DCC faq

Post all your DCC only problems, solutions and discoverys here.
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pete12345
Posts: 820
Joined: Fri Apr 14, 2006 7:53 pm
Location: Coventry

DCC faq

Postby pete12345 » Wed Oct 08, 2008 9:44 am

Q1) How do I fit a decoder?
A1) Depends on the locomotive. Many modern releases come with either 'DCC on board' with a decoder already installed, or 'DCC ready' with a socket into which a decoder can be plugged. Other locos need the decoder to be soldered in, but in many cases this is quite simple, with only the split-chassis designs needing more work.

Q2)Do I need to use hornby decoders with hornby locomotives etc?
A2)No. In general you can pick and choose a suitable decoder from any manufacturer. In fact, hornby decoders are generally not recommended due to their low output.

Q3)Do I need to use decoders from the same manufacturer of my command station?
A3) Not at all. Almost all DCC equipment is made to a common standard, so you can use whatever decoder is best suited to your locomotives, and operate it with a different manufacturers controller- it's all compatible (with a few specific exceptions)

Q4)What about wiring for DCC?
A4)Don't be fooled, it's a lot simpler than you might expect- simpler than conventional DC wiring. All you need to do is provide power everywhere, avoiding short circuits. There is no need to provide switched sections like with DC. A conventionally wired layout can be easily switched to DCC control by turning all section switches to on. Beware though, if you have any electronic track cleaners (such as made by relco or gaugemaster) you will need to remove these before running DCC or DCC locomotives. The high frequency signal can destroy decoders

Q5)Can I run DC locomotives on my DCC layout?
A5)While with most systems this is technically possible, it's not recommended. This works by 'stretching' half of the DCC signal to give a DC bias. However, the loco is still running on what is basically an AC supply (hence the horrible noise it makes when you put it on the track) and can quite easily destroy the motor. Do this at your own risk.

Q6)Can I run DCC locomotives on a DC layout?
A6)Absolutely. Most if not all (check the decoder instructions) decoders allow operation on a DC layout, though this can be disabled. The decoder detects the DC signal and responds accordingly (but remember the previous warning about electronic track cleaners.) If you are converting an existing layout to DCC it might be wise to convert your locos beforehand (running on DC) then switch the controller over when you have DCC'd all your locos.

Q7) Which points should I use for DCC?
A7) Short answer: whichever you are more comfortable with using with DC- it makes no difference. Long answer: While you don't need special points for DCC, properly wired electrofrog (live frog) points will always give you the best running, since there is no insulated section which can cause locos to stall on the points. I would recommend electrofrog points wherever possible.

More information can be found here:http://www.brian-lambert.co.uk/DCC.htm
and here:http://www.newrailwaymodellers.co.uk/Forums/viewtopic.php?f=24&t=15530

Feel free to add any other faqs if I've forgotten anything...

Pete
Last edited by pete12345 on Tue Feb 17, 2009 2:21 pm, edited 4 times in total.
Once an engine attached to a train, was afraid of a few drops of rain...

m.levin
Posts: 1981
Joined: Mon Jan 09, 2006 6:46 pm

Re: DCC faq

Postby m.levin » Thu Oct 09, 2008 8:45 pm

Q1) My locomotive moves but the lights don't work, on a dcc ready locomotive, with a new decoder.
A1) Try rotate the decoder plug. might be fitted the wrong way, this will give locomotive movement but no lights.
A2) Or There is a fault with the decoder or lighting circuit, if the lights worked on Dc before the chip was fitted, most likely the decoder.
A3) Or It hasn't got the correct amount of functions on the decoder for lighting.
A4) Or the locomotive doesn't have lights!


Q2) I fitted a Hornby decoder or other decoder, to my locomotive it ran for a bit then stopped, now it wont move, write CV's to the decoder or reset the decoder.
A1) It has most likley burnt out the decoder, by exceeded the max peak current output, from the decoder. common with Hornby decoders, due to the low motor max peak output current.
A2) The decoder might be faulty


Edit

Q3) Can I mixed Dcc and DC on the same layout?
A1) It is not recommend if the lines are connected. On 2 completely isolated/separate lines it is safe to do so. If you connect a Dcc and DC layout together, with no isolation it will most likely damage your Dcc controller if not both, its not worth the risk.

Q4) Can I connect scenic lighting (LEDs) to my Dcc track?
A1) LEDs use Dc voltage, if you use Ac it will most likely burn the LED out due to the reverse voltage. The voltage sent though the LED the opposite way, this wont light the LED!
A2) If you are using LEDs you will need to rectify and regulate the voltage. you will have to bring the voltage down to the LEDs max forward voltage. when you convert AC to Dc the voltage will increase, if the Ac voltage is 16v the Dc voltage WILL NOT come out at 16v but higher.
A3) you can connect to the the LEDs to the track and put a diode on the Cathode - Leg on the LED, to block the reverse voltage if the forward volage is higher then that of the track voltage.


If you are unsure DON'T do it, Electricity is dangerous, mains electric can kill and voltage as low as 12v can cause a fire. Think "Is it worth the risk?"

davejb
Posts: 16
Joined: Tue Nov 25, 2008 4:39 pm

Re: DCC faq

Postby davejb » Fri Mar 18, 2011 6:47 pm

Sorry,
this is way late to comment on an old thread, but I finally decided to read the DCC FAQ and when I read this I had to go 'whoa, hold on a moment......''

Q4) Can I connect scenic lighting (LEDs) to my Dcc track?
A1) LEDs use Dc voltage, if you use Ac it will most likely burn the LED out due to the reverse voltage. The voltage sent though the LED the opposite way, this wont light the LED!
A2) If you are using LEDs you will need to rectify and regulate the voltage. you will have to bring the voltage down to the LEDs max forward voltage. when you convert AC to Dc the voltage will increase, if the Ac voltage is 16v the Dc voltage WILL NOT come out at 16v but higher.
A3) you can connect to the the LEDs to the track and put a diode on the Cathode - Leg on the LED, to block the reverse voltage if the forward volage is higher then that of the track voltage.



A1 - an LED is a DIODE, it blocks the reverse voltage, why should it burn out?
A2 - Again, LED stands for 'Light Emitting DIODE', so you do not need to rectify the voltage, neither does the voltage change (AC peak voltage, as measured on an oscilloscope) is higher than DC voltage, but over time (50 Hz mains, so 0.02s) the energy delivery is the same...there is a root mean square relationship, 10V DC will peak at 14.1V in AC, but both deliver the same energy and are referred to as 10V systems. Converting AC to DC does not increase the DC, in fact the opposite is the case if you want to be pedantic,
A3 - You do not need to put a diode on the cathode, the LED is itself a diode. It is usually a much better idea to decide what voltage is going to be available, and then to attach a resistor of suitable value (something between 800 ohms and a kilohm for many applications) to EITHER leg of the LED. A red LED will probably light at about 1.7V or so, you need higher voltages as you head through the spectrum towards blue, from the top of my head I'd guess that maybe 2.8V would see a blue LED lit (check Maplins website for actual voltage needed if interested), so if you want 2V at the LED and you have 12V available your resistor acts as the second component in a potential divider so that you get 10V across the resistor and 2V across the LED.

I would say the biggest issue with simply connecting the LEDs to the track feed is it's totally unneccessary - given what we spend on our layouts, lash out on a £10 DC controller and use the track output as a variable voltage supply, which you use to power a 'lighting' bus seperate from the main track system.

Simples.
Dave

tuxychuff
Posts: 279
Joined: Mon Dec 14, 2009 5:50 pm
Location: 31A/CA

Re: DCC faq

Postby tuxychuff » Mon Apr 18, 2011 12:11 pm

Diodes do have a reverse breakdown voltage
This varies depending on the led but if you put too higher voltage against an led (esp a small one) it will break.

wefix
Posts: 5
Joined: Fri Apr 26, 2013 8:12 am

Re: DCC faq

Postby wefix » Sun May 19, 2013 9:47 pm

Rectifying AC voltage with one series diode will equal .707 of the AC voltage.

Rectifying with a full wave or bridge rectifier will produce 1.414 of the AC voltage.

A1 - an LED is a DIODE, it blocks the reverse voltage, why should it burn out?



If the inverse voltage is exceeded the LED will be destroyed.


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