Z21 with a Booster

[TartanTrax]

Hi again Despatcher,

 

I'm sorry but the kindest word for the reply Roco sent you is Balony.

 

I will explain: RailCom is a term for bi-directional communication between the DCC decoder and the command station (or the computer if you use a PC to control your trains). In order to allow the decoder a chance to have its say, the command station will produce a very brief short circuit (less than half a millisecond long) at the start of a packet transmission (called a preamble) where the left rail is effectively connected to the right rail. This period is called a cutout and is too short to be recognised by the command station as a short circuit. Decoders are required in terms of the DCC spec to cope with short power interruptions (in case your locomotive drives over a spec of dust or an insulated track joiner etc.) RailCom (patented by Lenz) seems to get the blame for a lot of things (the forums are full of examples) but it is a fact that, provided RailCom is implemented in compliance with the spec it will never be the cause of any problem you may be experiencing. Problems will occur due to decoders being outside of their specifications or if the Z21 is implementing RailCom outwith of the spec. It is a fact that driving a locomotive from an area with a cutout to an area without a cutout causes absolutely no problems at all. (I know because I've done it often.) Furthermore Roco claims on their website that the booster you are using is compatible with the Z21. I must assume they tested this rather than just printing something based on optimism. RailCom when switched on on the Z21 can be used for automation because the RailCom data will tell the Z21 where the locomotive is, which way it's travelling and at what speed so not a bad option to have. It is also possible to add a cutout to your booster should you wish.

 

Anyway, the short answer is whatever the problem is, it probably isn't RailCom. I notice you live in Kent which is not too far from where we are at the moment so if you want to have a chat or possibly meet to see if we can solve the mystery, feel free to contact me on the forum messenger application and I'm sure we can make a plan.

[TartanTrax]

Hi Dutch,

You can disagree with me if you want but you are still wrong. When Bernd Lenz wrote the RailCom spec he did a very decent job of it. (Likewise when he wrote the DCC spec.) One of the things he needed to cater for was the possibility that a train could pass from a section with a cutout to one without a cutout and this should not cause any problems. Moreover, what if a train were to park accross such an area with lit coaches? That would mean an area with a cutout would be connected to one without for potentially very long periods of time. It was for this reason that the spec stipulates that any device generating a cutout, should it detect DCC during the cutout, it must instantly cease to generate the cutout until this condition no longer exists. In fact if you reread your posting up to the place where you said "acts accordingly" and then inserted "stops generating the cutout to prevent a short circuit" you would have been 100% correct. If the Z21 doesn't do this I would be very surprised indeed as it isn't technically difficult and it is quite clear in the spec for RailCom that this must be done. A device that fails to do this should be regarded as broken.

 

As regards boosters, I am fairly sure that none of the Roco boosters are RailCom compatible. If we assume that the Z21 may indeed be broken as described above, this still leaves one with a few options: 1) If not wanting to use RailCom, simply switch it off on the Z21 and make do without it, 2) Use a RailCom enabled booster connected to the Z21. (I have seen some very reasonably priced boosters from Tams on Ebay.) or 3) attach a RailCom Cutout Generator to the track feed from the Roco booster. I would suggest doing the first one for now as it's the cheapest and the other options will always be available at a later date should he want to use RailCom after all.

 

If he still gets short circuits despite switching RailCom off, then RailCom is not involved at all but something may be preventing the voltages from his two transformers from floating. From his description this is what I suspect is the case but without knowing more regarding his wiring it's hard to guess where things may have gone pear shaped. 

[Despatcher]

I have had another reply from ROCO today! Amazing! It says much the same. It does though seem odd that the recommended Booster in the Z21 Manual is not actually totally compatible. I don't suppose they will do a refund/swap when the new ones appear! Although I am still really not sure what RailCom is and if I am missing out or not!

 

I need to play a bit a bit more but turning RailCom off enabled a loco to cross the gap. I need to check again at the weekend as I am working today and tomorrow and time is a bit sparse. I just need to check that I did in fact, in my hurry, turn the Booster feed to the Programming Track off and the feed for the Programming Track back to the Z21 before I ran the loco back over the gap. I have installed a two way switch as suggested and need to make sure before I confirm to the wider readership that the problem is now solved.

 

I also discovered that if my IPaD is not attached to the Z21 via the dedicated router then the Z21 "app" claims that RailCom is off. However when  my iPad  is connected to the layout through the router, I checked again and noticed RailCom was on and needed turning off. Fascinating. I'm still glad I bought the Z21 as I am learning many new things and it is making me really think, which for someone of my age is no mean feat! I also enjoy being part of this community even if I don't totally understand all the replies. I've said it before and I will say it again, RMWebs problem solving capability is immense.

 

Anyway, enough of that, for those who are interested, here is Roco reply number two:-

"thank you for your Z21-email-question! Please switch off "RailCom" at the Z21:
Temporarily the booster sends the DCC-digital-signals during the reserved time
of Z21 for RailCom-feedback. This voltage difference is recognized as short-circuit.
After appearance of a new, RailCom-abled generation of boosters you can use
RailCom all over your layout!

With kind regards

Modelleisenbahn GmbH
Your Roco Service- and Digital-Teams

www.roco.cc
------------------------------------------
Modelleisenbahn München GmbH
Triebstr. 14
80993 München
Deutschland
AG München . Handelsregister München B159908 . Firmensitz München
Geschäftsführer: Mag. Wolfram Haböck, Mag. Roland Weissenbacher"

[PaulRhB]

Yes I've noticed that the controls screen for points doesn't stay where it was when the app closes it all comes back correctly when connected. Interestingly on the iPhone you can scroll the throttle up and down when disconnected and get green bars but on the android tablet it only does so when connected! At least it does what it says on the tin when running

Here's a good description, really if you need feedback on certain things for automation and interlocking. I guess the ability to simulate fuel and water levels will interest some but its not necessary if you just like playing trains

http://www.lenzusa.com/techinfo/railcom.htm

[Timsytanker]

Could I use the booster just for points and signals?

[Adamphillip]

ok, resurrecting this thread from the dead, so, I know the reason for this, the Z21 and the booster are most likely running at different amps, as you loco crosses the gap it trips the over amp protection in one of the devices

[RFS]

36 minutes ago, Adamphillip said:

ok, resurrecting this thread from the dead, so, I know the reason for this, the Z21 and the booster are most likely running at different amps, as you loco crosses the gap it trips the over amp protection in one of the devices

 

No that's not the problem. The overload cut-out will only trip if the current draw exceeds the maximum and that won't happen with a loco simply crossing the gap. It needs a system short to do that. Until recently, I was running my layout with in two power districts with a 5-amp booster in one and a 3-amp booster in the other. What's important though is that both boosters provide the same track voltage. 

[Adamphillip]

6 minutes ago, RFS said:

 

No that's not the problem. The overload cut-out will only trip if the current draw exceeds the maximum and that won't happen with a loco simply crossing the gap. It needs a system short to do that. Until recently, I was running my layout with in two power districts with a 5-amp booster in one and a 3-amp booster in the other. What's important though is that both boosters provide the same track voltage. 

yeah, when using DCC boosters all the boosters need to be the same amp otherwise the 5-amp booster will trip the 3-amp booster's short detection when a loco goes over the joint between them, or that's what I've been taught

Edited July 27, 2019 by Adamphillip

[melmerby]

3 minutes ago, Adamphillip said:

yeah, when using DCC boosters all the boosters need to be the same amp otherwise the 5-amp booster will trip the 3-amp booster's short detection when a loco goes over the joint between them

What?

Where did you get that idea from?

They need to be in phase, They need to be the same voltage.

[Adamphillip]

1 minute ago, melmerby said:

What?

Where did you get that idea from?

They need to be in phase, They need to be the same voltage.

I think I heard about it when someone was talking about Freemo layouts on youtube

[Adamphillip]

I may just be repeating something I misheard