Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Will a 9 volt battery last longer on say a 330 ohm resister than a 150 ohm resister? I'm running two blue leds with the resister in series. I understand that a higher value resister will dim the leds slightly but was wondering if it also lengthens battery life.
The lower value resistor doubles the current so the life of the battery will be half.
A little 9V battery doesn't have much capacity for lighting LEDs continuously. You would almost see the LEDs dimming as the battery voltage runs down.
Have you ever seen the six tiny, skinny, expensive AAAA cells inside a little 9V battery? Four AA cells are cheaper and will last a lot longer.
You must keep the blue LEDs separate (not in series), each one with its own current-limiting resistor. Since 4 AA cells have a much greater capacity then the LED current can be increased to be brighter. A 100 ohm current-limiting resistor will supply each LED about 27mA when the four AA battery cells are new and they will last a lot longer than an expensive little 9V battery. :lol:
So in other words, wire the leds in parrallel. Give each led its own resister. Thats different than the info I have been getting off of the halloween sites. (The blue leds are being used as ghosts eyes for a halloween effect.) In all cases whenever I read instructions for hooking up two leds its always wired this way: pos side of battery to anode of 1st led. Negative side of battery to cathode of 2nd led with a resister wired in series between the two. And all this time I thought I was right.
You wire the LEDs in series when you have enough battery voltage for them. A blue LED has a voltage drop of about 3.3V, so a 6V battery made of four AA cells wouldn't be able to power two in series. If you had a 12V battery you could wire 3 blue LEDs in series.
If you used two 3.3V blue LEDs in series and a 330 ohm current-limiting resistor in series with a brand new 9V alkaline battery as shown, the LED current would be only 7.3mA and the LEDs wouldn't be very bright.
After about 5 to 10 hours of dimming, the battery voltage will be 8V and the LEDs' current= 4.2mA and be dim. At 8V the battery is nearly like new!
If you used two sets of a 3.3V blue LED with its own 100 ohm current limiting resistor and four alkaline AA cells, at the beginning their current would be 27mA and they would be very bright and after 10 hours they would have 22mA and still bright. After operating continuously for about 82 hours they would be as bright (dim?) as they started with a little 9V battery.
Your tricks and treats won't last long. Use your wimpy little 9V alkaline battery and two 3.3V LEDs in series and in series with a 100 ohm resistor. In the beginning their current wil be 27mA and they will be very bright and after 2 hours they would have 22mA and still be bright. After operating continuously for about 16 hours they will dim to zero.
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
