Powering my LED's

davehal9000 · Post by **davehal9000** » Fri May 28, 2010 12:07 pm

I've got like eight 5mm LED's i need to power in a model. I was told I can use a 9v battery but I'm reading the LED's won't last long. What battery combination would be best? Or should I go to hard power instead of batteries?

USS Atlantis · Post by **USS Atlantis** » Fri May 28, 2010 12:29 pm

Personally, I'd for a wall-wart (wall mounted, plug in transformer)

Second best - Batteries other than 9v

If the 8 LED's each draw 20ma (standard draw for most LEDs) then the power reserve/lifespan of batteries are as follows (assuming standard alkalines)

9v - 500ma - 3.1 hours
AAA - 1000ma - 6.25 hours
AA - 2000ma - 12.5 hours
C - 6000ma - 37.5 hours
D - 12000ma - 75 hours

Note that as you go up in size, the reserve power increases dramatically

Realize that you'll need multiple batteries to run LEDs - LED voltages run 1.8v (Reds) to 3.5v (whites/blues) - so you'll have to have enough batteries in series to supply at LEAST the voltage needed - then resistors to drop the voltage from what the battery supplies to what the LED needs - overpowering LEDs leads to blow-outs - like blowing a standard lightbulb - no more light

tetsujin · Post by **tetsujin** » Fri May 28, 2010 12:56 pm

USS Atlantis wrote:Personally, I'd for a wall-wart (wall mounted, plug in transformer)

Second best - Batteries other than 9v

If the 8 LED's each draw 20ma (standard draw for most LEDs) then the power reserve/lifespan of batteries are as follows (assuming standard alkalines)

9v - 500ma - 3.1 hours
AAA - 1000ma - 6.25 hours
AA - 2000ma - 12.5 hours
C - 6000ma - 37.5 hours
D - 12000ma - 75 hours

This assumes all 8 LEDs are connected in parallel. (8 individual circuits, utilizing 3V @20mA and wasting the rest of the voltage at 20mA)

On a 9V source you could hook up two or even three LEDs in series. Each LED would still get 3V drop and 20mA current, but less power would be wasted in resistors. Using a 9V battery as source, LEDs hooked up in pairs with the extra 3V @ 20mA dropped by resistors, the draw from the battery would be cut in half - from 160mA down to 80mA, so you could get around 6 hours that way.

Matching the LEDs exactly to the battery voltage means you can safely omit the resistor altogether - if you have 3 LEDs that run at 3V, you can connect them to a 9V battery with no resistor and waste no power. So you could power 8 or 9 LEDs and only draw 60mA from the battery - and get about 8 hours life. But most LEDs aren't exactly 3.0V at their full brightness - if they were a little over, then you could cut your light output substantially, or if they were a little under, then they might burn out. So I usually like to use a resistor to match the LEDs better to their power source.

davehal9000 · Post by **davehal9000** » Fri May 28, 2010 1:02 pm

The LED's I'm using have built in resisters

USS Atlantis · Post by **USS Atlantis** » Fri May 28, 2010 1:08 pm

Then you'll want to set your power supply to the manufacturers recommended voltage

Too little power - loss of brightness
Too much power - blown LEDs

davehal9000 · Post by **davehal9000** » Fri May 28, 2010 1:15 pm

I have no idea who manufactured them

USS Atlantis · Post by **USS Atlantis** » Fri May 28, 2010 1:22 pm

Did they come with any kind of info card?

If not, then I'd suggest start with 1.5v to test them - color normally indicates voltage requirements

Red & Yellow - ~2v
All Others - ~3v

davehal9000 · Post by **davehal9000** » Fri May 28, 2010 1:29 pm

They came in ziploc bags. I've sent an e-mail out to the guy I got them from to see what he recommends