Re: DCC Reversers

Marcus Ammann

Hi Mike

While the polarity of the track determines the direction a loco goes in DC,
in DCC it is the decoder that determines the direction, so changing the
polarity "right under the engine" will NOT affect the direction.

In DC the track voltage is applied directly to the DC motor.

In DCC, the track voltage is Square Wave A.C. of approximately 5,000 to
8,000 cycles per second (Hertz), is applied to a Bridge Rectifier in the
decoder that rectifies this A.C. voltage into DC and the decoder's
microprocessor determines the polarity of this DC voltage, to the DC motor
as set by the digital data in the DCC signal.

With a "quick" sense of the short circuit at the Gaps combined with the
"fast" changeover of the polarity, with the later electronic Auto Reversers,
the operator does not notice anything has happened. The sound does not even
stop (hiccup). With slow relay based Auto Reversers you may see the loco
hesitate and the sound may hiccup.


-----Original Message-----
From: WiringForDCC@... [mailto:WiringForDCC@...] On
Behalf Of Mike G
Sent: Friday, 14 May 2010 2:14 PM
To: WiringForDCC@...
Subject: RE: [WiringForDCC] Re: DCC Reversers

Now I am a bit more confused. If you are using a relay, if the turnout is
set one way and the polarity of the isolated section matches, the train runs
into it fine, then part way around you throw the turnout to allow the train
to continue back onto the main, the relay switches the polarity. Isn't this
switching polarity right under the engine? So why is this not a problem?

Mike G.

From: WiringForDCC@... [mailto:WiringForDCC@...] On
Behalf Of birchardvilleobservatory
Sent: Thursday, May 13, 2010 7:51 PM
To: WiringForDCC@...
Subject: [WiringForDCC] Re: DCC Reversers

And, that description was how I used a under $10 DPDT relay connected to my
switch motor auxiliary contacts to reverse the loop power depending on the
position of the "throat" turnout. The loop (or balloon track) power phase
always matches whichever way the turnout is thrown.

There are a lot of sidings, turntable, staging yard, and more hanging off
the reversing loop "balloon" tracks. Whole thing works perfectly once I
found the turnout I'd connected backwards to the track buss. Until I found
it, I had a short (duh!)

I found this some couple months ago at your site and it's saved me a bunch
for "autoreversers" I didn't need for such simple connections.

I guess the point is that the wiring for dcc site really is helpful
AND saves money too.


--- In WiringForDCC@... <>
, "wirefordcc" <wire4dcc@...> wrote:

In my section "DCC for Beginners" I have a description and graphics
regarding auto reversing.

I'll review everyone's comments on the topic and see if there is anything
I need to add.

Wiring For DCC

--- In WiringForDCC@...
<> , "Harvey McRae" <hlmcrae@> wrote:

I wish to add my "AMEN" to the answer given.. I was just going down my
of emails, to see what other answers were given.. I too think this is a
very good explanation.

Harvey L. McRae
838 McKenzie Rd.,
Kelowna, B.C. V1X2B3

----- Original Message -----
From: "John Polson" <ham6528@>
To: <wiringfordcc@...
<> >
Sent: Monday, May 10, 2010 12:55 PM
Subject: RE: [WiringForDCC] DCC Reversers


Great answer to the reversing loop question. I too was curious about
reversing loop control.

i did not know how the Digitrax reversing accessories work. I will be
looking forward to purchasing

this accessory as my Digitrax Super Chief/ Dave Frary's "Cactus Valley
line" layout expands.

Thanks! John

To: WiringForDCC@...
From: mammann@
Date: Mon, 10 May 2010 17:50:43 +1000
Subject: RE: [WiringForDCC] DCC Reversers

Hi emrldsky

Auto Reversers work like this.

The Reversing Loop is ISOLATED from the Mainline with GAPS or Isolated
Joiners in BOTH rails at BOTH ends of the Loop.

The Input to the Auto Reverser is fed from the Booster. The Output
now isolated Loop.

The train is running down the Mainline towards the Loop with the
to the route that you want. As the loco/train negotiates the selected
and reaches the Gaps, if the polarity of the rails at the "other side
Gaps (the Loop), is opposite to that of the rails where the loco/train
coming from (Mainline), then there will be a Short Circuit. The Auto
Reverser senses this short circuit and changes the polarity of the
that it is feeding to the Reverse Loop. Now the short circuit is
has been corrected. This happens so quickly, that the momentary loss
power was not noticed by the loco and the operator.

The same scenario happens when the loco/train exits the Reverse Loop,

The hassle with Reverse Loops in DC has been eliminated in DCC with
Reversers. Sound and Non Sound locos just keep going as nothing at all
happened. The sound does not even hiccup.

Hope this helps


-----Original Message-----
From: WiringForDCC@...
[mailto:WiringForDCC@... <>
Behalf Of emrldsky
Sent: Monday, 10 May 2010 12:14 PM
To: WiringForDCC@...
Subject: [WiringForDCC] DCC Reversers

Hi I am somewhat confused about exactly how the DCC reversers work and
the entire layout is affected. For example, the layout is a main line
parallel passing siding; there is a reversing loop at each end of the
line. There are 4 power blocks; the main line, the siding, reversing
and reversing loop 2. All block polarity switches are set to position
DC, after the train enters reversing loop 1, the polarity control
the main line block has to be thrown to position B so that the train
continue on without causing a short. Likewise, if the train is to use
siding, that switch must also be thrown to B, and the switch must be
to B for reversing loop 2 just as the train is to enter the it. Then
whole sequence must be repeated just before the train exits the
loop 2. And so it goes every time the train changes direction via the
reversing loops. That works fine for one train. So, how complex does
for two trains? or Three, or more. The number of power blocks grow
with the number of trains that are to be run at once.
Now comes DCC and the auto reverser. Does the entire layout, assuming
the same one, get its "polarity" switched back and forth? What happens
multiple trains?


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