Maybe an elementary question here....I did a search and did not find a direct answer.
I currently run DC, with multiple control cabs and common rail wiring. I intend to change to DCC in the future... someday.... .
With common rail, obviously I isolate or shut off sections of track by just shutting off power to the one rail with the cab selector switch.
When I switch to DCC I will have some tracks I will want to make electrically dead, such as staging or engine terminal tracks. An example is a partly hidden, dead-end staging yard where the last couple of feet of track are electrically isolated. You have to press a normally-open push button to connect that last bit of track. This prevents a misrouted train from flying into the end of the staging yard.
With DCC, is cutting off just one rail enough or should I change to double pole switches to control track power? With power to one rail there will still be half of the DCC power and signal coming into the locomotive. There is no return path so current can't flow - but I am just wondering. What's the best practice for isolating tracks like this?
George V.
Hi!
I'm a recent DCC "convert" and had the same question...... From what I gather, splicing in a SPST switch on either the feeder wire (or bus wire if more than one feeder goes to the section in question) to the desired section will work just fine. However, it was suggested to me to use a DPST and wire both feeders through it. While it may or may not make a difference, I am going to use the DPST method.
Mobilman44
ENJOY !
Living in southeast Texas, formerly modeling the "postwar" Santa Fe and Illinois Central
Most DCC systems have a 'panic' button on the throttle to shut down your train(no looking for which block you are in).
Jim
Modeling BNSF and Milwaukee Road in SW Wisconsin
Yeah, an SPST will do the job.
I went to DCC on this layout. I still wired my engine stalls in the roundhouse with shutoff switches. It helps particularly with sound engines. You might want a dead siding for passenger cars with lights, or cabeese. One dead rail is enough, though.
It takes an iron man to play with a toy iron horse.
georgevWith DCC, is cutting off just one rail enough or should I change to double pole switches to control track power? With power to one rail there will still be half of the DCC power and signal coming into the locomotive. There is no return path so current can't flow - but I am just wondering. What's the best practice for isolating tracks like this?
No. The results will be unpredictable. Could result in a runaway or locked decoder. I found this out the hard way when I accidently hooked my second track lead to ground. Took me a good 10 minutes to figure out what went wrong too.
Edit: Had a brain fart-please ignore my previous ranting above. See note below. - Sorry
It's always good practice to double gap with DCC anyway (AKA: house wiring). If you use boosters, you run the risk of burning them out due to power surges if they aren't opto isolated.
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
Simply stated, if you open a closed circuit anywhere, that circuit is DEAD .
ANY circuit (except three-phase AC, which we model railroaders don't use) can be opened by throwing a single SPST switch anywhere in the circuit's loop.
Using a DPST to open the loop in two places is overkill.
The SPST doesn't have to be a toggle or slide switch on the control panel. Relay contacts or the contacts on switch machines will do the job just as well.
As long as power is delivered to the locomotive through the rails the principles are the same. DCC, Marklin AC or analog DC, KISS rules. Don't make things more complex than they have to be.
Chuck (Modeling Central Japan in September, 1964)
A previous iteration of the BRVRR, originally common rail DC, just one rail was switched. When I converted it to DCC I had no problems with it that I remember.
On my current layout, all of my sidings, yard tracks and engine facility tracks are isolated. I control them with Atlas Connectors wired between the tracks and the DCC power bus. I've never had a problem, that I know of, with this arrangement. I made the change on the new layout because I read somewhere that isolating and switching both rails was recommended practice.
I don't know where I read this, probably on the DCC tutorials at Litchfield Station, http://www.litchfieldstation.com/ or Allan Gardner's Wiring for DCC http://www.wiringfordcc.com/ as they were my primary sources for DCC information.
In my experience, as outlined above, either method will work. Take your choice and take your chances.
Remember its your railroad
Allan
Track to the BRVRR Website: http://www.brvrr.com/
georgevWith common rail, obviously I isolate or shut off sections of track by just shutting off power to the one rail with the cab selector switch.
With power to one rail there will still be half of the DCC power and signal coming into the locomotive. There is no return path so current can't flow.
BTW - the DCC power IS the signal. That is the advantage of DCC over other the other command control systems digital or not.
Yes, if you shut off one rail and ground the one you shut off, you end up with half the DCC signal going through the decoder. Probably not a good thing. So don't ground the disconnected rail.
But if you have a large enough layout for multiple boosters, do NOT use common railbetween the booster districts. Gap both.
Consider DCC more like the 240V inpout to your house, not the 120 circuits to each outlet. There is a ground, and there is Rail A and Rail B. The total DCC waveform is across Rail A and B, but they are referenced by the H-bridge driver to the ground. One way of measuring track voltage is to check between Rail A and ground, and rail B and ground, and adding them. If address 0 (0 stretching DC) is disabled or set to stop, the voltages should be equal. If your system supports running a non-decoder loco on address 0, repeat the measurement but with address 0 cranked to full throttle in one direction or the other. One rail to ground voltage will be significantly higher than the other.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Mr Beasley, Randy, and Chuck are right. I don't know what I was thinking in my previous post. When you kill the leg/rail there is no current. In my case I grounded the second leg, not killed it. DURR! (It was a late night) Sorry for any confusion.
But double gapping between power districts is still a good idea.
-D
Many thanks for the answers, guys!
DigitalGriffin georgevWith DCC, is cutting off just one rail enough or should I change to double pole switches to control track power? With power to one rail there will still be half of the DCC power and signal coming into the locomotive. There is no return path so current can't flow - but I am just wondering. What's the best practice for isolating tracks like this? No. The results will be unpredictable. Could result in a runaway or locked decoder. I found this out the hard way when I accidently hooked my second track lead to ground. Took me a good 10 minutes to figure out what went wrong too. Edit: Had a brain fart-please ignore my previous ranting above. See note below. - Sorry It's always good practice to double gap with DCC anyway (AKA: house wiring). If you use boosters, you run the risk of burning them out due to power surges if they aren't opto isolated.
DG,
I am sure glad you decided to recant there at the last minute. I've just finished wiring a couple of layout modules for DCC and I also used single-side isolation for my storage tracks. I really didn't want to have to go back and rework all that wiring!
I have figured out what is wrong with my brain! On the left side nothing works right, and on the right side there is nothing left!