QUOTE (Jancsi @ 25 Feb 2008, 00:01)
<{POST_SNAPBACK}>The intended use is for street lighting as well as inside buildings. I want to use LEDs, not bulbs, bulbs are OK with AC. I am just finishing a large Marklin layout and have several transformers with 16V AC output.
Jancsi
Hi Jansci
OK, I understand.
First thing is, AC is not really right for LEDS. They should be used with DC for best results.
You have two choices - a DC supply (for example, an old mobile phone charger is OK for about 20 LED) or any other DC supply OR you can add a simple rectifier to your AC power supplies.
I have attached an image of the circuit. It needs only two parts really. You can make it quite easily and parts are very low cost.
(1) The "Bridge rectifier". Ask for one that is 2 amps to have lots of spare power. It should be a small black square or round device with 4 wires coming out of it. Two will have a ~ symbol beside them and these two attach to the transformer 15v AC terminals. The other two will have a - and + sign and these are the DC outputs
(2) The Capacitor. Ask for one as follows: "A 1000microfarad electrolytic capacitor of 25 volts or more" .
Connect as per the circuit diagramme and you will now have a reasonably smooth DC power for your LED's.
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Connecting the LEDs. Each LED will need a resistor. The resistor should be on the + lead of the LED. This is always the longer of the two leads on the LED.
Resistors are very cheap. You need "1/4 watt metal film resistors"
If you buy some of approximately 1,000 ohms, 3,000 ohms, 6,000 ohms and 10,000 ohms this will give you a choice of brightness with white LEDs. If you always use 1,000 ohms or more then you will always be safe connecting ANY colour LED to your power supply.
It is OK to connect many LEDs in parralel as long as they have their own resistors.
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Power consumption of LEDs.
This is very low. approximately 10 milliamps per LED (1/100 of an amp). This means that you will be able to safely connect at least 100 LEDs for each 1 amp (15VA) of transformer power. (so, if your transformer is 30VA = 200 LED!)
Regards
Richard
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