Euan
Hi All,

My layout is approx 23 ft x 8ft with 2 bus loops - the longest being about 40ft in total continuous length. This is not twisted but run as 2 separate wires. Power is delivered via DCC Concepts Alpha Power and then via Cobalt Alpha Box. My control is NCE Power Cab.

What possible problems could this cause to my layout? Would it, for example, cause any dangerous, non identified power spikes that could damage a decoder?

Thanks in advance for any input.

Euan
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Ron Solly Sol
Euan, my layout 12 x 20ft , has two main bus wires running around separated by about 2.5" then feeding sub-bus for sections & utilizing common return as well for all power supplies ( each with their own transformers) . I have the bus terminators/snubbers and no problems for the last 6 years with my NCE system
Ron
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Iain Morrison wimorrison
Are the rails on the track that carry the DCC signal twisted?

Because the wires are underneath the board rather than on the top doesn’t change anything 😉
Iain Morrison
Modelling h0e using Z21 with iTrain automation and Railcom
There are also unknown unknowns – the ones we don't know we don't know
http://www.wimorrison.co.uk
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Euan
I have only recently come across bus terminators and wonder if installing a few might provide a little more protection.

I have only had decoder issues in my large Hornby locos (Kings & Castle) so thought that the power bus is unlikely to just affect these engines (as opposed to the Bachmann panniers and prairie locos and Dapol railcar) but worth exploring anyway!
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AHJAY
I have long lost count of how many times I have discussed this on forums or email.

We cover this subject in several wiring documents on our website / help area. No, it will not cause spikes, but the spikes will be less controlled. Twisting is to do with power delivery under load and preservation of information delivery.

For your layout? If its not causing problems now then just leave it. However if your layout becomes electronically more complex or power devices are at a reasonable distance from the power sources then voltage drop WILL be significantly higher and other strange things may happen. Just stay aware of it..

With smaller layouts or those which are less electronically busy the importance is less, so for small or medium layouts it is no big deal, but in reality it is always an issue in relation to the delivery of both power and information.

The track-related discussion is totally irrelevant and a needless distraction from the discussion. If we accepted that then a power bus also becomes irrelevant.... actually the only thing that carries full power DCC is the main power bus. Track has gaps at regular intervals where points etc exist.

There are quite distinct advantages to the twisting related to the cancellation of induction created when two parallel wires are carrying a modulated waveform. The rate of twist matters too. Better power delivery is one of them. It can be seen and its effects are real.

DCC is a complex assymetric quare wave infinitely more complex than simple sine waves in AC etc. All DCC power bus situations are the same as any wiring that carries a waveform.

Why do you think that every cable leading to a digital device is twisted, that cables need laying out properly when carrying high power etc. How things are wired makes a difference. None of it is just done for fun and model railway electronics are not immune from the laws of physics.

------------

None of this is guesswork... just the laws of physics. Induction and its effects are real. They totally change the resistance of wiring in a significant way. The math is complex but the result is clear. My very strong recommendation is "Just do it".

I would not consider building a layout of any size for myself without twisting the power bus.

regards. Ahjay
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Briperran
I agree the bus terminators are a very good addition to any DCC layout. RE twisting bus wires i have never twisted bus wires mine always under the layout probably around 6 inches apart

Brian
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AHJAY
As many have. However please do not misinterpret good fortune as a correct approach.

Others have had problems that are then constantly blamed on other things. I have assisted many modellers whose "I did it my way" approach has resulted in the need to change things later, whereas those who consistently use best practice are always problem free... which is why we universally ONLY recommend things that work every time and confirm and test every thing that we recommend before we discuss it.

Ahjay
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Briperran
Yes it is perhaps better practice to do that if you are starting a new layout but i think its fair to point out anyone using block detection twisting wires can cause problems when using block detectors most people state do not use twisted wires if you use block detection so if you are 100% sure you are never going to use block detection then twist from the start. If you may be considering possible block detection in future you need to look more carefully at advantages and disadvantages.

Brian
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Euan
Like a lot of things I have discovered about DCC - I wish I had found this out earlier!

When I first installed the bus I bought a kit from Express Models - very handy as it had everything I needed to get started but the instructions showed an installation with wires untwisted and, not knowing any better, this is what I did! I'm now wondering should I remove the bus and reinstall with twisted wire?

Whilst talking about the power supply for the layout, should the Cobalt Alpha Power enclosure and the Cobalt Alpha Box get hot duing operation - because they do!!
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AHJAY
Brian, a bit of misinterpretation there.

(1) With inductive detectors, they use the effect we are talking about.
However....
(2) With inductive block detection, it is ONLY the wires between the detector and the track that need to stay untwisted.  That is why intelligent brands make inductive detectors as single units. There is actually a negative result by making them with several on one PCB because the wire length changes one to the other section-wise modifies effectiveness and efficiency.

Ahjay
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AHJAY
Euan
(1) Re the Alpha question:
You must have a reasonable static load to get them warm... we see no real heat at when used all on our large test layout. The parallel bus WILLcause an increased loading becuase track bus impedance is higher therefore power losses are higher.
However - warm is fine. The cases are not just pretty - they are also heat sinks. How warm they get will depend on where they ar eplaced because air flow is different. They will cope well with any power you can throw at them and go into overload before any limits are reached.

(2) Re should you change what's already done.
I understand your frustration with express models "kit". People also call 7x.02 wire "Layout wire" when it is woefully inadequate for most tasks and as a result there are so many failures for new modellers.
Unfortunately most retailers and sadly some brands do not have any real understanding of the real world or laws of physics. As to your existing wiring, I am NOT in favlour of making work unnecessarily so my pragmatic advice is - if it is running OK then leave it. If you get anything wierd in future OR are perhaps working on wiring anyway. change it.

regards, RAhjay
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Euan
Thanks Ahjay, I thought the question re heat and the cobalt boxes was worth asking - I have been very pleased with them and the Alpha central switches.

My main reason for posing the wiring question was that, as you know, I had the issue with TTS decoders failing and had never properly discovered the cause - I had plenty of theoires but nothing definitive. My most recent issue (which may prove to be nothing sinister) was my newly upgraded Hornby King Edward V - with its lovely Yochoos sound - has stopped working. Parked it in the engine shed and all was well - came to use it a couple of days ago (after approx 2 week gap) and dead as a dodo. Now, it may prove to be a failed connection, but I began trawling the internet for possible causes of decoder failure and discovered the whole twisted DCC bus thread and the possibility of huge increases in voltage.

I'm probably being paranoid but that can be the result when problems remain unidentified! I have ordered a pair of DCC bus terminators from DCC Concepts as it will do no harm and could add an additional level of protection - as these only cost just under £7 it's a bit of a no brainer!

Regards,

Euan
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AHJAY
Yep, about the lowest cost insurance on the planet

Ahjay
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Charles
To add my Two Penny Worth. Once had all sorts of problems with my layout running.
Solved it just by adding two Concepts Bus Terminators
My power bus is not continuous. IE an open ended U. It was thought this was causing the problem, although I doubt it.
Anyway its fixed.
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Euan
Thanks Charles - that's good to know. Fingers crossed!!
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