Roco / Fleischmann MultiMaus with Lenz Set 100 (LZV100 & LH101) via XpressNet

My Lenz "Set 100" is looking its age now but is still a perfectly functional DCC system, especially now that I've upgraded it to firmware v3.6 (giving access to all possible 29 decoder functions).

If it has a fault, it could be that the LH100 handheld controller is not particularly ergonomic. The newer LH101 has improved matters somewhat but if, like me, you're wanting to add another controller, it's still pretty expensive too.

The Roco MultiMaus (MM) is far from new and not nearly so sophisticated (especially when compared to their newer Z21 system). However, it does have the advantage of being a relatively inexpensive and ergonomic controller that is totally compatible with the Lenz XpressNet (slightly salted in my case!) ... well nearly, as I've just found out (more details below).

The MultiMaus (MM) is a great alternative to the Lenz LH100 controller and it's centre-off rotary speed controller is perfect for shunting. Another great feature is the loco. library where 5 digit/character labelling is possible and allows quick call-up without having to enter addresses.

N.B. If you're considering a MultiMaus, look out for firmware version 1.05 (or above) to ensure you have full access to all 29 decoder functions.

As mentioned above, there is a slight problem - if you try to "hot-swap" the MM controller (as you might if moving around a layout), it can cause the Lenz system to stop in its tracks - literally!

When you try to plug the MM into the Lenz XpressNet using the commonly supplied "flat" RJ12 (6-wire telephone-style) cable, you might see a "STOP" message and all active locos (and sounds) will be halted.

The Lenz system has some pretty sophisticated short-circuit and overload protection built-in and it seems it can be triggered by the "in-rush" current when (re)connecting the MM.

If the MM is already connected when the Lenz before the system is started-up, the problem doesn't seem to occur ... but that doesn't help if you're wanting to move the controller around your layout, possibly using the LA152 XpressNet expansion adapter shown here (temporarily enclosed in an old butter tub - up-cycling!).

The easiest way to avoid the in-rush current problem I have found could be to simply swap the "flat" RJ12 cable, commonly supplied with the MultiMaus (MM), for a "curly" Lenz DIN cable, as used by the LH90 hand controller - when using this cable, there appears to be no problem at all when connecting the MM to the Lenz XpressNet - you can hot-swap controllers without causing any "STOP" condition.

There is a slightly more complicated way of avoiding the in-rush current problem, caused when connecting the MultiMaus controller to the Lenz XpressNet, but it has the advantage of being extremely cheap = pennies!

A "thermistor" is like a resistor but, in NTC form, its resistance starts 'high' - effectively impeding any in-rush current - but reduces quickly when in use (more details here: https://en.wikipedia.org/wiki/Inrush_....

I used a tiny 10 ohm NTC thermistor, rated at 2 Amps (more than enough for the typical milliamp loads on the Lenz XpressNet) installed in series with the "L" line (+12V DC) of the XpressNet connection, anywhere between the Lenz command station and the MM (I installed mine between the command station and the LA152).

The demo. shows the MultiMaus working perfectly with the Lenz XpressNet adapter, after this modification has been made.

The locomotive is a Dapol Class 08, fitted with a Zimo MX644D decoder installed with Digitrains (Paul Chetter variant 2) sounds. N.B. this includes an "active brake" feature on Function 2 - in the demo. I have this latched (brakes on constantly) so the locomotive does not move in response to throttle adjustments, only the sound changes.