NCE PowerCab vs Roco MultiMaus

[Butler Henderson]

I have just checked the peak dcc voltage of my Multimaus using the Roco brick transformer, through a diode shunt in one leg of the dcc feed to reduce the voltage and discovered it was around 18v, but when I disconnected the mains sometimes it dropped straight to 0v and on other occassions first peaked at around 28v before dropping away. Decided to make use of a surplus 3.9A laptop power supply instead.

[Phil S]

When you say you 'disconnected' the mains  .. are you saying you unplugged or switched off the incoming mains supply to the transformer? - the result would depend on when in the mains cycle the interruption took place, and is 'unpredictable' ... for all transformers, as they are energy-storage devices, which store 1/2 cycle of mains energy as magnetic field, which in turn is then transferred to to secondary winding, and extracted as a larger current/lower voltage.

 

(A switched Mode Power Supply is more energy efficient because they chop the incoming 50-60Hz mains into a higher frequency ac signal, which is then passed to a smaller, more efficient transformer designed for the higher frequencies (eg a core made of dust, and not laminated sheets) and in which less energy has to be stored in the magnetic field (per half cycle) - which is why it can be smaller ... and smaller windings have lower resistance losses, all of which improves efficiency .... and then it is followed by electronic regulation of the output voltage, with additional protection against overloads, and a 'soft-start' to ramp up the voltage initially, avoiding huge surges .... although some SMPSs are not very good at limiting the mains input surge !!!

 

If your reading of '28V' volts was only 'momentary' then I wouldn't worry too much as the measurement process in a digital meter makes assumptions about waveform shape in ac, and expects 'smooth' dc.  Only a scope would give reliable transititory values.  However, that said, it is a further indication of why SMPS should be used for all power supplies - not just the Multimaus/Amplifier

 

IF your meter reading was on the output of the transformer, and by disconnecting the Amplifier, then it represents the Open Circuit voltage of the transformer, with no current being drawn - (no power-transfer) - this will always be higher 'than expected', as, with all transformers, the quoted value is when the FULL LOAD is being taken ... and the voltage drops under load due to internal inefficiencies.  

 

Regulating the output of 'Converntional' 50-60Hz transformers is not very efficient, and is down to the following device which rectifies it to dc ... where any regulation would typically be with linear devices .. resulting in more waste heat.   IF a switched mode regulator was used, then enrgy efficency could be achieved ... but this is usually a more expensive component:

EG When Raspberry Pi designed the Mk1 Pi, the regulator used was Linear, because it was a few cents cheaper: the result was more power supply problems, and heat and wasted energy  (but, a product which WAS able to go on sale and become a success!)  The success of the design has meant that components are bought in bigger bulk (with millions, rather than 2,000/10,000 made!), and the current model now has a switched mode regulator ..more efficent, and easier on power supplies... the world is saved 8-)

 

You also mentioned 'PEAK' voltage .... Peak is 1.4 x the RMS value quoted, and the rms is nearest to the dc equivalent.   28V pk is correct for a 20Vrms.

[Vistisen]

I own a Powercab, and a SPROG II which I use for programming. I have only used DCCfor a couple of years. But a long time ago I used the Hornby Zero1 system which had a feature I sorely miss on the powercab. If I used the Hornby to start a train running and then changed to another locomotive and controlled that, I'm sure that on switching back to the first loco it 'remembered' the speed setting. Whereas on the Powercab when ever you select a locomotive, even if if was just used a few seconds before, It always sets the speed to 0 on selection, and the locos skids to a halt, It might well be me that is missing a trick, but even it deos strike me as an obvious feature to have

[Phil S]

The option to 'take over' or 'retake control' of a loco is sometimes a setable option, and in others, a permanent feature ... perhaps in others, not a feature option at all 8-(

 

With a Massoth Navigator Handset (popular in G Scale - '2 handsets in 1' with 2-way wireless so it can display status, another loco, one selected, can be 'taken over' by turning the speed knob 'through' the last / current speed of the loco .... this is aided on the Massoth Navigator by the chnage of colour LEDs lighting the knob.

 

On a Multimaus - and I use them in multiple - ANY controller can take over ANY other loco ... simply by slecting its number (at which point, the LOCO DISPLAY FLASHES on the affected handsets) ... BY TURNING THE KNOB you take control, .... and the same applies to an 'abandoned loco' from the same controller...   I have most of my 'accidents' with locos left on hidden sidings, and I find I have changed to the next loco, without checking that the old loco was in 'Pause' / Zero speed setting ..... but creeping imperceptably slowly towards a point, at whuch it meets another train....

 

I recall a similar setting was somehow optional on LGB MTS .... a setting as to whether trains could be taken over if they were moving, or only if theywere at speed zero ... but I have not set or used this for many years.

 

Then, when using Software ef RR+Co / Rocomotion JMRI or ROCRAIL etc ... there is some variation between systems as to when and how easily control may be transferred between a 'real handset' and a computer throttle.

 

Another important aspect, is as to how many locos may be 'active' on the controller at any time ... regardelss of physical handsets, orr current limit ... but whther their data (speed, functions etc) are still included in the cycle of transmitted data.   This was 8 Locos on MTS, and user selectable on Massoth,and 32 locos on Multimaus, but 64 on Multimaus Pro, from my observations .... the latter resulting in a slower respinse cycle, whilst allowing more locos to be left with lights on and sound on .... but with some DECODERS this can also be remembered by the decoder itself .... which can be tested by issuing an ALL STOP and restarting the track power....

 

Have you tried the 'turning the knob' takeover method with the PowerCab??? (to see if it works)

[Butler Henderson]

If your reading of '28V' volts was only 'momentary' then I wouldn't worry too much as the measurement process in a digital meter makes assumptions about waveform shape in ac, and expects 'smooth' dc.  Only a scope would give reliable transititory values.  However, that said, it is a further indication of why SMPS should be used for all power supplies - not just the Multimaus/Amplifier

 

Hi Phil

 

I used multimeter set to dc in association with the peak dcc circuit shown on http://www.wiringfordcc.com/track.htm

[Phil S]

Hi Phil

 

I used multimeter set to dc in association with the peak dcc circuit shown on http://www.wiringfordcc.com/track.htm

Phil: This circuit does what it says: it measures the PEAK voltage  there is nothing to discharge the capacitor .... and if you are using it to measure the transformer output, and not the dcc track as the circuit intended, then you will be measuring the peak of the sinewave voltage: 28V 0-peak is 20V rms which is what I would expect when NO LOAD is connected ( the high impedance of the meter and circuit not counting as a meaningful load. ) ....This wil result in 18Vdcc on the track, which is within spec, however, the use of a regulated output from an SMPS at 18V dc whether the current is 0 or maximum, will result in 16Vdcc 0-peak voltage (as measured by a RRampmeter, or from a 'scope) - which is an optimal value for use (exceptt perhaps for some N gauge users such as Graham Farish ... Note that Roco / Fleischmann supply these quite happily with all their starter sets in H0, TT, N and HOe.  ... but thankfully now with SMPS regulated supplies ! 8-)   

 

There are times when the small differences should be considered - such as when using Strips of '12V LEDs' for lighting .... as these are non-linear in their power consumption, and the current through them DOUBLES if the applied voltage increases from 12.0V to 14V .. and the extra warmth is noticeable. As a Rule: resistance values should be chosen for the WORST CASE scenario - eg the off load voltage if unregulated; and so I allows for 24V for G Sale (as it is 0-24Vdc in analogue, and I use 18-22Vdc SMPS supplies to the Roco or Massoth Controllers respectively). ALSO the duty-cycle needs to be considered - is it 100% ON or only 50% ... in which case the power is halved .... Infra Red Remotes, for example, apply a much higher current for a very short time, when transmitting ... but the duty cycle is so low, they are okay.

 

A final observation: The 'final voltage' to the motor - when averaged - depends on the speed at which you are running your train.... a 16Vdcc track voltage and 14Vdcc track voltage can both run a train at a full 12V .... the 16V system on for about 6/7th of the time, and the 14Vdcc system for 100% ... whilst a 12Vdcc track voltage will never get past about 10V to the motor ...... this may affect HST Expresses more than Shunters...

[ExPatBrit]

I own a Powercab, and a SPROG II which I use for programming. I have only used DCCfor a couple of years. But a long time ago I used the Hornby Zero1 system which had a feature I sorely miss on the powercab. If I used the Hornby to start a train running and then changed to another locomotive and controlled that, I'm sure that on switching back to the first loco it 'remembered' the speed setting. Whereas on the Powercab when ever you select a locomotive, even if if was just used a few seconds before, It always sets the speed to 0 on selection, and the locos skids to a halt, It might well be me that is missing a trick, but even it deos strike me as an obvious feature to have

From the Powercab manual:

 

"RUNNING TWO LOCOMOTIVES WITH ONE CAB

 

#1 Select the first locomotive you wish to run (SELECT LOCO followed by its address then ENTER).

 

#2 Press RECALL to store this locomotive in one of the internal recall “slots” of the cab. The display of the cab will now show a locomotive of 000.

 

#3 Select the second locomotive and start running it.

 

#4 By pressing RECALL you can toggle back and forth between the two different locomotives. At any time you can select a new locomotive “over the top” of any locomotive already on the display. The existing locomotive will be forgotten by the cab with the new one taking it’s place. The one in RECALL will remain available for recall."

 

Possibly you're missing the use of the RECALL button?

[Butler Henderson]

Phil: This circuit does what it says: it measures the PEAK voltage  there is nothing to discharge the capacitor .... and if you are using it to measure the transformer output, and not the dcc track as the circuit intended, then you will be measuring the peak of the sinewave voltage: 28V 0-peak is 20V rms which is what I would expect when NO LOAD is connected ( the high impedance of the meter and circuit not counting as a meaningful load. ) .

No, I was measuring the voltage on the track / dcc bus to try to find out why two accessory decoders had blown up.