# Thread: 24V Dc Power Source and LEDs

1. ## 24V Dc Power Source and LEDs

Anyone see any problems in driving various coloured LEDs from a 24VDC power supply? I have one easily to hand. I know from LED Calculator I'll need around 1W, 1K2 resistors, maybe some different value resistors for colours/combined LEDs. I'm putting together a 737 fire panel, which will be pretty much eye-candy only. The 24VDC would also be handy to drive the fire bell I'm putting inside the pedestal.

I'm only looking to do some LED direct back lighting and button illumnination (using the 'test' toggle switch), nothing driven from software or I/O cards.

Cheers!

2. ## Re: 24V Dc Power Source and LEDs

24 volt is not a problem.
There is little data difference between the diodes of different colors. However, I have always used standard calculation on all LEDs, except for special and high bright LEDs

Do you need more of the same diodes to light together, consider to connecting them in series.
LED Resistor Calculator
LED Characteristics and Colours :: Radio-Electronics.Com

3. ## Re: 24V Dc Power Source and LEDs

Hi,

Thanks for that,...Another question!

Let's say I drive 5 green LEDs in series OK from a DC power source with a suitable resistor......But on the same flight deck panel I want to add a batch of white then red LEDs, each also grouped in series. So... now I have 3 groups of series LEDs and 3 suitable resistors, one for each colour/group.

Now, if I supply these 3 groups from the same DC power source, are these groups now in an equivalent parallel circuit? Are my series resistor values wrong? Do I have to calculate and design the entire LED circuit (green/red/white) first? ...And..each time I change anything do all my resistor values change?

Cheers for LEDs basics!

4. ## Re: 24V Dc Power Source and LEDs

As long as you parallel from the same point for each branch, your resistor calculations for each series leg will remain as previously calculated from the aforementioned webpage calculator; the voltage input(24vdc) to each parallel leg remains the same. It is the total current needed from the power supply that is divided between each leg - which you have already calculated via webpage calculator.

Refer to Kirchoff's Current Law:
Kirchhoff's Current Law

Also, Kirchoff's Volatge Law:
Kirchhoff's Voltage Law

Hope this helps.
JM