# Led's

Discussion in 'LEDs and Optoelectronics' started by Bluspark, Aug 1, 2011.

1. ### Bluspark

4
0
Aug 1, 2011
I am interested in using salvaged led's for lighting in my caravan. Mainly white Hi brightness types.

I have many different types and sizes mostly second hand; my problem is that I always have trouble in finding out what voltage and amperage to run them on. Most have no part No. or type indication.

I am fairly familiar with connecting multiples in series.

Finally I mostly want to use 12 vdc as my initial supply.

Thank you. Bluspark

2. ### nepow

99
2
Jul 18, 2011
Hi, To keep on the safe side you need to limit the current through the LED to a safe value with respect to the voltage applied to the device which for a white type is approx 3v _ 3.5v ... most wire ended LED's have a maximum safe operating current in the order of 20Ma so for a 12 volt DC supply and a single 3 volt LED the series resistance needs to drop 9 volts which by ohms law = 450 ohms... a standard or preferred value of 470 ohms would apply. Note: If you go above 12 volts then you will exceed the safe current limit!! If you are connecting several LED's in parallel included a resistor to each lead. For series connection add up LED's drop voltage and calculate the value of resistance required. This is one of many web sites that calculate the resistance required. http://ledcalc.com/
Hope this helps

3. ### TBennettcc

292
2
Dec 4, 2010

443
3
Jun 10, 2011
The easiest way is to hook the thing up to a lab-type constant voltage/constant current power supply and find out what voltage it takes to run the LED at its rated current. Of course, that's salting the bird's tail, as you need to know the rated current. If you don't have a datasheet, then you either use your engineering judgment or post a picture of the device and hope someone else knows what it is.

5. ### cindygaoled

5
0
Jul 29, 2011
1W LED 350mA 3.4V

292
2
Dec 4, 2010