# How to power 24pcs of 5w leds?

Hi,

I´m totally newbie here, so please be patient with me.
My mission is: I´d like to power 24 pcs of 5w LED´s. Below some info of them:

2pcs 5W Warm White LED 2700K~3000K High Power LED Light Lamp Emitter on 20mm PCB
12pcs 5W Red LED 660nm LED Bulb Lamp + 20mm Star PCB
20pcs 5W Blue LED 445-455nm+ 20mm Star PCB

So, in total it´s 120V. I´ve been told that those LEDs will take about 20mA each. Total: 480mA. Please correct me if I´m wrong here.

So finally to the actual question. I know I can connect those LED´s in series and light them up that way, but then I will need 120V power supply. Right? I don´t have one of those course. Is the situation this bad? Any other way?

The thing is, that I got a lot of 5V power supplys lying around. 800mA, 1A, 3A, But all 5V as I said.

Is there any way I could use one of my 5V supplys to light those 24 LED´s? Do I need to use a resistor in front of every single LED and connect them in parallel? if so, please explain it to me. which resistors and if the resistors or similar won´t work, is there any other way than to go with 120V parallel? I really hope my 5 volts in series will do the trick.

Here´s the link where from I bouht them:

EBAY LINK TO LEDS

In the specifications section under 5 Watt the warm white and royal blue will draw 700mA and the red one will draw 1.2 Amps.
For the blue and white the numbers jive, 7 Volts @ 700mA = 4.9 Watts.
For the red not so much, 2.2 Volts @1.2 Amps = 2.6 Watts.

I'm not sure where the 20mA figure came from.

Little longer answer- not quite sure where you are getting 120v from. Watts and voltage are two different things. Watts (power) is a function of voltage and current as in P=IxE. I=current, E=voltage, and P=watts.

Saying that, you are not getting 5 Watts with 20mA. If you read a little further down the page, you will see 5W led = 700mA EACH with the red pulling 1200mA (1.2A). All seem to need a forward voltage 0f 6-7Vdc. With what you have listed, you need a power supply of 7vdc (min) and 29.8A.

Are you trying to signal the space station???

By "120V" the OP probably meant 120 watts, which is 24 x 5 watts.

Obviously one would need a power supply capable of supplying more than 120 watts. 12 V at greater than 10 amperes would be a reasonable choice, with the LEDs in series to make up 12V strings.

Also you need a constant current driver for each LED to regulate the current. This is because the forward voltage drop on power LEDs changes as they warm up and as they age.

I´ve been told that those LEDs will take about 20mA each.

Then explain to the person that told you this that you are using high power LEDs. If he has already been told that, then stop taking advice from idiots.

You can buy [u]constant current power supplies[/u] capable of driving a series-string of high-power LEDs.

Ok thanks a lot for your answers. So I´ll have to skip the 5v power supply idea and think about some other way. And yes it was my mistake there… tried to say 120W instead of 120V. And I really don´t know where I got that 20mA per one led, I must have been read it from some forum or don´t know where. But your answers helped a lot… I´ll read them again and try to digest it all.

I got some stuff which might help. I´ll try to link those here, so please let me know if there´s some item I could use. Click the links and it takes you to the ebay page for further info.

2 pcs of 5A DC Buck Converter Constant Current Solar Battery Charger LED Driver w/PWM car

1 pcs of 5V 2–Channel Relay Module for Arduino PIC ARM DSP AVR Electronic

1 pcs of Effective Stable 1 Channel 5V Indicator Light LED Relay Module For Arduino F5

1 pcs 12V 4-Channel Relay Module with Optocoupler High Level Triger for Arduino

And yes I´m gonna use Arduino for this project, but just measuring temperature/humidity and nothing else. Arduino has got nothing to do with the leds. So that´s my plan… at least for now.
Please hit me with ideas and please try to explain it… well… like to child cause you know I don´t know much bout electronics.

So big thanks fore your answers… I really need them now.

And one more thing. Does it matter if the power supply is over 7vdc and 29.8A? How much those LEDs can handle?

And I also got 2pcs of power supplys “output DC12V 2A”. And one 12V supply marked 1.25A. Would these help to light up some LEDs at least? How many if so? Just trying to avoid buying new things here, but it sadly seems that I´m loosing the battle with these 5V and 12V weapons.

How much those LEDs can handle?

They can only handle UP TO their rating, not a jot more. It is up to you to supply a driver that takes the power available from the power supply and turns that into the voltage / current needed to drive the LEDs. Because the forward voltage changes then this driver circuit has to keep monitoring the current and adjusting the voltage so that the current is constantly at the right value. If you have lots of LEDs in series then you only need one of these drivers but you need more voltage from the power supply. If you only have a low voltage from your power supply you need one of these driver circuits for each LED.

None of your links address the lighting of the LEDs.

You already know what these leds can handle–700mA with a Vf of 6Vdc. That is each.

If you are wanting to fire one of those things up right now, you could use your 12v supply and a bunch of CL resistors. It’s not that the ohms will be high, it’s the power dropping across those resistors.

Using a led calculator app on my phone (I’m using electrodroid)
-Vcc=12v
-Vf led= 7v
-If led= 700mA
the resistor needs to be 7.143 ohms.

The led is dropping 4.9W and the resistor is dropping 3.5W. Use a 9v supply and the resistor drops to 2.8 Ohms at 1.4W.

Either way, the resistor has to drop a lot of power. IF those only pulled the 20mA you thought, the resistor would only be dropping 1/10th a watt.

The normal way to power a bunch of identical high power LEDs is with a constant-current power supply,
not a constant voltage supply, because with constant current you don't need a wasteful current limiting
resistor (which needs to dissipate heat too). Wiring a bunch is series is easier too.

With LEDs of different current rating you can't use this approach.

Thanks guys. I´ll go with a constant-current power supply as you have adviced me to do. But there´s still one thing that´s bothering me. What about these 2 pcs of "5A Constant Current Solar Battery Charger LED Driver w/PWM"?

Is there any possibility that I could use them somehow? I´m just hoping that I could get a larger range of power supplys to choose from.. or something. What do you think about these fellows? Link takes you ebay page.

Thanks.

5A DC Buck Converter Constant Current Solar Battery Charger LED Driver w/PWM car

Preta:
Thanks guys. I´ll go with a constant-current power supply as you have adviced me to do. But there´s still one thing that´s bothering me. What about these 2 pcs of "5A Constant Current Solar Battery Charger LED Driver w/PWM"?

Is there any possibility that I could use them somehow? I´m just hoping that I could get a larger range of power supplys to choose from.. or something. What do you think about these fellows? Link takes you ebay page.

Thanks.

5A DC Buck Converter Constant Current Solar Battery Charger LED Driver w/PWM car

That is a buck converter, it can only reduce voltage. You would not be able to drive multiple LEDs in series with that.

Preta:
Thanks guys. I´ll go with a constant-current power supply as you have adviced me to do. But there´s still one thing that´s bothering me. What about these 2 pcs of "5A Constant Current Solar Battery Charger LED Driver w/PWM"?

Is there any possibility that I could use them somehow? I´m just hoping that I could get a larger range of power supplys to choose from.. or something. What do you think about these fellows? Link takes you ebay page.

Thanks.

5A DC Buck Converter Constant Current Solar Battery Charger LED Driver w/PWM car

Read carefully what was said - you have some 700mA LEDs and some 1.2A LEDs - so you need
separate supplys, because a constant current of 0.7A cannot also be a constant current of 1.2A.

Or perhaps you don't need to run the 1.2A LEDs at full power? Then everything might run from 0.7A

You also more than one supply if you string exceeds the max voltage of standard supplies.

And you need a constant current LED power supply, not a solar battery charger - it should be
very obvious that those are two different things.

Thanks again.

And yes I´ve been thinking about that 2 different currents problem.

A little update to my original plan. I´ll reduce the amount of LEDs a little. Now I´m about to light up only:

4pcs of 5W LED: Warm White: 4 Chips,Voltage:(6V~7V),Current: 700mA
and the red ones:
13pcs of 5W LED: Red(660nm): 4 Chips,Voltage:(2.0V~2.2V),Current: 1200mA

17pcs in total.

Started to wonder one thing… not a perfect idea, but would it work?

I got 4pcs of 12V 1A power supplys lying around. If i connect them in series, I´ll get 28V 1A out of them… Am I right? I also have 1.25A and 2A (12V) versions which I could use, but is it possible to use same voltage, but different current power supplies in series? Which current that series then gives? lowest… highest? Does the supplys have to be exact the same current i case of connecting them in series?

But let´s say I got that 28V 1A for now. It´s not 1200mA i know but still. How many red LEDs could I use with that setup?

is it:

13*2.1V=27.3V ?

Sorry cause I´m totally newbie in these calculations. Do i need a constant current driver there then? Guess so.

And Mark.T. You said “And you need a constant current LED power supply, not a solar battery charger - it should be
very obvious that those are two different things.”

Could you explain this a little bit… How exactly this “5A DC Buck Converter Constant Current Solar Battery Charger LED Driver w/PWM car” difference from the “real deal” in this situation of mine. I mean when using normal supplies in series? Does the 5A mess up with the 1A somehow? Am I totally wrong here?

It says this in the description of my 5A converter:

"Some Application:

DIY voltage Regulator, with constant current, can protect the load.
The power supply for electronic equipment.
For a variety of battery charging, Setting the charging voltage and charging current according to the different voltage and battery capacity, with charging indicator, convenient to observe the state of charge.
solar panels power supply for battery charging, With constant current, which prevents battery overcharge.
Driver high-power LED, Free series-parallel combination, With PWM control input, Available SCM to Control the LED brightness (PWM control frequency range 100-300Hz).
Use as a car power supply, Power supply for electronic equipment."

And one more newbie question… Is it possible to reduce the current for those 4pcs of warm white 700mA LEDs if the situation that needs? Lets say from that 1A to 700mA with some sort of resistor or I don´t know what component. Is that possible?

Better to ask than try & fail & fry the LEDs and more, so sorry for a lot of stupid questions.

You have helped a lot already.

I got 4pcs of 12V 1A power supplys lying around. If i connect them in series, I´ll get 28V 1A out of them.. Am I right?

No.

12 * 4 = 48V

Which current that series then gives? lowest.. highest?

Lowest - remember the current rating of a power supply is the maximum current it is capable of supplying. The actual current depends on your load.

Could you explain this a little.. How exactly my "5A DC Buck Converter Constant Current Solar Battery Charger LED Driver w/PWM car" difference from the "real deal"?

Sure once you tell us what the "real deal" actually is.

And one more newbie question.. could it be possible to reduce just the current for those 4pcs of 700mA if the situation that needs?

No. Not and run the LEDs at anything like full power. As you have been told before resistors simply don't cut it when it comes to power LEDs.

Grumpy_Mike:
No.

12 * 4 = 48V
Lowest - remember the current rating of a power supply is the maximum current it is capable of supplying. The actual current depends on your load.
Sure once you tell us what the "real deal" actually is.
No. Not and run the LEDs at anything like full power. As you have been told before resistors simply don't cut it when it comes to power LEDs.

Oh my.. Believe me I´m not that stupid.. of course 48V. What was I thinking? And I don´t know what the "real deal" is. Mark.T seems to know. I´d like to know how it actually does a different kind of job than mine (that 5A converter) is this case.

So how many red 1.2A LEDs I could light up with 48V 1A power supply? And yes I understand it´s not full power then.

But thanks Grumpy_Mike for correcting me

So how many red 1.2A LEDs I could light up with 48V 1A power supply?

Well if LEDs take a voltage of "DC Forward Voltage:2.2V~2.8V" then that is
48 / 2.8 = 17.14
but you need a few volts for the constant current to stables so I would say 15 LEDs, but that assumes you can get a constant current driver that can take 48V, that might be pushing it.

Well I got 2pcs of these 5A constant current converters. They can handle up to 30V each. So if I split the set in half and it should work.. right?

Then I don´t have a third current converter for those 4pcs of 700mA LEDs. Does those 4 LEDs even need a constant current converter.. any other option? And is there any other way to reduce to current from 1A to 700mA for 4 LEDs than adding that one more power supply?

Well I got 2pcs of these 5A constant current converters. They can handle up to 30V each. So if I split the set in half and it should work.. right?

No.
They are 5A constant current regulators, you don't want 5A going through the LEDs you want 700mA through them.

Does those 4 LEDs even need a constant current converter.

Yes they do.

And is there any other way to reduce to current from 1A to 700mA for 4 LEDs than adding that one more power supply?

I think you are misunderstanding something here. The way the current is reduced is to have a constant current regulator that regulates at 700mA.

Are you understanding what a constant current regulator actually does?

Based on what I have read so far, I think I'll sit this one out....