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Manufacturing 24v LED

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eng.majeed

New Member
Hello... i'm having a small workshop for control panels's & in our area 24v dc led's are not available. can any one guide me to make 24v dc led's with details.\please im waiting
 

picbits

Well-Known Member
Yes - work out the current limiting resistor needed for the LED you are using and solder it inline on one of the legs of the LED

For example, if you are using an LED which is rated at 2.2v 20ma from a 24v supply

24 - 2.2 / 0.02 = 1090 ohm resistor so you'd just pick the nearest value to that
 

Hero999

Banned
Use a >0.5W resistor.

I'd recommend a 1k2 resistor.
 

millwood

Banned
using resistors to drop that much voltage isn't very efficient - which may or may not be an issue for you.

you can parallel a serious of LEDs to help drop the voltage: 11 LEDs with Vfwd=2.2v will get you about 24v; or 5 LEDs and then a resistor of (24-5*2.2)/20ma=470ohm.

or you can use those lm317 or smps chips to form a constant current source to drive the LEDs - a better approach.

or you can use dedicated LED drivers for this: the best approach.

it all depends on what you want to do.
 

crutschow

Well-Known Member
Most Helpful Member
you can parallel a serious of LEDs to help drop the voltage: 11 LEDs with Vfwd=2.2v will get you about 24v; or 5 LEDs and then a resistor of (24-5*2.2)/20ma=470ohm.
You do not want to have 11 LEDs to give 24v without a resistor in series, the current draw would be very susceptible to slight changes in the diodes forward drop. I would want about a 4-5V drop across a resistor which would allow 19V/2.2 = 8.6 or 9 LEDs maximum in series. The resistor would then be (24 - 9*2.2) / 20mA = 210Ω.
 

k7elp60

Active Member
I would use only 10mA for the LED's. Even though a lot of LED's have a maximum current of 20mA, with my old eyes(68 years old) 10mA of forward current the LED's are still very visible.
 

RODALCO

Well-Known Member
24 V led

As you are using dc, the led will be bright enough at a 10 to 15 mA current.

Most people always seem to go for the maximum current (20 to 30 mA) of the LED.
IMO it reduces the reliability


Go for a 1k8 (1800 ohms) resistor rated at 1 Watt.

It is good practise to put a small diode in antiparrallel with the LED in case of reverse polarity which may damage the led.

1N914, 1N4148 etc.

At my YouTube channel (RODALCO2007) I have a few LED clips for single and multi LED lamps for 110 V dc and 240 Volts AC.
They show you where the parts go.

In your 24 volt DC case the resistor value is different as stated above.

I'm at the work computer which doesn't allowe me access to YouTube.

if you are interested i can post the link later today.

The different colour led's have different voltage drop across them, from about 1.7 (red) to 3.3 (blue) Volts.
With above resistor you should have no problems whatsoever.
 

Hero999

Banned
Most people always seem to go for the maximum current (20 to 30 mA) of the LED.
IMO it reduces the reliability
True.

Operating at maximum current doesn't increase the brightness much. The intensity of most LEDs falls once it gets above a certain temperate anyway. It wouldn't surprise me if, under certain circumstances, higher currents (within the maximum rating) actually reduce the brightness.
 

RODALCO

Well-Known Member
Thanks Hero999 for sharing my thoughts regarding the maximum current through led's.

I find that most leds in the 4000 - 12000 MCAD give full brightness at currents between 7 and 15 mA.

Amazingly is that good quality led's already emit usuable light at below 1 mA current if power consumption in a series resistor is an issue.

I measured the low led current when building the old citrus lemon battery cell for my 10 y.o. daughter over the weekend. A blue led at 0.4 mA and 2.5 Volts with 5 lemons in series. :)
 

Hero999

Banned
I've managed to very dimly light a white LED by holding one led and touching the other onto a grounded object such as a radiator. Wow it's magic I've discovered a free energy source? No it's just mains hum but it's still impressive how it's enough to light an LED.
 

RODALCO

Well-Known Member
Lemon and LED < 1 mA

YouTube - Lemon and salt water batteries

Cool !! Hero999 it is amzing how bright these led's are at those small currents,
You were basically acting as an areal.

Look at above Y.T. link where I ran a blue LED on 5 lemons.
 
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