LED power

Discussion in 'The Projects Forum' started by blueram, Aug 19, 2007.

  1. blueram

    Thread Starter New Member

    Aug 19, 2007
    Hello all
    I am hoping to find sombody with a little more knowledge than I have, most of my experience was with video games, pinball machines and other coin machine devices going back too the pre solid state days, I am working on a project to which I would like to add 8 Leds that can be mounted indivually to illuminate an area of about 5 inches at a distance of about 8 inches away, they also need to be waterproof and powered by a 9volt battery. I have searched the internet and ebay etc etc and am now wondering if there is such a thing as a waterproof LED and a waterproof or water resistant 9Volt battery case. I also know I will need to have resisters in between the LEDs but don't know the values required. If anybody would know where to find such items or be able to help with the name of a supplier it would be greatly appreciated thanks alot if anyone can help.

    Thanks All
  2. nanovate

    Distinguished Member

    May 7, 2007
    How waterproof do you need it? Look at NEMA 4 and NEMA 6 rated enclosures and waterproof connectors. There are plastic cases that are clear also that are NEMA rated.

    With knowing what LEDs you are using I can give the following example:
    The forward voltage of LEDs is included in their specific datasheet. It can be from ~1V to over 2V depending on the color, type etc. The simplest way might be to hook up three sets of 3 LEDs each set in series but the sets are in parallel with each other. So 9V is across the three LEDs and the resistor sized to give about 25mA using R=(9V - 3*(Vf_LED))/25mA. The problem with this solution is that it will be dimmer as the battery drains but it is simple. A better solution is to use a constant current source or LED driver chip.