DCC wiring

Bilton Junction
Posts: 34
Joined: Wed Dec 31, 2008 1:02 am

DCC wiring

Postby Bilton Junction » Fri Mar 27, 2009 1:55 am

I hope the DCC Aficionados don't wince to much at this question. I'm wiring up a P4 tailchaser which is about 70 feet round on the main lines. I'm using steel rail. I originally bought a ZTC controller (perhaps not the wisest choice in retrospect as it went back to base twice before it was discovered that half of the LCD display was missing which made programming interesting to say the least) I have been using ZTC self adhesive copper tape (I think rated at 15 Amp) with tinned copper droppers at least every 18-24 inches. There are separate copper tape buses for up and down lines. I tried to keep the copper tapes as parallel as possible but a few detours around point motors were necessary. I have used heavy gauge wire from a 13 Amp mains cable reel soldered to the copper tapes for connections between boards with brass terminal blocks. I tested the yard area first and I must say I wasn't all that impressed that the control of a chipped loco. was all that much better than with it running unchipped in DC mode. I'm starting to have misgivings when I read advice to use a heavy gauge wire bus with the wires twisted around each other to minimize distortion of the control signal. The tape doesn't look very substantial compared to the massive wires joining the boards. Would there be any point in running extra twisted bus wires around the boards with connections feeding directly to the tapes on each board separately rather than linking the boards end to end and relying on the copper tapes for a 70 feet run? Should it be wired up as a conventional ring main or end to end?
Carl Watson

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Tim V
Posts: 2865
Joined: Tue Jul 29, 2008 4:40 pm

Re: DCC wiring

Postby Tim V » Fri Mar 27, 2009 7:18 pm

Others could give better replies,
1. I would seriously consider having power districts to start with, i.e. break up the layout into sections, better for fault finding.
2. Nothing wrong with the tape, but 13A mains cable has a much smaller surface area. Should be OK though.
3. I'm surprised you get poor control, I have only seen an improvement in performance using DCC, but what decoders are you using? Some are better than others, and especially if you are using the ZTC unit for programming. Straight out of the box, ZIMO are excellent for example.
Tim V
(Not all railways in Somerset went to Dorset)

davebooth

Re: DCC wiring

Postby davebooth » Sun Mar 29, 2009 8:18 am

[quote="Bilton Junction"]I hope the DCC Aficionados don't wince to much at this question. I'm wiring up a P4 tailchaser which is about 70 feet round on the ......snipped ; I tested the yard area first and I must say I wasn't all that impressed that the control of a chipped loco. was all that much better than with it running unchipped in DC mode. ....snipped again!

When I first started I too was disapointed with the lack of smooth control and particularly slow running; in my case it was worse than my analogue set-up.
I changed the Lenz, simple decoders for similar, but with back emf and immediately had better control than with dc and I have never looked back. So check if the decoder you used has the back emf feature.
I've used Lenz,ZTC,Zimo, Bachmann and Rocco decoders and found that no programming, other than loco address, was needed and all run beautifully. I tried a Hornby decoder and that caused me to delete Hornby from my list of suppliers for DCC equipment!!! That's a long story and hopefully they've improved since then but they 'aint having any of my money while I find out!
My layouts are only shunting planks so volt drop is no problem. As an electrical engineer, I would suggest that running any 15A rated conductor ( but are you sure that that tape is genuinely 15A rated?) around the layout to feed track droppers etc. would ensure that you have no problems caused by volt drop. Volt drop is a product of current and the resistance of the current's path,and the resistance is proportional to length of wire run. And, unless you are going to be running several locos at any one time, and/or old fashioned, low efficiency motors, then your current demand is unlikely to be so high as to cause undue levels of volt drop. This problem is more associated with the American style, very large layouts with very many trains running at any one time.
Having said all that, then Tim's suggestion of having wiring sections which can be swithced out makes a lot of sense for those times when you have an electrical problem. Isolating wiring/track sections until the fault is cleared will help find the source of the problem rather more quickly, and you may not have to shut down the whole layout; - important at exhibitions.

derekrussan
Posts: 158
Joined: Tue Jul 22, 2008 12:02 pm

Re: DCC wiring

Postby derekrussan » Sun Mar 29, 2009 12:13 pm

I am not an expert on DCC, but I am an electronics engineer.
Bilton Junction wrote: I tested the yard area first and I must say I wasn't all that impressed that the control of a chipped loco. was all that much better than with it running unchipped in DC mode.

Have you checked that any capacitors fitted to the loco for DC running were removed. Often manufacturers claim DCC ready and you still have to cut the capacitors off. They really mess up the control loops for the chips and can add some really weird effects, such as loco's not stopping until power is interrupted.
Also do not use a smart DC controller, the attempt of a DC controller to sense feedback and apply a control loop can fight with the DCC chips own ability to control and produce lumpy running.
Bilton Junction wrote:I'm starting to have misgivings when I read advice to use a heavy gauge wire bus with the wires twisted around each other to minimize distortion of the control signal.

I do not know where you read this advice but such effects only apply at radio frequencies and you should not see such problems with the frequencies DCC uses. The systems are tolerant to the minor distortions introduced in the wiring. Heavy gauge wire is enough, 13A mains cable is cheap and good.
davebooth wrote: This problem is more associated with the American style, very large layouts with very many trains running at any one time.

You do not need trains running to draw current, a yard full of loco's with lights on and sound systems ticking over can add up, also do not forget really thirsty functions such as coach lighting and short term heavy loads like point motors. Maybe we have all got too used to relatively low current motors.

Derek
Derek Russan, Eileens Emporium.


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