) Field of the Invention  
           [0003]    This invention relates to the operation of different types of model electric railroad trains and more particularly, but not by way of limitation, to a system for operating both AC powered three-rail model trains and DCC powered two-rail model trains simultaneously and independently of each other on the same track.  
           [0004]    Model trains have been popular with children and adults since the first railroads were built. Since the beginning, there has been continuous but slow effort to make the model trains more realistic and operation more nearly match fill-sized trains. The earliest model trains were kid&#39;s toys pushed by hand across the floor. In the first years of 1900, Joshua Lionel Cowan introduced the first battery powered trains and then trains powered by an AC transformer. Controlling the AC voltage allowed the train speed to be varied. Later, Ives added a stepper relay called an “E-Unit” to their trains. By interrupting the power, the stepper relay would cycle, applying a polarity reversal to the motor and reversing the direction to the train. By 1906 Cowan introduce three-rail track to solve a problem, know as the “reverse-loop problem,” created when a track looped back upon itself, shorting one outside rail to the opposite side.  
           [0005]    The problem of controlling multiple AC powered trains has proven to be intractable. The simple, traditional method has been to divide the track layout into power blocks or “districts.” By switching different transformers to the electrically isolated blocks containing the trains, it is theoretically possible to control as many trains as there are transformers and blocks. In practice, operating more than one train at a time by switching power to different blocks as the train moves about the layout overloads the operator. Yet, because of the lack of a suitable option, block switching is still the primary means to control multiple AC powered trains.  
           [0006]    With the perfection of low cost permanent magnet motors and inexpensive solid-state power supplies in the second-half of the century, Direct Current (DC) became the favorite means to control model trains. These DC powered model trains were predominately the smaller HO and N gauges; all were two-rail. The reverse loop problem was not really solved but the impact was mitigated by solid-state switches that sensed the short caused by a train crossing the phase reversal boundary of a reverse loop. The solid-state switch reversed the polarity of that reverse loop track section. These current reversal switches require the model railroader to understand the track topology that creates a reverse loop and then determine where to put the reverse loop switches.  
           [0007]    In the seventies, numerous schemes were tried to add command control to the two-rail model trains. Because the incompatibility of the different schemes was hurting the industry, the model train manufacturers agreed upon a digital command control protocol known as DCC (Digital Command Control), The National Model Railroad Association formalized the protocol as NMRA specifications S-9.1 and S-9.2. DCC has since become popular for two-rail model trains of all scales. The DCC command control system provides for independent operation of many locomotives and accessories without electrically insulated blocks and toggle switches to control power routing. While it is possible to apply a DCC signal to the center rail of a three-rail track it is seldom done because of incompatibility with other three-rail AC trains and track layouts.  
           [0008]    In the mid-1990s, Lionel introduced a system called the Trainmaster® command control system, also known as TMCC. In the traditional format, the speed is controlled by varying the voltage. With TMCC, the track is supplied with a constant AC voltage and signals are digitally transmitted to the train. However, TMCC is limited to 10 engines per system unit. TMCC uses a proprietary carrier system with a low-level radio signal. The TMCC radio signals travel through the air and are subject to interference. It is common, for instance, for control to be lost when a TMCC train enters a tunnel made of metal mesh. Furthermore even though there is some compatibility with traditional AC controlled trains, it is not possible to independently operate a traditional AC engine and a TMCC engine in the same power block simultaneously.  
           [0009]    Recently Dallee Electronics, Inc. produced a command control system, first used by Atlas, LLC, called Locomatic™, which provides for additional control. The Locomatic™ is a pass-through device wired between the transformer and the track. The Locomatic™ system provides control for sounds, lights, speed, direction and other features. However, the Locomatic™ system is even more limited than the TMCC system since operation is permitted for only one engine of any type per power block.  
           [0010]    MTH Electric Trains has recently demonstrated a different digital command control system. The suggested unique wiring suggests that the system will not operate well on large layouts because of transmission line effects. The company also states that this system is not compatible with Lionel&#39;s newest three-rail AC engines. This system suffers the same limitation of the other three-rail command control schemes in that it not possible to independently operate a traditional AC engine and a command control engine in the same power block simultaneously.  
           [0011]    Other developers, notably Severson and Quinn of QSI, Inc., have achieved limited control by changing AC wave shape or by adding DC offsets. These schemes have the advantage that the control information is the same amplitude as the power voltage providing a more robust signal but suffer from having limited bandwidth and offer no other advantages over the systems described above.  
           [0012]    The compatibility restriction is a serious limitation since three-rail AC powered trains have remained essentially unchanged for nearly a century with the existence of enormous numbers of three-rail AC trains. These trains would essentially become obsolete with the widespread acceptance of any of the above AC command control schemes. The incompatibility results because interrupting the power to control the traditional AC trains interrupts power to control the command control trains as well, causing everything to halt.  
           [0013]    A different problem associated with model train power sources is the limited currents that can be safely supplied to heavily loaded model trains. The electrical current, about ten amps, available on the track rails is high enough to start fires in some situations. Yet this current is insufficient to prevent some long, heavy trains from stalling. Manufacturers that have produced AC transformers with higher current capabilities have been unable to get the power supplies UL listed because of the unsafe current levels.  
           [0014]    Another problem found in prior art is that if there is a short circuit on a section of track, all the track and motors are disabled within that electrically isolated block of the track. Accessories tied to that section of track would also be disabled. Thus, most model railroaders wire accessories with entirely separate wiring. This however brings its own problem; the feeder wires complicate and clutter the layout.  
           [0015]    A further problem is that most of the existing schemes of deploying power to the trains use the track rails as the electrical contact to connect adjacent sections with “rail joiners,” electrical contacts that slide on or into the butted rails. The rail joiners often make unreliable electrical contact and cause an additional voltage drop. Many model railroaders solder the rail joiners to improve reliability. However, this step makes the layout less portable and is time consuming to construct.  
           [0016]    None of the above mentioned model train power control systems used with engines and two-rail and three-rail tracks specifically disclose the unique features, structure and function of the subject model railroad train control system as disclosed herein.  
         SUMMARY OF THE INVENTION  
         [0017]    A primary object of the subject system is to combine one or more traditional AC powered three-rail model trains with one or more modern DCC two-rail model trains to operate simultaneously and independently on the same track.  
           [0018]    Another object of the train control system is through the use of one or more high current drive signal modules connected to the track, power and commands can be sent via the outer two rails of the track while remaining compatible with existing three-rail AC powered trains.  
           [0019]    Yet another object of the system is by combining traditional AC transformer control with the technical advances of the National Model Railroad Association&#39;s DCC system, superior performance and vastly expanded capabilities are achieved.  
           [0020]    Still another object of the system is the high current drive signal modules includes power transistors for rapid high voltage output and return current path for the DCC equipped two-rail trains and the AC three-rail model trains.  
           [0021]    The train control system includes one or more current limited voltage source modules connected to the track for providing modulated voltage to each engine. Each module has two identical channels composed of power transistors for a left track power output and two identical channels composed of power transistors for a right track power output. The outputs rapidly switch, alternately, between ground potential (zero volts) and up to 48 volts. The transistors provide a return current path for both the DC or DCC two-rail engine and the AC three-rail engine. The power transistors are individually current limited and have a response time in a range of 1 to 5 microseconds. The fast response time means trains with shorting wheelsets will not cause excessive current from the power supply, since the average current is very low. The action of the current is limited in one phase and does not effect the operation of the other phase.  
           [0022]    These and other objects of the present invention will become apparent to those familiar with different types of model train track systems when reviewing the following detailed description, showing novel construction, combination, and the various embodiments of the invention as herein described, and more particularly defined by the claims, it being understood that changes in the embodiments to the herein disclosed invention are meant to be included as coming within the scope of the claims, except insofar as they may be precluded by the prior art. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    The accompanying drawings illustrate complete preferred embodiments in the present Invention according to the best modes presently devised for practical application of the principals thereof and in which:  
         [0024]    [0024]FIG. 1 illustrates a top view of a traditional three-rail track system connected to alternating current for driving an AC train engine.  
         [0025]    [0025]FIG. 2. illustrates a top view of a two-rail system track system connected to a digital command control or DCC for driving a DCC train engine.  
         [0026]    [0026]FIG. 3 illustrates a block diagram of the subject invention connected, for example, to four track sections having railroad cars with shorting and non-shorting axles.  
         [0027]    [0027]FIG. 4 illustrates a top view of a track system using one of the current limited voltage source modules connected to the track so that either an AC or DCC controlled train can operate on the track, but not at the same time.  
         [0028]    [0028]FIG. 5 illustrates a top view of another track system using three of the subject modules connected to three section of the track so that the AC train and the DCC controlled train can operate at the same time, but only on separate sections of the track. FIG. 6 illustrates a top view of still another track system having a plurality of modules connected to a number of sections of track whereby the track is laid out so that either AC or DCC trains can run simultaneously on the same track and without restriction.  
         [0029]    [0029]FIG. 7 is a perspective view of a connector with wiring used for attaching the voltage source module to a section of the railroad track.  
         [0030]    [0030]FIG. 8. is a circuit diagram of the current limited voltage source module  
         [0031]    [0031]FIG. 9 is a circuit diagram of a current source module.  
         [0032]    [0032]FIG. 10. illustrates a side view of a model train engine with one of the current limited voltage source modules used as an engine module with the engine to run on either two-rail or three-rail track systems FIG. 11 is a circuit diagram of the engine module used for installing in the model train engine shown in FIG. 10.  
         [0033]    [0033]FIG. 12 is a continuation of the circuit diagram of the module shown in FIG. 11. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0034]    In FIG. 1, a top view of a traditional prior art three-rail track system is illustrated and having general reference numeral  10 . The three-rail track system  10  includes two outer rails  12  and  14 , or left and right rails, connected to ground  16  and a center rail  18  connected to a source  20  of AC voltage for driving an AC train engine. The three-rail system applies the AC voltage to the center rail  18 . This voltage  20  is picked up with a center-rail pick-up roller that powers the train and is then returned through the wheels that are in contact with the outside rails  12  and  14 . The model train is not shown in the drawings. Normally, both outside rails  12  and  14  are grounded but it is only necessary that one rail be grounded, since the metal wheels and axles short the outer rails together.  
         [0035]    In FIG. 2, a top view of a prior art two-rail system track system is illustrated and having general reference numeral  22 . The two-rail track system  22  includes two outer rails  12  and  14  connected to a left digital command control signal  24  or DCC Left and a right digital command control signal  26  or DCC Right. Two-rail track systems  22  apply a differential voltage, DCC or otherwise, across the two rails  12  and  14 . DCC includes a command control protocol for independently controlling any number of trains on a track layout. This differential voltage is picked up by the train wheels for powering the train.  
         [0036]    In FIG. 3 the subject invention includes broadly a current limited voltage source module having a general reference numeral  28 . In this illustration, four of the modules  28  are shown having a left rail output drive lead  30  and a right rail output drive lead  32  connected to the left and right rails of track sections  34 . The left, right and center rail of the track sections  34  are not shown in this drawing. It is important to note that, in this example, the opposite ends of each track section  34  are separated and insulated from each other.  
         [0037]    In this drawing, the two track sections  34  on the left are shown receiving wheels  36  of a first railcar  38  or engine thereon. The first railcar  38  includes shorting axles  37  connected to wheels  36  engaging the left and right rails. A second railcar  40  or engine is shown with wheels  36  engaging the two center track sections  34 . A third train car  42  is shown with wheels  36  engaging the two track sections  34  on the right. The second and third train cars  40  and  42  include non-shorting axles  39 .  
         [0038]    The center rail of the track sections  34  is connected to an AC voltage source by an AC output lead  44  connected to an AC transformer  46  having a ground  48 . Each of the modules  28  are connected to a left rail input lead  50 , a right rail input lead  52 , a 16 volt power lead  54  and ground  48 . The leads  50 ,  52 ,  54  and  48  are also connected to a power source module  56 . The power source module  56  is connected to a DCC command generator  58  via the left lead  50  and the right lead  52 . The module  56  is also connected to a DC power supply  64  via a 20 volt power lead  66 .  
         [0039]    The module  28  amplify the DCC signals from the DCC command generator  58  to provides a +16 Volts DCC signal, current limited to 5 Amps, to the left and right rail of the track section  34 . These signals will power a DCC engine or an AC engine. If, however, the AC engine or cars with shorting wheelsets is on one of the track section  34 , the module  28  for that particular track section will immediately go into a current limit so that excessive currents will not flow through the wheelset. Only the positive voltage excursions are current limited. The rail held at ground potential is not current limited and can handle AC ground return currents up to 40 Amps.  
         [0040]    In FIG. 4, a top view of a simplified first track system having general reference numeral  68  is illustrated. The first track system  68  includes outer rails  12  and  14  and a center rail  18  connected on one of the current limited voltage source modules  28  shown in FIG. 3. The module  28  is connected to the track system  68  so that either an AC or DCC controlled train can operate on the track, but not at the same time.  
         [0041]    In FIG. 5, a top view of a second track system having general reference numeral  70  is illustrated. In this example, three of the subject modules  28  are connected to three independent track sections  34  of the track system  70  so that an AC train and a DCC controlled train can operate at the same time, but only on separate track sections  34  of the track.  
         [0042]    In FIG. 6, a top view of a third track system having general reference numeral  72  is illustrated. In this drawing, a plurality of the current limited voltage source modules  28  are shown connected to a number of individual track sections  34 . In this example, the track system  72  is laid out so that either AC or DCC trains can run simultaneously on the same track and without restriction and as illustrated in FIG. 3.  
         [0043]    In FIG. 7, a perspective view of a connector block  72  is shown mounted on one of the current limited voltage source modules  28  with electrical leads  44 ,  48 ,  50   52  and  54  as shown in FIG. 3. The connector block  72  is used for attaching the module  28  to the underside of a portion of a track section  34  as shown  
         [0044]    In FIG. 8, a circuit diagram of the current limited voltage source module  28  is shown. As discussed in FIG. 3, the inputs to the module  28  are the left rail input lead  50 , the right rail input lead  52 , the  16  volt power lead  54  and the ground  48 . The 16 volt power lead  54  and the ground  48  are bypassed with a Capacitor C 4 . Capacitor C 4  supplies the switching transient currents for the module  28 . The DC power supply  64  is only required to supply a steady state of current. The heart of the module  28  is an H-Bridge Driver U 2 . This part, a Harris HIP4082 semiconductor, is powered through Diode D 1  connected to the VDD pin and with the VSS pin connected to ground  48 , Diode D 1  isolates U 2  from the switching transients; Capacitor C 1  holds up the VDD voltage during the transients. This VCC voltage is also connected to the VDD pin of Voltage Comparator U 1 . The VSS pin of U 1  is likewise connected to ground  48 . U 1  is an industry standard dual voltage comparator and is used in this circuit to sense over-currents. The left and right leads  60  and  62  from the DCC command generator  58  are connected to the BLI and ALI pins of U 1 , respectively. These inputs are the left and right low-side driver inputs. The high-side driver inputs, the AHI and BHI pins of U 2 , are connected to the outputs of the Comparator U 1  to take advantage of a unique characteristic of the HIP4082. The AHI and BHI pins of U 2  are interlocked internally with the low-side drive inputs. Thus these inputs can be held high continuously during normal operation. If either comparator output drops due to an over-current condition, the high-side drive is removed for that channel but the low-side drive continues to function. Since the LEFT and RIGHT DCC drive signals are of opposite polarity but have otherwise identical timing, one of either the LEFT TRACK DRIVE or RIGHT TRACK DRIVE signals is always grounded. In this embodiment the DIS pin of U 2  is tied to the ground  48 , continuously enabling U 2 .  
         [0045]    The HIP4082 uses an internal charge pump circuit to provide sufficient drive for N-Channel FETs. Diode D 2  and Diode D 1  rectify the right and left charge pump voltages; Capacitor C 2  and Capacitor C 3  filter the rectified signals. The charge pump voltages are fed into U 2  pins AHB and BHB. The right side, low-side driver, FET Q 4 , is driven by U 2  output ALO through Resistor R 15 . Resistor R 15  combined with the inherent gate capacitance of Q 4  provides a slight delay in Q 4  turn-on and turn-off. FET Q 2  and Resistor R 13 , connected to U 2  output BLO perform the equivalent function for the left side driver. The right side, high-side driver, FET Q 3 , is connected to U 2  output drive pin AHO through Resistor R 14  and paralleled Diode D 7 . Resistor R 14  has a higher value than the corresponding low-side Resistor R 15 . This higher resistance value causes FET Q 3  to turn on much slower than the low-side driver. The delay is set at about one microsecond to allow Comparator U 1  enough time to sense a short circuit on the output before the current becomes excessive. Diode D 7  quickly discharges Q 3 &#39;s gate capacitance when the drive signal falls so that Q 3  turns off without significant delay. FET Q 1 , Resistor R 12 , and Diode D 6  perform the equivalent function for the right side, high-side drive. Resistor R 12  and Diode D 6  connect to U 2  output BHO. The DIS input pin of U 2  is an input delay adjustment. Resistor R 11  is selected to create a minimum delay between activation of the high and low side drives without shoot-through current.  
         [0046]    Resistor R 16  and Resistor R 17  are each connected between the 16 volt power lead  54  and high-side FET Q 1  and FET Q 3 , respectively. Resistor R 16  and Resistor R 17  are 0.1 ohm current sense resistors. They are connected to positive inputs of Comparator U 1  through a voltage divider comprised of Resistor R 4  and R 10  for the right side and voltage divider Resistor R 3  and R 9  for the left side. Speed-up Capacitor Cx and Capacitor Cy are paralleled across Resistor R 3  and Resistor R 4 , respectively, to increase the sensitivity of Comparator U 1  to the rapid rise of the current when the left and right rail drive leads  30  and  32  outputs are shorted. Right side Comparator U 1  output is connected back to the positive right side input through Resistor R 5 . This relatively low value resistor causes the comparator to latch up if an over current level is sensed. The latch-up condition is cleared when the drive outputs switch phases by Diode D 4 . Diode D 4  is connected from the right rail drive lead  32  output and the negative input of U 1 . Resistor R 6  is likewise connected between left side comparator output and the positive input of U 1 . Reference voltage divider comprised of Resistor R 2  and Resistor R 8  set the voltage level at the right side comparator input to trip at a right side current level of five Amps. Reference voltage divider comprised of Resistor R 1  and Resistor R 7  set the voltage level for the left side comparator input in a similar manner. Diode D 5  is connected from the left rail drive lead  30  output and the left side negative input of U 1  to clear left side latchups.  
         [0047]    In FIG. 9, a circuit diagram of a current source module is shown and having general reference numeral  74 . The primary function of the current source module  74  is to steer return currents back to their sources. The ground return connections for the AC transformer  46 , the DC power supply  64 , and the DCC command generator  58  are all connected together in the second module  74 . Normally currents from both the AC transformer  46  and the DC power supply  64  flow through the ground connection of the current limiting voltage source module  28  back to their respective sources. However, if one rail of an AC powered train becomes isolated from the wheels, for example due to dirt on the wheels, the transformer  46  will attempt to return current through the 16 volt power lead  54  to the module  28 . This voltage could pump-up the 16 volt power lead  54  and possibly damage the DC power supply  64  and the connected modules  28 . The power buffer, U 3 , in the current source module  74  can both source and sink current. Thus, AC currents appearing on the 16 volt power lead  54  are shunted back to the AC transformer  46  by the output stage of the power buffer. A 16 Volt Zener Diode, provides the reference voltage for the power buffer.  
         [0048]    In FIG. 10, a side view of a profile of a model train engine  76  is shown with an engine module. The engine module is shown having a general reference numeral  77 . The engine module  77  is mounted on the engine  76 . With the engine module  77  incorporated into the engine  76 , the engine is now able to run on either two-rail or three-rail track systems. The engine module  77  is connected to a DCC Decoder  78  and an E-Unit  80 . The Decoder  78  and the E-Unit  80  are connected to a relay  82  connected to the engine&#39;s motor  84 .  
         [0049]    In FIGS. 11 and 12, a circuit diagram of the engine module  77  is illustrated. The engine module  77  is not necessary to operate the modules  28  and the track systems described above since one or more modules  28  can run conventional DCC equipped trains as well as unmodified three rail AC trains. In a preferred embodiment, the engine module  77  is used to modify a locomotive to operate on traditional three rail layouts, two rail DCC layouts and, of course, the present invention layouts.  
         [0050]    For example, power enters the engine module  77  through Wipers  1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 , and  8 . Wiper  1  and Wiper  2  contact the outer rear wheels  36  of a wheelset  86 . A full-wave bridge rectifier comprised of Diode D 8 , Diode D 9 , Diode D 10 , and Diode D 11  rectify the DCC signal from Wiper  1  and Wiper  2  if a DCC signal is present on the outer rails  12  and  14 . Wipers  3 - 8  and Diodes D 12 -D 23  likewise rectify the DCC signal from the other three wheelsets  86 . The four sets of bridge rectifiers composed of Diodes D 8 -D 23  are connected in parallel. These rectifier outputs are +15VOLTS and +15VRET. The +15VOLT signal powers the standard decoder  78  and the coil of relay  82 . Power to the relay  82  transfers power from the decoder  78  and the normally closed contacts of the relay to the wipers of relay  82 . Engine motor  84 , connected to the wipers of relay  82  is thus powered by the decoder  78 . Wipers  1 ,  3 ,  5 , and  7  are also connected to the anodes of Diodes D 24 , D 25 , D 26 , and D 27  to obtain a replica of one polarity of the DCC signal. The cathodes of Diodes D 24 , D 25 , D 26 , and D 27  to the Red input pin of the Decoder  9  to supply the serial digital commands to the decoder  78 . Resistor R 18  acts as a pull-down current sink to prevent the signal on the cathodes of Diodes D 24 , D 25 , D 26 , and D 27  from floating during the low intervals of the DCC signal.  
         [0051]    Inductor L 1  is also connected between Wipers  1  and  2 ; Inductor L 2  is connected between Wipers  3  and  4 . Inductor L 3  is connected between Wipers  5  and  6 . Inductor L 4  is connected between Wipers  7  and  8 . These center-tapped inductors have sufficient inductance that they appear as essentially an open circuit at DCC frequencies. However, in the absence of a DCC signal on the wipers, and if an AC signal is present on wheelsets  86 , AC current flows from the wipers through the inductors to the center tap pins of those inductors. The currents in the two sides of the inductors generate opposing magnetic fields and cancel, making the inductors appears as short circuits to the AC current. These center-tapped inductor pins form the return path for the AC current that flow from the wheelsets  86 , through the E-Unit  80  (stepper relay of a type common in the industry) back to the inductor center-taps. The output of the E-Unit  80  is connected to the normally open contacts of unenergized relay  82 . Thus, engine motor  84  obtains power from the E-Unit  80  in the absence of a DCC signal.  
         [0052]    Should one side of an inductor become disconnected from its side of the track, the inductance at of the inductor at 60 Hertz is sufficiently low that the inductor rapidly saturates and appears to the AC current as a short circuit. Therefore only one roller of rollers  88  on the wheelset  86  needs to make contact with the track section  34  for normal operation of the engine module  77 .  
         [0053]    As illustrated in FIG. 3, each track section  34  is independently powered by a separate modules  28 . Straight sections of standard three-rail track are commonly 10 inches long. Curve sections may be slightly longer or shorter. In any case, this is normally less than the length of standard railroad cars and engines. Since each wheelset  86  on a car can independently pick-up power from the rails, it is only necessary that a single wheelset  86  be unshorted to power that car or engine. The left-most car  38  in FIG. 3 is a traditional railroad car with shorting wheelsets. These wheels bridge the two first track sections  34 , shorting the module  28  and causing it to go into current limit. The second car&#39;s left most wheelsets are setting on the shorted track section  34  and therefore does not get power. However, because the track sections  34  are short enough, the right most wheelset of the center car  40  can get power from the unshorted third track section  34 . Therefore, with most combinations of traditional railroad cars with shorting wheelsets and DCC decoder equipped cars with non-shorting wheelsets, the traditional cars do not inhibit operation of the decoder equipped cars.  
         [0054]    The crossed left and right rail drive leads  30  and  32  shown in FIG. 3 and connecting the track section on the right to one of the modules  28  represent a phase reversal of the DCC signals from one track section to the adjacent section. This situation will occur if the track layout topology connected one outside rail  12  to the opposite rail  14  is a “Reverse Loop” or “Wye” track configuration. In the example shown, the left-most wheelset of the car  42  on the right senses a different polarity DCC signal than the other three wheelsets. In this example, the DCC signals would cancel and not be sensed by the DCC Decoder as the car is crossing the phase reversal. Normally, this would not be a concern since phase reversals only occur in a few places on a layout. However, the bridge rectifiers would independently generate the voltage to operate any functions, such as lights, that had been commanded earlier.  
         [0055]    While the invention has been particularly shown, described and illustrated in detail with reference to the preferred embodiments and modifications thereof, it should be understood by those skilled in the art that equivalent changes in form and detail may be made therein without departing from the true spirit and scope of the invention as claimed except as precluded by the prior art.