# PCB Heaven

## General Category => Maths, Geometry, Physics and others => Topic started by: MiriaM on September 08, 2008, 08:23:30 AM

Title: Serial leds or parallel leds?
Post by: MiriaM on September 08, 2008, 08:23:30 AM
I have a series of LED lights, each one 12 volt 3watts.
Is it better to connect them Serial or parallel? What is to be the difference?
Title: Re: Serial leds or parallel leds?
Post by: spic0m on September 08, 2008, 17:18:22 PM
Depends, what is your power source and how many leds you have?
Title: Re: Serial leds or parallel leds?
Post by: kam on September 08, 2008, 18:10:50 PM
Hi miriam!

Well... Each piece will draw P = U x I => I = P / U => I = 3 / 12 => I = 250mA

So, you have 3 LEDs, each one rated 12V 250mA.
When you connect them parallel (that is most proposed) then you will need a power source of 12 volts and a total of 750mA
(UTOT=U1,2,3 and ITOT=I1+I2+I3).

If you connect them in series, then you need a power source of 36 volts of 250mA
(UTOT=U1+U2+U3 and ITOT=I1,2,3).
Furthermore, in series connection, if one LED fails then this is what happens. If internally it breaks the circuitry series, then all LEDs will stop working as no current can pass through the broken LED. If the broken LED internally short-circuits, then there is a danger that the other two LEDs will be burned as they will have to manage all the supplied voltage divided by 2. So, instead of 12V each, will be supplied with 36/2 = 18V each.

Thats why prefer parallel connection. It is easier to have a source of 12V 750mA rather than one 36V...
Title: Re: Serial leds or parallel leds?
Post by: Supernova on September 08, 2008, 22:42:12 PM
You may also have mixed connection, for example you have 2 sets of 2 in-series LEDs and these sets conencted in paralele:

|------(LED)----(LED)------|
------|                                      |-------
|------(LED)----(LED)------|

If each led is 12V 250mA, then this will be 24V 500mA... If you get what i mean.
Title: Re: Serial leds or parallel leds?
Post by: MiriaM on September 15, 2008, 22:36:17 PM

And do i have to use some kind of resistor for these?
Title: Re: Serial leds or parallel leds?
Post by: Mercury on September 16, 2008, 12:02:33 PM