DIGITAL COMMAND CONTROL AND
OVERHEAD TROLLEY WIRE OPERATION

By George L. Huckaby & John McWhirter

December 1, 2007

Just after the Southern California Traction club was founded in 1975, we started getting queries about using Digital Command Control (DCC) for operating trolley cars from overhead wire. Some wanted to see us do it. Others said flatly that it would never work. Some of the public and a few model railroaders, who had never seen trolleys operating from a live overhead wire with trolley poles, thought that our display was operated by DCC, but we always said it was not. Because we feel that the next generation of model railroaders will probably embrace DCC, as it is today or some derivative, we continuously made inquiries of other trolley modelers, other clubs and model train shops. The inquiries produced responses in the complete range of extremely positive to totally negative.

When we saw the MTH K-4 with both sound and smoke around the end of 2006, most of us knew that DCC or some derivative was the future of module railroading, if there was to be future at all. We ended up acquiring two of them. But we still had to find out whether it would be feasible for overhead wire operation of HO scale model trolleys. So last year we started to complete a home layout started back in the early 1990s.  The layout had been started prior to the founding of the SCTC and designed as an analog (non-DCC) operation with cab control using standard Atlas Selectors.  In February 2007, we purchased a Digitrax Super Chief, got two portions of the layout operating but never got any overhead wire erected. In August 2007, we converted one trolley car to DCC using a Train Control Systems (TCS) M1 two-function Decoder.  After the first attempt at installation resulted in a “fried” decoder and TCS sent a replacement, the replacement was successfully installed in the car and the car ran in the analog mode. But we noted that the car ran 10 to 12 mph slower with the decoder than it ran previously.

During the summer, we kept seeing and hearing all the new great locomotives coming out and noted the reasonable prices for some of them. The sounds range from poor to great and the study of sound systems got as interesting and involved as the investigation into DCC itself. We started to wonder what if the traction hobby would benefit of there were similar sounds in a trolley car. After making two visits to San Francisco in both August and September listening to and recording the sounds of PCCs, Peter Witts and Breda LRVs, our desire to find out whether DCC would work in the overhead wire mode intensified as model trolleys with sounds could be fantastic. After all the possibility of shorts, a major problem in DCC operation, was almost eliminated when running under overhead wire.

We started talking to everyone who claimed to have knowledge of DCC and they generally were in two major classes. The DCC protagonists were all in favor of it and thought it was fantastic. All of the DCC detractors were either not familiar with DCC or never had tried overhead wire operation, so we stopped talking to them quickly. We even visited the Bakersfield, CA club in May and ran our two sound-equipped PRR steam engines using Digitrax hardware and software. It was a learning experience and for the most part it was a rewarding experience. But we could find no one who had operated trolleys under live overhead wire with DCC. We had seen DCC operation at an East Penn meet and thought that it should work. But we kept hearing that power interruptions caused by dirty overhead wire would "…drive the decoder nuts…." The problems we had with the subway module with the cars just stopping for no apparent reason, made us again hesitant to try DCC on overhead wire powered cars. But when the Digitrax PM42 was removed from the subway module and replaced with another power manager, that problem disappeared. For over 18 months, we had been talking with a very knowledgeable DCC enthusiast, Bob Santelli of both the “Old & Unfriendly” and now the “New & Friendly” Allied Model Trains. Everything he had told us to date had been proven to be accurate so when he told us that he felt that overhead wire operation was not only possible but also feasible, that was the last reasonable obstacle to at least trying DCC.

So we chose to use the Custom Traxx demonstration module 970 for upgrade to DCC. The module was constructed in 1997 to demonstrate the feasibility of operating trolleys from overhead wire, and could be used to finally prove whether DCC works with overhead wire.  This module is exactly 36” by 32” and consists of both a complete circle of track and a main street that could be connected to another module. The module had been originally constructed with Hartel track, which was capable of two-rail operation.  When the crossings started to deteriorate and cause stalls with certain cars, they were replaced with ORR Track, ensuring only overhead wire operation for the entire module. By the time we were considering DCC operation of the module, only two Hartel turnouts remained on the main loop and were not used. All tracks on the main street had been replaced with ORR girder rail and turnouts. Hartel track existed mainly on the loop.

Module 970 had been operated using an Innovator 3000 throttle since it was constructed. After another consultation with Bob Santelli, on October 11th, we visited the new Allied Model Trains and purchased a Digitrax Zephyr, an entry level DCC System, and carefully read the instructions provided. We wanted to retain the Innovator 3000 to run in the analog mode and also be able to operate in the DCC mode, so Sunday, October 14th was the beginning of the installations. A DPDT switch was installed and special cables made to attach the Zephyr to the module were made. Then the module and the Zephyr were moved a home location for extended testing. Early the next day, our only DCC equipped car was a Bowser PCC car equipped with an A-line 20040 flywheel kit and a Train Control Systems (TCS) M1 two-function decoder. The car had been finished as Philadelphia Transportation Company PCC car 2128 in the “Safety” paint scheme. It had a trolley shoe long oxidized since its last run, but without any attempt at cleaning, was placed on the track and analog operation was attempted. After some erratic running, one drop of ACT-6006, Track and Rail Cleaner was placed on the under side of the overhead wire and running improved to flawless within seconds. The car was allowed to run for two minutes in the analog mode until it was time for the moment of truth.

[Note: Our experience with the ACT-6006 cleaner over the past year has eliminated the majority of the “dirty wire” problems with overhead wire operation in the analog mode. We have had modules stored in a trailer in an unheated, non-air conditioned garage for almost six months when the modules were set up in September at the Natural History Museum. We achieved flawless operation within seconds after application of a few drops around the display. Such flawless operation continued for the entire two days of the display. ACT-6006 is a product of Aero-Car Lubricants, P.O. Box 336, Western Springs, IL 60558, ph 708-246-9027, fax 708-246-7648, www.aerocarlubricants.com, harkan@sbcglobal,net]

Then the Zephyr was pulled out of the box and the directions followed exactly. The DCS50 Command Station was connected to the module using a specially fabricated cable made the day before. Then the PS315 power supply was connected to the power station and plugged into 120 volt AC power.  Car 2128 had been running flawlessly in the analog manner and was stopped. The DPDT switch was moved into the DCC mode. 

[Note: We learned the hard way that when changing from the DCC to analog mode and vice-versa, that a delay should be allowed for the decoder to adjust from the change. No not change modes while the car is moving. Bring the car to a stop. Wait five seconds and then we change the power from analog to DCC. ]

The Command Station was activated, giving the "cS" indication and then "Loco". Track power was activated and number "2128" was entered into the system, addressing this particular car. The key switch was moved to the forward position and immediately the headlight flashed brightly on and off.  It was initially thought that the headlight had burned out. The direction/brake control, which resembles the key on a streetcar controller, was moved to the forward position. Then the throttle, which resembles a streetcar controller handle, was slowly advanced and the car moved effortlessly around the module. It seemed to run much smoother in the DCC mode but that we felt that could be our imaginations.  We used the brake to stop the car and then hit “0” and the headlight turned on. As much as we loved the Innovator Controllers since being introduced to them by George Solovay in the early 1990s, we were astonished at how smooth the car ran under DCC and how bright the headlight was. We braked the car to a halt and went into reverse. The headlight went out as soon the car moved backward. We braked the car again and when we moved the controller into the forward position, the headlight came on and the car moved forward again smoothly. We flipped back to the analog mode and the car ran as it had always. We went back to the DCC mode and started the car. Again it seemed to run smoother than in the analog mode. We were beginning to realize that this was not our imagination.

Prolonged testing and evaluation of DCC operation on overhead wire would now begin and was scheduled to be completed prior to the end of November 2007. PTC PCC 2128 was to be our "guinea pig" for experimentation. We believe that we crushed a decoder during assembly because we did not take sufficient care in locating the decoder inside the car. The replacement decoder, new out of the package, would not run in the analog mode. Since the decoder still had the original two-digit address, '03', at the time, we changed CV 29 to 6 and that corrected the problem. Then we readdressed the car as '2128'. During the testing of this car, the car stopped running and could not be gotten to run. We found that we had 'fried' the decoder by switching to quickly between analog and DCC in our testing. We obtained a replacement decoder and without testing it, we installed it in the car only to find out that it was not functional. This taught us our First Lesson - Test Decoders Prior To Installation! Digitrax DCC controllers come with a tester and we recommend using it religiously in the future. We are fortunate to have one of the testers formerly made by Loy's Toys.

Attention now turned to SCTC 4, a Bachmann Brill Suburban in a Happy Holiday green, cream and dark red paint scheme. In May 2006 a Bowser 125143 mechanism with floor had been installed in this car along with an A-line 20040 flywheel.  At the same time, this car had been converted to run under overhead in the analog mode using trolley pole reverse but had not run since. On October 12th, the car was converted to DCC using another TCS M1 decoder. We did this conversion at Allied Model Trains under the supervision of Bob Santelli. We gave the car a testing using alligator clips and the end of the conversion and it tested as expected. So it was time to check this car out. The trolley pole reverse wiring was kept intact even though trolley pole reverse has no effect in the DCC mode. The car was placed on the track, without cleaning either the wheels or the trolley wheel contact, to run in the analog mode. The car ran well in the analog mode but when the switch to DCC was made and “04” was addressed; it ran flawlessly but in reverse in the DCC mode. We assumed that the car was wired incorrectly so we switched the black and red wires. The car ran fine in both analog and digital modes after that with no further modifications.  So we have developed a wiring plan that we plan to use for cars using trolley pole reverse.       

The third car for conversion to DCC was an S. Soho Los Angeles Railway Class M car 2602 painted in the silver and yellow paint scheme. It was originally wired for trolley pole reverse in March 2007 and had been operated last in July. On Thursday, October 18th, another TCS M1 decoder was installed in this car. So we followed our own schematic and installed a TCS M1 decoder and experienced the front trolley pole hook problem first hand. The clue was when the car would not even run in the analog mode. The car had run in the analog mode just before the decoder was installed and we were surprised that the car would not run at all. But when we applied alligator clips to both of the trolley poles, the car came to life. This can be a problem when trolley pole reverse remains in a decoder equipped car. This was the second lesson learned - Trolley Pole Reverse Wiring Can be Retained - But there can be a penalty!

We found that keeping trolley pole reverse in a DCC model can compound the very problem many feared.  With overhead wire operation with trolley poles there is only one 'hot' electrical contact, the small trolley shoe or wheel against the overhead wire but normally there are four to eight ground contacts to the track. Trolley pole reverse passes all four to eight ground contacts of the ground circuit through that single front trolley pole hook, making another single contact. By this time we had wished that we had made all trolley pole hooks with flat bar stock rather than round wire. In the DCC mode the flat bar stock provides better contact for passing both the line voltage and computer signals. So your can keep trolley pole reverse on a DCC equipped model for running on analog layouts but there is that small price. Strong trolley pole springs, especially in the stowed position will definitely help alleviate any problems here. And there is always the use of ACT-6006. After we took care of this problem, the car ran perfectly. We recommend that modelers test cars in the DCC mode also with alligator clips before doing anything else when the car does not run. For the trolley pole equipped cars with headlights, we are revising our way of wiring the cars internally. Instead of two printed circuit strips running the length of the car, there is now one strip and it is the common (Blue wire from the decoder) for both headlights. If the car has both headlights and taillights, three strips could be used. The second will be for the front headlight (White wire) and rear taillight and the third for the rear headlight (Yellow wire) and front taillight. We used that method when we converted our fourth car, a modernized MTS PRT/PTC 5200 class 1923 Brill car, 5333.

The Southern California Traction Club has added DCC capability to the club test track using a Digitrax Zephyr unit. It will be used to test and program trolleys for use on the new downtown loop and subway cars for the subway line. In doing this we connected both power sources to the tracks using a DPDT switch similar to that used on the Custom Traxx demonstration module 970.

Another thing that we learned was to not place the decoder directly on top of the motor. At one time, we had the irritating problem of a car that would not run assembled but ran perfectly unassembled. We checked all the connections and could not locate the problem. When we finally figured it out and moved the decoder, the problem went away. It was making contact with the motor casing. This decoder ran for four days and quit. We did do damage during the installation process. It just took time to fail.

By the end of the week, we were sufficiently confident to schedule a demonstration of DCC operation with overhead trolley wire at the "New & Friendly" Allied Model Trains on Saturday, October 20th. We brought the module and set it up on a table and started running the cars. We even had time to replace one broken ear and one overhead frog while the cars were running.

Bob Santelli and George Huckaby are shown behind the demonstration module while demonstration cars were running. The demonstration cars started running at 9:30 AM in the analog mode but by 9:45 AM, DCC operation started using three decoder equipped cars. Shown in the photo are four of the five cars running during the demo. At most times two cars were run on the layout. We used the Zephyr throttle to control the Brill Holiday Trolley shown in the lower left corner of the module, while we used our DT400 hand held throttle to control two others. Many time, we allowed a customer to run one of the two cars. Most were surprised at the level of control and the smoothness of the operation. Four of the cars running use Bowser 1999 units as power. Of those four, three are using the Bowser motor. The fourth, SEPTA LRV 9011 has been upgraded to a Mashima 40322 can motor. All of them have had the A-line 20040 flywheel kit added. The fifth car, a Soho LARY Class M with the original spring belt drive which has been remotored with an A-Line 40324 can motor.

At this time, we had operated five cars in both the analog and DCC modes on overhead wire and track that is ten years old on a module that has seen transported around three states. All of the cars run adequately on both the analog Innovator 3000 and the Zephyr DCC unit. DCC is not a ‘snap’, but we can see the possibilities even though we have yet to learn how to do some of them. Some of them are possible right now. We feel that we must embrace the technology. In ten years almost every engine will be sold with some type of decoder and over 50% will have some sort of sound. We will have to adjust to the requirements of this new electronics. The overhead wire and track carries not only the 14VAC for power but also for computer signals. If there is not enough contact area for both voltages to pass, the computer loses out and the decoder stops functioning. We tend to think of today’s DCC technology in the same manner as some of us accepted the original 1950s color television sets. They were a really big deal then.  We can still remember seeing the first one.  There are refrigerators now smaller than that set was. You could not even run a vacuum sweeper on front of them or move the set in your living room without a TV repairman. Today, they are not even considered a major item and are almost maintenance free. The TV repairman has virtually disappeared.  Overhead wire that has not seen operation in a long time is just as hard to get running.  Once cars started running, they tend to remain running. We also found it better not to touch the trolley shoe or wheel where it contacts the overhead wire after a dewirement. We handle only the pole.

PTC 5333 taught us more lessons when we installed our fourth DCC decoder. With this car, we had already installed 12 volt lamps for headlights but we were going to use 1.5 volt lamps for the red taillights, as they were the smallest lamps that we could find (1.2mm). This is where we made our mistake. We were under the impression that the line voltage from the Zephyr was 12 volts (They were at one time), so we made our calculations for the resistance needed to be installed in series with the 1.5 volt lamps as follows:

Line Voltage (v) = 12.0
Lamp Voltage (lv) = 1.5
Lamp Amperage (I) = .030a (30 mA)

To find the correct resistance, we must calculate the voltage difference between the bulb and the line and than calculate the amount of resistance (R) to handle the voltage drop (E).  

Line Voltage - Lamp Voltage = v - lv = 12.0 - 1.5 = 10.50 volts (E)
Resistance (R) = E/I or  10.50/.030 or 350 ohms

We had acquired some 370 ohm, 1/4watt resistors and had placed them in series with the 1.5 volt red lights but the 1.5 volt lights were far too bright and kept burning out so we decided to do what we should have done in the first place and find out what the line voltage was. We then used our RRampMeter (www.amhobby.com) and measured our line voltage at 14.0 volts. So when we recalculated, we got different results:

Line Voltage - Lamp Voltage = v - lv = 14.0 - 1.5 = 12.50 volts (E)
Resistance (R) = E/I or  12.50/.030 or 417 ohms

No wonder we were burning out bulbs. We obtained some 470 ohm resistors and installed them and the headlights & taillights in the car worked perfectly. We immediately began testing the car to see if the lights would not burn out. In the midst of all this we found 23.5 volts occasionally on the overhead/track. We checked our track voltage when the headlights on the cars looked extremely bright. Overhead/Track voltage should be about 14.0 volts. We considered our Zepher or the power supply as defective and had then replaced by Allied. The third lesson was - Have the proper test equipment on hand and use them. In this case it is our RRampMeter.

The fourth lesson learned was - Use only single sided printed circuit board for the interior wiring on metal shells. During our many lamp and resistor changes during the conversion of PTC 5333, we managed to destroy the substrate and cause some leakage to the chassis. This caused the rear headlight to remain on regardless. Even the use of the '0' button on the controller would not put the headlight out. After we substituted some single sided printed circuit board, that problem disappeared.

After our successful October 20th display of the demonstration module at Allied Model Trains, the next two displays were at the International Railfair in Roseville, CA on November 10-11, 2007, and again at Allied Model Trains on November 17, 2007. Both demonstrations were conducted without any major problems and by the time the third demonstration at Allied Model Trains was completed, we have had several different experiences with DCC operation under overhead wire.

As of this date, these are the lessons learned when using overhead wire with HO scale trolleys powered by Digital Command Control:

1. While good contact with the overhead wire is critical, reliable operation with pole trolleys is very possible with clean, well maintained wire. The larger the contact surface is with the overhead wire, the better. Trolley shoe castings seem to work better than the trolley wheel castings. The NMRA Specification wheel turnings also work well. Stronger than normal trolley pole springs also help here.

2. Cleaning overhead wire is a must prior to starting operation.  Analog operation is more suitable for seldom used or dirty overhead wire. Keeping both methods of operation available is recommended. The use of ACT-6006 dramatically assists the operator is cleaning wire and improving electrical contact.

3. Wiring for Trolley Pole Reverse can remain when decoders are installed by connecting the red and black wires from the decoder to the trolley poles but the trolley pole hook contacts must be solid. Good strong springs on the front pole when in the stowed position and flat bar stock for the trolley pole hooks are strongly recommended.

4. Analog cars converted to run on overhead wire will most likely run in reverse in the DCC mode. This is due to the convention started years ago in wiring the trolley pole. If this is a problem and you foresee operating in both analog and DCC modes, add a decoder to the car. It will most likely run smoother in the analog mode anyway.

5. Frequent operation is really helpful in keeping overhead wire clean for operation, especially operation with DCC.

6. Decoders should be tested prior to installation. We have found 'new' decoders to be bad and to have other than factory settings. We regularly use our tester formerly made by Loy's Toys.

7. Take great care where the decoder is to be placed inside the model. Trolleys are much smaller than diesels and motors and flywheels are often very close to the roof. Decoders for trolleys operating from overhead wire will most likely be placed on the underside of the roof, so take great care ensure that the decoder will not be struck by the motor or flywheel when the chassis is reattached. If that happens, even so slightly, the decoder will most likely be ruined.

8. Make sure what your line voltage is on your DCC system. It affects how you pick lamps and LED's for your cars. The RRampMeter is so valuable for this. We had a DCC system fail on us and deliver 23.5 volts to the track. The RRampMeter made us aware of this problem.

9. If you choose to use printed circuit strips to minimize the internal wiring, use strips made only from single sided printed circuit board.

10. This may be the most important of all the lessons learned. If you are a beginner, visit your local hobby shop and and/or find someone knowledgeable in DCC to guide you in the anomalies that may arise. There are no mysteries; only knowledge not yet obtained. We fried one decoder and had two others quit on us. We even found defective DCC Systems. We eventually found out specific reasons why! And we may have caused some of the failures ourselves.

So by this time, you can guess, we are practically sold on DCC and have not yet even tried many of the many features. It will change the way model railroaders run model trains, especially with the smaller layouts. And it will really change model trolley operations.  There will be probably be fewer of us in years to come, but it will be really exciting for those few. We can foresee automatic car stops, doors that open and close and light rail vehicle train sets.  How about destination signs that will be able to be changed to different routes just like some buses and light rail vehicles do right now?  Self contained motor trucks and full interiors may be just “around the corner” and DCC and its successors and improvements will bring all that.  We started controlling horsepower with reins, then by a controller. Next it was a pedal and now it is computers. We cannot even think about what will be used to control horsepower next but whatever it is will give us more control over more horsepower.  The same will happen to model trains, trolleys, subways and light rail vehicles.

So far, we are enjoying our learning experiences with DCC. There have been problems, some which took some analysis but we emerged a lot smarter. There have been collisions, some spectacular, as we learn to use the DCC throttles. But we are getting a little more comfortable with it every day. Of course, this lesson is reporting our experiences with DCC on our small portable modular layout in the Southern California environment. Other modelers may exhibit other experiences, and we request these modelers relate them to us. If they so, we will then share them with you.