I've be asked many times when demonstrating DCC sound at shows what performance can be expected from decoders running on pure DC.

So I've put together a few notes to explain how things work, using ZIMO decoders as my example. (I have also addressed operating non-sound decoders on analogue too, for completeness).

I've also added some notes on Stay Alives on analogue since there is a link between sound performance and back-up power.

  Driving ZIMO DCC decoder equipped models on analogue (DC)
   
  I am most familiar with ZIMO decoders so this advice applies specifically to this brand. Much, if not all, may equally apply to any other brand. To avoid repetition or need for technical explanations, I’ve used the terms ‘power’, ‘voltage’ and ‘current’ very loosely to mean ‘turning the control knob’. I am aware of the difference, but it has no direct relevance to the explanations below.
   
  All ZIMO DCC decoders can be set to operate on DC. It is normally the default state.
   
  When this condition is set and the decoder detects power without a DCC signal it automatically switches to analogue control.
   
  However, it is important to remember that the decoder still controls power to the motor plus any lighting or sound which may be fitted. It’s not as if the decoder ‘opts out’ and allows analogue power to reach the motor directly.
   
  The decoder will interpret a change in voltage as an instruction, but needs a minimum to be able to operate at all. For the sake of discussion, let’s assume that will be 2.5v
   
  If you increase the power from your DC controller from 0v to say 2v nothing detectable will happen.
   
  If the power is increased to say 3v, the decoder will illuminate any lights which are programmed to operate when on DC.
   
  If the power is increased to say 5v and a sound decoder is fitted, the sound will play. In the case of diesel sound projects, this will normally include a start-up routine, following which the Standing or Idling sound will play continuously until further voltage changes occur.
   
  If the power is increased to say 7v the motor will begin to turn and the model will move. If there is a sound decoder on board, the sound project will be triggered to change the sound from Idle to another appropriate engine sound. This may also be accompanied by other automatic sounds such as a Start Whistle or Horn and a Brake release sound. (this will determined by the author of the sound project).
   
  NOTE. It’s important to remember that these thresholds exist (though not necessarily the exact voltages) as they will give you a surprising degree of control given the simple nature of DC controllers.
   
  Further increases in voltage up to the normal 12v DC maximum will increase the motor speed and trigger further engine sound changes as appropriate. (Usually increased revs with diesels or faster ‘chuffs’ with steam locos).
   
  Since the operational range is now restricted to the portion of the control knob’s movement representing 7v-12v, movement will need to be made with extra care in order to control speed and sound.
   
  Reducing power has the reverse effect. The motor will slow down and any sound will spool down or slow until the voltage is below the threshold for movement. It may well be that in order to stop the model from moving the actual voltage can be reduced to less than the 7v needed to start movement.
   
  Be that as it may, there will come a point at which the motor is no longer powered, but the sound continues to play (Idling) and any lights remain illuminated.
  If power is reduced further, the next threshold will be passed and so the sound will cease. In this case it will ‘fizzle out’ as there will not be sufficient power available to drive the decoder’s amplifier. (But see ‘Stay Alive’ below).
   
  At this point, the model will be standing motionless and silent but with lights illuminated.
   
  Reducing volts to zero or isolating the track will cause the lights to extinguish.
   
  Putting all this into practice requires just that. With practice you can achieve remarkably good control of lights, sound and motion.
   
  Good luck.
   
   
  Stay Alive
   
  Disclaimer: The use of Stay Alive technology should not be considered as a way to avoid paying close attention to track laying, track wiring, cleaning or other maintenance tasks. However, as the use of Stay Alives is not detrimental to models running under perfect conditions we would all like, but kick in automatically when used in environments which are less than ideal, some would argue that they are a useful back-up to have.
   
  A commonly used method of enabling models to run without hesitation on poorly laid, cleaned or maintained track employed in DCC equipped models is to add capacitors which are capable of providing temporary on board power. These are often referred to as ‘Stay Alive’ or ‘Keep Alive’ caps. ZIMO calls them ‘Electronic Flywheels’.
   
  These automatically take over when track power is lost and continue supplying power until their reserves are depleted, in which case the model will stall, or the decoder senses DCC power again in, which case the model will continue to run under full control and the Stay Alive will be recharged ready for any further power disruptions.
   
  The degree of assistance which can be provided is related to the capacitance of the Stay Alive capacitor(s), although the duration can be reduced by instructing the decoder to continue running the motor for a fixed duration without power. On ZIMO that’s achieved with CV153. If the model does not reach track with a DCC signal within that limit, it will stop moving.
   
   
  So with all these benefits why not use Stay Alives on analogue?
   
  There are several basic hurdles in the way of this which arise from the differences between DC and DCC.
   
  The fluctuating power on DC used to control speed and direction makes it difficult to arrange for the charging of these capacitors (which are polarity sensitive).
   
  There’s no way that a simple DC model can determine whether a reduction in power has resulted from a power outage, dirty track or a deliberate and controlled act by the operator.
   
  There may be some other technology which can overcome these issues, but I don’t know what that could be.
   
  I do know, however, that DCC decoders can control the charge/discharge of Stay Alive caps, and in some cases be able to limit their duration. I also know that DCC decoders are able to run successfully on DC.
   
  ZIMO decoders are the only brand that I know of which are capable of doing both of these at the same time. Due to their advanced on board software, they can distinguish between incidental loss of power and a controlled reduction for speed regulation purposes.
   
  This means that ZIMO sound decoders can regulate Stay Alive caps equally as well on DC as on DCC.
   
  (Other brands are either silent on the issue or like Lenz and ESU specifically point out that their Stay Alives will not operate on DC).
   
  This also means that normal operation of sound on DC is enhanced with the addition of Stay Alive caps.
   
  In the driving tips above, I referred to sound which would ‘fizzle out’ if the voltage was reduced below the ‘sound’ threshold. This was because the trigger to play the ‘shut down’ sequence occurred at the same point as the decoder’s amplifier was shut down due to insufficient power.
   
  With a Stay Alive fitted, this is different. The decoder will be triggered to play the ‘shut down’ sequence, but as the Stay Alive will now supply power, the amplifier remains operational and will play the sequence in full (if its capacitance is sufficient). Happy days.
   
  So, it is now possible to halt the model with the decoder still playing Idling sounds, after which by a further controlled reduction in volts, the engine sounds can be shut down as they would on DCC whilst still maintaining illuminated lights.
   
   
  If that all sound too good to be true, you can view and hear it in action here:
   
  https://youtu.be/fbf-liTuswM
   
  Best regards,
   
  Paul
  

If anyone is going to Warley show this weekend, swing by the Hornby Magazine Layouts and you will see and hear a couple of 009 sound-fitted locos operating on analogue control. (Heljan Manning Wardle and Bachmann's delightful Baldwin 4-6-0).

Paul

Impressive  :thumbs

What DC controller did you use Paul, as I've read some types don't work very well with a DCC chip.

Feedback controllers for example.



Ed

Thanks Ed.

I have a Spectrum Magnum which I bought second hand from my local  railway model shop to test DC models before sound fitting. I know  nothing of it's specifications, but I think it's quite old and looking just now, I was surprised to  find Bachmann Industries Europe ltd printed on the underside, so I'll  ask them for details.

Regarding permitted controller types?
Well, let's just say that not all decoders are created equal, and there's a good reason why I only use ZIMO after 20 years or more experience of DCC.

Maybe the reports you heard/read were about other brands?


The ZIMO Small Decoder Manual says that FeedBack controllers are OK for their decoders, see below:

Extract:

3.5 Analog operation
All ZIMO decoders are capable of operating on conventional layouts with DC power packs, including
PWM throttles, in analog DC as well as in analog AC (Märklin transformers with high voltage pulse for
direction change).
To allow analog operation
CV #29, Bit 2 = 1
must be set. This is usually the case by default (CV #29 = 14, which includes Bit 2 = 1), but analog operation
may be turned off in many sound projects (sound decoders). It is recommended to turn analog
mode off when operating strictly on DCC!
The actual behavior during analog operation, however, is strongly influenced by the locomotive controller
(power pack). Especially in conjunction with a weak transformer, it is easily possible that the track voltage collapses when the decoder (motor) starts to draw power which, in the worst case, may
lead to intermittent performance.
There are some adjustment possibilities for analog operation where motor control and function outputs
are concerned; these CV’s can of course be read-out or programmed only with a DCC system or
other programming device.


 In earlier versions of the manual there used to be a warning to avoid using high frequency track cleaners (e.g.Relco) which may damage decoders. It may still be in there, but I've not spotted it yet, and as there are 79 pages of jam-packed info in the manual it will take more scrutiny. My advice would be to avoid these devices when operating decoders.

Best regards,

Paul

Hi Paul,

Nice review. The issue of charging the capacitor with varied voltage would I think apply to an older system. What happens with a PWM DC controller where the voltage remains constant but the duration changes (that is what goes on in a decoder running in DCC). Just takes longer to charge? 

I have no idea how fast a capacitor charges. My Soundtraxx Tsunamis took about 10 minutes, judging by the time it took the decoder to start responding to signals.

I suspect thinking battery rather than capacitor would get rid of these problems. 

Nigel

I think it's fair to say that my gast was flabbered when I watched Pauls video of the R&H 48DS being driven on DC with sound. Amazing.

Nigel,

Thank you for your appreciative comment.

I suspect 'thinking battery' closes one's mind to that which I have just demonstrated works in the real world. Your imagined problems with capacitors that you propose batteries would solve simply do not exist. It's like a 'straw man' argument.

The main problem with charging capacitors from analogue arise from the fact that to change direction, the polarity of the rails must be reversed. Since the capacitors and supercapacitors used to provide stay-alive functionality are polarity sensitive, they would, when charged, explode at the next change of direction without some additional control circuitry. Same reason it would not be good for a battery, I suppose.

I've no idea about Tsunamis, they've never had a good enough motor control for me to use in my locos, (or any useful UK sounds) but the supercapacitors I fitted to the Hornby 48DS take a few seconds to fully charge. None of that's really relevant though as stay alives do not need to be fully charged, or even charged at all,for the decoder to begin to respond to signals, so you can start running immediately. The caps will charge up whilst the model is running on track power.

I've investigated battery and radio control, but knowing what I do I'm just not interested in all the bother of finding space needed for using batteries - too much accomodation required for ancillary kit and the batteries themselves to be anything like as useful or versatile as a DCC decoder and a decent stay-alive (for DC or DCC) in my view.

I'll post a video shortly of my 009 gauge Manning Wardle which is equipped with a sound decoder, speaker and stay alives. This model has been operating all weekend at Warley National show (on analogue). Try getting a battery and the associated control equipment into one of these models.

Since small interuptions in track supply normally require relatively small amounts of power to overcome, and the technology I've illustrated is more than sufficient to cope, I believe using batteries is overkill. A useful technology for those for whom it might be useful, perhaps, but not the answer for most of us.

Here's how supercapacitor technology is being used in it's logical extension - real trams running 5k on a 30 second recharge at station stops.




I think this would be a far more useful way to take the 'dead rail' idea forward to practical mainstream modelling applications.

Imagine, supercapacitor equipped models, capable of continuing at the same speed for, say, 30cm, track powered everywhere except at tricky areas like crossovers and points which remain electrically isolated (dead rail). The model uses on board power from the supercapacitor Stay Alives to cross these dead rail areas and when on all other track, charges up the supercapacitors ready for the next dead section.

Oh, wait a minute, isn't that the same thing that would happen on poorly laid, poorly wired and poorly maintained track work? Haven't we talked about this before? LOL.

I'll stick with what I know works and I can demonstate working.


So, until something comes along with genuine advantages for the models and scales in which I have an interest, it'll be DCC with stay-alive supercapacitors for me all the way.

Best regards,

Paul

Hi Paul,

 "Straw Man"? Hmm. An intentionally misrepresented proposition that is set up because it is easier to defeat than an opponents real argument?  Or: A person regarded as having no substance or integrity? I'll take the first. Although I fail to see where the misrepresentation is. Or what the argument is. You touched on the solution with the dedicated charging station for a tram. Same goes for a LiPo. Which is a viable alternative to a capacitor if there is room. BTW, I don't criticize Zimo decoders. Rule I. 

Not sure who has the closed attitudes here. I have used both capacitors and LiPo batteries.  DC operation has zero interest for me, so I cannot make any real comments on the advantages of one decoder brand versus another in this setting. There are positives and negatives to both capacitors and batteries. And I am not the one conducting research to see if there is an unmet need or market for a DC capacitor. I suspect the real Straw Man is the proposition that unless you have a capacitor your locomotive will not run properly. Bit like "your car engine will run better with premium grade fuel", when all it needs is an injector service.
I just thought I would alert members to the fact that dual mode DCC/DC sound decoders have been around for some time (at least 2009). ESU, QSI, Sountraxx, MRC….

Nigel

Edited after my initial response.

Nigel,

I've shared evidence based information in good faith which some may find useful or enlightening.

I've nothing further to propose on this issue.

Best regards,

Paul