LED power

Thread Starter

Peter007ish

Joined Nov 30, 2022
2
Hi all, i have absolutely no electronic experience since i was a schoolboy. I am a model maker and for a project i am requiring multiple single LED's. These are to be various types of lighting effects of different colours. I wish to have these be supplied constantly so rather than using battery i want mains supply. Can any one tell me what i need to make this a reality. I am using standard 9v coloured LED's. Thank you in advance.
 

Dodgydave

Joined Jun 22, 2012
10,591
Leds have a voltage rating and current maximum limit, so depending on how many leds you have will determine how much current and voltage you need.
Any links to the leds you have in mind?

For example a single Red led is around 2V at 20mA and White leds are about 3V , if you're putting these in Parallel with a series resistor for each led then a 5V phone charger will work.
 
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BobTPH

Joined Jun 5, 2013
6,076
Link to the LED? There is no “standard” 9V LED that I know of. Presumably, these are LEDs with a resistor to make them run off 9V, but we also need to know the current rating and how many of them you will be using to suggest a power source.
 

dl324

Joined Mar 30, 2015
15,445
Welcome to AAC!
I am using standard 9v coloured LED's.
There are no standard LEDs, particularly any that operate at 9V.

LEDs that sequence through multiple colors with no additional circuitry will have a microcontroller in the package along with multiple LEDs. I have some that I connected directly to a CR2032 battery.

Do you have a part number or datasheet?
 

DickCappels

Joined Aug 21, 2008
9,510
Per @Dodgydave in post #2, if you can, switch to discreet LEDs with series current limiting resistors.
1669824250660.png
Because even the highest voltage (single chip) LEDs need 4 volts or less, allowing you to use a cheap 5 volt cell phone charger for a power supply.
1669824909957.png
The are inexpensive and usually pretty safe. All you need is a USB cable (like one cut off a dead mouse) and you are all set.

Many people on this website can help you choose the current limiting resistors for your chosen LEDs.
 

Thread Starter

Peter007ish

Joined Nov 30, 2022
2
Leds have a voltage rating and current maximum limit, so depending on how many leds you have will determine how much current and voltage you need.
Any links to the leds you have in mind?

For example a single Red led is around 2V at 20mA and White leds are about 3V , if you're putting these in Parallel with a series resistor for each led then a 5V phone charger will work.
i have around 100 individual leds.
 

ThePanMan

Joined Mar 13, 2020
520
Welcome to AAC.

Something about LED's:
1) They have a forward voltage rating (Vf)
2) They have a maximum current limit. Exceed that and you're burning up your LED
3) They are not considered "Voltage Driven" devices, they are current driven devices.

Before we can give you a definitive answer to your question you need to decide (and tell us) how many LED's you're going to operate off a single power supply (PS). Nevertheless, here's the rule for a single LED.
PS voltage minus the Vf of the LED. Assume you have an LED that has a Vf of 3 volts and a PS rated at 5 volts.
(5 - 3) = 2 volts
Next you choose the current you wish to drive them at. The more current the brighter they are. Exceed their max rating and they will burn out. Let's assume you have an LED whose max recommended current is 20 milliamps (0.02A or 20mA).
You know you have two volts to work with. Divide that by the amperage (0.02) You get "100". 100 what? Ohms (resistance).
Using a 5V PS and a 3Vf LED to run at 20mA you need a 100Ω resistor.

Again:
(V-Vf)÷A=Ω If you remember your math, do the parentheses first, then divide by the desired amperage. That gives you the safe resistance to run your LED at the desired current.

Now: If you have a higher voltage supply, say a 12V supply you can take those same LED's and total up their Vf. No, you can't use four LED's at 3Vf, you need some head room. You choose three LED's for a total of 9Vf.
(12V - 9Vf) ÷ 20mA = 150Ω. You can put three LED's in series (one connected to the next to the next) with a single series 150Ω resistor powered from a 12 volt source and you're fine.

You can also put LED's in parallel. Suppose you have a 12V PS capable of 2 amps. Using the string just mentioned you can (in theory) run 600 sets of LED's. (12 ÷ 0.02 = 600) Each string of three LED's and its own series resistor, you can power almost 600 sets. Why "Almost"? Because there are line losses and the possibility that when you approach 2 amps on the PS the voltage can begin to drop.

If you're building a model and want a single LED in each room (assumed) then a single LED with a single series resistor on a 5V power supply will light it up just fine. I've seen lots of 5V PS's that are rated for 700mA. So you can run quite a few LED sets off of one 5V PS. 35 should work just fine. But that's using a 5V PS rated at 700mA on 20mA LED strings.

Different color LED's have different Vf's. In general they typically run on about 20mA, but can be run at much lower currents, depending on how bright you want them to be. I've personally run a superbright LED at 5mA and it was plenty bright. But that doesn't matter, what matters is what you want. If you want max brightness then build for max recommended current (consult your data sheet if you have one) and build for that.
 
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