A DCC autoreverser will not work on DC, or on a DC engine running on address zero on those DCC systems that allow it. The polarization flip that allows autoreversers to work on DCC will just cause a DC engine to reverse, not continue through the loop at the end.
It takes an iron man to play with a toy iron horse.
an auto-reverser is essentially a circuit breaker with the added capability of reversing the polarity of the output.
it monitors the current to either rail. It recognizes a "short" if the isolation gap at any of the boundaries of the reversing section is bridged and the polarity doesn't match. It quickly reverses the polarity to the reversing section so that there is no longer a "short"
either mosfets or DPDT relays can be used to reverse polarity. It may also use mosfets with a relay to disable power if there is a persistent short.
here's an example of a circuit breaker controlled by a processor (not shown) that can be used to reverse the polarity to the rails using a relay (not shown)
there is a 0.22 Ohm resistor in each path that is used to detect a short. when there is enough current, the voltage across it is sufficient to cause the (Q1) transistor conductor and alert the processor using the opto isolator (U1a).
The processor can momentarily disable the bias to the back-to-back mosfets to momentarily disable power to the rails while it changes the state of a relay. The back-to-back mosfets allow current to flow in both direction. a mosfet behaves like a diode (conducting) when the polarity across it is reversed. The other mosfet needs to be biased to conduct. This allows it to control the alternating DCC voltage.
A short can be detected in either rail and either/both rails disconnected from power using the mosfets. An additional pair of back-to-back mosfets could be added to replace a relay.
greg - Philadelphia & Reading / Reading
Hello, Mel,
What you don't say in your post above, is how you're presently dealing with reversing on the crossover leg, when you're operating DC. There are a variety of approaches, which I'm not going to discuss right now.
However, for DCC operations, it's simple enough.
For dual DC/DCC operations, I would envision you'd need to have two separate feed systems to the layout. I wouldn't expect the auto-reverser to work very well, if at all, on DC.
I hope this helps.
// Michael
Mel,
I see your point.
My dad's American Flyer (AC operation) was a simple 4' X 8' oval with a reversing crossover leg, plus a couple of sidings. The crossover leg was powered through a slide switch, which we kids were supposed to operate while the locomotive was on the crossover leg. I'm not sure how he had it wired. If we were agile and attentive, and got the slide switch thrown at the right time, the loco would go through to the main without stopping. Otherwise, if would just stop when it got to the gap.
It would be good if your grandkids could operate on the crossover by themselves. If I think of something else, I'll let you know.
Best // Michael
MisterBeasleyThe polarization flip that allows autoreversers to work on DCC will just cause a DC engine to reverse, not continue through the loop at the end.
seems that with block detection, you would know whether to reverse the polarity of the reverse or mainline sections
gregc MisterBeasley The polarization flip that allows autoreversers to work on DCC will just cause a DC engine to reverse, not continue through the loop at the end. seems that with block detection, you would know whether to reverse the polarity of the reverse or mainline sections
MisterBeasley The polarization flip that allows autoreversers to work on DCC will just cause a DC engine to reverse, not continue through the loop at the end.
mfm37For DC operation the block ahead of the train must have its polarity changed before the engine enters.
that's what i ment by using block detection. I guess it wasn't clear that it could be used with a circuit breaker to detect the crossing and using the block detection to determine whether to reverse the polarity of the reverse or mainline sections. (yes, it may need to keep track of which block is occupied just before the crossing).
RR_MelThat’s the way I run my layout, with the block switches. I might not need a auto reverser, my 11 year old great grand daughter was reading my posts and said that I could teach her how and that she could teach her 5 year old sister how to flip the toggles.
Your grandkids may be more clever and astute than you'd imagined. I'm impressed that the elder one read the posts. So teach the young lady how to work the toggles, and why. She'll catch on and teach her sister. You may well have a budding engineer on your hands, or two.
And, as for the grandchildren, you GO, girls!