Massoth reverse loop module

[Tim Brien]

The Massoth module is touted as both analogue and digital capable. As a point of fact this is true, but in reality it really is either analogue OR digital, due the way the unit operates in both modes. Analogue ops switches the main track and requires an independent DC power supply greater than 14 volts. In digital mode the unit switches the loop itself and apparently, to improve operation, factory supplied diodes are fitted to the four track sensor leads. In analogue mode these diodes must NOT be fitted. With this in mind, my only option is to utilise the digital operation mode only of the module.

In my masochistic intent, I want to retain links to the past with my analogue railway due the great number of analogue locomotives that I have and yet still embrace the digital age. I have learned so far that digital and diodes do not play together, thus my analogue bridge rectifier operated reverse loop power supply will need to be isolated ('on/off' switch?) when in digital mode. I am more than happy with the way this archaic set up operates and thus wish to retain it for analogue use.

Therefore, the installation of the Massoth module will require care to ensure it is isolated when I am operating my railway in analogue mode. I thought that disconnecting the main track input to the module ('on/off' switch?) would hopefully disconnect the unit from analogue track power input, plus not providing an independent power supply would further protect the unit. In analogue mode the module senses loop polarity and switches the main track. In digital it senses main track polarity and switches the loop itself. I am open to ideas.

Also, the sensing/polariity change worries me. Very few of my cars have plastic wheelsets. Massoth advises that all cars with metal wheelsets MUST be inside the loop to prevent a trailing wheel (outside the loop) tripping the input sensor and causing a short circuit. The unit cannot protect itself from this scenario. I am sure that I am not the only one who uses metal wheels, so how does one avoid this situation? A longer loop is definately NOT an option. I have already decided that one reverse loop will be dedicated to analogue use only so I really do not want to lose the second loop!

 

[Zerogee]

Don't forget that you don't HAVE to use the sensor tracks to operate the Massoth unit in DCC mode - they are an option to (possibly) improve operation slightly and reduce wear and tear, but it will also quite happily work in the old short-circuit mode that the original LGB units do - and many people have operated those for years without problems. I don't know if that would simplify things for you at all?

Jon.

 

[Neil Robinson]

Also, the sensing/polariity change worries me. Very few of my cars have plastic wheelsets. Massoth advises that all cars with metal wheelsets MUST be inside the loop to prevent a trailing wheel (outside the loop) tripping the input sensor and causing a short circuit. The unit cannot protect itself from this scenario. I am sure that I am not the only one who uses metal wheels, so how does one avoid this situation?

One method I've seen published, probably on here or its predecessor, G Scale Mad, is to isolate each rail by making two cuts close together rather than just one. This will leave a very short dead section similar to a dead frog turnout.
I only run analogue so I've no personal experience of this. I suspect there may be an issue of securing any very short piece of rail and that this may be resolved by using a little epoxy adhesive or screwing the rail to the base plastic.
Locos and other rolling stock such as lighted coaches that have internal wiring linking wheels together will still short out though. Loco skates may also short if the dead rail section is short enough.

 

[steve parberry]

Also, the sensing/polariity change worries me. Very few of my cars have plastic wheelsets. Massoth advises that all cars with metal wheelsets MUST be inside the loop to prevent a trailing wheel (outside the loop) tripping the input sensor and causing a short circuit. The unit cannot protect itself from this scenario. I am sure that I am not the only one who uses metal wheels, so how does one avoid this situation? A longer loop is definately NOT an option. I have already decided that one reverse loop will be dedicated to analogue use only so I really do not want to lose the second loop!

If it is going in a true reverse loop then there is not a problem as long as the sensor tracks are close to the point as the train will collided with itself and derail the rear car removing the short circuit issue

 

[Tim Brien]

Jon,
I would prefer the track sensing method, however, the module does default to short detection protection (if activated) should the track sensing method fail to detect the polarity of the incoming train into the loop.

Neil,
this basically is what the module does, although with the module, the short isolated lengths of track 'sense' the polarity of the locomotive and change the loop polarity to suit. Lighted coaches would need a bridge rectifier at each power pickup (bogie/truck) to prevent a short occurring, although the issue of metal wheels themselves still has me a little perplexed. The polarity outside the loop (main track) is unchanged. It is only the polarity inside the loop that is altered. Therefore, if a metal wheelset is detected by the sensing track, then I believe that the module would simply alter the loop polarity to suit. I can see an issue if car wheelsets are used for power pickup as the car pickups would bridge both sides of the sensing track (loop entry) with opposing polarity, but multiple bridge rectifiers would sort that out for each 'powered' car.

 

[Tim Brien]

As I will be eventually powering a reverse loop with both analogue and digital power (not at the same time), I needed to isolate the units from each other. As a redundant feature, I always provide double feeds to my track in case of failure, thus I have two sets of feeders from the double bridge rectifiers (more redundancy built in) to the loop. As I needed to isolate the reverse loop module from the analogue output of the bridge rectifiers, I installed two 'on/off' double throw switches. The loop power feed (input) is attached to the switch 'common/centre' pins. In one position the loop is fed by the analogue/bridge rectifier supply. In the other position the loop is (will be) fed by the reverse loop module for digital ops.

As a safeguard, I am wondering if the loop module main track input should be able to be isolated from the rails when the railway is used in analogue mode.

 

[Tim Brien]

With reference to above as regards isolating module main track input when operating with analogue power input, I have wired the module track input through the relaxed contacts of a relay. DCC power will not trigger the relay so power should input the module whenever DCC power available. When in analogue power mode, the track power input will activate the relay around 5 - 6 volts, thus disconnecting the main track input to the module. Maybe overkill but as my knowledge of DCC power is very limited I decided to isolate the module when using analogue power.
PS. Unfortunately all above is incorrect. I tried my defunct DCC controller (still outputs a signal) and it actually triggered the relay, so I will now need to replace the relay with an on/off switch.

 

[don9GLC]

Tim,
You need to keep in mind that DCC and analog behave quite differently when the 'polarity' of the track supplies is reversed. With a DCC loco forward is still forward. With analog its track direction that defines loco behavior (east-west, for example). Hence the Massoth reverse loop unit is not perverse: it needs to operate in one mode or the other. The electrical requirements are opposite.

On the topic of your damaged DCC central station and its output, I strongly suspect that the output you are able to measure is a fault. I would hesitate to regard any test operations as definitive until you have it working properly.

It's possible to design a reverse loop module that operates on DCC or analog. It's even possible to have them operate together. But you really must consider why you would want to do that. Its not cheap. It's definitely technically complicated. And it needs to be considered over the whole layout and operating conditions, rather than bit by bit. You had a somewhat sophisticated analog set up, largely redundant with DCC. But there are other features of DCC (for example block control. shuttle operation, route selection, etc) that you might want to consider. And you should not give up your useful analog features if you need to operate in that mode. But can you afford it, and do you have access to the technical support that a complicated control system requires? Inevitably DCC will advance technically and your experiences may encourage you to try more sophisticated features.

In crude terms, DCC puts a computer on the loco. Analog allows an external computer to do much more, but DCC also allows external computer control, giving even better control. No overwhelming technical advantage to either system, except if you have to use only 'off the shelf' items.

Combining the two systems is not an 'off the shelf' solution, if you have reverse loops and shuttle operations, for example. And as for dead sections before track ends there are so many solutions; again not off the shelf.


Garden model railroads tend to be fairly simple and not take advantage of the DCC features that smaller scales employ. Except possibly sound.

My advice (worth what you paid for it) is to consider what extra features you expect from DCC. Then consider if you want analog operation. If you want both then consider the fact that you will need a detailed electronic design to allow both, and that there will be a cost in design, implementation and updates (as things develop).

This is a theoretical answer to a largely theoretical question. Feel free to PM me on specific solutions.

Don

 

[Tim Brien]

Don,
my failed central station still outputs signals to trigger sounds, so some DCC signal must be output. It is the motor output that seems gone. The only drawback so far with integrating DCC and analogue (not at the same time), is one of my reverse loops will remain analogue ops only. My main siding will be able to operate analogue and DCC simultaneously as the two sections may be isolated by a half metre section of track, preventing one loco from straying into the other operating system. A flick of a switch and the whole railroad becomes DCC compliant.

I do find it strange though that one relay (unless it was my only failed relay), failed to work on DCC and yet another did. Due my lack of effects on analogue power on the Massoth module, I will be isolating the main track input (DCC) and the reverse loop input power (DCC) when operating in analogue mode. I know the module may be both analogue and digital capable, however, power input is opposite depending on powering method being used. Digital takes power from the main track and powers the loop, while analogue takes its input from the loop and powers the main track polarity.

 

[don9GLC]

Hi Tim,
In theory a reverse loop module wired for analog operation could be used on a DCC layout, but in practice this is impracticable with 'of the shelf' items.
Basically with analog your train goes (forward) in a certain direction, say from left to right when you turn the speed control to the right. Once the train has got round a reverse loop you still want it to go forward when you turn the speed control to the right so you have to reverse the supply to the main line. Otherwise it would just reverse back into the reverse loop when it had got round and probably end up shorting the supply!
You could do this with DCC but you would not be switching just one section of the main line. You would be switching the whole central station output, which could be as much as 12A, So you would need expensive high power electronic components to switch the supply. That's why DCC reverse loop modules switch the reverse loop which will only have one train.

One simple way of connecting a reverse loop for both analog and DCC operation is to do it manually. This means stopping each analog train to switch the track supply to the loop (with a DPDT switch, or even a relay linked to the turnout) then reverse the controller. DCC locos can continue with just the switch being thrown with perhaps a slight stutter.


In my experience most miniature relays operate with DC applied to their coils. It is possible to get relays that operate with AC coils. They tend to be larger for power circuits. If I understood correctly your defective central station has a DC output and also operates the sound section of your decoders. In my view you do not have enough information to tell if any or all of your relays will operate with a normal DCC supply.

I have checked my Massoth central station at no load. There is no dc output when loco 0 (analog) is at stop. With the system set for a track voltage of 23V I measure 20.5V roughly on a true rms meter. The DC output when loco 0 is at full speed is around 16V. At a setting of 15V track voltage I get 14V true rms.

You seem to have made good progress in finding solutions to most of your dual operation problems, and I'm not sure that I can offer any further useful advice, but it sounds very much like your DCC central station needs to be repaired.
Regards,
Don

 

[Tim Brien]

Don,
thankyou for your extensive reply. I really need to await my new DCC system (about a week) and then purchase a loop module and put theory in to practice.