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Author Topic: How to wire up 50 LEDs  (Read 644 times)

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Offline Jimbo123

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How to wire up 50 LEDs
« on: October 27, 2019, 04:17:26 PM »
Hi all, I bought myself an N gauge layout 6x2 which was almost finished. It has about 12 Metcalfe cardboard buildings glued on, I think the previous owner used superglue. I have noticed that the building do have floors in them. So, some buildings may have more than one LED fitted inside. My plan is to fit 3 volt LED lights inside the buildings, with resistors as well. I also plan on fitting platform lights and street lights. I would guess between 40-50 lights in total. What I need is suitable power supplies, which would powerful enough, but try to be as least as possible to keep the cost down also keep the wiring down a little. Any bright ideas? Cheers

Offline ntpntpntp

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Re: How to wire up 50 LEDs
« Reply #1 on: October 27, 2019, 04:48:19 PM »
It would be more efficient to run two or 3 or 4 LEDs in series from - say- a 12V or 15V DC supply, with a suitable resistor in series with  each string.

I use the LED calculator below for calculating resistors for a single LED.  If you have multiple LED in series just add up their total forward voltage.  Remember with LEDs you must always allow a higher voltage supply than the total forward voltage drop, and always include a resistor (the primary function of the resistor is to limit current not drop voltage).

http://led.linear1.org/1led.wiz

So... lets say you have a 12V supply and your LEDs  have a 3V forward voltage drop. Let's assume 15mA  (which is quite a lot for a modern LED so you may get away with less):  For a string of 3 LEDs the calculator wold suggest a 220 Ohm resistor. 

If you have  48 LEDs in 16 parallel strings of 3, the total current requirement at 15mA per string would be 240mA (or about 0.25A).

If you buy a supply capable of 0.5A that gives you plenty of headroom, and if you can find a 1A supply that's even better as you have loads of headroom in case you need to run some strings with just 1 LED (and a suitable resistor) and/or some other 12V lights.


Just as a comparison, if you were to wire those same 48 LEDs individually in parallel with a 12V supply each would need a 680 ohm resistor and the total current draw at 15mA per LED would be 0.72A.    (3x as much power).  That's why running LEDs in series wherever you can is more efficient.
« Last Edit: October 27, 2019, 05:01:44 PM by ntpntpntp »
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!
https://www.ngaugeforum.co.uk/SMFN/index.php?topic=50050.0

Offline Jimbo123

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Re: How to wire up 50 LEDs
« Reply #2 on: October 27, 2019, 05:01:12 PM »
Hi, I was supplied with these resistors.. 470ohm 1/4W 0.25W Metal Film Resistor ±1% 1 Ohm to 1K Ohm. I get a bit lost with all the technical jargon, which would be the best way to use these with the 3mm led I have? here is a link https://www.ebay.co.uk/itm/200pcs-3mm-5mm-LED-Emitting-Diodes-Assortment-Kit-White-Yellow-Red-Blue-Green/233330882048?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2648 thanks for helping.
« Last Edit: October 27, 2019, 05:02:34 PM by Jimbo123 »

Offline ntpntpntp

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Re: How to wire up 50 LEDs
« Reply #3 on: October 27, 2019, 05:10:31 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.

« Last Edit: October 27, 2019, 05:12:04 PM by ntpntpntp »
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!
https://www.ngaugeforum.co.uk/SMFN/index.php?topic=50050.0

Offline Nigel Cliffe

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Re: How to wire up 50 LEDs
« Reply #4 on: October 27, 2019, 05:13:40 PM »
I'd put a resistor on every LED, and wire them in parallel to a power supply.   The reason being its easier to swap a single resistor to get the brightness level required for each LED.    However, if wiring in series, make sure that similar brightness is appropriate for them in each installation. 

3mm LEDs are rather big for streetlights, etc.. 

(I'd be enormously tempted to do it a different way: a string of addressable LEDs and an Arduino (under £10) to control them.  Thus, only three wires which daisy-chain around everywhere (can cut string of LEDs and extend with three wires), and every LED can be remotely controlled for colour and brightness, turned on/off individually, etc..    ). 

- Nigel


Offline ntpntpntp

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Re: How to wire up 50 LEDs
« Reply #5 on: October 27, 2019, 05:16:29 PM »
Hi, I was supplied with these resistors.. 470ohm 1/4W 0.25W Metal Film Resistor ±1% 1 Ohm to 1K Ohm.

Just reading that again, so what have you actually got? are they all 470 ohm resistors or have you got a range of values?  I'm concerned about the "1 Ohm to 1K Ohm" bit??? ( I suspect they may mean the 1% tolerance range is available from 1 Ohm to 1K Ohm)
« Last Edit: October 27, 2019, 05:18:05 PM by ntpntpntp »
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!
https://www.ngaugeforum.co.uk/SMFN/index.php?topic=50050.0

Offline Phoenix

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Re: How to wire up 50 LEDs
« Reply #6 on: October 27, 2019, 05:23:11 PM »
Hi Jimbo,

If the lights are in buildings, perhaps this might be an idea .....

https://www.festive-lights.com/5m-white-indoor-christmas-tree-lights-50-leds-green-cable

For £4.25, 50 lights wired up with a power supply supply sounds a pretty good bargain  :D

With all best wishes

Kevin

 :beers:

Offline Jimbo123

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Re: How to wire up 50 LEDs
« Reply #7 on: October 27, 2019, 05:28:01 PM »
I'd put a resistor on every LED, and wire them in parallel to a power supply.   The reason being its easier to swap a single resistor to get the brightness level required for each LED.    However, if wiring in series, make sure that similar brightness is appropriate for them in each installation. 

3mm LEDs are rather big for streetlights, etc.. 

(I'd be enormously tempted to do it a different way: a string of addressable LEDs and an Arduino (under £10) to control them.  Thus, only three wires which daisy-chain around everywhere (can cut string of LEDs and extend with three wires), and every LED can be remotely controlled for colour and brightness, turned on/off individually, etc..    ). 

- Nigel

The 3mm leds are to be hidden in the buildings, the street lamps are the ones you buy that look like.. well.. street lamps, tho most suppliers try to sel you ones way to tall. :-( Have you got a diagram to do it the way you say.. Daisy chain them? thanks
« Last Edit: October 27, 2019, 05:29:20 PM by Jimbo123 »

Offline Jimbo123

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Re: How to wire up 50 LEDs
« Reply #8 on: October 27, 2019, 05:31:01 PM »
Hi, I was supplied with these resistors.. 470ohm 1/4W 0.25W Metal Film Resistor ±1% 1 Ohm to 1K Ohm.

Just reading that again, so what have you actually got? are they all 470 ohm resistors or have you got a range of values?  I'm concerned about the "1 Ohm to 1K Ohm" bit??? ( I suspect they may mean the 1% tolerance range is available from 1 Ohm to 1K Ohm)

These are what I have  https://www.ebay.co.uk/itm/1-4W-0-25W-Metal-Film-Resistor-1-1-Ohm-to-1K-Ohm/262472631890?ssPageName=STRK%3AMEBIDX%3AIT&var=561277847931&_trksid=p2057872.m2749.l2649

Offline Jimbo123

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Re: How to wire up 50 LEDs
« Reply #9 on: October 27, 2019, 05:33:49 PM »
Hi Jimbo,

If the lights are in buildings, perhaps this might be an idea .....

https://www.festive-lights.com/5m-white-indoor-christmas-tree-lights-50-leds-green-cable

For £4.25, 50 lights wired up with a power supply supply sounds a pretty good bargain  :D

With all best wishes

Kevin

 :beers:

Nice one, saves a lot of soldering

Offline ntpntpntp

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Re: How to wire up 50 LEDs
« Reply #10 on: October 27, 2019, 05:36:29 PM »
Hi, I was supplied with these resistors.. 470ohm 1/4W 0.25W Metal Film Resistor ±1% 1 Ohm to 1K Ohm.

Just reading that again, so what have you actually got? are they all 470 ohm resistors or have you got a range of values?  I'm concerned about the "1 Ohm to 1K Ohm" bit??? ( I suspect they may mean the 1% tolerance range is available from 1 Ohm to 1K Ohm)

These are what I have  https://www.ebay.co.uk/itm/1-4W-0-25W-Metal-Film-Resistor-1-1-Ohm-to-1K-Ohm/262472631890?ssPageName=STRK%3AMEBIDX%3AIT&var=561277847931&_trksid=p2057872.m2749.l2649

OK so you do have a bunch of 470 ohm resistors.  Worth clarifying!
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!
https://www.ngaugeforum.co.uk/SMFN/index.php?topic=50050.0

Offline Jimbo123

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Re: How to wire up 50 LEDs
« Reply #11 on: October 27, 2019, 05:38:54 PM »
Hi, I was supplied with these resistors.. 470ohm 1/4W 0.25W Metal Film Resistor ±1% 1 Ohm to 1K Ohm.

Just reading that again, so what have you actually got? are they all 470 ohm resistors or have you got a range of values?  I'm concerned about the "1 Ohm to 1K Ohm" bit??? ( I suspect they may mean the 1% tolerance range is available from 1 Ohm to 1K Ohm)
yes, 200 of them

These are what I have  https://www.ebay.co.uk/itm/1-4W-0-25W-Metal-Film-Resistor-1-1-Ohm-to-1K-Ohm/262472631890?ssPageName=STRK%3AMEBIDX%3AIT&var=561277847931&_trksid=p2057872.m2749.l2649

OK so you do have a bunch of 470 ohm resistors.  Worth clarifying!

Offline Jimbo123

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Re: How to wire up 50 LEDs
« Reply #12 on: October 27, 2019, 05:50:03 PM »
Hi Jimbo,

If the lights are in buildings, perhaps this might be an idea .....

https://www.festive-lights.com/5m-white-indoor-christmas-tree-lights-50-leds-green-cable

For £4.25, 50 lights wired up with a power supply supply sounds a pretty good bargain  :D

With all best wishes

Kevin

 :beers:

Nice one, saves a lot of soldering

That would solve the problem with the building lights but not the street lights, maybe I should just use trial and error and see how bright they are with different power supplys

Offline Jimbo123

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Re: How to wire up 50 LEDs
« Reply #13 on: October 27, 2019, 06:03:53 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

Offline ntpntpntp

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Re: How to wire up 50 LEDs
« Reply #14 on: October 27, 2019, 06:10:57 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
« Last Edit: October 27, 2019, 06:17:07 PM by ntpntpntp »
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!
https://www.ngaugeforum.co.uk/SMFN/index.php?topic=50050.0

 

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