LED series parallel array

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Thread Starter


Joined Dec 9, 2011

I'm looking for some advice on a project I'm under taking. I'm hoping to convert the rear lights of my car to LED, the fabrication bit I can manage, the electronics bit I'm unsure on.

Essentially this is what I hope to achieve:

I've found this website: http://led.linear1.org/led.wiz from which I can work out resistor value's.

From what I can gather the above array's are done with 4 LED's in series in a parallel array to make up the width required.

To achieve this do I work out the resistor value for the 4 LED's and thats it? I'm right in remembering that in parallel circuits each string has the same voltage, and in series the voltage is shared?

Will there be any issues between different widths arrays with the LEDs emitting more/less light?


Joined May 9, 2009
Sadly this is against the TOS and I'm sure it will be closed! There are a lot of reasons this is not allowed. The #1 reason is liability; there's no guarantee that the LEDs you install will be properly rated for automotive environments (brightness, viewing angle and colour are of course important, but also don't forget reliability and safety.) You don't want you brake lights to fail and then find out your insurance company won't pay out because they aren't original.

You don't want to design for 12V. Your LEDs need to work on a nominal 13.8V and must be able to survive a transient event of 60V for about 100ms. That's about 25x more power for 100ms; many LEDs will be permanently damaged by this and it's not uncommon for these transients to be present in automotive electrical systems.

Thread Starter


Joined Dec 9, 2011
I'm not sure what transient meant, is it fluctuation? Can this be corrected with a regulator or something?

How is this over come with modern vehicles that have LED tail lights?

Any clue's to how the above array might have been made up?

More than likely these will end up as being show lights. But isn't a bulb going out just as likely (or more so) to happen as a LED array going, just a bit more work to replace a led array.


Joined Apr 5, 2008

I am closing this thread as it violates AAC policy and/or safety issues.

6. Restricted topics. The following topics are regularly raised however are considered “off-topic” at all times and will results in Your thread being closed without question:

  • Any kind of over-unity devices and systems
  • Automotive modifications
  • Devices designed to electrocute or shock another person
  • LEDs to mains
  • Phone jammers
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  • Transformer-less power supplies
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