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Author Topic: LED lighting - power supply  (Read 505 times)

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Offline Doltic

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LED lighting - power supply
« on: December 14, 2019, 09:23:24 PM »
Hello!

Just a quick question - currently in the process of planning my little TMD layout. I'm running DCC and it all has to be pretty modular due to the flat constraints

I was thinking, for the numerous LEDs to drop the voltage at the 12v input jack using a voltage regulator to ~3-2V and then wire the LEDs to that.

Would that be feasible?

Conor
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Offline Malc

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Re: LED lighting - power supply
« Reply #1 on: December 14, 2019, 10:08:25 PM »
Just use a suitable resistor instead of a regulator.
The years have been good to me, it was the weekends that did the damage.

Offline Bramshot

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Re: LED lighting - power supply
« Reply #2 on: December 15, 2019, 10:17:38 AM »
Better still in my opinion, wire the leds in groups of 3 in series plus a suitable resistor for each group, that way you get 3 x the leds for your power supply rating.

Online ntpntpntp

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Re: LED lighting - power supply
« Reply #3 on: December 15, 2019, 10:37:13 AM »
Even with a voltage regulator you must ALWAYS use a resistor.    Its purpose is to limit current through the LED not drop the voltage (LEDS are considered "current driven" devices).

I agree with @Bramshot that wiring LEDs in series is more efficient use of the available power than wiring each one in parallel. Just recalculate the series resistor for each group based on the total forward voltage drop of the LEDs in the series string.
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Online themadhippy

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Re: LED lighting - power supply
« Reply #4 on: December 15, 2019, 11:26:17 AM »
depending on the requlator used you may be able to configure it as a constant current source,however a resistor is much simpler

Offline Doltic

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Re: LED lighting - power supply
« Reply #5 on: December 20, 2019, 10:51:34 AM »
Hey

Okay, thanks for the information. I will proceed accordingly and ditch the idea with the regulator

Conor
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Online Bealman

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Re: LED lighting - power supply
« Reply #6 on: December 20, 2019, 07:22:14 PM »
I installed a 5m strip of RGB leds along the skirting board behind our Christmas tree the other day, which I powered with an old 12V 1A plug pack (wall wort).

It looked great, until the pack blew up and tripped the circuit breakers of Chez Bealman.

Lesson: Multiple leds draw a surprising amount of current. A 3-5A supply should have been used.
Vision over visibility. Bono, U2.

Offline springwood

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Re: LED lighting - power supply
« Reply #7 on: February 08, 2020, 07:25:12 PM »
I'm about to purchase some modern two-headed lights (off ebay) for my stations. As per below link:

https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=222079628345&_sacat=0

Question; I will be looking to have a number of these (possibly 9 or 10) on my mainline station to all come on via an on/off switch on the panel. I only have fixed 12v dc coming from one of my controllers so looking for guidance on wiring these up. In series or parallel? Resistors? Any diagrams most welcome.

Thank you, Robin

Online ntpntpntp

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Re: LED lighting - power supply
« Reply #8 on: February 08, 2020, 08:49:46 PM »
@springwood  looks like the ones you've ordered don't come with resistors, and the seller says operate them on 3V at 20mA.    As has been mentioned in this forum loads of times LEDs are current driven devices  not voltage driven, so you MUST use a resistor calculated to limit the current (in my opinion even if only supplying them with 3V )

I have recently fitted similar street lights. You could wire them in parallel with your 12V supply, each with its own resistor, but it's more efficient to share the current flow so I wired 3 of them in series (so nominally 9V forward voltage).

You may well find that 20mA is way too bright for these little light sources, I usually calculate resistors to set the current at about 5mA on these tiny LEDs and see how they look. I can always reduce the resistance a bit if necessary, or even go higher if I just want a subtle glow.  I keep a selection of resistors in stock as they're only pennies and always useful to have some values to play with  ;)

I use this LED resistor calculator

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

For 12V, assuming 9V forward voltage for 3 LEDs in series and 5mA the calculator reckons a 680 ohm resistor (it moans that 9v is too high a forward voltage for an LED, but still calculates an answer for you  ;) )

Oh and just for completeness in case you don't fancy trying the "3 in series" approach, if you want to run each LED with its own resist or, in parallel across your 12V supply, then  the calculator says for 20mA you need a 470 ohm resistor, and for 5mA you'd need a 1k8 resistor. 

I think worth noting that most suppliers of LED lights for model railways will sell them with at least a 1k resistor (often pre-fitted)  which limits the current to around 10mA at 12V, but this guy just says run them direct on 3V. As I said at the very beginning, I wouldn't  :no:

[edit]  Oh and one final PS: I wouldn't be surprised if the "12V" output of your controller may be quite a bit higher than that when under little or no load. Have you put a volt meter across it?
« Last Edit: February 08, 2020, 08:54:56 PM by ntpntpntp »
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Offline springwood

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Re: LED lighting - power supply
« Reply #9 on: February 13, 2020, 11:49:46 AM »
Just coming back to this thread for a moment. The ebay link I gave is for stuff from a Chinese supplier!! With all the news of the coronavirus circulating, I have to say I am not sure whether to order. Maybe being over cautious..should I play safe and just source similar ones from the likes of layouts4u.net? What do you think?

Offline Delboy

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Re: LED lighting - power supply
« Reply #10 on: February 13, 2020, 11:58:51 AM »
Just coming back to this thread for a moment. The ebay link I gave is for stuff from a Chinese supplier!! With all the news of the coronavirus circulating, I have to say I am not sure whether to order. Maybe being over cautious..should I play safe and just source similar ones from the likes of layouts4u.net? What do you think?

@springwood
It is difficult to know how the virus will affect supplies from China as according to the news people are beginning to filter back to work. I have order many items from there and delivery is always somewhat varied. I have received items as quick as 1 week and sometimes waited up to a month.
I personally, as you are talking "low cost items", under the circumstances would source them locally unless of course you are in no hurry to get on with the lighting project.
Regards,
She who must be obeyed says I am spending too much time on this forum. I love her dearly but what does she know?

Online ntpntpntp

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Re: LED lighting - power supply
« Reply #11 on: February 13, 2020, 12:08:44 PM »
@springwood  just beware of "UK stock" ebay listings that look ok until you look closely and see the far-east address! Your link is an example, purporting to be from Ireland but ....?   

Mind you I think some of the larger sellers do have "satellite warehouses" in other countries and send stuff out locally.

You will find genuine UK suppliers offering the same stuff, with a bit of a markup of course.  Depends how desperate you are for them and/or for cheapest price.
« Last Edit: February 13, 2020, 12:10:23 PM by ntpntpntp »
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Offline Delboy

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Re: LED lighting - power supply
« Reply #12 on: February 13, 2020, 12:16:22 PM »
@springwood  just beware of "UK stock" ebay listings that look ok until you look closely and see the far-east address! Your link is an example, purporting to be from Ireland but ....?   

Mind you I think some of the larger sellers do have "satellite warehouses" in other countries and send stuff out locally.

You will find genuine UK suppliers offering the same stuff, with a bit of a markup of course.  Depends how desperate you are for them and/or for cheapest price.

The problem is some Chinese companies are rather naughty and put a UK flag on the advert but do not have a "satellite warehouse" in the UK. Others, are usually genuine if they advertise a UK Flag and also state that their items are posted from within the UK. I usually look further down the eBay advert and check the sellers address.
She who must be obeyed says I am spending too much time on this forum. I love her dearly but what does she know?

Offline Railwaygun

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Re: LED lighting - power supply
« Reply #13 on: February 13, 2020, 01:33:21 PM »
Just coming back to this thread for a moment. The ebay link I gave is for stuff from a Chinese supplier!! With all the news of the coronavirus circulating, I have to say I am not sure whether to order. Maybe being over cautious..should I play safe and just source similar ones from the likes of layouts4u.net? What do you think?

@springwood
It is difficult to know how the virus will affect supplies from China as according to the news people are beginning to filter back to work. I have order many items from there and delivery is always somewhat varied. I have received items as quick as 1 week and sometimes waited up to a month.
I personally, as you are talking "low cost items", under the circumstances would source them locally unless of course you are in no hurry to get on with the lighting project.
Regards,

the problem of millions of people going home after the New Year holiday, and the possibility of more cross-infection will probably lead to a new surge of infection.

there is a china thread here

https://www.ngaugeforum.co.uk/SMFN/index.php?topic=48262.msg617006;topicseen#new

and the People's Revolutionary Front for Promotion of N Gauge purged this one

https://www.ngaugeforum.co.uk/SMFN/index.php?topic=48202.0





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