DCC Communication and power supplies

[act]

I recently bought a hornby DCC track about 8 x 4, prior to this never owned a trainset, so all new to me.

If I'm right in my understanding the communication of the command signals is via the DC volt output of the Controller, which appears to have very limited current capabilty.

Can I therefore have a further 12/15 VDC supply connected to the track and points etc, in addition to the DC connection from the controller.

In effect there will be 2 DC power supplies in parallel, the controller outlet used in the main to send DCC comands and the other supply to provide the current

Comments appriciated

ACT

 

 

[Chrissaf]

Please do not think that my reply below is being 'heavy handed' no offence is intended at all. I am just very concerned that you might actually try out your assumptions for real. To do so could potentially do serious damage to your newly purchased equipment. So my reply is worded strongly for your own protection.

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You must not under any circumstances connect a DC supply (or any other secondary supply) to a DCC powered track (the one exception being a DCC booster.)

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First of all 'What controller have you got?

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It is very important that you tell us what controller you have so that we can give targeted advice. For example you may not even actually have a DCC controller. Track is track, it is not DCC or DC specific. It is the controller and the type of locos you place on the track that make it DCC.

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In the absence of knowing what controller you have got, what follows is generic in nature and assumes that you do indeed have a DCC controller.

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A DCC controller will normally have an output labelled as 'Track'. In the case of Hornby branded DCC controllers, these are labelled 'Track A&B'.

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A DCC controller may also (not all do) have an additional output labelled any of the following or variations of......DC Output, Aux Output, AC Output etc.

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These additional outputs MUST NOT be connected to the track OR ANY other DCC equipment / devices. Accessory decoders for example.

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The output labelled 'Track' must be the only connection between the DCC controller and the track.

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Thus not only must the DC / AC / Aux output not be connected to the track, then any other outputs that might be labelled as 'Boost' and/or 'XpressNet' on the controller must not be connected to the track either.

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These additional outputs are provided as an option to power additional NON DCC equipment such as 'Signals' and/or DC/AC operated point motors. They have absolutely no role to play in operating DCC equipment. The 'Boost' and 'XpressNet' output have special DCC uses that are not relevant further to this reply at this time.

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If I'm right in my understanding the communication of the command signals is via the DC volt output of the Controller, which appears to have very limited current capability.

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This understanding is incorrect. DCC is a digital encoding scheme which is overlaid on top of a Bi-polar (pseudo AC) waveform with a 'peak to peak' Square wave voltage of 28.8 volts capable of providing currents of up to 4 Amps (Hornby controllers with the 4 Amp power supply option). Digital data consists of sending a sequential code of digital ones and zeroes called Binary 1 & Binary 0 - see waveform below.

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On a scope the DCC waveform looks like this.

/media/tinymce_upload/183e9e7c73bc5db4133449a61141cdbf.jpg

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This DCC waveform must not come into electrical contact with any DC/AC power supply output or even another DCC controller. This DCC waveform is what is sent to your track via the 'Track A&B' output on the controller (Hornby branded ones).

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In effect there will be 2 DC power supplies in parallel, the controller outlet used in the main to send DCC commands and the other supply to provide the current for the running gear and points etc.

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Absolutely not the case...for the reasons previously given.

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As I said at the very beginning of this reply. Tell us exactly what equipment you have got by model and part numbers and we can then tailor a more accurate targeted response to explain what you can and can't do with the system you have purchased.

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TIP: As this is your very first post, just be aware that the 'Blue Button with the White Arrow' is not a 'Reply to this post' button. If you want to reply to any of the posts, scroll down and write your reply in the reply text box at the bottom of the page and click the Green 'Reply' button.

 

[act]

Thanks Chrissaf for your speedy reply...however I did think about putting diodes in series with 12 v lines to isolate from the controller, but I think you are going to say yes that protects the controller, but the diodes will also prevent the signal path from functioning.

Not trying to be smart just want to cover all the bases before I commence the wiring of the layout.

I have broad sholders, negative comments are fine

Your comment please

 

ACT

[Chrissaf]

Whatever you think you know about electrickery (spelling intended) then forget it. DC and DCC cannot be mixed even with diodes. DCC and DC are two completely different systems. As an analogy, what you are suggesting is a bit like trying to use a common length of pipe to share the transportation of Gas and Water. DCC and DC must be kept completely and totally separate and independent.

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You have now used up your initial newbie 2nd post without answering the 'What controller and kit have you got?' question. You won't be able to answer this important question until tomorrow.