lighting PSU

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mikehextall
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lighting PSU

Postby mikehextall » Sat May 07, 2011 9:55 am

Hi all

ive read alot of posts regarding electronics especially when it comes to powering LED lights, can someone give me a link to a power supply i would need in order to do this as ive tried searching but dont really know what im looking for, lets assume i want enough power to light a road 4 feet long just for an example.

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Flashbang
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Re: lighting PSU

Postby Flashbang » Sat May 07, 2011 10:39 am

Hi
Opt for a dc power supply unit (PSU). Its output voltage can be anything from 5 volts to 20 volts. You will need suitable series resistors for each LED. There OHM value will be determined by the LED forward voltage rating and its forward current rating.

Some use former mobile phone plug in wall chargers as PSUs Others will use 12 volt dc PSU like these PSU Example link. While former 18 to 20 volt Laptop PSU can also be used.

To calculate the resistor needed take your supply voltage and minus the LEDs rated forward volts. Then divide the answer by the forward current in milliamps. The figure obtain is the minimum resistor value in OHMs. You then select and use the next available resistance value or one of a little higher value if wished.
Example.... PSU 12v. LED Forward volts 2.2. LED forward current 0.01A (10milliamp). Sum is 12-2.2/0.01=980 (or 12-2.2=9.8. 9.8/0.01=980) The nearest resistor to use would be 1000 OHMS (1K0) at 1/4watt or higher wattage.

The calculator does the maths for you.....http://www.led.linear1.org/led.wiz

Ensure your total load does not exceed the rated output of the PSU. e.g. a 500ma PSU can power 50 LEDs running at 10ma each or 25 LEDs running at 20ma each. Just add up the total number of lit LEDs and times that by their individual current rating.
Last edited by Flashbang on Sat May 07, 2011 10:42 am, edited 1 time in total.
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Roger (RJ)
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Re: lighting PSU

Postby Roger (RJ) » Sat May 07, 2011 10:40 am

The answer to this question is like "How long is a piece of string".
Much more detail is needed to give a precise answer and there are different ways of wiring up the LEDs to the power supply

1 All LEDs in parallel. - Takes more current and every LED needs to have a resistor fitted.
2 Groups of two or more (depending on the voltage of the power supply) LEDs in series, each group connected to the power supply through a single resistor. - Uses less power and less resistors but if one LED or resistor fails the other LEDs in the group will not light.

This type of power adaptor should be able to run quite a few LEDs.

Don't forget that you will need to fit resistors in the circuit to prevent the LEDs being destroyed

This website will help you to work out what value resistor to use and provide a little circuit diagram

EDIT. An old trainset controller can be used to light LEDs. You'll still need resistors though.
Last edited by Roger (RJ) on Sat May 07, 2011 10:47 am, edited 1 time in total.

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Roger (RJ)
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Re: lighting PSU

Postby Roger (RJ) » Sat May 07, 2011 10:41 am

SNAP! :D

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Silver Surfer
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Re: lighting PSU

Postby Silver Surfer » Sat May 07, 2011 11:55 am

I think I'm correct in saying, if you use a 12volt DC PSU and only 12volt LED's you won't need any additional resistors as they're already built in.

If you connect them up the wrong way they won't work but, neither will you destroy them, so just connect them the opposite way.....
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mikehextall
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Re: lighting PSU

Postby mikehextall » Sat May 07, 2011 10:19 pm

ok i see from the example PSU's that they all have the traditional connectors you would use to plug them into a phone, how would i plug them into a string of LED's?

Sorry for sounding stupid but i really have no clue but really want to learn

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Roger (RJ)
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Re: lighting PSU

Postby Roger (RJ) » Sat May 07, 2011 10:22 pm

Cut the plug off

mikehextall
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Re: lighting PSU

Postby mikehextall » Sat May 07, 2011 10:27 pm

thats what i thought lol was just checking

mikehextall
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Re: lighting PSU

Postby mikehextall » Sun May 08, 2011 9:43 am

Does the R921 power supply contain the unregulated output for us with LED lighting as ive seen suggested in other posts?

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Flashbang
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Re: lighting PSU

Postby Flashbang » Sun May 08, 2011 10:43 am

mikehextall wrote:Does the R921 power supply contain the unregulated output for us with LED lighting as ive seen suggested in other posts?

Hi
Does this particular controller have a separate wall plug PSU or does the mains (230volt) feed directly into the controller?
If you mean a wall plug type PSU then no. It provides 16 volts ac which is not suitable.
If you mean the train controller part (With the wall plug PSU feeding it. Or it being a directly mains fed type) then yes. The 'track' output terminals will be dc. But do be a little cautious, as often these train set controller can output around 18 to 20 volts dc. Also you need to ensure the forward/reverse switch is maintained in the correct position to keep the positive feed correct on the 'track' output terminals.
Last edited by Flashbang on Sun May 08, 2011 10:48 am, edited 1 time in total.
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mikehextall
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Joined: Wed May 04, 2011 6:50 pm

Re: lighting PSU

Postby mikehextall » Sun May 08, 2011 10:47 am

ok thanks, think i will stick with a seperate PSU as suggested in the thread


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