Date   

Isolating the motor

David MacLeod <davermacleod@...>
 

Hello,

I am installing a Digitrax non-sound decoder in a very old British steam locomotive. I have not been able to isolate the motor from the frame because the motor has two nubs that fit into two corresponding notches on the frame. This is what secures the front of the motor. The back of the motor attaches to the frame with a single screw. Both motor brushes are isolated from the frame. If I solder the Gray/Orange wires directly to the brushes, will this blow the decoder?

Thanks,

Dave MacLeod


Re: Reverse Loops and Occupancy Detection

Vollrath, Don <dvollrath@...>
 

Ed,

 

If you use a current transformer occupancy sensing device like the NCE BD20 and arrange for it to measure track current between the A-R unit output and the track it will work just fine. It doesn’t matter which track lead goes through the transformer hole of the BD20, nor the actual direction/polarity of the A-R track. Other brand products using the isolated current transformer measurement technique will work equally as well.

 

Other schemes that measure current to the input side of an auto-reverser will indicate continuous A-R track occupancy due to the small but continuous measurable current flow it takes to operate the A-R unit. Diode drop type occupancy sensors will have the same issue. Also, diode drop type occupancy sensors are usually not isolated from rail power making them difficult to deal with the rail swapping connections of the A-R controller if/when attempted to be connected to the output side of the A-R controller.

 

However – If the polarity of your A-R section is controlled by a relay or DPDT switch contacts of a turnout machine… you might be able to measure only track current flow as it goes into (only) the DPDT switch and be compatible with almost any type of track current occupancy sensing device.  

 

DonV

 

From: WiringForDCC@... [mailto:WiringForDCC@...]
Sent: Sunday, July 10, 2016 6:59 AM
To: WiringForDCC@...
Subject: [WiringForDCC] Reverse Loops and Occupancy Detection

 




I would like to add occupancy detection to an existing hidden reverse loop.  Is the detector affected by the reversing operation? In other words, when the loop reverses does it cause a current to flow in the power leads that would cause the detector to change its reading?

 

Ed Robinson

 





Reverse Loops and Occupancy Detection

Ed
 

I would like to add occupancy detection to an existing hidden reverse loop.  Is the detector affected by the reversing operation? In other words, when the loop reverses does it cause a current to flow in the power leads that would cause the detector to change its reading?


Ed Robinson



Re: Booster workload by measuring input?

Mark Gurries
 

Don is right.

Adding more information, 

Different booster have different electrical designs.   Digitrax used a "linear regulator method “ of regulating the track voltage and current limit where as NCE has a very efficient internal switching power supply to regulate the voltage and current limit**.   The switching power supply keep the booster cool which is why there is no heatsink on NCE boosters.
 
So in addition to the high capacitance smoothing out the current to an average current as opposed to a peak current, the relationship of current input and current output can be even FARTHER apart depending on the booster’s internal circuit design.

In terms of some kind external measurement there is a closer relationship of current in versus current out with Digitrax.   But it still not an accurate indication and some kind of scaling factor will have to applied.


**Excludes the latest NCE boosters that are provided with a NCE DC power supply specifically for them (PB5, DB5 & SB5).    With these new designs now have the provided NCE power supply determine the booster's output track voltage and current.

On Jul 8, 2016, at 10:26 AM, 'Vollrath, Don' dvollrath@... [WiringForDCC] <WiringForDCC@...> wrote:



You can get a crude indication of booster load by measuring amps on the input side of the booster. But there may not be a  close correlation between input and booster output amp numbers. The primary booster rating limitation is supposedly on output current (ie – amperes) going to the track. Putting an ammeter on the input wires to the booster is an indication of Power (volts x amps or speed x torque) being consumed. But there usually is temporary energy storage/buffer capacitors inside the booster to accommodate booster output current to circulate. So it is possible for more amperes to circulate between the booster output and track than what appears as amperes on the input side of the booster. Especially true if there is ‘extra’ voltage available to power the booster. Try measuring both at once with a heavy booster load and tell us the results in your particular case.
 
DonV
 
From: WiringForDCC@... [mailto:WiringForDCC@...] 
Sent: Friday, July 08, 2016 11:17 AM
To: WiringForDCC@...
Subject: [WiringForDCC] Booster workload by measuring input?
 


We're using pretty much all Digitrax boosters in the club setup, and I'd like to have a constant, consistent reference to how hard a booster is working.  I would like to know if I need to shift loads or recommend purchasing another booster.

Would putting a standard Ammeter & Voltmeter between the power supply and booster give me a pretty decent idea of what the booster is pulling?  (Most of the digital meters I'm seeing are sold as a combo ammeter/voltmeter.  Just the ammeter would probably be good enough.)  Would I have to apply a corrective factor, or would a, say, 4A measurement from the power supply be pretty close to 4A booster output?

Puckdropper 





Best Regards,

Mark Gurries
Electrical Engineer
DCC Website & NMRA DCC Clinics: www.markgurries.com




Re: Booster workload by measuring input?

Vollrath, Don <dvollrath@...>
 

You can get a crude indication of booster load by measuring amps on the input side of the booster. But there may not be a  close correlation between input and booster output amp numbers. The primary booster rating limitation is supposedly on output current (ie – amperes) going to the track. Putting an ammeter on the input wires to the booster is an indication of Power (volts x amps or speed x torque) being consumed. But there usually is temporary energy storage/buffer capacitors inside the booster to accommodate booster output current to circulate. So it is possible for more amperes to circulate between the booster output and track than what appears as amperes on the input side of the booster. Especially true if there is ‘extra’ voltage available to power the booster. Try measuring both at once with a heavy booster load and tell us the results in your particular case.

 

DonV

 

From: WiringForDCC@... [mailto:WiringForDCC@...]
Sent: Friday, July 08, 2016 11:17 AM
To: WiringForDCC@...
Subject: [WiringForDCC] Booster workload by measuring input?

 



We're using pretty much all Digitrax boosters in the club setup, and I'd like to have a constant, consistent reference to how hard a booster is working.  I would like to know if I need to shift loads or recommend purchasing another booster.

Would putting a standard Ammeter & Voltmeter between the power supply and booster give me a pretty decent idea of what the booster is pulling?  (Most of the digital meters I'm seeing are sold as a combo ammeter/voltmeter.  Just the ammeter would probably be good enough.)  Would I have to apply a corrective factor, or would a, say, 4A measurement from the power supply be pretty close to 4A booster output?

Puckdropper



Booster workload by measuring input?

Puckdropper
 

We're using pretty much all Digitrax boosters in the club setup, and I'd like to have a constant, consistent reference to how hard a booster is working.  I would like to know if I need to shift loads or recommend purchasing another booster.

Would putting a standard Ammeter & Voltmeter between the power supply and booster give me a pretty decent idea of what the booster is pulling?  (Most of the digital meters I'm seeing are sold as a combo ammeter/voltmeter.  Just the ammeter would probably be good enough.)  Would I have to apply a corrective factor, or would a, say, 4A measurement from the power supply be pretty close to 4A booster output?

Puckdropper


Re: DETECTION BLOCKS - Occupancy Detection

Steven Haworth
 

I used a pair of BD8 units from these guys:
http://www.wsaeng.com/

Wonderful stuff, and it works with both DCC and non-DCC, with lots of options for the output, and VERY detailed user manual (which is free online at the site, btw).

For my layout, I'm using these to drive panel and trackside occupancy lights.

Wiring - I run wiring from each block (both rails isolated) to a wiring panel (one per town / area).  From there, I group all the feeds from one side into a common rail, and route the individual feeds from the other rail (for each block) through the BD8 circuit.

Again, the user's manual on the site has full details and very thorough explanations, of this scheme as well as most other block-detection schemes.



- Steven Haworth
RGS history - http://www.rgsrr.info/
Blog - http://rgsrr.blogspot.com/


Re: DETECTION BLOCKS

Ed
 

Thanks Mark. You confirmed the way I thought it worked.

Ed Robinson


Re: DETECTION BLOCKS

rg <richg_1998@...>
 

Below is a link to detection curcuits this guy has used. Might give some ideas. 
I bought his dcc ampmeter curcuits which work as advertised. 

Rich



On Monday, June 27, 2016, 9:57 PM, lehighman@... [WiringForDCC] wrote:



I am building a new layout using DCC and want to install signals.  I understand that this requires I set up a detection block(s) for each signal.  Blocks are also set up to distribute power throughout the layout or to add reversing sections. My question involves my confusion regarding how each of these blocks fits together.  I isolate power blocks by cutting each rail going into and out of the block – a total of 4 cuts per block.  I feed power to the block through feeder wires connected to both rails about every 3 feet.  What cuts do I make to set up a detection block? As best I can tell, I only need to isolate one rail for each detection block with a cut on either end and run the power lead to that rail thru the detection circuit with the other rail being powered by the normal track feeder.  Is this correct? I also need to determine the location and length of each detection block – is there a good reference to read to help me there?


Ed Robinson





Re: DETECTION BLOCKS - Occupancy Detection

Vollrath, Don <dvollrath@...>
 

Glen,

One way to detect track block occupancy is to measure current drawn by a loco when on those tracks. One can put diodes in series with the track to provide a detectable ~0.75V per diode and easily determine when a loco drawing current is on that section of track. The method you speak of probably used a full wave rectifier bridge with the AC connections in series with the track leads and the + & - DC leads shorted together. A 1.5V bulb connected across the AC-AC leads would provide an occupied/empty indication, while the nearly constant voltage drop of the diodes protected the bulb from over-voltage. The basic idea can work great for DC or DCC… If that is all you want it to do.

 

However, there are some limitations and drawbacks. 1) The 1.5V drop of the diodes is undesirable for DCC. In the olden days of DC one was used to constantly adjusting the throttle to maintain the desired loco speed… And there was usually plenty of voltage available from the controller to overcome the ‘lost’ 1.5 volts to maintain race-track speeds. So when the loco encountered a monitored section of track, one simply ignored a speed change or made yet another adjustment of the throttle to maintain the speed. 2) With DCC there is little extra voltage headroom to overcome the 1.5V necessary to operate the sensor. And our expectations are that the loco will be able to maintain operating speed as it enters or leaves a monitored section of track. 3) Note that for the incandescent bulb to light up, the loco must draw enough current to light up the lamp… 30-45 ma. Locos may be detected but not trailing cars with 5-10 kOhm resistor wheelsets. 4) The simple incandescent bulb will work on AC or DC and is somewhat intolerant of ‘minor’ voltage fluctuations of the diode bridge carrying current to the track. An LED is not a very good candidate to take its place because it works with only one polarity (ie – DC) and needs protection from allowing too much current to flow (10’s of milliamps) to prevent burnout. There are similar schemes using opto-couplers of today instead of incandescent lamps to yield an electrical signal isolated from track voltage.

 

There are other track current detection products available today using the voltage drop of a single diode plus more sensitive electronics to yield a yes/no answer of track occupancy. But these also are not necessarily isolated from the electrical circuits of the track. Measuring DCC current flow via a ‘current transformer’ such as that used by the NCE BD-20 and other similar products from other manufacturers provides an electrical signal of occupancy without any undesirable voltage drop and also electrical isolation from that of the track. These can be sensitive enough to detect trailing cars with resistor wheelsets.

 

DonV

 

 

From: WiringForDCC@... [mailto:WiringForDCC@...]
Sent: Tuesday, June 28, 2016 1:21 PM
To: WiringForDCC@...
Subject: [WiringForDCC] DETECTION BLOCKS - Occupancy Detection

 




Back in the ‘80’s I operated on a layout that had block occupancy indicators. Simplicity at its best.

 

A bridge rectifier with a 1.5v lamp wired across the bridge. All it was required to do was to light a bulb in the control panel. These were used in tunnels and blind track sections out of the sight of operators.

 

Could this be used with DCC? Would the 1.5v output light an LED?

 

Glenn

 


From: WiringForDCC@... [mailto:WiringForDCC@...]
Sent: Monday, June 27, 2016 21:58
To:
WiringForDCC@...
Subject: [WiringForDCC] DETECTION BLOCKS

 



I am building a new layout using DCC and want to install signals.  I understand that this requires I set up a detection block(s) for each signal.  Blocks are also set up to distribute power throughout the layout or to add reversing sections. My question involves my confusion regarding how each of these blocks fits together.  I isolate power blocks by cutting each rail going into and out of the block – a total of 4 cuts per block.  I feed power to the block through feeder wires connected to both rails about every 3 feet.  What cuts do I make to set up a detection block? As best I can tell, I only need to isolate one rail for each detection block with a cut on either end and run the power lead to that rail thru the detection circuit with the other rail being powered by the normal track feeder.  Is this correct? I also need to determine the location and length of each detection block – is there a good reference to read to help me there?

 

Ed Robinson

 

 

 





DETECTION BLOCKS - Occupancy Detection

Glenn
 

Back in the ‘80’s I operated on a layout that had block occupancy indicators. Simplicity at its best.

 

A bridge rectifier with a 1.5v lamp wired across the bridge. All it was required to do was to light a bulb in the control panel. These were used in tunnels and blind track sections out of the sight of operators.

 

Could this be used with DCC? Would the 1.5v output light an LED?

 

Glenn

 


From: WiringForDCC@... [mailto:WiringForDCC@...]
Sent: Monday, June 27, 2016 21:58
To: WiringForDCC@...
Subject: [WiringForDCC] DETECTION BLOCKS

 




I am building a new layout using DCC and want to install signals.  I understand that this requires I set up a detection block(s) for each signal.  Blocks are also set up to distribute power throughout the layout or to add reversing sections. My question involves my confusion regarding how each of these blocks fits together.  I isolate power blocks by cutting each rail going into and out of the block – a total of 4 cuts per block.  I feed power to the block through feeder wires connected to both rails about every 3 feet.  What cuts do I make to set up a detection block? As best I can tell, I only need to isolate one rail for each detection block with a cut on either end and run the power lead to that rail thru the detection circuit with the other rail being powered by the normal track feeder.  Is this correct? I also need to determine the location and length of each detection block – is there a good reference to read to help me there?

 

Ed Robinson

 



Re: DETECTION BLOCKS

Glenn
 

I would suggest getting a book on DC (analog) wiring and follow the directions for two-rail wiring, not common rail, and cutting gaps in both rails where you want a block to end. You will need a detector for each block.

 

There is no set of rules for block length.

 

Glenn

 


From: WiringForDCC@... [mailto:WiringForDCC@...]
Sent: Monday, June 27, 2016 21:58
To: WiringForDCC@...
Subject: [WiringForDCC] DETECTION BLOCKS

 




I am building a new layout using DCC and want to install signals.  I understand that this requires I set up a detection block(s) for each signal.  Blocks are also set up to distribute power throughout the layout or to add reversing sections. My question involves my confusion regarding how each of these blocks fits together.  I isolate power blocks by cutting each rail going into and out of the block – a total of 4 cuts per block.  I feed power to the block through feeder wires connected to both rails about every 3 feet.  What cuts do I make to set up a detection block? As best I can tell, I only need to isolate one rail for each detection block with a cut on either end and run the power lead to that rail thru the detection circuit with the other rail being powered by the normal track feeder.  Is this correct? I also need to determine the location and length of each detection block – is there a good reference to read to help me there?

 

Ed Robinson

 



Re: Use of auto reversers

Vollrath, Don <dvollrath@...>
 

Jim,
Auto-reversers are needed only when the train or loco can somehow be turned around to still run 'forward' but in the other direction on the same track.
Your description of a 'single track continuous loop' doesn't seem to do that... until you start describing multiple points of cross-overs between mainline tracks.
If you squeeze a simple oval into a folded dog-bone shape with parallel mainline tracks running to and from the loops at the ends, and then expect to have crossovers between the mainline tracks... then you have a reversing section issue.
Take a look at http://www.wiringfordcc.com/track_2.htm#a43 and scroll downward to read about the possibilities.

DonV

-----Original Message-----
From: WiringForDCC@yahoogroups.com [mailto:WiringForDCC@yahoogroups.com]
Sent: Tuesday, June 28, 2016 9:01 AM
To: wiringfordcc@yahoogroups.com
Subject: [WiringForDCC] Use of auto reversers

As you will see from this post, I'm new to DCC. I have a question regarding using a single track continuous loop.

I will have a classification yard that will be entered by trains moving along the track in two locations when passing the yard . Does this create a need for an auto reverser? If so where should it be placed?

Also since there will be numerous places where the track will cross (such as at industry sidings) should auto reversers be used in these locations?


------------------------------------
Posted by: Jim Rizzolo <jimrizzolo@yahoo.com>
------------------------------------

http://www.WiringForDCC.com
------------------------------------

Yahoo Groups Links


Re: Use of auto reversers

David Klemm
 

Jim,

The best way I determine the need for an auto reverser is to draw my track plan with 2 different colors for the rails. So for example I use red and black and then I look for spots where where black and red intersect. 

BTW, no one here will be able to answer you just based on your words. A diagram will be a must. 

David Klemm
6s Plus

_____________________________

From: Jim Rizzolo jimrizzolo@... [WiringForDCC] <wiringfordcc@...>
Sent: Tuesday, June 28, 2016 11:50
Subject: [WiringForDCC] Use of auto reversers
To: <wiringfordcc@...>


 

As you will see from this post, I'm new to DCC. I have a question regarding using a single track continuous loop.

I will have a classification yard that will be entered by trains moving along the track in two locations when passing the yard . Does this create a need for an auto reverser? If so where should it be placed?

Also since there will be numerous places where the track will cross (such as at industry sidings) should auto reversers be used in these locations?




Use of auto reversers

Jim Rizzolo <jimrizzolo@...>
 

As you will see from this post, I'm new to DCC. I have a question regarding using a single track continuous loop.

I will have a classification yard that will be entered by trains moving along the track in two locations when passing the yard . Does this create a need for an auto reverser? If so where should it be placed?

Also since there will be numerous places where the track will cross (such as at industry sidings) should auto reversers be used in these locations?


Re: DETECTION BLOCKS

Mark Gurries
 


On Jun 27, 2016, at 6:57 PM, lehighman@... [WiringForDCC] <WiringForDCC@...> wrote:



I am building a new layout using DCC and want to install signals.  I understand that this requires I set up a detection block(s) for each signal.  Blocks are also set up to distribute power throughout the layout or to add reversing sections. My question involves my confusion regarding how each of these blocks fits together.  

Electrical blocks do not exist in the prototype and are use to contain shorts.  The ultimate length limits  are defined by the booster distance coverage.   Within a given booster district, these blocks are created by the use of DCC circuit breakers or some device used to disconnect track power.  The Power District tracks are defined by functional working areas (Yards, Brand Lines, Staging) or key tracks like main line versus industrial sidings.  Think of what people will be doing and how to prevent what other people are doing from electrically short circuit protection point of view.   A well design power district plan will allow a lot of operators to remain operating trains despite a given engineer dealing with a derailment.

Signal blocks are defined by "control points" which typically defined by turnouts that control main line train flow (passing siding or interlocking).  

Between control points on the main line, detection blocks  are spaced apart so there is ample notification for given trains about other trains so they can stop.  Everything is defined by an operational safety point of view which has nothing to do with electrical blocks..   For model railroad purposes, it simply becomes the length of the longest train length you wish to model on you layout. 

Example:  Simple loop with 3 signal aspects.   If you train length is 12Feet long, you will need 4 signal blocks which means you need 48 Feet of loop track to always allow the train to see a green signal ahead of it.   The block are as follows:  

1) The block the trains is in
2) Red Block behind the train protecting the train from behind
3) Yellow Block also protecting you from the train from behind.
4) The Green Block ahead of you.

There is a more to this especially if you want to follow some prototype implementation of signalling.

ABS signalling only protects you from trains BEHIND you going in the same direction.  Does nothing to help you SAFELY see what is ahead in terms of trains but would indicate if you were taking the main line or passing siding.  Dispatcher still authorizes all movement via train orders.

APB is bidirectional ABS that does allow you to see both train AHEAD AND BEHIND.  Dispatcher still authorizes all moments via train orders.

CTC is dispatcher controlled signals.  Authority is granted by signal indication.

Some single track signal systems only monitored control points and did not care about trains between them.  All the signals along the way were advance signals telling them what to expect to see at the next control point..

I isolate power blocks by cutting each rail going into and out of the block – a total of 4 cuts per block.  I feed power to the block through feeder wires connected to both rails about every 3 feet.  What cuts do I make to set up a detection block?


No problem here from an electrical connection point of view..

You now have to translate you DCC power districts into signal blocks by looking at the length of the electrical blocks relative to your train length.

IF a power district block is long enough to hold a train, it can be used as a signal block too.

If a given power district block is to short length wise, it must be combined with another adjacent power district block detection wise to create one that is long enough.


If one was to design a layout with signals.  It is alway best to define signal blocks first and then see if they can be used as power districts.  Typically it works out very well.

As best I can tell, I only need to isolate one rail for each detection block

Correct.

with a cut on either end and run the power lead to that rail thru the detection circuit with the other rail being powered by the normal track feeder.  Is this correct?


Correct.

Best Regards,

Mark Gurries
Electrical Engineer
DCC Website & NMRA DCC Clinics: www.markgurries.com




Clean Track Is Necessary For Good DCC Oppreation.

aztecmfg@...
 

FS Track Cleaning Cars in scales from "Z" to "G".

<aztectrains.com>

<aztecmfg@...>

John Claudino

 


DETECTION BLOCKS

Ed
 

I am building a new layout using DCC and want to install signals.  I understand that this requires I set up a detection block(s) for each signal.  Blocks are also set up to distribute power throughout the layout or to add reversing sections. My question involves my confusion regarding how each of these blocks fits together.  I isolate power blocks by cutting each rail going into and out of the block – a total of 4 cuts per block.  I feed power to the block through feeder wires connected to both rails about every 3 feet.  What cuts do I make to set up a detection block? As best I can tell, I only need to isolate one rail for each detection block with a cut on either end and run the power lead to that rail thru the detection circuit with the other rail being powered by the normal track feeder.  Is this correct? I also need to determine the location and length of each detection block – is there a good reference to read to help me there?


Ed Robinson



Re: Light on turntable arch

Vollrath, Don <dvollrath@...>
 

Rich,

 

Not having reverse polarity protection to an LED powered directly from the DCC supply can cause a shortened lifetime of the LED. Yes, the LED seems to light correctly with current flowing in one direction, as when the DCC voltage reverses the LED does not light up but a human does not notice the blinking. HOWEVER most LEDs will suffer reverse voltage breakdown and conduct current in the reverse direction. Rated reverse voltage varies with LED color and manufacturing batch… usually only 5-7V. [look for the PIV spec on the data sheet.] So even with the resistor still in series to limit current… the forward plus reverse power dissipation creating internal heat in the LED is far greater than intended when operating in this mode. An extra hot semiconductor junction (the tiny part that gives off the light) shortens the lifetime. White or blue LEDs will be affected the most. Putting a diode in series or anti-parallel with the LED will work to protect the LED.

 

DonV

 

From: WiringForDCC@... [mailto:WiringForDCC@...]
Sent: Sunday, June 26, 2016 11:03 AM
To: WiringForDCC@...
Subject: Re: [WiringForDCC] Light on turntable arch

 



A 1k, 1/4 watt resistor works. My NCE Power cab panel has a common 3mm red led with resistor across the DCC output.

 

Rich

On Sunday, June 26, 2016, 10:20 AM, riogrande491 riogrande491@... [WiringForDCC] <WiringForDCC@...> wrote:



David -

 

Making it work is pretty simple. The DCC track signal actually has both positive and negative polarities, so the LED can light up full-circle, except for the dead-bands when the polarity on the bridge reverses.

 

However, there is a very important detail to which we must first attend. LEDs don’t like being connected backwards to a voltage greater than about 5 volts, and a typical DCC installation runs about 15 volts. If we don’t do something, about half the time the LED will experience a 15 volt reverse voltage. Soon they can grow dim or entirely fail. Others might be happy for the life of the layout. So if we don’t want risk tearing into the turntable to replace the LED, we need a way to prevent the reverse polarity from causing a future problem.

 

For the sake of discussion, let us assume that you will use a 1K ohm a/k/a 1000 ohm resistor in series with the LED. The particular resistor value is relatively unimportant. Let us also assume that the resistor is located underneath the turntable deck. Connect a small diode, typically a 1N914 or 1N4148 (a small diode with a glass body and two leads) across the two wires running up to the LED. Polarity is important! If it is wrong, the LED won’t light, and it is time to swap the diode end-for-end. If the LED lights up, and connections are secure, life is good!

 

The usual polarity of a 3mm LED can be found by the length of the leads. The longer one is usually positive or +. On a diode, one end has a band. That is the cathode or - connection. Just solder the cathode or - of the diode to the wire running to the longer lead of the LED, or +. Then it should outlast both of us.

 

All the best!

----------------------------------------------

Bob

 

 





Re: Light on turntable arch

rg <richg_1998@...>
 

A 1k, 1/4 watt resistor works. My NCE Power cab panel has a common 3mm red led with resistor across the DCC output.

Rich



On Sunday, June 26, 2016, 10:20 AM, riogrande491 riogrande491@... [WiringForDCC] wrote:



David -

Making it work is pretty simple. The DCC track signal actually has both positive and negative polarities, so the LED can light up full-circle, except for the dead-bands when the polarity on the bridge reverses.

However, there is a very important detail to which we must first attend. LEDs don’t like being connected backwards to a voltage greater than about 5 volts, and a typical DCC installation runs about 15 volts. If we don’t do something, about half the time the LED will experience a 15 volt reverse voltage. Soon they can grow dim or entirely fail. Others might be happy for the life of the layout. So if we don’t want risk tearing into the turntable to replace the LED, we need a way to prevent the reverse polarity from causing a future problem.

For the sake of discussion, let us assume that you will use a 1K ohm a/k/a 1000 ohm resistor in series with the LED. The particular resistor value is relatively unimportant. Let us also assume that the resistor is located underneath the turntable deck. Connect a small diode, typically a 1N914 or 1N4148 (a small diode with a glass body and two leads) across the two wires running up to the LED. Polarity is important! If it is wrong, the LED won’t light, and it is time to swap the diode end-for-end. If the LED lights up, and connections are secure, life is good!

The usual polarity of a 3mm LED can be found by the length of the leads. The longer one is usually positive or +. On a diode, one end has a band. That is the cathode or - connection. Just solder the cathode or - of the diode to the wire running to the longer lead of the LED, or +. Then it should outlast both of us.

All the best!
----------------------------------------------
Bob



3501 - 3520 of 12975