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Hi Ken!

You asked:

QUESTION: Is there some other way, that I'm not seeing and should

be

much worried about, to short out the decoder and that is what
generates all this talk and fears?

If the decoder is properly wired, not under rated for the load, and
does not take a dip in the "very realistic lake", chances are that
only a motor failure could take out a decoder.

My perspective is from garden scale where 3, 5 and 8 amp decoders are
the norm. (so are real lakes) So, this may not apply to you if you
are in one of the small scales.

What we have learned from garden railroads may be important in small
scales too.


Burning out decoders:
1 - Stall current:


Most people measure the stall current wrong. You have to monitor the
input voltage and the current with the motor locked.

For example if the supply only puts out 5 amps at 18 volts and you
measure 4 amps but don't look at the voltage, (which may have dropped
to 9 volts) you could wrongly believe that the stall current is only
4 amps, when in fact it may draw 10 or 11 amps at the full 18 volts.
All to often I've seen people measure the maximum output current of
their power packs when they thought they were measuring stall current.
Most decoders can not handle more than their rated stall current for
more than a second.

DO NOT ASSUME THAT IF YOU NEVER STALL YOUR LOCO OR THE WHEELS WILL
SLIP FIRST, THAT WILL SAVE YOU.

When you first give a motor it's first kick from a decoder, the motor
is stooped. IE! IT IS STALLED!!! A motor will always draw it's stall
current for some period of time before it starts moving.

The point is, Always make sure the stall current (or peak current)
rating is grater than the stall current of the motor. If the loco
manufacture does not tell you the stall current of the motor, measure
it while monitoring and maintaining full voltage.

It seems likely to me (because I have seen this happen more than
once,) an under sized decoder straining to get cars moving will fail
when there is a derailment somewhere in the train . The
operator/owner blames the failure on a short because of the
derailment. He defends his conclusion because he saw lights on the
layout flicker. In reality, the decoder was blown because the
derailment stalled his loco and the lights flickered when vital parts
of the decoder melted.

Burning out decoders:
2 - Failed motors:

Poor quality motors can fail. They can short out. In this case a fuse
between the motor and the decoder (not between the decoder and track)
might protect the decoder. However, if a failed motor shorts out it's
windings, it will draw much more current than the stall current. If
that happens for more than a few milliseconds the H-bridge will be
fried. Most fuses will not open the circuit fast enough to provide
any meaningful protection for the motor output of the decoder.

In garden railroads, experienced railroaders opt for decoders with
built in over current, short circuit and thermal overload protection.
( Such decoders will simply flash all the lights if mis-wired and
placed on a track.) All that fancy circuitry probably does not fit in
HO or N. ( But then you guys don't put tachometer monitored brush-
less DC cooling fans on your decoders either.) :>)

In Garden scale popular locos like the SD45 have four motors, each
drawing more current than your whole train. If a motor fails it is
usually replaced. Even if is decided not to repair the loco, we
usually remove the decoder for use in some other loco, We have almost
no custom decoders designed for a single loco, one or two sizes fit
all. If a small scale loco burns out the motor and it can't be
repaired, then the decoder possibly will not fit in some other loco
it was designed for. Because of this, and considering the cost of a
decoder, it may not we smart to put try to put expensive protection
circuitry in small scale locos.

If you want to protect the decoders from motor failures, then there
is only one way I know of to do this. Limit the available current to
the decoder to the maximum amount of current they can safely supply.
That is what power managers like the PM42 are designed for, and why
some people use power districts with multiple smaller boosters rather
than one giant booster.

For example on my "G" scal layout, I could use 3 amp decoders in some
locos, but I don't. I use 5 amp decoders, that can dandle 10 amps
peak. My boosters are all 8 amps each, so if a motor shorted out, the
decoder only has to handle 8 amps, even tho it is designed to handle
10. As a result, the booster for that train will always cut off
before the decoder is damaged.

Don't know if this helps answer your question, but it's the best I
can come up with.

B0B

Exactly, Bob! While I'm really, really new (as in weeks) to DCC and
not an electrical guru at all, I have read and heard so much about
the crying fear of decoders being blown because there is a short. I
agree that if there's a derailment and the wheels short (like your
crowbar example)that's a power supply concern and not a decoder
problem.

Ignoring the "obvious" wiring errors, the only way I can see a
decoder
being blown because of a short is if:
1)the decoder output is connected directly to the rails, which is
possible if the motor is not, or rather no longer, isolated
2) or if the wires, or some component on the PCB, ground outs on the
metal chassis,
3) or the wires somehow become cross connected because their solder
connection breaks and the wire moves or their insulation is worn away
4) the decoder self destructs internally because of heat or excess
current draw or component aging

Seems to me most of these are preventable in the first place by
studying the loco, the decoder and its needs, existing wiring if any
and the careful placement, wire routing, connecting and soldering of
the decoder and its connecting wires, including the speaker and its
leads.

QUESTION: Is there some other way, that I'm not seeing and should be
much worried about, to short out the decoder and that is what
generates all this talk and fears?

Thanks in advance. Ken

--- In WiringForDCC@..., "bobgrosh" <bobgrosh@h...>
wrote:

--- rotortips <Rotortips@s...> wrote:
Has anyone tried to use a thermal circuit breaker or 1
Amp fuse
between an engine pick-up wire and the decoder to
protect the decoder
from short circuits?

No
First!!!
A fuse does not protect the item being powered. It protects the

power

supply.

--- rotortips <Rotortips@s...> wrote:
Has anyone tried to use a thermal circuit breaker or 1
Amp fuse
between an engine pick-up wire and the decoder to
protect the decoder
from short circuits?

No
First!!!
A fuse does not protect the item being powered. It protects the power
supply.

If your decoder shorts out, burns up or melts and draws the maximum
amout of current your supply can provide, the circuit breaker ( or
electronic equivilant inside the booster) will disconnect power from
the rails to prevent damage TO THE BOOSTER. It can not prevent damage
to the decoder, because the decoder is already damaged. Adding a fuse
to the engine simply duplicates the fuse that is already in the booster.

Second!!!

There is nothing that can "protect" a loco from a short circuit!

Nor is there any need to protect a loco from a short circuit. If you
have a shots circuit on your layout (IE laying a crowbar across the
rails) then the voltage on the track is "shorted out". That is to say
that there is no voltage (or almost no voltag) across the rails. A
short can no more do damage to the loco than turning off the power or
lifting the loco from the track. In fact, better power supplies include
a "crowbar" circuit. This is a circuit that monitors the output of the
power supply, and, if the supply malfunctions and starts to put out TO
MUCH VOLTAGE, the circuit shorts out the supply output in order to blow
the supplies fuse.

B0B

Fuses react much too slowly to offer protection to the dainty components inside a decoder.
DonV

don't think they will fit in scales lower than O

zekda99
--- rotortips <Rotortips@...> wrote:


---------------------------------
Has anyone tried to use a thermal circuit breaker or 1
Amp fuse
between an engine pick-up wire and the decoder to
protect the decoder
from short circuits?

Rotortips









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Has anyone tried to use a thermal circuit breaker or 1 Amp fuse
between an engine pick-up wire and the decoder to protect the decoder
from short circuits?

Rotortips

Thanks for the reply, Allan. I appreciate your time and expertise!
The switch itself is properly wired, and I even added the jumper
wires for the point rails like you suggested. And I understand which
polarity needs to power the frogs per postion of the two sets of
points. The real question I have is control. How do I control the 3
seperate frogs to provide the correct polarity for the 4 possible
track positions?

I saw the section on setting up a micro switch/piano wire for a
single frog. Is there a particular switch machine or circuit board I
could build to deal with the various "if" scenarios associated with
a 3-way turnout??

Thanks again!

DAVE

--- In WiringForDCC@..., "wirefordcc"
<wire4dcc_admin@c...> wrote:

Dave,

I'd like to answer your question, but I haven't seen one of these
turnouts yet. Even if I had, it would be hard to describe in

words.

I'll try to see one at my local hobby shop the next time I go and

I'll

make a drawing. Don't hold your breath waiting for the drawing.

I'm

working full time and going to school at night. My weekends are

taken

up studying. The drawing won't likely appear in my web page until

the

end of the semester.

In the interim, I suggest the following: Draw out the turnout.

Make

3 drawings; one each for the 3 routes the train can take. Label

the

stock rails + and - and follow it through the turnout. By noting
which set of points was moved to change the polarity of the rails,

you

will know which frog needs to be controlled by which set of points.

Allan

Hello Everybody.

I am in the middle of planning a new layout. My layout has been DCC
controlled using an older Digitrax Empire Builder system. However
now that I am expanding I have many many questions and the answers I
find are written in engineering eze and I do not fully understand
what they are saying.

Before I flood everyone with a bunch of questions should I make each
question a separate post or should put them all in one long e-mail.
I have looked through Allens site and answered all the track rolling
stock how to solder it up questions. The ones that are left deal
with the hardwar and features and the potential of what it can do or
how can I make it do what I want it to. I like how digitrax is set
up and think I want to keep using it. Given the space I have to fill
and the and the gerneral lack of population where I live I have to
run my layout pretty much by myself. So I need some way to dispatch
all of this but I do not want to hook up a computer because that
will detract from the 1969 feel I am trying to convey.

Thanks and once I am informed as to how I should post my questions I
will post away.

James

--- In WiringForDCC@..., "Marcus Ammann" <mammann@o...>
wrote:

Hi jeffln55

You have to wire up a DCC layout the same as a DC layout, with all

the

relevant plastic rail joiners where there is a possibility of a

short, just

like any layout.

You don't have to wire in any "blocks" that are used in DC layouts

to

isolate locos because the DCC decoder has a unique address and

will only

respond when addressed, leaving all other DCC locos on the track,
stationary.

Power districts, a form of blocks, is recommended for most medium

to large

layouts for troubleshooting etc. A small single operator layout

will operate

satisfactory with only one power district.

Visit Allan Gartner's Wiring for DCC at



for answers to all your questions.

Marcus.



-----Original Message-----
From: WiringForDCC@...

[mailto:WiringForDCC@...] On

Behalf Of jeffln55
Sent: Monday, 17 October 2005 10:52 PM
To: WiringForDCC@...
Subject: [WiringForDCC] So no plastic rail joiners needed when

using DDC to

run locos ?

Hi well are no plastic rail joiners needed to run DDC powered

Locos.

So no blocks correct?

Now all that is needed is the decoder added and run correct.

Thanks

this will be a new layout so wiring is not started as of yet.







Yahoo! Groups Links

Thanks okay understood.

Lucky I asked first.

Hi jeffln55

You have to wire up a DCC layout the same as a DC layout, with all the
relevant plastic rail joiners where there is a possibility of a short, just
like any layout.

You don't have to wire in any "blocks" that are used in DC layouts to
isolate locos because the DCC decoder has a unique address and will only
respond when addressed, leaving all other DCC locos on the track,
stationary.

Power districts, a form of blocks, is recommended for most medium to large
layouts for troubleshooting etc. A small single operator layout will operate
satisfactory with only one power district.

Visit Allan Gartner's Wiring for DCC at



for answers to all your questions.

Marcus.

Hi well are no plastic rail joiners needed to run DDC powered Locos.

So no blocks correct?

Now all that is needed is the decoder added and run correct.

Thanks

this will be a new layout so wiring is not started as of yet.

Hi asterrymc

12 volt lamps are ok for loco headlights when operated on DC due the
headlight only illuminates dimly when going slow and bright when going
faster. This also applies with constant brightness circuits and the lamp is
brighter with slow operation. When the loco stops the light is extinguished.

In DCC the headlight is illuminated bright when it is selected on and stays
illuminated with the loco stationary. Only off when selected off. This can
mean the headlight can be illuminated all the time while the power is
supplied to the layout. Light is on all the time.

A 40 mA incandescent dissipates about 1/2 a watt and this over a long time
will certainly cause some heat.

This is one of the reasons that I change all my incandescent lamps to
Prototype White LEDs. Incandescent lamps make lots of heat and a little
light, while a LED makes a lot of light and a little heat. Secondly a LED
generally only needs about 10 - 15 mAs of current.

I suggest for you next installation you use LEDs for the headlights.

Make sure you use Prototype White, Golden Glow or similar ones that don't
have the blue tinge that normal white LEDs have. The white LEDs are ok for
late model diesels, but not early and steam engines.

Marcus

Dave,

I'd like to answer your question, but I haven't seen one of these
turnouts yet. Even if I had, it would be hard to describe in words.
I'll try to see one at my local hobby shop the next time I go and I'll
make a drawing. Don't hold your breath waiting for the drawing. I'm
working full time and going to school at night. My weekends are taken
up studying. The drawing won't likely appear in my web page until the
end of the semester.

In the interim, I suggest the following: Draw out the turnout. Make
3 drawings; one each for the 3 routes the train can take. Label the
stock rails + and - and follow it through the turnout. By noting
which set of points was moved to change the polarity of the rails, you
will know which frog needs to be controlled by which set of points.

Allan

My first attempt at installing a DCC decoder in an old style Life-Like
GP18 (N scale) took much longer than I thought and with perseverance I
succeeded. The loco ran smoothly and the decoder functions all
worked. I even added a light for reversing. After running it for a
while I noticed that the grain of wheat bulbs I had installed where
starting to melt the case badly. I used 12V bulbs - how do I overcome
this heat problem for the next install?

Brian, as my branch line is really a preserved line with a main line
connection, engines crossing from main to branch will not be an every day
occurrence,so Iam prepared to put up with the two throttle option for now. But one more
problem has just come to light, I cant find my Compact!! I thought it was in
its box, but its empty! and I`ve spent the last hour looking for it. I will
have to re-think this idea through, the only reason I started this was to try
and avoid a short stopping the whole layout with out spending money on more
equipment. You have been very helpfull and I`ve learnt some thing in the
proccess. I dont suppose you live in Wiltshire? David.

David,
There is one thing I assumed.

Can the Lenz Compact be connected as a booster? Can you plug the command bus from the Lenz 100 into the Compact? If you don't know this, you'll have to check on the Lenz site.

If they can't be interconnected, then you will essentially have two independent railroads. When a loco drives across the gap, it'll stop, but there will be no short. You'll have to pick up a throttle connected to the other controller, and drive away....

Let me know if you have trouble when you actually hook it all up.

David,

It isn't strictly necessary to get an Accurate voltage reading (within
a few percent), although that is certainly possible. If the rails are
out of polarity, any AC meter will read something, maybe not steadily,
but it'll bounce around near, say, 10v (I'm making that number up),
While if the rails are in polarity, the reading may bounce around near
.1V. I hope you get the idea.

A simple test fixture would be a 16v (or 20 or 24) light bulb
connected to two aligator clips. Attach one clip to each side of the
rail and turn on the juice. If the light lights, switch the wires off
the booster (The branch line booster), and try again. Of course, you
turned the power off before you disconnected the feeder bus, right? If
the light still lights up, then I need to turn in my Electrical
Engineering Degree (Which will upset my mother no end!).

DCC Specialites.com makes and Tony's and Walthers sells, is a thing
call the RRAmpMeter, which can measure True RMS voltage, A thing you
need for DCC. It's not necessary for this project, but if the boosters
are too far out of amplitude with each other, you may want to set
your booster's output voltage. It is unclear to me whether Motor
Starting voltage is in actual volts, or a relative range. For a given
system, the two are indistingushable(sp?) from each other. However, if
MY system is set at 12.2v and YOURs is set at 18.7v, will our Locos
run significantly differently? Does it matter? But I digress.

Another thing that will tell you if the rails are in polarity or not,
is to run a loco over the gap. If its stops, you have a problem. :-)

If I understand your question correctly, Yes, the branch should have
bus wires seperate from the rest of the layout; feeding the output of
two boosters into each other is bad. Just be sure there is no polarity
difference at the rail gap. If your volt meter doesn't read zero volts
(AC) across the gap (of each rail) then you have a problem, switch the
wires coming off the boost, that should fix it.

Since you have a seperate set of bus wires, you need corresponding
feeders for the branch.

Thank you Brian for your help, very usefull this group,thanks again.Dave.