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How To Use The Märklin Connect-6021

Are you running 2-rail? Don't stop here. The Märklin Digital system is for 2-rail as well - and speaks DCC! Read my article on choosing Märklin Digital.

Märklin Connect-6021 will tie two generations of digital systems together.

On exhibitions, people some times ask me if they need to throw away their old Märklin Digital components when investing in the Märklin Central Station (Märklin #60215).

The answer is simple: No, you do not!

Most older Märklin Digital components can be used with the Central Station by using the Connect-6021 (Märklin #60128). The component allows you to use your Control Unit (Märklin #6021), Keyboard (Märklin #6040), Memory (Märklin #6043), Control 80 and Control 80 f (Märklin #6035, #6036).

What Is The Benefit Of Connect-6021

The major benefit is that you in one take, can re-use most of your older Märklin Digital components with the new generation. You do not have to throw anything away. This makes the transition from the older system into the new system much smoother and easier.

When you connect the Control Unit with the Central Station, the Control Unit will also inherit some of the features of the Central Station.

Digital Protocols
One of the great advantages of the Connect-6021 is that your Control Unit are now able to control locomotives that speak DCC and mfx as well. This was not possible prior to connecting it with the Central Station. This means that you are not limited to using the MM-controlled locomotives with the Control Unit.

Every protocol (DCC, mfx and MM) can now be reached from the Control Unit.

Can I use the Connect-6021 with 2-rail as well?
Yes, of course. The Control Unit will control your 2-rail locomotives without any problems. With Connect-6021 the Control Unit will support the same protocols as the Central Station (DCC, mfx and MM).

If you are a 2-railer using DCC or mfx, you probably do not have any older Märklin Digital equipment, but should you have a Control Unit laying around, you can use it as an extra controller.

How Does The Connect-6021 Work?

The Connect-6021 can be considered a translator from the old Märklin Digital system generation to the generation of the Central Station. The Connect-6021 operates as a component of the CAN-bus, just as the Mobile Station, Booster, S88 LINK and other modules. This means that you connect your Connect-6021 to either the Booster outlet on the Central Station, or the Terminal (Märklin #60125). I use the Terminal in my setup, because it provides me with more flexibility.

The setup is easy, connect the Connect-6021 to the Terminal and you're on your way. The picture is from the German User's Guide.

Setting Up The Connect-6021

First of all you need to turn off the power to your entire layout. This is always a good idea, when connecting new critical components.

Then you need a power source for your Control Unit. You can use the transformer that came with it, or you can use a newer Märklin power source. I use the switched mode power pack (Märklin #60061) along with the Converter (Märklin #60130). I use the Converter, because the Control Unit needs AC power to operate. The Converter converts the DC from the power pack to AC.

Before you connect the power, you connect the Control Unit to the right side of the Connect-6021. All control components (Control Unit, Control 80 and Control 80 f) goes on the right side of the Connect-6021. The switchboard components (Keyboard and Memory) goes on the left side of the Connect-6021.

You connect the Connect-6021 to a Terminal, or to the Booster outlet on your Central Station.

When all your components are connected, you can turn on the power to the layout and turn on the Central Station. When the Central Station comes online, it will recognize the Connect-6021 and provide you with the option to assign locomotives to it.

Assigning Locomotives

Because the Control Unit is an older system, you will have to assign locomotives to it. The reason for this is that the Control Unit only controls addresses between 01 and 80. All addresses above cannot be reached. When you assign a locomotive, it will automatically receive a virtual address between 01 and 80 that you can use when operating the locomotive with the Control Unit. 

A few seconds after coming online, the Central Station would have recognized your Connect-6021. Now you're ready to assign locomotives.

On your Central Station's setup screen, click the wrench.

Now use the arrows to navigate the options, and click the 6021 option.

On the 6021 page, you can now assign locomotives to the Control Unit. You assign a locomotive by clicking "Lok hinzufügen" (or "Add Locomotive" in the English version).

Now select a locomotive from the list. You can select more than one, you can add as many as 80 locomotives to the Control Unit. When you are done, click accept.

The newly added locomotives will be added to the list along with their assigned virtual address (the number in the right column).

If you are unsatisfied with the automatically assigned virtual address, click the button "Adresse ändern" ("Change Address" in the English version) and assign a new address.

Note: You may not use an already assigned address. This will not work.

Worth knowing about virtual addresses: Virtual addresses are, as the name implies, virtual. They only exist in the communication between the Control Unit and the Central Station. The virtual address is not the same address as the one in the locomotive. You do not need to change the address in your locomotive in order for it to work with the Control Unit.

When you are done assigning locomotives and setting up virtual addresses, click the accept button and reboot the Central Station. The User's Manual is not clear on this subject, but I have found that I need to reboot the Central Station when I make changes to the Control Unit locomotive roster.

When the Central Station comes back online (allow 10 - 15 seconds for the Central Station to recognize the Connect-6021), call up one of your locomotives on the Control Unit and have fun!

Worth Knowing About Connect-6021

You should know that there are a few limitations to consider. Knowing about these limitation will help you decide whether or not this setup is for you.

Keyboard (Märklin #6040)
The Keyboard can be used out of the box. It will automatically take control of the decoders that it would normally control. Meaning that Keyboard #1 will control decoders with the addresses 1 - 16, Keyboard #2 will control addresses 17 - 32 and so forth.

Note: When you push a button on the Keyboard, the Keyboard-tab in the Central Station will change status for that button accordingly, but not the other way around. This means that you cannot rely on the LED status on your Keyboard. You can only rely on the status that you see on the Keyboard- or Layout-tab in the Central Station.

Memory (Märklin #6043)
The Memory will activate routes just as you programmed it. It will not change its behaviour according to the routes in the Central Station. This means that you have to be aware that you do not create conflicting routes when using a Memory component. I advise you to consult the Connect-6021 User's Manual for more information on using the Memory.

What Will Not Work

As you might have expected, trees do not grow into Heaven. There are things that you do not get with the Connect-6021, I have covered the limitations with the Keyboard and the Memory in the last section.

The following components will not work with the Connect-6021:

  • Older Märklin Digital DCC components (e.g. Arnold controllers)
  • Central Control (#6030) and derivatives
  • Central Unit (#6020, #6027) and derivatives
  • All Trix digital components (except for the Trix Mobile Station 2)


Although the setup does have some limitations with regards to communication between the two systems, I think of the Keyboard in particular, the setup is very useful. I can imagine that someone who invested heavily in the older Märklin Digital system, might hesitate to buy the new equipment because it feels like letting the entire investment go. This does not have to be the case with the Connect-6021.

Having the Control Unit and Keyboard as extra controllers and switchboard is a cool feature, and even though you go further into the new generation of Märklin Digital with the Mobile Station, the S88 LINK and more, you can still find use for your older equipment. I can imagine that you might re-assign your Control Unit and Keyboard to operating a yard or perhaps a little siding somewhere on your layout.

If you own a Control Unit and want to find a new use for it, try the Connect-6021. I think you will be happy with it, and the fact that you can still use your old controller.

What do you think? Do you have this setup, or are you planning to get it? Do you know of benefits that I have not covered? Please leave a comment!

Happy Modelling!

Beginner's Guide To Digital Operation: What Is A Booster?

Larger digital model railways often need several boosters to operate. But what is a booster really? Let me try and take some of the mystery out of the equation and put this in layman's terms.

What The Booster Does

An analogy. Most people have a smartphone or some sort of music player. When you are the only one listening to your music, this works just fine. You can use your headphones and enjoy your music. Sooner or later, you want more people to be able to listen to your music.

Let's say you want to throw a party, and you want all the people in the living room to listen to your music. What do you do? You install a speaker. Unfortunately, your music player cannot supply your speakers with enough juice to get the music going. What do you do? You install an amplifier for your speakers.

But your party is a large one, and you want people in the garden to listen in as well, then you install another amplifier for the speakers in the garden. Step by step, you raise the limit on how many people that can listen to your music.

On the model railway, the booster is the amplifier, and the locomotive- and accessory decoders are the people listening to the music. The more locomotives you want to run at the same time, the more boosters you need.

Power Consumption

First of all you need to understand a bit about power consumption. On your model railway your locomotives, stationary decoders, coaches with lighting etc., all consume power while operating. If you add all this up, you have the total power consumption of your layout.

All digital command stations need a booster to work. The booster is the thing you connect to the track. For ease of use, most digital command stations have a built-in booster, just as your smartphone contains a small amplifier. This makes it easier for the modeller to set up the first train set.

You can say that your digital command station contains a command generator component, and a booster for delivering the commands to the locomotives. The booster also adds the power that your motors will run on.

The booster inside your digital command station will have an upper limit on how much power it can supply. For H0- and N-scale this is usually 3A (Ampere). Larger scales may raise that bar to 5A.

The math is simple: If your layout consumes more power than the booster can handle, we have an overload situation. There is simply not enough power to run your layout. An overload will result in the booster shutting the layout down.

This is where the second booster comes in (second, because the command station is a booster in itself).

Simply put: Installing a second booster raises the upper limit on how much power your layout can consume.

Installing A Booster

To install your second booster, you will need to separate your layout into two independent power sections. I call these sections "booster sections". The new booster section will be controlled by the new booster that you install. If you plan to install additional boosters, you will have to create a booster section for each new booster.

Important: All the sections must be completely isolated from each other. If you do not do this correctly you may create a short.

You connect the booster to the track in the newly created section. Besides the track, you also connect the booster to your digital command station. Usually, there is a booster plug on your digital command station. Remember, that the booster sends the commands from the command generator to the track. So naturally, it will need to be connected to the digital command station in order to know which commands to send.

That's bascially it for the booster. You are now able to run more locomotives. A locomotive passing between the booster sections will never know the difference, because all boosters are connected to your digital command station.

Alternate Booster Use

Another use for a booster is with accessory decoders (e.g. point decoders). The idea is that you dedicate a booster (or the booster in the digital command station) to power all your accessory decoders, but not the track. I call this an accessory booster section. Other boosters will handle the track power.

Normally, if a short happens in a booster section, the booster controlling that section will shut down the section**. With it goes all the decoders and locomotives powered by that booster section. This can be a problem.

By powering the accessory decoders through an accessory booster section, you have the advantage that if a short happens in one of the track booster sections, all decoders in the accessory booster section will still work and can be operated. This can come in handy if a locomotive creates a short in a powered frog. You can then set the point right, without having to move the train with your hands.

** The behaviour of the booster in an overload situation depends on the make of the booster. Most boosters shut down their own section, but some digital systems shuts down the entire layout. In this case, the idea will not work. In this case, you are better off installing a circuit breaker and have it monitor the different sections instead.


Q: When do I need a booster?
A: You need a booster if your layout consumes more power than your digital command station can handle.

Q: I have a large layout, do I need a second booster if the power has trouble getting around? I only run 1 - 3 locomotives, but mostly only 1 locomotive at the time. My digital command station can supply 3A.
A: No, you do not need a second booster for that. If you have dead zones around your large layout, try installing additional feeder wires in those sections. The power probably has difficulties getting there.

Q: I have a Märklin 3-rail layout, and I was told that I have to connect the ground from all the boosters with the common ground of the layout. That does not comply with you saying that I have to completely separate the boosters?
A: It is true, that with the Märklin Digital system (of the newer generation, and some of the older generations) you can connect the ground with the common ground of the layout. But please be aware that this is only possible because the system is designed to allow this. You cannot be sure that this is the case with every other systems (and some generations of the Märklin Digital system). It is not a necessity to connect the booster to the common ground on the Märklin Digital system though. 
The code is to keep things simple: I will always recommend separating the boosters, also when using the Märklin Digital system. Just be aware that when doing feed back, you will have to connect the feed back module ground to the ground of the booster section that it provides feed back for. Otherwise the feed back will not work.

I hope this article clears up some of mystery about understanding when a booster is needed, and why.

Happy Modelling