Power Connectors for
Garden Railroad Applications

d. bodnar  revised 01-18-13

Many of our garden railroad projects can benefit from the addition of removable connectors that expedite installation, removal and repair of electrically powered devices.  For example, each of the buildings on my railroad contains one or more LEDs to illuminate them at night.  These LEDs need to be replaced from time-to-time, not because they burn out, but because the leads corrode and rust through.  To simplify replacement each LED connects to the power feed in the building with a simple two conductor connection.  In this article I would like to describe a number of different connectors that I use and have found to be valuable.  They vary significantly in size and range from those that can handle very little current to some that can handle 10 or more amps.

Polarized Two Conductor Connectors
The connectors mentioned in the introduction are ideal for a number of different applications, especially those that require properly polarized DC power.  As you probably know LEDs, and many other electronic devices, require that plus connects to plus and minus connects to minus.  In the case of LEDs a reversed connection just prevents them from illuminating and no real harm is done.  Other devices, like sound cards and other electronic circuit boards, can be destroyed if polarity is reversed even for an instant.  The connectors that I use with the LEDs have a keyway molded into the male and female ends so that the red wire is always hooked up to the red wire and the black to the black.

These connectors are frequently referred to as "JST Connectors" and can be purchased online from DealExtreme.com.  The part number is 15234 and it can be viewed with this link:
http://dx.com/p/jst-cables-10-pair-15234 .  The price is less than $3 for 10 pair including shipping. 

You can also find them on eBay.  One vendor that I found is selling 50 pair for about $10.00.  Just search eBay for "JST Connector".  Many of the vendors are in China and delivery time can be several weeks or more.  Shipments can be received more quickly from US vendors but the cost is generally higher.

To give you an idea of the quality of these connectors, I use them to connect flashing LED lights that I have on my bicycle helmet to a small lithium ion battery.  I plug & unplug this connector at least one time each time I ride, 5 or more days each week.  In nearly three year's use the connector has never failed.  Not bad for something that cost less than $0.30!

Please note that I have no connection to Deal Extreme but I do find their prices to be among the best on the Internet.  Receiving shipments can take many, many weeks but is usually worth the wait.

Polarized High Current Two Conductor Connectors
To connect high power devices, such as batteries that power locomotives or track power connections, connectors that can easily pass high current are needed.  While many varieties of high current connectors exist I have found, in terms of price and ease of use, that the connectors shown here are a good choice.  They are frequently referred to as "Deans Plugs" and can be purchased from Deal Extreme and other vendors.  They are usually sold in pairs with one female connector (shown on the left) and one male connector (shown on the right).  The female connector is attached to the side of the circuit that is the power source, such as a battery or power supply, and the male connector goes to the device to be powered.

The Deal Extreme part number is 10788 - here is a link: http://dx.com/p/high-current-ultra-plugs-t-connector-10-10-pack-shrink-tubing-20-pack-set-10788

Many vendors on eBay also sell them.  Just search for "Deans plugs".

The plugs frequently are sold along with lengths of heat shrink tubing.  This is because you must solder your wires directly to the ends of the plugs and insulate the exposed connections with the heat shrink.  In this photo two wires have been soldered to the terminals on the plug awaiting the heat shrink tubing.  To give you an idea of size the wire that is soldered to the terminals is #14 copper.

You need to use a very hot iron to successfully solder to these plugs.  This is especially true when you use heavy copper wire for the connections.  Hold the connector in a "third hand" fixture and take your time and you will get a good solid bond.

In this photo heat shrink tubing has been placed over the joints and one of the two pieces has been heated to shrink it.

Bullet Connectors
Bullet connectors" is a name given to a number of different connectors that are generally gold in color with a single male and a single female connector.  They are frequently used in battery powered radio control applications but work well with garden railroads, too. 

The ones I have worked with come in three different sizes, 2mm, 3.,5mm and 4mm.  Like the Deans plugs the wires to be connected need to be soldered to the connector and then covered with heat shrink tubing. 

Bullet connectors are designed to join single wires, not pairs like the first two styles described above.  That is, you must use two pairs of the connectors to connect a battery or other power source.  If used in this way be very careful to observe the colors of the wires that you are connecting as reversing polarity is definitely a possibility.

4.0mm Bullet Connectors
The 4mm bullet connectors can handle high current loads.  Some of the eBay listings for them claim 80 amps.  That may be a bit exaggerated but these connectors can surely handle any power requirements that we might have in a garden railroading application.

They work well when used to deliver power from a trailing battery car to a locomotive.  As an added bonus when soldered up and covered with black heat shrink tubing they resemble the air hoses that run between cars.

Search eBay for "bullet 4mm".

3.5mm Bullet Connectors
The 3.5mm connectors are identical to the 4mm ones except that they are just a bit smaller.  Their current handling capacity is, again, more than we are likely to need for our applications.  Because of the smaller size they might look nicer between a locomotive and a trailing car.  The photo  below shows the male end (on the left) and the female end (on the right) after soldering but before being covered with heat shrink tubing.

Here we see two pairs of connectors with heat shrink installed.  When oriented in the manner shown, that is with a male and a female end on each side, they can be used to connect and maintain proper polarity without using colored wire.  This helps to keep them looking like air hoses when used between cars.

As you can see the connector is completely insulated when the ends are pushed together.  To find them search eBay for "bullet 3.5mm".

2mm Bullet Connectors
The smallest bullet connectors that I have come across are 2mm in diameter.  They are a bit longer than the larger bullet connectors but can handle nearly as much current as their larger cousins. 

They do have one handy characteristic for garden railroaders.  They are just about the right size to fit into the brass power takeoffs that many LGB locomotives have on them.  Here they are plugged into the back of an LGB Stainz locomotive.

The holes in the locomotives are just a bit over 2mm in diameter and I found that splaying the contacts with a sharp tool makes them fit very well.  You could also try adding a thin layer of solder to the connector to enlarge its diameter a bit.

To make a connection that looked more like air hoses I drilled 2mm holes in the back of the locomotive, as shown here, and had the power wires exit the rear of the engine.  Note that the wire on the left is pushed in the whole way hiding all of the brass of the connector while the one on the right is only partially inserted.

The Deal Extreme part number is 14996 - here is a link: http://dx.com/p/2-0mm-gold-plated-banana-bullet-connectors-with-heat-shrink-tubing-20-pair-14996.  Or you can search eBay for "bullet 2mm".

Polarized 3 Conductor Connectors (Servo Cables)
The connectors discussed thus far are all for single or double wire connections.  When I need to connect three wires I frequently turn to polarized servo cables.  These are normally used, as the name implies, to connect to or extend connections to servos.  They are not designed for high current use but should be able to handle supplying power to a sound card or to an array of LEDs.

They can also be used to replace the connection between some locomotives and tenders.  If you use two pairs of these connectors, one male and one female at each end, you effectively have a six conductor connection.

The Deal Extreme part number is 11985 - here is a link: http://dx.com/p/300mm-3-pin-servo-leads-connection-extension-cables-10-pack-11985   This is for 300 mm cables - longer cables, 500 and 1000 mm in length, are also available.

Single Conductor Connectors
When space or size is an issue and I need a really small connector I turn to using male and female, single conductor breadboard jumpers.  The first photo shows the male jumpers...

and this photo shows the female.

Just cut each jumper in half and extend to whatever length you need by adding more wire.

The Deal Extreme part number for the male jumpers is : 80208 - here is a link: http://dx.com/p/breadboard-jumper-wires-for-electronic-diy-70-cable-pack-80208

The female part number is: 55454 - here is a link: http://dx.com/p/single-port-female-to-female-jumper-wire-set-50-pack-20cm-length-55454

These connectors provide a very small connection between cars if, for example, you want to share power between illuminated passenger cars. 

Male Header Pins
You can also purchase just the bare male pins that fit into the female jumpers.  Their Deal Extreme part number is: 144191 - here is a link: http://dx.com/p/2-54mm-1x40-pin-breakaway-straight-male-header-10-piece-pack-144191

Each strip is composed of 40 pins that can easily be broken or cut into smaller segments to match your needs.

Three Conductor Screw Terminal Connectors
For screw terminal connectors that you might use on a home-made circuit board see Deal Extreme part number: 122491 - here is a link: http://dx.com/p/3-pin-screw-terminal-block-connectors-20-piece-pack-122491

These screw terminal blocks are also available in two terminal versions.  Each connector block has slots molded into its side that allows you to gang multiple blocks together so that you can create blocks of varying numbers of connections.

In this photo there are 2 two conductor blocks joined together at the top and a three and a two conductor at the bottom. 

Multi-Conductor Connectors
I have also found a source for multi-connection cables that can provide up to 12 or more connecting wires.  These are generally low current connectors that are used to charge lithium polymer batteries.  The ones shown below can be found on eBay.  Some have a male and female connector on the same cable and some have a male connector that is intended to be soldered to a circuit board.

4 conductor - search for "JST  3S"


5 conductor - search for "JST 4S"


6 conductor - search for "JST 5S"


7 conductor - search for "JST 6S"


I hope that this quick overview of connectors, their characteristics and use will be of assistance the next time you need to connect some electronic or electric device on your railroad.  As always, please let me know if you have any questions:  dave@davebodnar.com