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Electrical Engineering

Electrical Engineering

posted 1 year 1 week ago

Electric Locomotive Parts

  I will now explain about the significant Locomotive Parts of a Metro Train System.

This diagram shows an AC electric locomotive, i.e a locomotive collecting AC power from an overhead line.  The red lines on the diagram indicate the single phase AC circuit, the green lines the DC circuits and the purple lines the 3-phase AC circuits.  A locomotive using DC traction current is similar, except that there is no single phase AC circuit or transformer.  The current passes directly from the pantograph (or shoe) to the main and auxiliary inverters.

Asynchronous Motor

Modern traction motor type using three phase AC electrical supply and now the favored design for modern train traction systems.  Can be used on DC and AC electrified railways with suitable control electronics and on diesel-electric locomotives. See the article on AC and DC Motors.


Axle Brush

The means by which the power supply circuit is completed with the substation once power has been drawn on the locomotive.  Current collected from the overhead line or third rail is returned via the axle brush and one of the running rails.


All trains are provided with a battery to provide start up current and for supplying essential circuits, such as emergency lighting, when the line supply fails.  The battery is usually connected across the DC control supply circuit.

Bucholz Relay

A device inserted in the oil cooling circuits of electric locomotive transformers to detect low oil pressure.  In this event, the relay trips out the power system.  Often a source of spurious circuit breaker trips if not carefully calibrated.


Most DC electric traction power circuits use a camshaft to open or close the contactors controlling  the resistances of the traction motor power circuit.   The camshaft is driven by an electric motor or pneumatic cylinder. The cams on the shaft are arranged to ensure that the contactors open and close in the correct sequence.  It is controlled by commands from the driver's cab and regulated by the fall of current in the motor circuit as each section of resistance is cut out in steps.  The sound of this camshaft stepping can be heard under many older (pre electronics) trains as they accelerate. 

Cannon Box

Sleeve used to mount a traction motor on axle in electric power bogies and sometimes including an axle brush.

Chopper Control

A development in electric traction control which eliminates the need for power resistors by causing the voltage to the traction motors to be switched on and off (chopped) very rapidly during acceleration.  It is accomplished by the use of thyristors and will give up to 20% improvement in efficiency over conventional resistance control.

Circuit Breaker

An electric train is almost always provided with some sort of circuit breaker to isolate the power supply when there is a fault, or for maintenance.  On AC systems they are usually on the roof near the pantograph.  There are two types - the air blast circuit breaker and the vacuum circuit breaker or VCB.  The air or vacuum part is used to extinguish the arc which occurs as the two tips of the circuit breaker are opened.  The VCB is popular in the UK and the air blast circuit breaker is more often seen on the continent of Europe.


Similar to a relay in that it is a remotely operated switch used to control a higher power local circuit.  The difference is that contactors normally latch or lock closed and have to be opened by a separate action.  A lighting contactor will have two, low voltage operating coils, one to "set" the contactor closed to switch on the lights; the other to "trip" off the lights.  Click here for diagrams and more detail.


Generic term for any solid state electronic system for converting alternating current to direct current or vice versa. Where an AC supply has to be converted to DC it is called a rectifier and where DC is converted to AC it is called an inverter.  The word originated in the US but is now common elsewhere.

Cooling Fans

To keep the thyristors and other electronic power systems cool, the interior of a modern locomotive is equipped with an air management system, electronically controlled to keep all systems operating at the correct temperature.  The fans are powered by an auxiliary inverter producing 3-phase AC at about 400 volts.

Creep Control

A form of electronically monitored acceleration control used very effectively on some modern drive systems which permits a certain degree of wheel slip to develop under maximum power application.  A locomotive can develop maximum slow speed tractive effort if its wheels are turning between 5% and 15% faster than actually required by the train speed.

DC Link

Used on modern electronic power systems between the single phase rectifier and the 3-phase inverter.  It is easier to convert the single phase AC from the overhead line to the 3-phase required for the motors by rectifying it to DC and then inverting the DC to 3-phase AC.

Dynamic Braking

A train braking system using the traction motors of the power vehicle(s) to act as generators which provide the braking effort. The power generated during braking is dissipated either as heat through on-board resistors (rheostatic braking) or by return to the traction supply line (regenerative braking).  Most regenerative systems include on board resistors to allow rheostatic braking if the traction supply system is not receptive.  The choice is automatically selected by the traction control system.  See also the Dynamic Brake section of our Brakes Page.


Train or locomotive mounted expanded steel resistor used to absorb excess electrical energy during motor or braking power control.  Often seen on the roofs of diesel electric locomotives where they are used to dissipate heat during dynamic braking.

Ground Relay

An electrical relay provided in diesel and electric traction systems to protect the equipment against damage from earths and so-called "grounds".  The result of such a relay operating is usually a shut-down of the electrical drive.  Also sometimes called an Earth Fault Relay.

GTO Thyristor

Gate Turn Off thyristor, a thyristor which does not require a commutation (reverse flow circuit) circuit to switch it off.  See Thyristor


Most recent power electronics development.  It is replacing the GTO thyristor as it is smaller and requires less current to operate the switching sequences.  See Transistor upon which the technology is based.


Electronic power device mounted on trains to provide alternating current from direct current.  Popular nowadays for DC railways to allow three phase drive or for auxiliary supplies which need an AC supply.  See also converter with which it is often confused.

Jerk Limit

A means by which starting is smoothed by adjusting the rate of acceleration of a train by limiting the initial acceleration rate upon starting.  It could be described as limiting the initial rate of change of acceleration.  Also used in dynamic braking.

Line Breaker

Electro-mechanical switch in a traction motor power circuit used to activate or disable the circuit.  It is normally closed to start the train and remains closed all the time power is required.  It is opened by a command from the driving controller, no-volts detected, overload detected and (were required) wheel spin or slide detected.  It is linked to the overload and no-volt control circuits so that it actually functions as a protective circuit breaker. 

Master Controller

Driver's power control device located in the cab.  The driver moves the handle of the master controller to apply or reduce power to the locomotive or train.

Motor Blowers

Traction motors on electric locomotives get very hot and, to keep their temperature at a reasonable level for long periods of hard work, they are usually fitted with electric fans called motor blowers.  On a modern locomotive, they are powered by an auxiliary 3-phase AC supply of around 400 volts supplied by an auxiliary inverter.

Notching Relay

A DC motor power circuit relay, which detects the rise, fall of current in the circuit, and inhibits the operation of the resistance contactors during the acceleration sequence of automatically controlled motors.  The relay operates a contactor stepping circuit so that, during acceleration of the motor, when the current falls, the relay detects the fall and calls for the next step of resistance to be switched out of the circuit.  See DC Resistance Control and Camshaft.  

No-Volt Relay

A power circuit relay, which detected if power was lost for any reason and made sure that the control sequence was returned to the starting point before power could be re-applied.  See Motor Protection.

Overload Relay

A power circuit relay, which detected excessive current in the circuit and switched off the power to avoid damage to the motors. See Motor Protection above.


The current collection system used by locomotives and trains on routes electrified with overhead lines. The pantograph (often shortened to "pan") is held up by compressed air pressure. It is designed to collapse if it detects an obstruction. It can also be lowered manually to isolate the locomotive or train.


A converter consisting of thyristors and diodes which is used to convert AC to DC.    A modern locomotive will usually have at least two, a "Main Rectifier" for the power circuits and one or more for the auxiliary circuits.



A remotely controlled switch which uses a low voltage control circuit.  It will close (or open) a switch in a local circuit, usually of higher power.  To see the principle of how it works, look here. 

Resistance Control

Method of traction motor control formerly almost universal on DC electric railways whereby the power to the motors was gradually increased from start up by removing resistances from the power circuit in steps.  See more here.    Originally this step control was done manually but it was later automatic, a relay in the circuit monitoring the rise and fall of current as the steps were removed.    Many examples of this system still exist but new builds now use solid state control with power electronics.


Short form of SEParate EXcitement of traction motors where the armature and field coils of an electric motor are fed with independently controlled current.  This has been made much more useful since the introduction of thyristor control where motor control can be much more precise.  SEPEX control also allows a degree of automatic wheel slip control during acceleration.


Equipment carried by a train and used for current collection on track mounted (third rail) power supply systems.  Shoegear is usually mounted on the bogies close to the third rail.  It is often equipped with devices to enable it to be retracted if required to isolate the car or on-board system which it supplies. 

Synchronous Motor

Traction motor where the field coils are mounted on the drive shaft and the armature coils in the housing, the inverse of normal practice.  Favoured by the French and used on the high speed TGV Atlantique trains, this is a single-phase machine controlled by simple inverter.  Now superseded by the asynchronous motor.

Tap Changer

Camshaft operated set of switches used on AC electric locomotives to control the voltage taken off the main transformer for traction motor power.  Superseded by thyristor control.


A type of diode with a controlling gate which allows current to pass through it when the gate is energized.  The gate is closed by the current being applied to the thyristor in the reverse direction.  Thyristors (also referred to as choppers) are used for traction power control in place of resistance control systems.  A GTO (Gate Turn Off) thyristor is a development in which current is turned off is by applying a pulse of current to the gate.


A set of windings with a magnetic core used to step down or step up a voltage from one level to another.  The voltage differences are determined by the proportion of windings on the input side compared with the proportion on the output side.  An essential requirement for locomotives and trains using AC power, where the line voltage has to be stepped down before use on the train.


The original electronic solid state device capable of controlling the amount of current flowing as well as switching it on and off.  In the last few years, a powerful version has been applied to railway traction in the form of the Insulated Gate Bipolar Transistor (IGBT).  Its principle advantage over the GTO Thyristor is its speed of switching and that its controls require much smaller current levels.

Wheel Spin

On a steam locomotive,  the driver must reduce the steam admission to the cylinders by easing closed (or partially closed) the throttle/regulator when he hears the wheels start to spin.  On diesel or electric locomotives, the current drawn by individual or groups of traction motors are compared - the motor (or group) which draws proportionally less amps than the others is deemed to be in a state of slip - and the power is reduced.  Some systems - EMD Super Series for one - measure known wheel speed against ground speed as registered on a Doppler Radar.  Many locomotives additionally use sand, which is applied to the wheel/rail contact point to improve adhesion.

Wheel Spin Relay (WSR)

A relay in older traction motor control circuits used to detect wheel spin or slide by measuring the current levels in a pair of motors on a bogie and comparing them.  The idea is to prevent motor damage by preventing an overspeeding motor causing an unacceptable rise in current in the other motor of the pair.  If detected, the imbalance causes the control circuits to open the line breakers and reset the power control to the start position like a "no-volt" relay.

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Electrical Engineering

posted 1 year 1 week ago

Metro Train Systems - Electrical:

There is a wide variety of electric traction systems around the world, which have been built according to the type of railway, its location and the technology available at the time of the installation. Many installations seen today were first built up to 100 years ago, some when electric traction was barely out its diapers, so to speak, and this has had a great influence on what is seen today.

In the last 20 years there has been a gigantic acceleration in railway traction development. This has run in parallel with the development of power electronics and microprocessors. What have been the accepted norms for the industry for, sometimes, 80 years, have suddenly been thrown out and replaced by fundamental changes in design, manufacture and operation. Many of these developments are highly technical and complex, the details of which are therefore beyond the scope of these texts.

Because these changes have been so rapid, there are still plenty of examples of the original technology around and in regular use, so I have covered these in my articles. This is useful, since it helps the reader to get to grips with the modern stuff.

Power Supply

To begin with, the electric railway needs a power supply that the trains can access at all times. It must be safe, economical and user friendly. It can use either DC (direct current) or AC (alternating current), the former being, for many years, simpler for railway traction purposes, the latter being better over long distances and cheaper to install but, until recently, more complicated to control at train level.

Transmission of power is always along the track by means of an overhead wire or at ground level, using an extra, third rail laid close to the running rails. AC systems always use overhead wires, DC can use either an overhead wire or a third rail; both are common. Both overhead systems require at least one collector attached to the train so it can always be in contact with the power. Overhead current collectors use a "pantograph", so called because that was the shape of most of them until about 30 years ago. The return circuit is via the running rails back to the substation. The running rails are at earth potential and are connected to the substation.

Third Rail

3rd Rail Diagram - 3rd001.gif (4481 bytes)

This diagram shows a DC 3-Rail Traction System with the location of the current rail in relation to the running rails. The third rail system uses a "shoe" to collect the current on the train, perhaps because it was first called a "slipper" by the pioneers of the industry (it slipped along the rail, OK?) but it was not very pretty to look at, so perhaps someone thought shoe was a better description. Whatever the origin, shoe has stuck to this day.

Shoes and Shoegear

Types of Shoes - 3rd002.gif (7668 bytes)

The diagram above shows a top contact third rail system but there are other types as shown in this diagram.  Third rail current collection comes in a variety of designs. The simplest is what is called "top contact" because that’s the part of the rail upon which the pick-up shoe slides.

Being the simplest, it has drawbacks, not the least of which is that it is exposed to anyone or any thing which might come into contact with it. It also suffers during bad weather, the smallest amount of ice or snow rendering top contact third rail systems almost unworkable unless expensive remedies are carried out. Side contact is not much better but at least it is less exposed. Bottom contact is best - you can cover effectively most of the rail and it is protected from the worst of the cold weather.

This DC 3rd rail Top Contact Collector Shoe (London Underground - Central Line) has remote lifting facilities. All shoes need some way of being moved clear of the current rail, usually for emergency purposes. The most common reason is when a shoe breaks off and its connecting lead to the electrical equipment on the train has to be secured safely. The other shoes on the same circuit must be isolated while this is done, unless the current is switched off from the whole section - perhaps disabling several other trains.

Isolation used to involve inserting a wooden "paddle" between the shoe and the current rail and then tying the shoe up with a strap or rope. More recently, mechanical or pneumatic systems have been devised to make it possible to lift shoes from inside the train remotely from the driving cab.

NYC shoegear.jpg (50087 bytes)

Most types of top contact shoes simply hang from a beam suspended between the axleboxes of the bogie. The suspension method was originally just a couple of slotted links to compensate for movement which allowed gravity to provide the necessary pressure. Later systems had radially mounted shoes to provide more stable contact through lever action. Top contact systems with protective covers over them, like the New York Subway (photo left), needed radially mounted shoes anyway to allow them to fit under the cover.

Bottom Contact Shoe - 3rd005.gif (322012 bytes)

Side and bottom contact shoes are spring loaded to provide the necessary contact force. An example of a bottom contact shoe as used on a German metro line is shown in the photo (left). Some top contact systems have also used spring loading but they are mechanically more difficult to control because of the hunting action of the bogie and the risk that the shoes will get trapped under the head of the rail and turn it over.


You will often see trains with only one pantograph but, on trains which use shoes, there are always several shoes. The contact with the overhead wire is not normally broken but the third rail must be broken at junctions to allow for the continuity of running rails. These third rail breaks, or "gaps", as they are called, can lead to loss of power on the train. The power losses can be reduced by locating shoes along the train and connecting them together by a cable known as a busline. In spite of this, there can be problems. Woe betide the driver who stops his train with all the shoes "off juice" or "gapped". Yes, it happens more often than you think and yes, before you ask, it's happened to me. It is an embarrassing nuisance only solved by being pushed onto the third rail by another train or by obtaining special long leads with a plug at one end for the train and shoes at the other end for the third rail. Of course, it does cause a long delay.

DC Traction Supply - 3rd003.gif (5456 bytes)

Current rail gaps are also provided where the substations feed the line (diagram, left). Normally, each track is fed in each direction towards the next substation. This allows for some over supply and provides for continuity if one substation fails. These substation gaps are usually marked by a sign or a light which indicates if the current is on in the section ahead. A train must stop before entering the dead section. Since the current may have been switched off to stop an arc or because of a short circuit, it is important that the train does not connect the dead section to the live section by passing over the gap and allowing its busline to bridge the gap. Some of the more sophisticated systems in use today now link the traction current status to the signalling so that a train will not be allowed to proceed onto a dead section.

At various points along the line, there will be places where trains can be temporarily isolated electrically from the supply system. At such places, like terminal stations, "section switches" are provided. When opened, they prevent part of the line for being fed by the substation. They are used when it is necessary to isolate a train with an electrical fault in its current collection system.

3rd Rail Uses

Although 3rd rail is considered a suburban or metro railway system, 750 volt DC third rail supply has been used extensively over southern England and trains using it run regularly up to 145 km/h. This is about its limit for speed and has only spread over such a large area for historical reasons.


What about the electrical return?  There has to be a complete circuit, from the source of the energy out to the consuming item (light bulb, cooking stove or train) and back to the source, so a return conductor is needed for our railway. Simple – use the steel rails the wheels run on. Provided precautions are taken to prevent the voltage getting too high above the zero of the ground, it works very well and has done so for the last century. Of course, as many railways use the running rails for signalling circuits as well, special precautions have to be taken to protect them from interference.

The power circuit on the train is completed by connecting the return to brushes rubbing on the axle ends. The wheels, being steel, take it to the running rails. These are wired into the substation supplying the power and that does the job. The same technique is used for DC or AC overhead line supplies.

AC or DC traction

It doesn’t really matter whether you have AC or DC motors, nowadays either can work with an AC or DC supply. You just need to put the right sort of control system between the supply and the motor and it will work. However, the choice of AC or DC power transmission system along the line is important.  Generally, it’s a question of what sort of railway you have. It can be summarised simply as AC for long distance and DC for short distance. Of course there are exceptions and we will see some of them later.

It is easier to boost the voltage of AC than that of DC, so it is easier to send more power over transmission lines with AC.  This is why national electrical supplies are distributed at up to 765,000 volts AC . As AC is easier to transmit over long distances, it is an ideal medium for electric railways. Only the problems of converting it on the train to run DC motors restricted its widespread adoption until the 1960s.

DC, on the other hand was the preferred option for shorter lines, urban systems and tramways. However, it was also used on a number of main line railway systems, and still is in some parts of continental Europe, for example. Apart from only requiring a simple control system for the motors, the smaller size of urban operations meant that trains were usually lighter and needed less power. Of course, it needed a heavier transmission medium, a third rail or a thick wire, to carry the power and it lost a fair amount of voltage as the distance between supply connections increased. This was overcome by placing substations at close intervals – every three or four kilometres at first, nowadays two or three on a 750 volt system – compared with every 20 kilometres or so for a 25 kV AC line.

It should be mentioned at this point that corrosion is always a factor to be considered in electric supply systems, particularly DC systems. The tendency of return currents to wander away from the running rails into the ground can set up electrolysis with water pipes and similar metallics. This was well understood in the late 19th Century and was one of the reasons why London’s Underground railways adopted a fully insulated DC system with a separate negative return rail as well as a positive rail - the four-rail system. Nevertheless, some embarrassing incidents in Asia with disintegrating manhole covers near a metro line as recently as the early 1980s means that the problem still exists and isn’t always properly understood. Careful preparation of earthing protection in structures and tunnels is an essential part of the railway design process and is neglected at one’s peril.

Overhead Line (Catenary)

OHL Diagram - ohl001.gif (9615 bytes)

The mechanics of power supply wiring is not as simple as it looks (diagram, left). Hanging a wire over the track, providing it with current and running trains under it is not that easy if it is to do the job properly and last long enough to justify the expense of installing it. The wire must be able to carry the current (several thousand amps), remain in line with the route, withstand wind (in Hong Kong typhoon winds can reach 200 km/h), extreme cold and heat and other hostile weather conditions.

Overhead catenary systems, called "catenary" from the curve formed by the supporting cable, have a complex geometry, nowadays usually designed by computer. The contact wire has to be held in tension horizontally and pulled laterally to negotiate curves in the track. The contact wire tension will be in the region of 2 tonnes. The wire length is usually between 1000 and 1500 metres long, depending on the temperature ranges. The wire is zigzagged relative to the centre line of the track to even the wear on the train's pantograph as it runs underneath.

catenary-wire-x-section.gif (2622 bytes)

The contact wire is grooved to allow a clip to be fixed on the top side. The clip is used to attach the dropper wire.   The tension of the wire is maintained by weights suspended at each end of its length. Each length is overlapped by its neighbour to ensure a smooth passage for the "pan".  Incorrect tension, combined with the wrong speed of a train, will cause the pantograph head to start bouncing. An electric arc occurs with each bounce and a pan and wire will soon both become worn through under such conditions.

More than one pantograph on a train can cause a similar problem when the leading pantograph head sets up a wave in the wire and the rear head can’t stay in contact. High speeds worsen the problem. The French TGV (High Speed Train) formation has a power car at each end of the train but only runs with one pantograph raised under the high speed 25 kV AC lines. The rear car is supplied through a 25 kV cable running the length of the train. This would be prohibited in Britain due to the inflexible safety approach there.

A waving wire will cause another problem. It can cause the dropper wires, from which the contact wire is hung, to "kink" and form little loops. The contact wire then becomes too high and aggravates the poor contact.

HSSI at LW ER.jpg (60118 bytes)

Overhead lines are normally fed in sections like 3rd rail systems, but AC overhead sections are usually much longer. Each subsection is isolated from its neighbour by a section insulator in the overhead contact as shown in this picture below. The subsections can be joined through special high speed section switches. 

To reduce the arcing at a neutral section in the overhead catenary, some systems use track magnets to automatically switch off the power on the train on the approach to the neutral section. A second set of magnets restores the power immediately after the neutral section has been passed. The next photo shows a set of track magnets.

Track Magnets.

Catenary Suspension Systems

Various forms of catenary suspension are used (see diagram below), depending on the system, its age, its location and the speed of trains using it. Broadly speaking, the higher speeds, the more complex the "stitching", although a simple catenary will usually suffice if the support posts are close enough together on a high speed route. Modern installations often use the simple catenary, slightly sagged to provide a good contact. It has been found to perform well at speeds up to 125 m/hr (200 km/hr).

At the other end of the scale, a tram depot may have just a single wire hung directly from insulated supports. As a pantograph passes along it, the wire can be seen to rise and fall. This is all that is necessary in a slow speed depot environment. I haven’t yet mentioned trolley poles as a method of current collection. These were used for current collection on low speed overhead systems and were common on trams or streetcars but they are now obsolete.

DC overhead wires are usually thicker and, in extreme load cases, double wires are used, as in Hong Kong Mass Transit’s 1500 v DC supply system. Up to 3000 volts overhead is used by DC main line systems (e.g. parts of France, Belgium and Italy) but below 1500 volts, a third rail can be used. In operating terms, the third rail is awkward because of the greater risk of it being touched at ground level. It also means that, if trains are stopped and have to be evacuated, the current has to be turned off before passengers can be allowed to wander the track. Third rail routes need special protection to be completely safe. On the other hand, some people consider the overhead catenary system a visual intrusion. Singapore, for example, has banned its use outside of tunnels.

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Electrical Engineering

posted 1 year 2 months ago

You will need the following items
  • transparent or translucent vinyl tubing (I used 1/4 inch ID, about the minimum size I could work with)
  • several 3mm 4Volt ultra bright LED (Larger size LED will need a larger diameter tubing)
  • electrician's fish tape or long stiff wire (needed during assembly)
  • fine gauge speaker wire ( I used 26AWG wire)
  • Ultra sharp push pin (an awl or needle will also work)
  • firm stable work surface
  • small ruler
  • harpie pen
  • hot glue gun
  • nexpensive flashlight
  • small flush cut side cutters


Prepare your LEDs

You will need to trim the LED leads to an extra sharp point using the flush cut side cutters. This will allow the easy insertion of the LEDs into the wire.
It is best to stagger the cut leads both for easy identification and for easier insertion into the wire.
Prepare the wire
It is best to stagger the cut leads both for easy identification and for easier insertion into the wire.
It is best to measure the LED spacing to make the rope pleasing to look at. I chose a 4 inch LED spacing.
The wire is marked at regular intervals with the sharpie.
The first LED is inserted into the end of the speaker wire. I chose this type of wire for two reasons. The first is that it has a clear casing which transmits some of the light to the opposite side that the LED is mounted on. And the second is that the wire consists of two separate colours, One silver and the other gold. 
The LED has a flat mark around the lower rim which identifies the cathode (negative side) coincidentally I prepared my LEDs with the shorter lead identifying the cathode as it did from the factory.
I chose the mantra short to silver when I assembled the string. You carefully and a straight as possible push the sharpened LED leads into the exposed wire at the end.
Insert LEDs into the wire.

At the marked points on the wire you will need to make two small parallel (one silver and one gold) holes at a 45 degree angle through the wire sheath into the conductive wire core. Do no go all the way through. 
Once you make one set of holes you will have to insert the LED. The holes will tend to close up making the insertion harder if you wait. 
Firmly push the LED leads into the small holes and along the wire core. You will only be able get them in about 1/8 to 1/4 of an inch before the leads bend. This is sufficient for good contact.
You will have to repeat this procedure until all of the LEDs are placed.
Disassemble the flashlight and test the string
I chose an inexpensive LED flashlight from a local discount store. I has the required parts and batteries for a reasonable price.
You will have to disassemble the head of the flashlight 
With my flashlight:
unscrew the lens cap and lens cap cover. 
You will be left with a lower case, battery carrier, batteries and on/off switch.
The cathode is connected to the case by stripping off some of the silver wire coating and wedging the bare wire between the base and lens cap cover.
The light circuit board has a wire protruding from it, you will have to remove it if you do not want the flashlight to light up. I removed it...
Press the power button. If your LEDs do not light then reverse the leads. If any individual LEDs do not light either insert them farther of reverse them.
Once you are satisfied with the string turn it off.
The gold coloured wire is stripped bare and wrapped around the spring which attaches tot he anode. The lens cap is then reassembled minus the lens to allow the wire to pass through.
Secure the LEDs and feed the tube 


You will need to use the hot glue gun to secure the LEDs in there respective positions. 
The glue will keep the LEDs from coming out of the wire. Do Not skip this step...
The cooled off glued string has to be pulled into the tubing either by a long stiff wire or electrician's fish tape as shown. The wire will tend to stick to the vinyl tubing so you will have to use a little patience and wiggle the wire and tube so that the wire pulls freely. Do not fore it otherwise the LEDs could be damaged or the wire could break. It is not advisable to the some sort of lubricant as it will not look good when it is turned on.
Once the wire is pulled though, the ends are sealed with a liberal amount of hot glue. The LED end has to be glued all the way past the led to the wire otherwise the led could pull out of the wire. stick the nozzle of the glue gun all the way in and back it out gently to achieve a flush glue seal.
Congratulations you now have a custom made battery operated LED light rope.
All told mine cost me less than $7...
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