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There is a lot made of turnouts being DCC
"friendly". But most of the companies touting "DCC
friendly" fail to tell you the "whole" story. We like
Peco InsulFrog turnouts because they are 100% DCC friendly, not just
partially friendly. This is especially important for beginners and
people who have a hard time understanding electrical matters. While live
frog turnouts can be used with DCC, there are things the user must know
and take into consideration in order to use them successfully. With Peco
InsulFrog turnouts, you just install them like another piece of track,
and use them. And they are of the highest quality for not much more
money than cheap turnouts.
There are three points to being DCC friendly:
- Wheel flange
clearance between stock rail and open point
- Frog and frog rail
changing polarity
- Point vibration
causing power/signal problem
Most so called DCC friendly
turnouts address point 1. Some address point 2. Most do not address
point 3 (which we will cover in detail below).
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1. Wheel flange clearance between the stock rail
and open point
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With power routing turnouts, both points usually
carry the same polarity. Iillustration #1 at right shows how the power
flows on a normal power routing turnout. Polarity is shown with Red and
Green lines drawn over the rails.
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You can see that the open point has the opposite
polarity. If the clearance between the stock rail and open point is not
enough to allow the wheel flange to go through without touching the
point, you will have a short circuit.
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Note: These short circuits generally don't matter when
operating with DC analog because the typical power pack doesn't put out
enough current to harm anything (they generally put out only enough
power to run one train). When a short circuit happens, the power pack
simply puts out all the power it can for the short period of time the
short circuit is occurring, and no harm is done. But with DCC having
enough current on the rails to run ALL the trains, a short circuit can
cause harm. Therefore, Short-Circuit Protection is built into boosters.
When a short circuit occurs, the booster shuts down and the trains stop.
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This issue is totally irrelevant with Peco
InsulFrog turnouts for two reasons. As you can see in Illustration #1,
there is plenty of clearance for even the fattest wheel flange. But more
important, the open point never has the opposite polarity. Illustration
#2 shows how power flows in a Peco InsulFrog turnout.
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The insulating frog point (shown in blue) is
only 5/16 of an inch long. The total span of rail without power is 11/16
inches long. Rarely would you ever have more than one wheel at a time on
this gap of power.
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Live frogs are good for nature, but are not
needed for model railroads anymore. In the past, when locos didn't have
all-wheel power pickup, and the power pickup they had wasn't very good,
you needed all the power you could get on every wheel that had power
pickup. This made live frogs all but a requirement for a good-running
railroad. But with the quality built into today's locos, the power
provided by a live frog just isn't that important any more - providing
you keep your locos properly serviced. In fact, with DCC, they can be a
detriment. There are many web sites with all kinds of information on how
to keep the frog from causing a short circuit: to include installation
of 1157 automotive bulbs to feed the power, and other things. But, if
you don't really need power there, why go to all that trouble when you
can install a turnout that doesn't have that problem to start with.
Giving up this one small area of power is a small price to pay for a
turnout that's overall easier to use.
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2. Frog and frog rail changing polarity
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Some people call this Power Routing, some call
it Live Frog. Illustration #1, above, shows how a power routing turnout
is powered when closed for the through route. Illustration #3 shows how
it is powered when thrown for the divergent route.
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You can see that all the track pieces in the
middle changed from green to red. With Peco InsulFrog turnouts
(Illustration #2, above), all the track pieces stay the same regardless
of which way the turnout is set.
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The reason this is called power routing is that it can make the
unselected route dead. In the illustration above, you can see that both
rails of the through route have the same polarity. This means a loco
can't run (the through route is dead). With DC analog, people used this
to be able to run a loco onto a siding to let a train pass. But with
DCC, this is not needed (simply because each engineer is controlling
their trains independently regardless of track power).
With DCC, it's more important to have good solid track wiring to
all rails. Running power through the point contacts is not as positive
as connecting the siding directly to the track power bus.
You can read more about turnout point power below.
You can read more about accommodating the switching of polarities
of power routing turnouts in the About
ElectroFrog Turnouts section.
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3. Point vibration causing power/signal problem
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With
DCC, power to the points is far more important than power to the frog.
The typical turnout provides power to the points via slip joints, brass
contacts, or some other method. The problem is, when your loco is
traversing the points, the points vibrate. And with just that little bit
of movement, power is interrupted. It's only for just a fraction of a
second, but just long enough to mess with the signals. Unlike a spot of
dirt on the rail, a whole truck of your loco will be on it. This means
that 1/2 of your power pickup for that side is gone for that fraction of
a second. At first blush, this wouldn't seem too much of a problem, and
usually isn't - after all, you still have as much power in the other
truck as locos used to have. But, with so many more things that DCC does
than you could do before, this kind of power interruption can cause
spikes that can be disruptive.
Peco turnout points get power from two directions.
But more importantly, both of those directions are more positive than
most other turnouts provide.
- The
points make contact with the stock rails like all others. But, only
Peco has a spring that forces the points tightly to the stock rails.
Besides providing good solid electrical contact, it also resists
vibration caused from locos running on it.
- The
points also have wipers which make contact to the bottom of the
stock rail. So, with the spring holding the point tightly against
the stock rail, and the wiper making contact to the bottom of the
stock rail, it has two points of contact for power transfer at that
end of the point.
- The
points also have a unique pivot connection to the closure rail. It
doesn't just ride on the pivot pad as points do on some turnouts. It
has two tabs that stick through a hole in the pad, and bend over to
secure it to the pad. This provides contact from the tabs to the
hole in the pad, as well as between the top of the pad and bottom of
the point (again, two (not one) points of contact from that end).
Since the frog rail is connected to the closure rail, connecting
track power to the frog rails will feed power to the points via the
closure rail pivot point. The point gets power from both directions:
from the point and wiper with a spring to hold it tight, and from
the pad contact with prongs to hold it tight and also transfer
power.
No other turnout has all these advantages for DCC.
If you absolutely need to have Power Routing Live
Frogs, read about how Peco's ElectroFrog turnouts work in the About
ElectroFrog Turnouts section.
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