Help with basic LEDs

[Dale(294engr]]

Originally Posted by Ladiesman217

Hey everyone, our team decided to use LEDs on our robot for the first time this year, but we have no idea how we can power these things legally. We just want something very basic, we turn the robot on, the LEDs turn on. thats it. if you have any recommendations for LEDs (purple specifically) please let me know! Thanks

First select the source and quantity of Purple LEDs you wish to use.

Individual LEDs come with and without internal current limit (resistors)

Group strings of LEDs are available
Xmas types 110vAC NOT 12.6v DC in robot would need rewired - a pain
Motorcycle 12.6v strings recommended (see below for link)

Each color of LED has a specific Forward Voltage drop
(say 1.1v for red up to ~3.6v for blue/white)
with a specified maximum forward current rating..

Together with the known supply voltage,
the correct current limit resistor may be calculated....

Rvalue = (Vsupply - (#LEDs in series * Vfwd)) / Ifwd in Amps

Rvalue_redLEDexample = 12.6v - (8eaLEDs * 1.1v) / .030 = 127 ohms

so use a 1/4w or greater wattage carbon resistor of approx. 127 ohms

Wwiring up & ruggedizing such a string is a bit of pain, but a great learning experience / project for one on team not engaged in other duties.

Best is buy an existing commercial product such one listed below:
(purple-violet) designed for 12v motorcycle use!
for $14.99 on sale as of 1/20/14:

http://www.amazon.com/PURPLE-LED-Neo...productDetails

Product Description

4 PIECE LED NEON LIGHT KIT Complete Kit Comes With The Following: ●4 Separate LED Neon Lights With Wire Leads Use for all 12Volt Systems ●Two Styles of Mounting Hardware: Surface Mount for Anywhere, and Flush Mount for Plastic or Metal up to 1/8" Thick ●All Wire and Connectors for installation ● Switch with Leads ●Complete Installation Instructions ●Less than an hour to install THESE ARE RADLITES LED's THE HIGHEST QUALITY LED'S IN THE WORLD WITH THE LATEST TECHNOLOGY!! ●LED's will run over 100,000 Hours.. 11 years continuous! ●Very low Power Consumption 30ma each, 33 LED's per amp. You can leave them on all night and not drain your battery. ●Very small and easy to hide, and LED's do not generate heat. ●Brightest most efficient lighting, used everywhere!!

(I haven't used this product - I just googled it, but sounds perfect for your robot.. tho I'm a bit confused how 30mA per amp 33 LEDs statement relates, I think they are trying to say there are 4 strings of purple LEDs)

best feature: already ruggedized & for motorcycle use!, mounting, etc)

Connect it to a 20A resettable breaker and you are good to go (will turn on with 120A main breaker... you may wish to add a toggle switch as an additional local control.. or use a spike as suggested by others if you wish remote control (flash them via software, etc.)

I recommend aiming them down at floor or at structure within your robot so as to not challenge rules regarding interference with other robots vision system.

Good luck... Dale