Simple DCC Question?

With DCC do you still need polarity switches when setting up or converting layouts with reversing loops? I am considering it possible the electronics could read the polarity changes and instantly switch the drive polarity to allow continuous travel around a reversing loop and back through the layout. Or is this just too much to ask for?
John Soon to build a 4 x 8 HO

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This is already taken care of by the manufacturers of DCC systems. There are several "auto-polarity, auto reverse" modules made by several manufacturers. Visit the websites of the major manufacturers and dealers.
www.digitrax.com
www.lenz.com
www.ncedcc.com
www.tonystrains.com
Larry Madson

Or you can have the polarity switched on the loop while the train is in it. Use the turnout control to through a DPDT relay or switch.
larry madson wrote:
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John Cassara wrote:
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Just as with DC you need an isolated train length+ block where the polarity can be reversed. The difference is that with analogue you hold the polarity of the track the train is on and reverse the polarity of the rest of the layout, whereas with DCC you can(must?) hold the polarity of the layout and reverse the polarity of the reversing loop block.
With analogue all you need is a rectifier bridge to power the loop block and a cheap DPDT latching relay to throw the M/L polarity (in parallel with the turnout) while in DCC you need a relatively expensive 'reverse loop module'.
Regards, Greg.P.

Gregory Procter wrote:
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With DCC you can reverse either the polarity in the loop or outside the loop. All that is important is that when entering or exiting the loop the track polarities match.
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The exact same relay thrown by the turnout contacts can be used with DCC. In DC this relay switched the polarity the the mainline. In DCC this relay can throw the polarity of either the mainline or the reversing section. For simplicity with multiple loops changing the polarity within the loop is often done.
With simple reverse loops (one entry one exit) a relay is by far the least expensive approach.
With complex reversing sections (multiple entries and exits like a double K section), you can use relays but it can get very tricky. For the average DCC modeler, an automated reversing module is much easier for complex reversing sections as the wiring is trivial.
Stan Ames

Stan Ames wrote:
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I made the comment on the assumption that there is an entire layout system beyond the reversing loop in question, possibly including other reversing loops and even an analogue loco on address "0".
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Certainly! All those DCC modules for reversing loops are therefore "snakeoil" remedies.
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So the automated reversing module is the Luddite answer ;-)
Regards, Greg.P.

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Yet more mis-information from the uninformed G. Procter. You don't know what you are talking about G. Procter. Go educate yourself and stop pulling answers out of your arse. Reversing can be done all the same ways that DC can do it plus the DCC cpu has built-in automatic sensing/reversing capability. I don't care how you control your trains, but you need to stop disseminating erroneous information.
-- Ed Davis snipped-for-privacy@comcast.net

Ed, M., snipped-for-privacy@comcast.net wrote:
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What exactly do you consider I got wrong, other than being born? What misinformation? Try just for a moment no to be an obnoxious pratt and add something constructive to the discussion.
Regards, Greg.P.

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Once again, you're absolutely wrong about DCC.
A DCC reverse loop can be wired using a simple DPDT switch, just as with DC, except it's even simpler because you don't have to change the mainline polarity. The direction of travel with DCC is independent of track polarity, so you can change the polarity of the loop while the train is traversing it. You CAN automate the process with a not-so-expense module (Digitrax's $80 unit can control 4 sections), but it can be accomplished with the simple manual DPDT switch.
-- Bill McC.

We have always wired a DC layout with Double Pole Center Off toggles. If there is a short in a block, you can find it by turning off toggles until power is restored to the rest of the layout. I now use six pole rotary switches,but only wire in five throttles at the max so the last pole (#6) can be an OFF position. Two double pole switches are sill need as an East/West direction switch and the other as a forward and reverse to save ware on the power pack switch.
For the reverse loops, a reversing polarity toggle is positioned on the control panel and wired so the toggle points to the direction a train will enter the loop. Once the train enters the loop, the East/West switch is flipped to correct the mainline polarity for coming out of the loop.
Oh, Oh, Here we go again.
-- Phil Anderson Up hill slow, down hill fast, tonnage first, safety last.
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Here we go again? Why? I don't think anyone would have any argument/criticism with anything you wrote. [except for writing "ware" where you meant "wear" :-) ] It's an entirely rational, logical, efficient, even elegant, way to wire a layout for DC multiple cab control.
The only bone of contention is Greg's continued uninformed, misleading, and just plain incorrect posts about DCC.
-- Bill McC.

I've been reading the tepid (thank goodness) war between DC and DCC adherents. So, I'll toss my few cents in. For the record, I converted to DCC in 1997 and never looked back.
When I got back into hobby in 1996 (inactive since 1963), I build one of the Atlas layouts (#8, I believe). It could run two trains in loops simultaneously with some switching possibilities. I wired it up for two cab DC block control. With common rail wiring, it was pretty easy as far as power was concerned. But operating with my 7 year old (at the time) and even me with my feeble older brain, I seemed to be worrying more about which blocks were set to which transformer etc. and not having that much fun.
So, I bit the bullet and got a Digitrax Empire Builder with two throttles. Initial wiring was easy: just set all the block to one transformer or the other and hook up the DCC power wires. Since I had Athearn locos at the time, installing the included DH121 was more trouble than wiring the layout. (I've gotten much better at it since); since I retired from the computer software industry (thanks, Oracle and Uncle Larry), little things like CVs were not a complicating factor for me (see more on CV's below). So, I was up and running in about an hour.
I was sold after operating for about 10 minutes. Wow. I didn't care where block boundaries were, I just pretended I was a locomotive driver and ran my train. We had pretend "signals," so much like a real driver, if it was red, I stopped, etc. My 7 year old was onboard as well.
When I built a new layout (see web site below for pics), it was DCC from the start: blocking was only done to deal with short detection and to be able to increase the power available when I upgraded to a Chief with an 8amp supply and PM42's for short circuit detection and protection.
Was the wiring easier? Probably not much: you run a pair of bus wires out to each power district from the PM42, much like you would for a DC system with blocks and block switching. But I like operating it better than a DC system. Others may feel differently and that's OK with me: it's not a religion. Is it cheaper than DC? Definitely not since I don't use automatic signalling, etc.
All that said, my turnouts are outside the DCC system and the Tortoise machines run from a traditional control panel. I like the GUI of the control panel rather than entering a switch number and a switch position. My CP has lights indicating the switch position, etc. So I'm still old school there.
A note on CV programming: for non-sound decoders, there are only a few CVs to set: the loco address, start voltage and maybe max voltage if available as a speed limit, and CV29 is either 6 or x26 depending on 2 or 4 digit addressing. I rarely use speed tables, so that's about it.
If I have need for complicated loco lighting (like with F7s with upper mars+red light, and lower white light, like the Genesis Santa Fe stuff), yes, then I have a few more CVs to play with, but when you get the hang of it, it is pretty simple. And since I actually document each loco's CV settings, if I change decoders or have to reset them for some reason, it's fairly mindless to reprogram the CVs.
Sound decoder like those from QSI and Soundtraxx have a bunch more CVs you might use, but again, in general I find that I only wind up changing the volume setting (lower, please).
So for those who are trying to decide what to do, go run a DC and DCC layout for a bit and see what style of driving locomotives and running a railroad is the most FUN for you. If you decide on DC, it doesn't cost you that much to change your mind later and add DCC. Those block controls don't have to be ripped out, the reverse loop stuff can stay the same, etc. The transformers will find other uses (they are unlikely to be suitable for DCC power).
Remember: this is NOT a religion and there is no right answer, and the answer might even change over time for particular users.
The goal is to enjoy the hobby not convert others to your way of enjoying it.
Ed
in article DiIwd.2118$ snipped-for-privacy@newsread3.news.pas.earthlink.net, Bill McCutcheon at snipped-for-privacy@earthlink.net wrote on 12/17/04 1:35 PM:
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Amen, brother! ... er, I mean ... well said!
-- Bill McC.

Bill McCutcheon wrote:
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It's certainly undesirable to change the mainline polarity with DCC. However, if one runs an analogue loco on address "0" or one converts an existing layout from DC to DCC, retaining DC cab capability, then the main-line has to be reversed. In a complex reversing loop situation (as mentioned by Stan) where there are multiple entrances and exits, there are multiple opportunities for trains to be crossing opposed polarity sections at the same time.
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No argument there - I effectively said that. (other than address "0")
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The DPDT answer is pure Luddite territory. We can move beyond that surely.
Regards, Greg.P.

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Nothing Greg has said above is incorrect. Reversing polarity of the main layout using DC or DCC is not the best way to do things, even though it is commonly suggested.
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Cheaper to automate it by using relay wired to your turnout switch.

: With DCC do you still need polarity switches when setting up or converting : layouts with reversing loops? I am considering it possible the electronics : could read the polarity changes and instantly switch the drive polarity to : allow continuous travel around a reversing loop and back through the layout. : Or is this just too much to ask for? : : John : Soon to build a 4 x 8 HO : : There are electronic circuits available to do the switching automatically - and you shouldn't notice it. Tony's has a lot of information and some products - see: http://www.tonystrains.com/tonystips/dccprimer/wiring/reverse-loop.htm