Mark Gurries
on DCC Friendly
Maybe I can
help from a technical standpoint.
First the term DCC Friendly.
All switches
are DCC Friendly if properly used, in gauge and matching wheel sets are also in
gauge. In other words, everything follows the NMRA Standards. The only issue is
to not attempt to run a engine that is to big for the
given turnout you are going through.
The reality
is:
1) Seldom do
people check the wheels and track to see if they are in gauge.
2) Many of
us cannot help but want to run that big loco through that two small switch
anyway!! Run that Big Boy though the #4 switch!
3) DCC power
is much less forgiving of shorts than plain old DC power.
The same
short that a DC powerpack can care less about and
simply forgive is NOT so forgiven with a DCC system. In other words all those
electrical flaws in your track that you never knew about under DC suddenly
become noticeable under DCC.
So
regardless of best intentions, switch manufacture must update the track design
to minimize the potential for shorts if they are going to be successful in
sales in the long run. Hence this term "DCC friendly"
has become to mean a track switch that has been changed
or improved electrically compared to the previous version to meet the new reality
of the situation. The challenge of course is to come up with a good looking
switch and integrate all the new internal "wiring" at the same time.
With that
said, let get into the details
There are
three electrical aspects to a switch
1) Point
rail polarity.
2) Frog
polarity.
The Power
Routing feature turns out to be very much interrelated to the above due to
practical issues.
POINT RAIL
POLARITY
Point rail
polarity is about the polarity of the point rail that is in the OPEN position.
Naturally the point rail that is closed MUST take on the polarity of the stock
rail it touches.
Power
routing turnouts will electrically short both point rails together so they both
pick up the polarity of the point rail that is closed. This also means the
closer rails, frog and diverging rails can all be shorted together. Commercial
Power Routing switches are made by
Shinohara
Code 100, 70, 55
MicroEngineering Old style.
Peco ElectroFrog
Walthers old style code 83
Here is the
problem with power routing turnouts. If the turnout is relatively sharp (#6 or
less) and the locomotive you're using has a long wheel base (2-10-2 for
example), often the engine will short out on the point rails when taking the
diverging route.
Why? If you
draw a straight line which represents the driver length and tire width of the
one side of the drivers (wheel base) and try to fit the line into the gap
created by the open point rail side, you will see that at some point any one of
the drivers will be FORCED to come into contact with the back side of the open
point rail as it passes
through!
Since the
open point rail polarity is the same as the opposite closed point rail, the
contact of the driver creates a strong short circuit.
The key is how
wide is the gap between the backside of the open point rail and the stock rail.
The wider the gap gets, the point rails look un-prototypical
in terms of spacing distance to each other but prevents the short circuit. The
narrower it gets, the better cosmetic look, but shorts will become possible
even on shorter wheel base length engines.
Blind
drivers may or may not help much here. Often the open point rail sticks up a
bit in the air above the rail height allowing the blind driver to come into
contact. OR the blind driver will actually roll over the open point rail and
create contact.
To become
more DCC friendly, many manufactures have eliminated the power routing feature
and re-introduced the same switch using the more traditional non-power routing
configuration where the point rails are insulated from each other and are
ALWAYS the same polarity as the stock rail the come into contact with. Now that
same long wheel base locomotive driver can come into electrical contact with
the open point rail with no consequence.
FROG POWER
This has
NOTHING to do with being DCC friendly...period. The question is about smooth
engine movement through the frog of the switch. Frog can come in 3 variations.
1) Insulated
"Plastic" Frog
Since the
frog represents the electrical shorting of opposite rails, the frog is forced
to be designed in such a way as to prevent the short.The
simplest solution is to make the frog electrically dead or "insulated
frog". Unfortunately this is what creates the stall problem and the longer
the frog gets, the worse the problem gets. Long wheel
base or engine with lots of pickup wheels need not worry,
but trying to get the 0-4-0 through will make you mad! However from a power point of view, there
are no shorts of any kind at any time. Not a perfect solution but the easiest
and cheapest to make. The companies that make this style are:
Peco Insulfrog
Bachmann old
style (toy train)
Roco/AHM
Atlas Snap track.
Almost all
brass track
2) Power
Routed metal Frog
With power
routing switches, this whole frog power issue goes away. The entire frog and
rails leading to and away are all electrically tied together since the wheel
that must go through the frog is controlled by the point rail position. In
other words both mechanical switch position and electrical polarity needs are
one in the same. The problem of course is the point rails as discussed before. So one problem is traded for another. Again
not a perfect solution.
Shinohara
Code 100, 70, 55
MicroEngineering Old style
Peco ElectroFrog
Walthers old style code 83
3) Insulated
metal Frog
If you could
insulated the rails on both sides leading to the frog from the frog but keep
the frog metal, then you would have a insulated "METAL" frog. If you leave the frog
alone, the switch will not perform any better than the Insulated
"Plastic" Frog. But if you can somehow get the point rail position to
activate an electrical switch which chooses which stock rail the frog shall get
power from, then the frog is "alive" and no engines will stall.
Combine this feature with the no DCC issues with the point rails shorts. The
downside is that no one has been able to integrate the electrical switch into
the track switch which simply means the installer is left to figure out how to
power the frog.
Fortunately
there are solutions provided by many Switch machines manufactures that have
electrical contacts that can be used to power the frog. So this to is not a
perfect solution, but it does get ride of the biggest problem or point rail
shorts and ALLOWS one the ability to solve the dead frog problem at the same
time. The companies that make this style are:
Walthers Code 83
MicroEngineering new style
Atlas Code
83
Bachmann
EZ-Track
It should be
said that Atlas switches, with the exception of SNAP TRACK SWITCHES, have
always been the type 3 above with the code 100 product line. Specifically
the Atlas "custom line". It should also be noted that some
manufacture make is easy to solder a wire to the metal frog compared to others.
So may find it to difficult and thus despite the metal frog, is forced to leave
it in insulated mode.
Opinion: The
unfortunate side of Atlas code 100 was that there were better cosmetic looking
switches offered by other companies. In many ways, if Atlas had designed its
code 100 custom line like it did the code 83 line, it would have owned the
market till code 83 became so popular. Actually I happy that did not happen
since code 100
Translates to a very rare 155 Lb rail size. The wave of
popularity and quick conversion to Code 83 by manufactures has given us the
chance to address almost all of the track switch shortcomings. Win Win!
Best
Regards,
Mark Gurries
Linear
Technology
Power Supply
& Battery Charger Applications Engineer/Manager
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Model
Railroad Club and NMRA DCC presentations are at:
http://www.siliconvalleylines.com/index.html
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Enthusiast (Love SAE equipment)
http://members.ebay.com/aboutme/gurriesm/
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