Update 27 Mar 2009 I’ve received a very polite email from Shuhei Nagasue-san, the head of NGDCC, informing me that I have incorrectly under-specified his competitor’s product. Nagasue-san tells me that the Kato FL12 is very much capable of 4-digit addressing. I have modified the table below, and my review accordingly in the light of his comments. ありがとうございます！
Most Japanese trains are Multiple Unit (MU) trains—trains with no distinct locomotive, but whose motive power is distributed throughout the train. Typically models of MUs place the electric motor in one of the center-most cars, rather than at one end or the other of the train.
JR East E531
This means that a model of an MU needs at least three DCC decoders for a full conversion: One decoder to control the headlights and taillights in the cab car at one end, another decoder to do the same in the cab car at the other end, and one decoder to control the motorized car in the middle. This situation is unique compared to locomotive-driven trains, which require only one decoder to handle all of these functions, because the functions are all localized in one vehicle.
In this article, I explore the options available to the Japanese rail modeler for controling the directional lights in the two cab cars in an MU model with DCC. In a future article, I will explore the options available for controlling the motorized car in an MU model.
The Perfect Cab Car Decoder
The perfect cab car decoder would have the following properties:
- Cheap—With three decoders per train, equipping a train for DCC can get expensive quickly.
- Small—Cab cars usually have very detailed interiors with interior lighting. A large decoder would spoil that view.
- 2-function—There are only two functions to control: Headlights and taillights. Additional functions—including a motor-drive, are unnecessary, and only take up space and cost.
- Directional lighting—The headlights and taillights should alternate automatically depending on the direction of travel.
The perfect cab car decoder might have one or more of the following properties, depending on the model and desires of the modeler:
- 3-functions—In addition to the headlights and taillights, some like to control the car’s interior lighting via DCC as well.
- Able to drive bi-polar circuits—Many lightboards are difficult or impossible to hack apart in the way that most DCC decoders require; a decoder that can be connected directly to an unmodified lightboard is often very handy.
- Headlight dimming—Japanese trains dim their headlights when passing through or standing at passenger stations.
- Bidirectional support—When using Transponding or RailCom, bidirectional systems work best when the decoder sending signals is at the lead of the train—in the cab cars.
Actual Decoders: Summary Table
Of course, no decoder currently on the market (outside of Japan) meets these criteria. Here is a table of what is currently available to the English-speaking market (Europe, United States, Australia).
Click on or hover over any element in the table for a description of that element.
| TF4 | 73900 | FL4 | FL12 | LokPilot Fx micro V3.0 | M1 | Z2 | LF101XF | DF12r3 | DF11r3 | |
|---|---|---|---|---|---|---|---|---|---|---|
| Manufacturer | Digitrax | Uhlenbrock | TCS | Kato | ESU | TCS | TCS | Lenz | NGDCC | NGDCC |
| Rating | ☆☆☆☆ | ★★☆☆ | ★★☆☆ | ★★☆☆ /★★★☆ | ★★★☆ | ★★★☆ | ★★★☆ | ★★★☆ | ★★★★ | ★★★★ |
| Price | $21 | $25 | $19 | $16 | $40 | $32 | $35 | $25 | $23 | $20 |
| Price per Star | $∞ | $13 | $10 | $8/$6 | $13 | $11 | $12 | $9 | $6 | $5 |
| Recommended? | ✓ | ✓ | ✓ | |||||||
| Height | 4.1mm | 2.4m | 3.43mm | 3.5mm | 3.43mm | 2.79mm | 2.6mm | 2.3mm | 2.3mm | |
| Width | 7.8mm | 7.5mm | 9.14mm | 9mm | 9.12mm | 6.6mm | 12mm | 11.5mm | 11.5mm | |
| Length | 11.7mm | 10.8mm | 14.86mm | 13.5mm | 14.4mm | 12.95mm | 24.1mm | 18.5mm | 18mm | |
| Functions | 4 | 4 | 4 | 2 | 4 | 4 | 4 | 6 | 3 | 2 |
| Dirctional Lights? | ✕ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ |
| Bi-Polar? | ✕ | ✕ | ✕ | ✕ | ✕ | ◯ | ◯ | ◯ | ◯ | ◯ |
| Dimmable Lights? | ✕ | ✕ | ◯ | ✕ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ |
| 4-Digit Address? | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ |
| Transponding? | ◯ | ✕ | ✕ | ◯ | ✕ | ✕ | ✕ | ✕ | ✕ | ✕ |
| RailCom? | ✕ | ✕ | ✕ | ✕ | ◯ | ✕ | ✕ | ✕ | ✕ | ✕ |
| Max Current (cont. func.) | 125mA | 600mA | 200mA | 125mA | 140mA | 1200mA /100mA | 1000mA /60mA | 150mA | 50mA /7mA | 50mA |
| Max Current (peak func.) | 250mA | |||||||||
| Max Current (cont. total) | 600mA | 500mA | 280mA | 1300mA | 1120mA | 120mA | 140mA | |||
| Max Current (peak total) | 1000mA | 2000mA | 2000mA |
Reviews
Digitrax TF4
The TF4 does not support direction-dependent lighting. As such, whatever other features it may have, it is unsuitable for controlling the headlights and taillights in cab cars.
Summary: Do not use!
Links: Digitrax website, TF4 webpage, TF4 manual.
Kato FL12
Kato now manufactures many MU models with a special nook in the undercarriage designed to take one of Kato’s new line of streamlined decoders (designed by Digitrax). Kato calls these models “DCC Friendly”. The FL12 especially designed for these models’ cab cars. Installation into “DCC Friendly” cab cars is as easy as a DCC conversion gets: You open a small hatch, and you almost literally drop the decoder in. It is then completely concealed in the undercarriage. This is a very nice arrangement.
But many Kato models still in production—most of their shinkansen (bullet train) models for example—are not DCC Friendly. For these, and other non-Kato models, the FL12 can still be used, but it must be soldered in like a traditional wired decoder. The FL12 is nevertheless the smallest decoder in the line-up. While it doesn’t offer many fancy features, like headlight dimming (but see the next paragraph!), it does just enough to get the job done. This is likely a product of the small form factor requirements for this chip.
However, the small decoder does manage to find room to implement Digitrax’s proprietary Transponding feature, which allows CV readback in operations mode with the Digitrax BDL168/RX4 block detectors.
I had previously claimed that the FL12 does not support 4-digit addressing, nor CV readback. Shuhei Nagasue-san, of NGDCC has shown that I am mistaken on both counts. The FL12 does support 4-digit addressing. Moreover, the FL12 does also support CV readback in service mode (on the programming track), but in most cases the loads attached to the function outputs are too small to satisfy the requirements for an acknowledgement. So the decoder’s transmission can only be detected by some particularly sensitive programmers—which excludes my Digitrax Zephyr. Although the FL12 is the smallest decoder in the line-up, the small size comes at the cost of a heavily attenuated feature set. The lack of 4-digit addressing alone will be unattractive to many. Indeed, axed in the name of diminution was what I thought a part of the DCC spec: CV readback and command acknowledgement in service mode (on the programming track).
Summary: Good (and recommended) for Kato’s “DCC Friendly” MU models, and adequate for non-DCC-ready models.
Links: Kato Decoder product page, FL12 manual.
Uhlenbrock 73900
If size is what matters, the Uhlenbrock 73900 is as small as they come, over 2mm shorter than TCS’s diminutive Z2 (though a hair wider). For a function decoder, it can handle quite a lot of current. However, the feature set of this decoder is at the absolute bare minimum for what we want out of a cab car decoder—not a bad thing, if we don’t mind sacrificing dimming headlights for small size! But there are less expensive (and easier to obtain outside of Europe) options that do more if the small size isn’t so important.
Summary: Easily the smallest function decoder, but it doesn’t offer headlight dimming—a standard for American decoders. A little pricey for what little functionality it offers.
Links: Uhlenbrock website, 73900 webpage, 73900 manual.
TCS FL4
Looking at the specifications, this decoder doesn’t offer too much, but for us, this may be a virtue. Indeed, the FL4 still provides exactly those features that we want for a cab car decoder. The FL4 is second only to the Uhlenbrock decoder for tiny size—and at two-thirds the price. The “goof-proof” warranty is just icing on the cake.
Summary: A basic function decoder that gets the job done cheaply. Recommended.
Links: TCS website, FL4 manual.
ESU LokPilot Fx micro V3.0 (52624)
The ESU decoder (almost) does it all, even RailCom. It doesn’t offer support for bi-polar circuits, but this is the only feature missing. But the kitchen sink doesn’t come for free: The LokPilot Fz micro is hands-down the most expensive decoder in the lineup. Although it is small and full of features, the price tag is enough to consider other options. If you absolutely must have RailCom, the ESU is the only way to go. The rest of us should look elsewhere.
Summary: An incredibly full-featured decoder. It does most of what it needs to for a cab car, and very much that it doesn’t need to. The price of this decoder is, as a result, extravagant.
Links: ESU website, LokPilot Fx micro V3.0 webpage, LokPilot v3.0 Family manual.
TCS M1 & Z2
Although the M1 and Z2 are motor decoders, they are designed with very flexible motor-drive leads. The motor leads in both models (indeed, in all TCS motor decoders) can be set to be controlled by the function buttons. In this mode, F2 toggles the leads on or off, and the direction/brake control controls the polarity of the leads. In this way, the motor leads can be used to control a bi-polar lighting circuit, with automatically switching directional lighting! A very nice feature, but because the outputs are rated to over an amp, the price for these decoders is quite a lot more than most function-only decoders. The Z2 is also among the smallest decoders available, a bonus.
Summary: An excellent feature set, but because these are motor decoders, you will be paying motor decoder prices.
Links: TCS website, M1 manual, Z2 manual.
Lenz LF101XF
The Lenz decoder does much of what a good cab-car decoder should, including support for bi-polar circuits. It also does quite a lot more. All this functionality comes at a price: the LF101XF is far and away the largest decoder in this lineup, about twice as long as nearly every other decoder featured in this review, and as wide as the others are long. That said, the LF101XF is still small enough for many applications, and Lenz has managed to keep the price relatively modest. Indeed, the cost-to-benefit ratio of the LF101XF rates it a recommendation.
Summary: An excellent feature set, but more bells and whistles (metaphorically speaking) than are necessary to do the job make for a decoder a bit bigger than is necessary. Recommended.
Links: Lenz website, LF101XF manual.
NGDCC DF11r3 & DF12r3
NGDCC is a Japanese manufacturer that caters specifically to the Japanese market. So their decoders are tailored exactly to the needs of the Japanese rail modeler. However, these decoders are not available outside of Japan. And, of course, the DF11r3 (2-function) and DF12r3 (3-function) are designed specifically for use in cab cars. As such, they meet all the necessary criteria, and nearly all the preferred criteria for the “perfect decoder”, above. I include them in this listing for completeness.
These decoders must be purchased in sets of four (enough for two trains).
Summary: Designed specifically for Japanese cab cars, has most or all of the desired features with nothing extra. But, sadly, these decoders are not available outside Japan!
Links: NGDCC website, DF11r3 webpage, DF11r3 manual, DF11r3 CV list; DF12r3 webpage, DF12r3 manual, DF12r3 CV list.
Boring Explanations
Stars
☆☆☆☆ Do not use. Unsuitable for cab cars.
★☆☆☆ Adequate. Suitable for cab cars, but you could do better.
★★☆☆ Fine. Suitable for cab cars. Often will have the best feature set for the least price.
★★★☆ Good. Well suited to cab cars. Has more or better features than most.
★★★★ Perfect! An ideal decoder for cab cars. Has most or all of the best features, but is often also the most expensive.
Price per Star
This is the ratio of the decoder’s price to it’s rating in stars. The number is a rough guide to the cost-to-benfit ratio. Lower numbers represent a better cost-to-benefit ratio; higher numbers represent a worse cost-to-benefit ratio.
Directional Lighting
When a prototypical MU is moving, the headlights at the front of the train are on, and the taillights at the rear of the train are on. When the train switches direction, the headlights and taillights switch too. A decoder that supports directional lighting will automatically switch the headlights and taillights depending on the direction of travel set by the throttle, with no user intervention necessary. This is a very important feature for a function decoder used in cab cars to have.
Bi-Polar Circuit Capability
A bi-polar circuit is simply a circuit with two leads that behaves differently depending on the direction of current across the leads. The directional lightboards in cab cars are bi-polar circuits: When the current flows one way, the headlights come on. When the current flows the other way, the headlights go off, and the taillights come on.
A DCC decoder function lead can only control one light circuit at a time, because they can only generate current flow in one direction. Thus, the lightboards must typically be cut apart into two distinct lighting circuits before a decoder’s function leads can be attached. However, some lightboards are too small or delicate to easily cut apart in the way needed. In these cases, a decoder that can provide current flow in two directions can be connected directly to the leads of the lightboard without having to cut it apart. This is a tremendously helpful feature, but is only rarely necessary.
Dimmable Headlights
As in the United States, Japanese rules of operation require trains to dim their headlights when passing or standing at passenger stations. Although a subtle feature, many modelers enjoy prototypical lighting effects in their trains. Typically, a decoder that supports this feature will dim the lights when F4 is pressed. Any function decoder that supports “Rule 17″ operation of the lights will support this feature.
Bidirectional Communications
RailCom and Transponding are two different systems of bidirectional communications over DCC. Normally, DCC is a one-way signal: From the command-station to the decoder. There is normally no method for DCC decoders to respond. RailCom and Transponding are methods for the decoder to send a response to the command-station. This is really useful for automated control of a layout, but is not a necessary feature to implement basic block occupancy detection, although both methods require a block occupancy detector detector to work. I won’t get into a discussion of the advantages or disadvantages of each system; you can read more about those elsewhere on the Internet.
RailCom is an open standard developed by Lenz and adopted by the NMRA as a Recommended Practice for DCC. That is, it is now an official, if optional, part of the DCC specifications. RailCom responses can be detected by a Lenz LRC130 RailCom detectors and reported to a computer via the Lenz LRC135 RailComBus USB adapter.
Transponding is Digitrax’s proprietary standard for bidirectional communication, and is currently only implemented in Digitrax decoders and Kato decoders designed by Digitrax. Transponding responses are detected by a Digitrax RX4 detectors, which must themselves be attached to a Digitrax BDL168 block occupancy detector. Transponding events can be communicated to a computer via the Digitrax PR3 LocoNet USB adapter.
Maximum Current Ratings
The current rating of a decoder tells you the largest load you can connect to the decoder. Each light, motor, speaker, etc., draws a certain amount of current; attaching too many will cause the decoder to overheat and perhaps even die.
A manufacturer often lists two or more different current ratings. A current rating is either for each function individually, or the total current for all functions combined. Moreover, a current rating is either a continuous rating or peak rating.
Continuous Current per Function is the amount of current a decoder function lead can handle over an indefinite time period. For example, if the literature claims a 125mA continuous function current rating, then you can attach a lamp that draws up to 125mA to that function, and leave it on as long as you please.
Peak Current per Function is the amount of current a decoder function lead can handle for short bursts. Incandescent lamps, when they first turn on, have an inrush current that is ten times the current draw of that lamp. For example, a lamp that is rated as drawing 50mA will actually draw 500mA very briefly when it is turned on. So this rating is important to know when you are using incandescent lamps. LEDs do not have a significant inrush current.
Continuous Total Current is the total amount of current that the decoder can supply for all functions combined over an indefinite time period. The sum of the current draw of all lamps must not exceed this amount. This may limit the number of lamps or other loads you can attach to the decoder.
Peak Total Current is the total amount of current that the the decoder can supply for all functions combined for short bursts. This is particularly important for motor decoders, where the stall current of the motor (the amount of current the motor draws when it is stalled or locks-up) must be less than this number. Unless you will be using a large number of incandescent lamps (see above), this number is relatively unimportant for function decoders.