led track lighting

[tommyrob123]

hi everybody, just joined today and hoping for some much needed help...........
i have hornby select controller with a 15v aux output. i want to use this for led lampposts. how many posts can i use in line to one on/off switch and could i use bus wire system like the track. i have never used led's before so very new to this and indeed model rail in general. got track sorted with wiring so not all bad.
any advice greatly appreciated

[Brian]

Hi Welcome to the forum

As supplied the Hornby Select comes with a 1.0Amp power supply which TBH is barely large enough for four loco running. The 15v DC Auxiliary output is also feed from the same power supply, so whatever you connect to that 15v DC supply reduces the power available to the rails!

Good news is if all your lights are LEDs then they consume very little power - around 10 to 20milliamps (0.01A to 0.02A) for each lit LED or even less. Times the lit number by (as a rule of thumb) 10Ma (0.01) and you will have their total power consumption. e.g. 25 lit LED lamps would be 25 x 0.01 = 0.25 or 250 milliamp = 1/4Amp.

You have two options in my view....
A) Upgrade the Select power supply to the 4.0Amp version which will then give plenty of power in Amps to the rails and for lighting too.
B) IMO it is best is to use a totally separate power supply. This can be a 12 volts DC or even as low as 5 volts DC regulated supply. Something with around 1.0Amp will power many LEDs and allow other items to be feed too, if needed be. It also leaves the Select to just power the trains!

Things to ensure... LEDs are polarity conscious devises and must be connected to a DC supply the correct way around. They must also have a series resistor in one feed wire (doesn't matter which one) without the resistor the LED will blow immediately! Unless the LED is supplied to work at the rated voltage of the supply e.g. 12 volt rated LEDs. Many LED lights are supplied with a resistor, but if not then on 12v DC consider 1K (1000 Ohm) as the starting place and higher Ohm values will both reduce current and lower the LEDs brightness. Typical 12v Regulated 1.0Amp Power Supply Unit (PSU) Link to example 12v PSU

How you feed the lights is up to you but one or more On/Off switches are wired into the positive supply lead then that runs out to the layout. Where more than one switch is to be used, each switch will have its own separate positive switched feed running out to the layout. Thereby allowing various lights to be turned On/Off independently of other lights. All share a single negative return wire which runs from the layout back to the power supplied negative connection. Wire size will depend on wire run length and how many items are to be connected. Where LEDs only are used then 7/0.2mm wire will usually be fine, but if you want to you can use 16/0.2mm as all the main the feeds from the switch(s) and the return wire too and then use the smaller 7/0.2 tapped off the larger wires to feed induvial lights.

[PBoland]

I use an old power unit for all my LED lighting, 12 V DC, separate rocker switches for different sections of the layout. Also don't forget LED resistors if not supplied. Used to use a 12 V spare car battery and charger until it expired. Also power my auto reverser, works well

[tommyrob123]

thanks for your replies. i forgot to mention that i would be using a step down unit to take voltage down to 3v. would this make a difference to the connections?

[Brian]

Far too many Amps from a car or other GP battery! Needs a 1Amp or 2Amp fuse or circuit breaker immediately after the positive battery terminal. Up to 400 Amps can flow on a short circuit with a car/leisure battery.

Laptop PSU are great to reuse if they are 12 volt, but many are 19 to 22 volts so always carefully check. The other problem can be that they output around 4 Amps which is too high for most model railway LED lighting use. But by feeding the main 12v output into a distribution splitter and each sub circuit then fitted with a 1.0Amp fuse or circuit breaker makes everything much safer. Next problem can be the moulded DC plug. Frequently some are of odd sizes. Was easy when Maplins were open in the UK as you could pop in with your PSU and obtain a connector to fit, but much harder to so unless you actually know the size. Note Some Laptop battery chargers/PSUs use three wires! One is for sensing the battery power level!

Old Computer ATX etc power supplies have been popular, but in the wrong hands they are as lethal as a car battery. Many can produce around 20 plus Amps

Hence the recommendation for a lower current power supply - 1 to 2 Amps at 12volts DC is usually more than ample for all layout lighting needs in fact 2.0Amps is probably too much!

[Brian]

thanks for your replies. i forgot to mention that i would be using a step down unit to take voltage down to 3v. would this make a difference to the connections?

Question... Why do you want 3volts?