I know that most DCC decoders have the ability to run on DC but have never made any use of it. However I always assumed that one had to turn the function ON.
I have, rather late in the day, discovered this is not the case. The DC function is on by default. Furthermore decoder manufacturers recommend that if you rarely, if ever, use DC then it is a prudent safety precaution to disable the DC function.

The reason being that if you have a short and the power is returned the decoder has a split second in which to determine whether to use DC or DCC……if it guesses wrong and opts for DC then unexpected results occur. Typically the loco runs off at top speed like a headless chicken and there is a risk that the Cv values will have to be reset. This has happened on occasion in the past….I had no idea why it happened…put it down to an act of god!

Its actually very easy to turn the function off …..its controlled by Cv 29…….however the actual bit containing the switch seems to vary by manufacturer…..with Lenz it is Bit 3 and with Zimo Bit 2…….so a little care is needed otherwise a couple of keystrokes set the relevant Bit to zero and the function is disabled.

Every day one learns something new!

An interesting post John, particularly so, as I only learned today that some 'factory fitted' DCC locos can run on either DCC or DC without adjustment, as advised in the Dapol instruction booklet for the Mogul.
   
  I will check again tomorrow as to the exact wording to see it any warnings are given regarding short protection occurrences!
   
  It's a never ending learning curve                                                   
   
  Bill
  

I dont believe the shorts create anything fatal but if you only use the function occasionally it seems to make senset o turn it on only when required
Both Lenz and Zimo can run on either DC or DCC …..the technology sounds quite sophisticated…..you could have a circuit…. half powered by DC and the other by DCC with a loco performing uninterrupted circuits….the decoder seamlessly recognising and switching to the change in supply

Keep well

Hi John,

I don't have the reference to hand and it will take some digging to find but DCC Concepts told me to have DC off (CV 29 bit 3 =0) or it interferes with functioning of their stay alive. As I don't need DC on I do this by default on all my ZIMO chips.

Running like crazy with a stay alive is one symptom of having DC on if main power disconnects.

Colin

[user=2170]Colin W[/user] wrote:

Hi John,

I don't have the reference to hand and it will take some digging to find but DCC Concepts told me to have DC off (CV 29 bit 3 =0) or it interferes with functioning of their stay alive. As I don't need DC on I do this by default on all my ZIMO chips.

Running like crazy with a stay alive is one symptom of having DC on if main power disconnects.

Colin

Hi Colin

Thats is correct, the appropriate bit…..3 in the case of Zimo has to be set to 0 to switch off the DC running function.

I hadnt thought about the impact of this on Stay Alive…..it makes perfect sense and yet I have not experienced anything untoward with the dozen or so locos that I run regularly with Zimo and SA supercaps…..although I do have a lifelink safety device inserted between chip and SA. I will ask John Gymer of Youchoos about it.

Nevertheless  you have confirmed my decision to work through my roster and turn off the function on all locos

Keep well

Interesting topic John.  Myself rather than trying to fathom bits and bytes I use this simple online calculator posted by the 2mm society.                                       Cv 29 Calculator Link. 

  You can use it to work out the value you need to put in to CV 29 for various results. OR use it to backwards calculate what the Cv 29 Value IN one of  your decoders stands for. Very handy tool which keeps brain hurt to a minimum for myself when trying to work out what value I need ! :thumbs

Cheers


Matt

And Forgot to say,. Yes I make it a Habit to switch DC off to help avoid runaways and random cv re setting if there is a short  :thumbs

Thats a handy calculator…… thank you

…….but I am a bit confused….I dont think that that Zimo amd Lenz use the same bit for DC control……I have checked the manual half a dozen times……Lenz says bit 3 and Zimo bit 2…….this affects the decimal total……and I have disabled DC using these bits?

Glad I stumbled on this

Keep well

[user=434]John Dew[/user] wrote:

Thats a handy calculator…… thank you

…….but I am a bit confused….I dont think that that Zimo amd Lenz use the same bit for DC control……I have checked the manual half a dozen times……Lenz says bit 3 and Zimo bit 2…….this affects the decimal total……and I have disabled DC using these bits?

Glad I stumbled on this

Keep well

 

John,

Confusion arises because Zimo counts its Bits from #0, so #2 is in fact the 3rd setting (value =0/4) just as for other manufacturers. see.

https://www.nmra.org/sites/default/files/standards/sandrp/pdf/s-9.2.2_decoder_cvs_2012.07.pdf

you may need to search nmra CV values to bring up this document

Thanks Colin…….. that explains it.
I am turning DC off by using my Lenz system so I just have to select the bits# to set it off but I was concerned if I wanted do it by resetting Cv29…..so the deduction is a constant number….4

Thanks again

One advantage of NCE is that it asks you in English when setting up the decoder if you want to disconnect/turn off DC.
Don't have to concern oneself with CV29 & bits.

Glad I can still strike a bit of confusion now and then John ! 
   Sol I've just treated myself to a Sprog III AN Esu Decoder tester and brought back in to commission a motion Tablet running Windows 10. Now I can test Decoders and set them up, in or out of a loco, on a small test track with rolling road, in the comfort of a warm front room rather than having to disconnect my Z21 and bring it in from a baltic workshop to do the job.

  Now getting to grips with JMRI Decoder Pro and I see THAT has a simple tick box for DC on or off. It's been worth it as I've already been able to read, Identify and resurrect three decoders that were thought dead but had just been scrambled at some point in their life.  :thumbs



Cheers

Matt

Like SOL i use NCE so setting DC off is very simple.

Every loco of mine excluding the only ESU Loksound, have Zimo decoders, sound and silent. I always turn off DC running because of the reasons mentioned by others.

I don't know if I've put this up before but if you have large capacity stay alive Cap's, your loco's will run on until either the signal is restored or the cap's run out of steam… or diesel. I have the tiny Hornby 0-4-0 diesel shunter with a stay alive and it will run for 20 seconds with no juice at all; this ain't good. With Zimo decoders, sound or silent you can go to CV 153 and set the run time to a time of your choice in tenths of a second. Mine are set to 20 tenths, so a nice short run without a signal, but wait there's more. At 2 sec's the decoder goes into it's preset braking distance, not a dead stop. If like me, you use large braking distances because you, like me like to use the F2 brake key, you can go to CV 111 and once again it's your choice, but I enter 1. I then get a dead stop after 2 sec's.

You need to be up to date with your decoder versions for this to work and some of the older smaller decoders like MX621/620 can't be updated sufficiently for this.

Hope this helps someone.

The bit used to allow DC analogue operation is one of the few mandated (if provided) by the NMRA standards.

ZIMO decoders can, however, operate Stay Alive caps correctly on DC analogue, so the problems encountered with other brands will not apply. That John uses mainly ZIMO decoders probably explains why he's not had such a problem. Sometimes, the advantage of buying top quality decoders is not fully understood until the alternatives let you down by lack of in-depth design and development.

I usually turn off DC analogue option as I'm DCC only, so the provision makes no sense for my useage.

However, all UK factory sound fitted models have the DC option enabled by default, since that's the only way DC only users will ever get any sound (UK practice is that on DCC, sound is switched on with F key 1).

If you need to have the ability to run both DCC and DC analogue without changing the value in CV29, you can guard against the 'run aways' John described when using ZIMO decoders, by setting CV144 = 128. (I got that tip from  ZIMO's head programmer last time we met).

Peter, CV111, you've been doing some homework I see - well done!

Yes, you can set up the way the emergency stop (as opposed to manual brake key, whish can be adjusted with CV349) operates on ZIMO decoders with CV111*. Low values give more rapid stopping, larger values a more gentle effect. This was introduced as, for some users, immediate stops caused major derailments, so, as Peter says, you have the choice to set it up how you wish.

*Your decoder will require firmware version V37.28 (released July 2018) or later for this feature to be available. Another advantage of quality decoders is the ability to upgrade their firmware to take advantage of new features. This means that unless you have one of the very few older ZIMO types which are limited in this respect by the hardware, you can download the new software for free from the ZIMO website and load it to your decoders to make them, literally, good as new operationally. You will need access to a ZIMO update device or Roco Z1 to do this or know someone who can do this for you.

Best regards,

Paul

You flatter me Paul. I know what I know from you and Arnold at Zimo. I just pass it on when I can.