DCC Power Drain

Any questions about designing a model railway layout or problems with track work.
Harry20
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Joined: Thu Dec 31, 2020 3:53 pm

DCC Power Drain

Postby Harry20 » Thu Dec 31, 2020 4:22 pm

Hi I'm using a Hornby Select control unit and notice I have reduced power to locos when using more than 2 on the track. Thought the problem might be the controller but it checks out ok so wondered if I need some extra wiring? The controller has been great for 4 or 5 years and this is just happening now.

Layout is roughly 14 feet x 5 feet with 3 loops and various marshaling yards so I can have 5 or 6 locos working at once. Up to now the Select has been fine, I use a 4amp PSU but only have one power track R8421 in use. All locos have Hornby decoders fitted. Could it be I need another power track on the layout wired back to the controller to ensure power supply all round, be grateful for any help please.

Is it an idea to try this anyway, could it do any damage?

Thanks all

Bigmet
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Joined: Tue Aug 14, 2007 2:19 pm

Re: DCC Power Drain

Postby Bigmet » Thu Dec 31, 2020 4:56 pm

Running a continuous pair of 'bus wires' around the layout with regular track connections is recommended for DCC. You do need to be well organised so that you never cross over the connections resulting in a dead short.

What is required to enable this is not a bulk purchase of 'power tracks' but a soldering iron, solder and the ability to use it.

RFS
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Re: DCC Power Drain

Postby RFS » Thu Dec 31, 2020 5:46 pm

Supplying 4A of power to a layout of this size via a single feed is likely to cause serious problems. What you are seeing by "reduced power" is voltage drop at locations furthest from the feed. The risk is that when you get a short at these locations due to voltage drop, the Select does not sense the overload and hence does not cut out. Even 2A full power flowing through the short without being detected can cause serious damage very quickly.

Try the coin test on the layout: remove all locos from the layout and go round placing a coin (or simply use a piece of copper wire) and cause a track short at multiple locations. Does the Select cut out immediately? If not you need extra feeds at those locations.

As Bigmet has suggested, the easiest way is to run a pair of DCC bus wires round the layout (at least 1.5mm solid or 32 x 0.2 stranded) and connect dropper wires to the track every 3-4 ft.
Robert Smith

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RAF96
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Re: DCC Power Drain

Postby RAF96 » Fri Jan 01, 2021 7:27 pm

If you are relying on Hornby point clips (bent steel wire staple things) to fully power your layout across loops and sidings then you are in trouble. They are fairly high resistance and only design to pass power across a point onto one other loop or a siding or two, not to support running a fleet of locos from a single power input. You may find some of them have gone hot and melted into the point proving the point (no pun intended).
If you are using link cables check the slide in connectors as they are likely to have capacitors fitted which will corrupt the DCC signal, snip them out if you find them.
4-amp power supply should be adequate. I use one on my single garage sized layout with a power bus.
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Harry20
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Joined: Thu Dec 31, 2020 3:53 pm

Re: DCC Power Drain

Postby Harry20 » Sat Jan 02, 2021 11:49 am

Really grateful for your help, must admit you have got me head scratching though!
I chose DCC because I thought wiring would not be necessary but seems I'm wrong and honestly I don't really get electrics! I'm OK mechanically but electrics just don't seem to compute so could you give me an idiots guide to the wiring you suggest please?
I've checked out the point clips and they seem OK and the select does trip when I create a short as suggested so if i need to run bus wires around the track with droppers can you tell me what that exactly means please?
What do I solder to where and connect what to what, I know it sounds really billy basic but I could do with as much help as I can get. If it helps I could upload a picture of my layout.
Thanks again
Cheers

Bigmet
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Joined: Tue Aug 14, 2007 2:19 pm

Re: DCC Power Drain

Postby Bigmet » Sat Jan 02, 2021 1:42 pm

See how you get on with this well regarded guide by Brian Lambert:
https://www.google.com/search?q=brian+l ... e&ie=UTF-8

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Ironduke
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Re: DCC Power Drain

Postby Ironduke » Sat Jan 02, 2021 9:15 pm

Harry20 wrote:If it helps I could upload a picture of my layout.
Cheers


Always upload pictures if you can. We like pictures.
Regards
Rob


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