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Author Topic: How to wire up 50 LEDs  (Read 472 times)

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Offline Jimbo123

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Re: How to wire up 50 LEDs
« Reply #15 on: October 27, 2019, 06:16:34 PM »
@Jimbo123   OK, so a 470 ohm resistor would be about right for a 12V supply feeding 20 mA through each LED  (try it in that resistor calculator link to confirm).

I would have 2 comments: 

i) Different colours of LED have different forward voltage - for example off the top of my head I think red is more like 2V
ii) I think you may find 20mA may be too bright in some cases.  Quite often 15mA or even 10mA is plenty. 

This is where you need to get a suitable power supply and experiment with different resistors and different colour LEDs to find what looks best in your buildings. It helps to have some different resistor values to play with.  Make sure you don't go above 20mA though!  As a starting point, if you think the LED is too bright using one of your 470 ohm resistors, try it with two resistors in series which will drop the current down to more like 10mA.
The LEDs I`ll be using will all be white. If for instance I had a 24volt DC regulated power supply, could I wire up 9 of the LEDs in series without using a resistor? Thanks

No you must ALWAYS include a resistor, it's to limit the current as I mentioned earlier. 

White LEDs seem to be typically around 3.5V forward voltage.  So, plug 24V source, 21V forward voltage (6 x 3.5), 15mA current into the resistor calculator and it recommends a 220 ohm resistor.  Your 470 ohm resistor would limit the current to around 7mA in that situation, might not be bright enough but you need to experiment.    Or you could try 470 ohms with only 5 LEDs instead of 6, that works out at 15mA.
So.. could I then run another 5 LEDs in series with the 470 ohms resistor off the same power supply? Also could I run more than two lots? Thanks.

Online ntpntpntp

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Re: How to wire up 50 LEDs
« Reply #16 on: October 27, 2019, 06:20:53 PM »
[with a 24V dc supply] ...or you could try 470 ohms with only 5 LEDs instead of 6, that works out at 15mA.
So.. could I then run another 5 LEDs in series with the 470 ohms resistor off the same power supply? Also could I run more than two lots? Thanks.
Yes you can run as many parallel strings of 5 LED (each string with its own 470 ohm resistor and each drawing 15mA)  as your 24V DC supply can comfortably handle, so that depends on the current supply capacity of the power supply?  Remember to leave plenty of headroom - I prefer to draw only 50% of the rated maximum.   What is the current rating of your supply?

Nigel is correct with his earlier comment that if you do simply give each LED its own resistor and wire in parallel to the supply you do get more individual control (you can use a higher value resistor if you want some LEDs to be more dim than the others). At 24V DC you'd be looking at 1.5K ohm resistors for 15mA (or higher for dimmer LEDs) and you're still drawing more load from the power supply, as I mentioned in my first reply.

[ps] The "individually addressable LEDs" Nigel also mentioned are different things entirely, in that they have additional integrated control circuitry with each LED.
« Last Edit: October 27, 2019, 06:30:09 PM by ntpntpntp »
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Offline Jimbo123

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Re: How to wire up 50 LEDs
« Reply #17 on: October 27, 2019, 06:28:48 PM »
[with a 24V dc supply] ...or you could try 470 ohms with only 5 LEDs instead of 6, that works out at 15mA.
So.. could I then run another 5 LEDs in series with the 470 ohms resistor off the same power supply? Also could I run more than two lots? Thanks.
Yes you can run as many parallel strings of 5 LED (each string with its own 470 ohm resistor and each drawing 15mA)  as your 24V DC supply can comfortably handle, so that depends on the current supply capacity of the power supply?  Remember to leave plenty of headroom - I prefer to draw only 50% or the rated maximum.   What is the current rating of your supply?

Nigel is correct with his earlier comment that if you do simply put each LED in parallel with its own resistor you do get more individual control (you can use a higher value resistor if you want some LEDs to be more dim than the others). At 24V DC you'd be looking at 1.5K ohm resistors for 15mA (or higher for dimmer LEDs) and you're still drawing more load from the power supply, as I mentioned in my first reply.
Darn thing keeps logging me out.. I think the power supply is either 2.5 amps or 3 amps. It`s in the shed at the moment, to dark and wet to try and find it lol I don't want to buy many more resistors, they cost more than I use.. If you get mt drift.

Online ntpntpntp

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Re: How to wire up 50 LEDs
« Reply #18 on: October 27, 2019, 06:34:41 PM »
I think the power supply is either 2.5 amps or 3 amps. It`s in the shed at the moment, to dark and wet to try and find it lol I don't want to buy many more resistors, they cost more than I use.. If you get mt drift.
Oh that sounds fine.

Resistors cost peanuts, it's worth having a set of different values in stock to play with.

https://www.ebay.co.uk/itm/600pcs-30-Values-1-4W-Metal-Film-Resistors-Resistance-Assortment-Kit-Set-1-JT/123954360854
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Offline Jimbo123

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Re: How to wire up 50 LEDs
« Reply #19 on: October 27, 2019, 06:46:58 PM »
@Jimbo123   OK, so a 470 ohm resistor would be about right for a 12V supply feeding 20 mA through each LED  (try it in that resistor calculator link to confirm).

I would have 2 comments: 

i) Different colours of LED have different forward voltage - for example off the top of my head I think red is more like 2V
ii) I think you may find 20mA may be too bright in some cases.  Quite often 15mA or even 10mA is plenty. 

This is where you need to get a suitable power supply and experiment with different resistors and different colour LEDs to find what looks best in your buildings. It helps to have some different resistor values to play with.  Make sure you don't go above 20mA though!  As a starting point, if you think the LED is too bright using one of your 470 ohm resistors, try it with two resistors in series which will drop the current down to more like 10mA.
The LEDs I`ll be using will all be white. If for instance I had a 24volt DC regulated power supply, could I wire up 9 of the LEDs in series without using a resistor? Thanks

No you must ALWAYS include a resistor, it's to limit the current as I mentioned earlier. 

White LEDs seem to be typically around 3.2V - 3.5V forward voltage.  So, plug 24V source, 21V forward voltage (6 x 3.5), 15mA current into the resistor calculator and it recommends a 220 ohm resistor.  Your 470 ohm resistor would limit the current to around 7mA in that situation, might not be bright enough but you need to experiment.    Or you could try 470 ohms with only 5 LEDs instead of 6, that works out at 15mA.

[edit] Here's a table giving typical forward voltage for difference LED colours

OK, that lot just goes over my head. Lets simplify things. I mostly have 12 volt power supplies going spare. Using these LEDs that I have, what would be the best way to wire them up, so that the bulbs are of reasonable brightness and what resistors would I need?

Online ntpntpntp

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Re: How to wire up 50 LEDs
« Reply #20 on: October 27, 2019, 07:05:46 PM »
@Jimbo123
The simplest way is to put one 470 ohm resistor in series with one LED and hook it to the 12V power supply. 
Do the same with the next LED and hook it to the power supply in parallel.
... and so on....

Using 470 ohm resistors might mean the LEDs are very bright at 20mA current (try it and see what you think?)and the power supply won't be able to handle as many LEDs in total as it could with a bit of re-jigging to run LEDs in series as I suggested right back at the beginning. 

You do need to be aware of the maximum current the power supply can provide. Add up all the LED's 20mA requirements and try not to go beyond about half the maximum current the supply is rated for - especially with unregulated supplies as the voltage will simply drop as you add more load.

If the LEDs are too bright, and you don't want to bother buying some other different resistors, then you have two simple things you can try: two LEDs in series with one resistor (make sure you get the polarity corrrect) or two resistors in series with one LED. The first option will halve the voltage the LED sees (so they might refuse to light at all), the second option will halve the current (should just make the LED less bright).  Neither should cause any damage, so again try it and see what happens?

Personally I would probably get 680 ohm, 820 ohm, and 1k resistors to try.  1k is commonly used for LEDs being driven from 12V-15V
« Last Edit: October 27, 2019, 07:11:01 PM by ntpntpntp »
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Offline Jimbo123

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Re: How to wire up 50 LEDs
« Reply #21 on: October 27, 2019, 07:28:36 PM »
@Jimbo123
The simplest way is to put one 470 ohm resistor in series with one LED and hook it to the 12V power supply. 
Do the same with the next LED and hook it to the power supply in parallel.
... and so on....

Using 470 ohm resistors might mean the LEDs are very bright at 20mA current (try it and see what you think?)and the power supply won't be able to handle as many LEDs in total as it could with a bit of re-jigging to run LEDs in series as I suggested right back at the beginning. 

You do need to be aware of the maximum current the power supply can provide. Add up all the LED's 20mA requirements and try not to go beyond about half the maximum current the supply is rated for - especially with unregulated supplies as the voltage will simply drop as you add more load.

If the LEDs are too bright, and you don't want to bother buying some other different resistors, then you have two simple things you can try: two LEDs in series with one resistor (make sure you get the polarity corrrect) or two resistors in series with one LED. The first option will halve the voltage the LED sees (so they might refuse to light at all), the second option will halve the current (should just make the LED less bright).  Neither should cause any damage, so again try it and see what happens?

Personally I would probably get 680 ohm, 820 ohm, and 1k resistors to try.  1k is commonly used for LEDs being driven from 12V-15V
Thanks, I have just found all those resistors on Ebay, I`ll order them now. That will sort out the street and platform lights. I am tempted to buy those fairy lights, they would save a lot of soldering, time and look neater under the board. Thanks for your help, Jim

 

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