I am currently using my original DC block wiring and I operate in both DC and DCC modes using DPDT switches to control my blocks in both modes and I have no problems other than remembering to throw the correct switches.
My question is; is there a simple way to go with a DCC type automatic polarity control system that would work in either mode?
I have well over 70 locomotives and I only have 12 of them DCC decoder equipped. I currently operate in DC mode about 75% of the time.
I don’t consider myself a DCC guru, but I can tell you that a DCC auto reverser won’t work with a DC loco because they reverse the polarity under the train.
The auto reverser detects a short when the loco bridges the gap between the main line and the reversing section. It then reverses the polarity on the reversing section. This could for DC as you are entering the reversing section, but as you are leaving the reversing section, it again detects the short when you hit the main and reverses the polarity again. This time because your DC loco is sitting on the reversing section the loco would instantly reverse direction.
DCC autoreverser do not work on DC, so you wither have to make the jump, or continue to use the DPDT toggles. DC, you reverse the main before exiting the loop. DCC, you can do either (which is why the existing DPDT toggles for DC work fine with DCC) - the polarity of the DCC signal does not determine direction of travel. So you can flip the main to match (same as DC) or flip the reverse section right under the moving train (what DCC autoreversers do).
If the route is always the same, you could repalce teh DPDT toggles with switch machine tontacts, or, better, a relay operated by the switch machine contacts (for higher current capacity and longer life) so that when you throw the turnotu it automatically sets the correct polairty - since it otherwise works the same as the existing DPDT toggles, it will work for DC or DCC. The restrction is that there must be consistent routing through the reverse section. In the more trivial example of your basic loop at the end of a long ‘straight’ mainline, it woudl mean you always enter the loop to the right and go counter-clockwise, or vice versa - either way, but always the same way in and same way out. Since the turnout has to be changed to allow the train in and out, it works using the contacts. Of course if they are manual turnouts…
I didn’t know that the auto-reversers used short detection. I’ve been contemplating building my own using optical detection and relays. I currently use a home brew detection circuit for warning LEDs on my control panel that light up when turnouts are open to a oncoming train. I was hoping to find something ready made or in kit form.
I went to optical detection because it doesn’t care whether it’s DC, DCC or no power.
Mel
Modeling the early to mid 1950s SP in HO scale since 1951
You would have to use a DPDT relay to do this with optical detection. To my knowledge, the only way to do this. I have seen this question in various train forums and the same answer and the response is, DPDT switch.
I guess the hard way is the only way this time Rich. I was hoping for a magical box that didn’t need any brain power.
I have enough P&B KHA17 12 volt 4PDT 5 amp relays with sockets on hand to build a multi loop reversing system and I have enough room for everything inside my control panel. I used EURO connectors for my block distribution so that will make it easier to install.
This has been on my project list for years and it might be on my to-do list even longer. It’s been working with switches for years so that has a tendency to really slow things down.
The Circuitron AR-1 (not to be confused with the Digitrax AR-1) may be what you need. It uses IR sensors to flip a relay, by putting them at the proper points of the reverse section, it cna change the polairty of the main automatically as the train passes, replacing your DPDT toggle.
Dallee also has the TRAK-DTRL which effectively does the same thing but with current detection.
Both manufacturer’s web sites have wiring diagrams for their respective products.
