Electrically, the point rails are separate from the through rails and
provide switching of the two rails extending from the frog. There are
two bonding wires to connect the point rails to the rails beyond the
dead frog.
The point blades make contact with the through rails to electrify the
points and the rails beyond the frog. under the point blades are spring
sheet contacts which slide under the through rails to provide positive
electrical connection. These are prone to damage during ballasting as
watered PVA glue gets in and stops the springiness. Also ballast glue
can lodge on the underside of the through rails and isolate the contact.
We won't even think about ballast! As the spring strips/contacts are
dependant on the tension they have with the underside of each point
blade, they can't be retensioned if damaged.
The result of the contacts being damaged is that the current has to pass
between rail and point for the entire time that the loco etc is drawing
current beyond the frog and sparking does occur because this connection
is subject to dirt etc.
Regards,
Greg.P.
Elliott Cowton wrote:
Hi Elliott,
Taking a step back here, there are only three reasons I can think of as
to why you would be observing sparking:
1/ There is a short circuit
2/ There is a broken circuit
3/ You have an HF track 'cleaner' trying to rectify (2)
Applying some basic principals, (2) can be discounted if you haven't
got (3) because the current/voltage isn't high enough to cause a spark,
which leaves only (1). However, I cannot see how you can get a short
circuit like this with a dead-frog turnout, even if you do back-feed it
- the rails exhibiting the short would have the same polarity unless
they are being supplied from different controllers.
Which all leads me on to say.....are you really sure this is a dead
frog turnout ? All the symptoms you describe are characteristic of live
frog turnouts, not deadfrog.
If you need help with wiring live frog turnouts, have a look at
http://mrol.gppsoftware.com/livefrogwiring.asp - this is the only way
to properly wire live frog turnouts.
Hope this helps,
Graham Plowman
Elliott Cowton wrote:
Any loco sitting beyond the frog is going to draw current when the
turnout is aligned to that loco (or lighted train ...)
The spring conact under the point should be carrying the current, not
the stockrail to point touching.
I disagree. If the traction current to a loco beyond the frog passes
between stock rail and point, there will be (small) sparks.
No problem - feed the rail beyond the frog with the opposite polarity to
the stock rail and you get BIG sparks - however, in the description the
train keeps running so that isn't it.
turnout is aligned to that loco (or lighted train ...)
Yes, but the voltage and current is not sufficient to cause sparking in
general use. There must either be a short or a broken circuit. I merely
pointed out that an HF track 'cleaner' highlights this problem.
This is wrong. Both can and do carry the current in a Peco turnout.
between stock rail and point, there will be (small) sparks.
I'm not sure what you are describing here, but I would contend that if
there is any sparking at all, then there is some kind of electrical
problem such as a short or a broken circuit or perhaps: dirty wheels
and rails.
the stock rail and you get BIG sparks - however, in the description the
train keeps running so that isn't it.
This sounds like a live frog to me, not a dead frog.
I fear that like Jane, my suggestions are being 'bullied'.
I have built several very large layouts over the years and have
hand-built track on a number of occasions as well as used both live and
dead frogs, so I can assure you that I have plenty of experience of how
turnouts are constructed and wired, including Peco turnouts!
Peco turnouts are made in such a way that there are only a limited
number of things that can cause shorts or sparking. Dead frogs are
pretty much fool-proof unless steam roller wheels are being used which
bridge the frog and the other track is being back fed with opposite
polarity. As I pointed out, there is only one way to wire live frog
turnouts: http://mrol.gppsoftware.com/livefrogwiring.asp and providing
this method is used, live frogs will not cause a problem.
Based, on the information provided by Elliot, the symptoms he describes
suggest that the turnout may not be a dead frog. Like Jane, I can also
identify a live frog turnout just by looking at the crossing V (frog).
Elliot: Is there any possibility you could post a picture of the
crossing V ?
In the mean time, may I suggest to Elliot that he fits insulated joints
to the crossing V as indicated in
http://mrol.gppsoftware.com/livefrogwiring.asp and ensure that the
turnout is only fed from the toe (switch blade) end.
Graham Plowman
Certainly an HF track/wheel dirtier could cause the problem.
The original poster said the sparking was evident in darkness/low light
- a short circuit should cause the overload cut-out to trip = no
sparking ;-)
No, I'm right, otherwise why would Peco bother to put the spring contact
there, and why do Peco turnouts misbehave electrically when the contact
is damaged.
We're basically agreeing!
If the rail beyond the frog gets its current from the stock-rail/point
connection and there is a load (loco, lighted coach ...) on that track,
as there is when a train passes through and beyond said turnout, then
the point blade/stock rail contact is passing that current. Given poor
contact, there will be sparking. (or no go)
Not from me, I hope.
What you are suggesting would overload the cut-out whenever the turnout
was aligned. Elliot was describing the sparking when trains were passing
which is either a wheel intermittently connecting + to - or poor
connection of the traction current to one of the relevant rails.
As the train keeps going and the overload doesn't cut out it is _not_ a
direct short circuit.
I disagree here. Doing so would eliminate the self-switching function of
the Peco turnout to the following tracks and still leave the poor
traction current connection within the turnout.
No! It doesn't cause the problem. It is a tool which simply highlights
the presence of an already existing problem!
- a short circuit should cause the overload cut-out to trip = no
sparking ;-)
Well since I don't recall DCC being mentioned, then I assume DC is
involved, in which case, the cut out trip is quite slow and it is
possible that a momentary short is not enough to cause the cut out to
drop. This is one of the problems people blame DCC for because it has a
cut out system far in advance of any DC system and threfore, it drops
out due to momentary shorts caused by poor wiring. You can't get away
with this dodgy wiring in DCC.
there, and why do Peco turnouts misbehave electrically when the contact
is damaged.
No Greg, I am sorry, but you are wrong. Not all Peco turnouts (eg code
75, 009) have the spring contact (I am assuming you mean the little
tabs on the switch blades which tuck under the stock rails and make
contact) and they certainly don't always misbehave without them. So how
do they work ? They work in exactly the same way as the code 100
turnouts do if you remove the tabs. The tabs are an insurance policy,
not an absolute requirement. The turnouts will work without them, but I
will conceed that their absense can make Peco turnouts unreliable when
dirt gets on the sides of the stock rails. With live frogs, we simply
bond the switch rails to the stock rails and therefore, never have this
problem.
was aligned. Elliot was describing the sparking when trains were
passing
which is either a wheel intermittently connecting + to - or poor
connection of the traction current to one of the relevant rails.
As the train keeps going and the overload doesn't cut out it is _not_ a
direct short circuit.
See above. DC controllers will tollerate momentary shorts.
the Peco turnout to the following tracks and still leave the poor
traction current connection within the turnout.
We are speculating about a turnout which we haven't seen and we don't
know what the wiring is around it.
All sparking is caused by either a short or a broken circuit. In the
case of a dead-frog turnout, the number of ways a short can occur are
very limited, however, if the problem is a short, evidently the turnout
is being back fed with an opposing current, probably bridged by wheels
on the frog - a case for checking wheel standards and back-to-backs.
If you are relying on switch blades to do your switching for you then
you are asking for trouble in the future. All switching should be done
by point motor switches/relays for turnouts themselves and isolating
switches for the lines they service - anything but switch blades. And
since there appears to be a short situation, the only way to stop it is
to fit insulated joints and look at/rearrange the feeds involved.
Since neither of us is fully cogniscent with Elliot's situation, until
we see a close-up photo of the frog and get an idea of the electrical
feeds involved, there is little point in us arguing about it.
Graham Plowman
Further to my previous message, Elliot's original message states that
the problem occurs at the switch blade tips.
If any sparking occurs here then if the turnout is dead-frog, then it
is almost certainly being back fed by a reversed polarity - fed from
other end of yard by another controller or a live frog at the other end
of the yard ?
If sparking occurs and the turnout is live-frog, then it isn't wired
properly. See: http://mrol.gppsoftware.com/livefrogwiring.asp There is
also a case to check wheel standards and back-to-backs.
Graham Plowman
The third possibility is that the sparking at the point blade tips is
caused by current travelling to the loco motor. That would only occur
when the loco was on the track from the point blade on.
Live frog Peco turnouts work in the same electrical manner as dead frog
turnouts with the exception of the frog wiring.
(I think ;-)
Regards,
Greg.P.
caused by current travelling to the loco motor. That would only occur
when the loco was on the track from the point blade on.
True - I intimated to that effect in my last reply.
turnouts with the exception of the frog wiring.
(I think ;-)
Out of the box that is true with the exception that they don't all have
the tabs (eg code 75 range).
However, the out-of-the-box wiring is incorrect and needs to be
modified to http://mrol.gppsoftware.com/livefrogwiring.asp (Peco
actually makes code 75's to have these modifications) for them to work
properly - in this condition, the switch blades are electrically bonded
to the stock rails so there cannot be any 'sparking' between them. A
lot of clubs don't modify live frogs and use them as though they were
dead frogs and as a result, get themselves into all kinds of trouble
with shorts everywhere!
Regards,
Graham Plowman
I have to admit that my Code 75 turnouts went straight on to the layout
as soon as they arrived.
I wired them as simple dead frog turnouts but with the frog wired
through the on-motor switch from the stock rails.
I didn't get them wrong! =8^D
Hmmm, looks like I'm due for problems in the future - I've learned
something!
I'm a bit puzzled by your "...the out-of-the-box wiring is incorrect and
..."
In what sense is it "incorrect"?
Regards,
Greg.P.
something!
I'm a bit puzzled by your "...the out-of-the-box wiring is incorrect
and
..."
Because the switch blades are not electrically bonded to the stock
rails, the switch rails are not broken and the crossing V is not
properly isolated.
The reason Peco supply them the way they do is so that they (sort of)
function if you use them out of the box. If they were wired properly,
they wouldn't work out of the box because they would need an aux switch
to handle the crossing V.
Graham Plowman
Because if you don't break the links marked in yellow you will have a
dead short when you add the links marked in red.
Keith
NB. I thought Grahams page would explain it, but the idea is to divide
the point up into 3 pieces, left and right stock rail/blade sets and
the frog so that the frog polarity can be externally switched. The red
links provide power to the blades at the same polarity as the adjacent
stock rail so that, 1. you are not reliant on blade contact for power
2. the blade remains at stock rail potential when open so you can't
get shorts through the back of flange contacting the open blade.
His page says _what_ to do, but not _why_.
As I'm apparently trying to achieve an end that he has rejected, I need
to know why he says each modification should be done.
but the idea is to divide
I can see that that could be a problem for me long term as I hadn't
noticed the lack of under-blade contacts.
I've never had that problem so I'm not sure I need to fix it. :-)
I don't want to fix the problem of following track isolation through
insulated fishplates because I consider it to be a positive function.
Regards,
Greg.P.
You will if you run out-of-gauge wheels or wheels with large treads or
you get a derailment.
insulated fishplates because I consider it to be a positive function.
In that case, you live frogs will never be correctly wired and you will
have a potential short situation which should be corrected.
Graham Plowman
On 22 Mar 2006 14:26:22 -0800, snipped-for-privacy@gppsoftware.com wrote:
This is just not so Graham, use of the frog switching to give self
isolation of sidings is normal DC practice that I followed for 30+
years with no problems, largely eliminates the need for section
isolators except for platform ends and loco yards. With the points
wired correctly as you and I recommend the siding isolation feature
still works perfectly well using whatever switch you use for the frog
switching.
I have variously used point motor auxiliary contacts, relays,
microswitches and extra contacts on the panel switch, all with equal
success. My present layout has examples of the first 3 of these.
Keith
isolation of sidings is normal DC practice that I followed for 30+
years with no problems, largely eliminates the need for section
isolators except for platform ends and loco yards. With the points
wired correctly as you and I recommend the siding isolation feature
still works perfectly well using whatever switch you use for the frog
switching.
I have variously used point motor auxiliary contacts, relays,
microswitches and extra contacts on the panel switch, all with equal
success. My present layout has examples of the first 3 of these.
Absolutely agree with you on all points.
However, if one has more than one loco and one is operating DC, then
self isolation of sidings via their turnouts presents a problem: you
cannot store any other locos in them. That is why I said one should use
isolating sections within sidings otherwise you are into an operational
pattern which is compromised by the control system needing to keep
locos away from each other.
Graham
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