Hi all I require a bit of assistance. SWMBO visited a garden centre today and came back with a packet of LED's. They had been discounted after Xmas, and god love her, she thought that I may be able to use them on my layout. They are battery operated with a box that fits 3 X AA batteries. A pair of wires come out of this box. Which then splits into 10 pairs of wire. Each pair has 6 LED's on each of them. 60 in total. According to the packet each LED is 0.03W/3V giving 1.8W. I want to split the pairs into 10 separate lengths and power them from a variable power supply. First problem is that the data above suggests to me that although 4.5 Volts is being supplied by the batteries, only 3V is going to the LED's. (There is 6 hour on- 18 hour off timer on the box.) Second, can I run all 10 pairs off the power supply without resistors. Electrickery is not my strong suit. Help please, Jim
G`day Jim, If you are running a variable power supply you will definitely need resistors to protect the LED`s. You would have to calculate resistance based on the maximum output of the power supply, disregard the fact that it is variable. If for some reason the power supply is turned up to full power, you will cook the LED`s if they are not protected with resistors. With this method the power supply can act a bit like a dimmer. At full voltage the LED`s will be lit, however as you drop down the voltage, the LED`s will start to dim which can be handy for building lighting. I run my LED`s on an old 12 volt analogue speed controller. I use resistors to cope with 12 volts, however I run the LED`s at about 4 to 6 volts....so they are dimmed slightly. I must point out that I wire my LED`s individually, therefore 1 LED = 1 Resistor......this is called wiring in parallel. The other method is wiring in series......like a daisy chain....the same as your groups of six are wired. Wiring in series would still require protection with resistors, however the value would be different to a single LED. There is a whole stack of info on the net about LED`s so a bit of research may serve you well. I know a little bit but I am no expert by any means. Here is a link to a site where you can calculate quite easily, resistor values for LED`s based on input voltage. http://led.linear1.org/1led.wiz/ In the example below I have entered 12 volts as the power supply. 3 volts as the LED voltage and 30 milliamps as the LED current ( 0.03W) Click find R and it tells you the resistor required. Hope this has been of some help Jim. I`m sure there will be somebody else on here who knows a lot more than I do.
You could always get hold of a "Wall Wart" with either 4.5 volt or 3 volt DC output and run the whole lot from this. You may even have an old redundant one around that used to power stuff you no longer have. Even if you have to buy one, they're pretty cheap, some even have an inbuilt switch to change the output voltage, usually 3, 4.5, 6, 9 and 12 volts. Keith.
Hi Keith, I've got a couple of those that I was going to use. I just didn't need all 60 LED's in the same area, so I was going to split them up. I was thinking along the lines of one of the strings of 6 would light 1 building, with LED's lighting the different rooms. Jim
Jim, Have a play with the link Gormo sent and look at the "LED series/parallel array wizard". I put some numbers in and a suggested LED array came out. Screen shots below. 4.5V power Supply 6V power Supply According to the calculator the Forward Voltage for a white LED is about 3.3V (see blue ?) so to get it to light the power supply must be higher than that is why the 4.5V used. As the whole array as it is now only draws 600mA or 0.6A (1.8W from 3V), a "wall wart" with a current rating of 1A or greater would be plenty to power the whole thing. For your buildings you could construct a lighting bus connected to variable power supply and just tap into it at each building. You could set the variable supply to a voltage, as Gormo said pick one that gives a good level of brightness, and take the variable control off for safety and mount it up under the layout where it wouldn't be bumped, (in a box maybe?).
This may be of use? Mine came as a pair https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.co.uk/ulk/itm/113142725222 Or I may have ordered 2 Andy
