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What you wanted to know about LEDs but were afraid to ask

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It has been suggested by another forum member,who even named the thread,to give some basic info on the installation of LEDs to our layouts.

i do nt profess to be an expert in anything to do with this wonderful hobby and led s are no exception,however I made a ton of mistakes and cost myself more than a few pounds and all because I did nt know anything about the basics.Please feel free to correct me if you think I ve written anything incorrectly but please be gentle😂👍

hopefully this can help you to not make the same mistakes at I did.👍😀

Power supply come in various voltages but the norm for us I guess would be 3v,6v and 12v,this is the power output from the supply.

Leds come in various voltages,usually 3v.6v and 12v 

if the power supply is the same as the bulb then there’s no problem,but if it’s lower then a step down will need to be used.The usual way would be to simply fit a resistor to each led bulb.The other method would be to use a step down,these are usually used for cars but can be used on our layouts.The other alternative is to just buy the correct voltage supply for what you are going to connect.I use 3v for the street lights and a seperate 12v for the building lights.

Leds are normally 20ma each,this is the power it draws from the supply.

there are 1000ma to an amp.

A 1amp supply will power 50 LEDs but it’s advised to keep it below this number,I normally connect 40 per amp.so if

you had a 5amp supply you could power 250 LEDs,probably big enough for our layouts.




This is a rough picture of how I wire mine.This example is for 3v street lights and also has an in-line on/off switch(spst toggle switch)this is not a must as you can just switch it on and off at the plug.

i make a loom with connector blocks and fix it ,under the board in a central area to where the lights will be.From the power supply I wire the switch in line on the live connection and the neutral wires straight to the block.Then it’s just a case of wiring the lights to the blocks.If this was a 12v supply you would just wire it exactly the same but fit the correct resistor between the block and the bulb.





As I mentioned before above is a voltage reducer used on cars,it’s 12 v in and 3v out,these are also available in other voltages.This would simply be wired in between the supply and the connector blocks.

As I ve said,I m no expert and I m not suggesting that this is the way to do it but once I d learned the basics it s how I do mine and I ve had no problems at all.

I bought cheap power supplies from China and I m still using the same ones I bought five years ago.

One thing I would recommend is that you make sure that any power supply has an overload cut out.


Edited by Pauljag900
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The above description is good for LEDs with prewired resistors. These resistors make the LEDs 3V or 12V as they set a current limit for a selected voltage.


Bare LEDs have a turn on voltage (Vmin) and need an external series current limit to keep them from burning out. Several series connected LEDs could share one series current limiter but each parallel one needs its own. This is the reason many 12V 3 led strips have a single shared resistor.


The value of a resistor could be computed as the following:

(supply voltage - (sum of turn on voltages)) / desired current


The usual values for current are between 4 mA for high efficiency LEDs to 10-20 mA for normal ones. LED turn on voltages are from 1.5V for infrareds, 2.0 for visible reds to 3.3V for whites and up to 4.6V for UV blues.


This shows that a 12V supply can only turn on 3 white leds in series (Vmin = 9.9V). The advantage of using leds in series is that the current consumption is lower than in parallel and less power is wasted as heat by the resistors.


Two good LED circuit wizards:




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