>The main point I was trying to make is that it is not NECESSARY to
electrically
>isolate frogs since there are other ways to make things work properly.
Cheers....Ed L.
>"More on this later (gotta rush out right now) if you are still interested.
"
>Ed, inquiring minds want to know!
>Charles Weston
Well..since you asked. (This will teach you to open the door!)
The motivation to isolate frogs stems from those who have experienced short
circuits when using DCC. These shorts are usually caused by the backside
of a metal wheel grazing the open point of a turnout. This grazing also
happens with DC, but the effects are rarely noticed because DC is slow to
respond to a short. The wheel rolls by, the short goes away, and nobody
notices. With DCC and sophisticated electronics, the grazing short is
sensed immediately and the power source instantly turns off the juice to
prevent damage to fragile flanges and/or points. Thus, it appears that DCC
is causing the problem. But, in reality, the wheel grazing the point is the
problem and not the DCC.
So what to do..??
One solution is to buy a so-called DCC friendly turnout which has a factory
built-in isolated frog and appropriate wiring. With this arrangement both
points are always of the same polarity as the adjacent stock rail. If the
wheel grazes the point, there is no short circuit. I do not know of any RTR
DCC-friendly powered turnouts available in S scale.
Making your own turnouts (Fast Tracks, etc.) gives one the opportunity to
isolate the frog if that solution is what they want.
With turnouts that are already in place, it becomes more difficult to
isolate the frog, but it is not impossible. Cut four rail gaps, add some
wires and an electrical switch and you have the same end result. Most folks
use the auxiliary contacts on switch motors for this purpose. Some hand
throws also have an electrical switch which can be used for this purpose.
With an isolated frog, it is possible to position the open point very close
to the adjacent stock rail which makes for a more prototypical appearance.
Tom Hawley has a neat photo of this which I am sure he will share upon
request. This close positioning is closer than the typical NMRA or NASG
standards which are based on the avoidance of grazing rather than
eliminating the symptoms of grazing.
On the mighty NYC (my layout in case you did not know), the frogs are not
isolated. The metal wheels and turnouts are all constructed (or purchased
and modified) in strict accordance with the NMRA/NASG rail and wheel
standards. Please do not tell me this will not work. It works and works
very well. With this solution, the electrical pathway can be created by
point pressure against the adjacent stock rail. That method works very well
for me since I use the Switch Master turnout motors that exert a LOT of
pressure. Much stronger than the popular Tortoise. Some will say that
dirt, dust, etc. will eventually get in-between the point and the stock rail
and cause a lack of juice to flow down the closure rails. My layout is in a
clean living room-like environment and I have no problems like that. I
clean track about once per year and everything works fine.
One solution to the dirt/dust between the points and stock rail issue is to
use an auxiliary electrical switch to change the polarity of the entire
frog/closure rails/points portion of the turnout. This method also works
fine and can be done without any extra cutting of rail gaps beyond what
would normally be done anyway to insure juice flows into the turnout from
the point end.
Another solution involves the use of special light bulbs that act as sort of
a slow-acting circuit breaker. These bulbs allow the wheel to graze and
roll by without triggering a power source shutdown. This bulb is simply
wired to the frog per instructions and it does work well in most instances.
Still another solution involves the use of DCC circuit breakers that
accomplish much the same end result - grazing shorts are accommodated and do
not cause the power source to shut down. These DCC circuit breakers are
especially useful for dealing with a sudden inrush of current caused by
Tsunami and other sound decoders. Without a DCC circuit breaker, the
inrush current might be interpreted as a short and cause the power source to
shut down. With the DCC circuit breaker, this inrush effect is recognized
for what it is and the power source will not shut down. Some DCC circuit
breakers also have occupancy detectors built-in and can serve well for
several different purposes simultaneously.
Some folks simply use plastic wheels to prevent grazing shorts. Works very
well except for locomotives for obvious reasons. Of course, battery-powered
locos would not need metal wheels anyway. Or clean track either. Or
isolated frogs. Someday...it WILL come! (Recognize a joke?)
Unfortunately, the model press and well-meaning individuals have incorrectly
promoted the concept that frogs MUST be isolated in order for DCC to work
satisfactorily. My objection to that premise is that it is not true. Other
approaches can yield excellent results without any need to isolate the frog.
I have no problem with building a layout with isolated frogs if that is what
you choose to do. I do have a problem with people going to a lot of extra
work and agony when it is not really necessary since there are other
solutions which might be a lot easier.
Is all this perfectly clear without diagrams?
Hoping so....Ed L.
[Non-text portions of this message have been removed]
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