Zmodell Digital Decoder for AZL SD40-2 diesel locomotives

Alex,

I mentioned it in another thread, but wanted to make sure you learned of my experiences.

I installed your decoder in one of my SD40T-2s (SP, like you!). Not only was installation a breeze, but the running qualities are awesome! Slower speeds are more attainable, the LED lights look great, I can't say enough good things! I like the little bit of momentum you included by default.

I'm doing an RS3 installation this weekeend and can't wait to see the results.

Like others I'm trying to upgrade my entire fleet with DCC. A good portion of my fleet is older, I have a lot of SD45s, GP30s, GP38-2s etc. The decoders that are currently available for those units are in many cases tricky to install and to get running smoothly. Just wanted to mention that...

Thank you for your efforts, you are doing the world of Z scale a huge favor! I will repay you buy purchasing many of your decoders!

Steve W

Yes, some compatibility issues between the old command station and digital decoders can also be the reason for this issue. I experienced nearly the same effect with Digitrax decoders and certain European command stations like Marklin CS2/CS3 and some others. The locomotive starts running at the full speed immediately after switching the track power on, and starts following the inputs only after you do something on the command station - stop, start again, adjust speed, light etc.

Apparently, it happens because the command station and the digital decoder cannot establish a reliable communication with each other at the initial stage. The digital decoder then 'thinks' that it is on analog layout and just starts running in DC analog mode, using the full DCC voltage which gives the full throttle speed.

So, upgrading the command station could indeed be not a bad idea.

Regards,
Alex

Hi friends,

After analyzing quite a few examples of using the SD40-2 locomotive with an installed digital decoder, I would like to draw everyone's attention to some important things which it turned out are still not obvious to many. Although I am very thankful to everyone for kind words and appreciation of my products, I also received several reports about "uneven work of the loco in DCC" and so on. After a very short investigation of each single case, it always turns out that the key of the problem is not related to the digital decoder itself, but to the issues with proper maintaining the model and/or layout.

I would like to highlight the following points that relate both to Z scale in general and to particular SD40-2 model, too:

1. Please always keep in mind that absolutely clean tracks and wheelsets are crucial for reliable digital operation. It applies to all scales, but it is extremely important to Z scale, where we have all these strict limitations of size and weight. Dirty tracks and wheels disturb the DCC signal, and even the best decoder and command station may fail to communicate properly when the locomotive jumps over pieces of dust and fiber and slides over the spots of grease and dirt all the time. As a result, the locomotive may show jerky movement, not responding to DCC commands, and even the address may not be readable or readable improperly.

Please understand that even if the tracks on your layout seem to be clean, they may be actually dirty and prevent your rolling stock from running reliably. It is often very easy to check this - just wipe the 'clean' tracks with a cotton pad wetted with IPA or even with your own finger and you will be surprised when you see that the pad or your finger is dirty. Thus, regular cleaning of everything that conducts power is absolutely important (even if you don't run the trains for a while!).

Please also don't forget that requirements for the quality of electric contact between the locomotive wheels and tracks in DCC mode are higher than in analog mode - just because you need to transfer not only power, but also a high-frequency digital signal that can be easily distorted in case of unreliable electric contact between moving parts. Thus, the fact that the locomotive runs good in analog may not always mean that it will run the same in DCC. So please, before complaining that 'something is wrong' make sure you did all you can to improve the connection between your locomotive and the tracks and to help DCC commands between the loco and command station to flow undisturbed.

2. About energy storage modules: please understand that even the most efficient energy storage module equipped with the best capacitors cannot supply the power endlessly during power loss - simply because it is not a battery. In most cases, the time of 'bridging' is limited to less than a single second. Don't be surprised - it is more than enough for reliable DCC operation and for safe passing of problem sections like turnouts, crossovers, rail joints and dirty spots.

Longer buffering times (2-3 seconds and more) are possible only with supercapacitors (or double-layer capacitors, goldcaps etc.) with an effective capacity starting from 10 000 µF and higher. There are currently no supercapacitors on the market with suitable characteristics (necessary voltage, capacity and internal impedance) which can be fitted in such a small Z scale locomotive like SD40-2 and most other models.

So, if someone claims that he can supply his locomotive for as long as 2 seconds and more with a single 1000 µF capacitor - don't believe him, it is not true. If you want to check this on your own - connect such a capacitor to the oscilloscope, charge it to 12 volts, then load it with 30-40 mA (average current consumed by Z scale coreless motor), disconnect it from the power and look at the screen - you will see everything with your own eyes.

Additionally, here is one more downside of too capacious energy storage module. If you equip your locomotive with too big stay alive module, it often happens that during long power loss bridged with capacitors, the digital decoder starts 'thinking' that it is now on analog layout and not on DCC track anymore and switches to analog mode completely. As a result, you get a runaway locomotive on your layout that can be stopped only by cutting off the power.

To prevent this unwanted effect, some DCC manufacturers added a special setting to their decoders that limits buffering time to a certain value, regardless of the capacity of energy storage module. For example, ESU offers such setting in their decoders.

Here is also another important information to consider: please understand that the storage capacitor needs certain time to become fully charged, too. In case of very bad electric contact between the wheels and the track, you simply won't allow the capacitor to be fully charged, because in this case it will discharge faster than it charges. It means that even a presence of energy storage module requires at least some decent electric contact between the locomotive and the track. You should take care of cleanness of tracks and wheelsets in Z scale all the time.

3. Although SD40-2 is a very good model, user's experience already revealed some minor drawbacks which are worth of attention. I am talking about the electrical connection between the trucks and the chassis. It may often happen that the tabs coming from the trucks jump off the metal springs attached to the chassis and stay aside of them, causing the problems with electric contact. It may not be obvious from the first look, especially after disassembly of the model for maintenance or for the installation of the digital decoder.

So please always check if the brass tabs on the trucks are aligned properly with metal springs on the chassis and if they are also in a good contact with each other. Even a single misaligned tab may be the reason for unreliable DCC operation. Sometimes, it can be also useful to bend these springs downwards further in order to let them press on the tabs stronger and to provide better electrical connection. Recently, I received a report from one of the customers that he experienced such an issue and that he solved the problem successfully by further bending down the spring contacts on the chassis.

Thanks to everyone for reading all this - I hope it may be helpful to many.

Best regards,
Alex

I finally found the time to try out one of my Z-Model equipped SD40-2's on my layout.

One word, WOW!

It ran smoothly over all my turnouts and at an impressive slow speed. I confess that I have yet to clean my track after several months of inactivity, and I don't recommend running on dirty track, but I couldn't resist the urge to see the difference those capacitors made. No bumping the layout or nudging the engine to start, just crack the throttle and away we go.

I wish that your decoders didn't cost so much, but in this case they are worth every penny.

Thank you Alex.