Alright everyone, I am looking for help trying to figure something out. I have looked multiple places online, but there is always so much terminology used that it confuses me.
I am looking to do multiple LED's in a few kits that I am working on. I need them to be very efficient to the point to hope to run multiple LED from a common power source like a couple AA or something of that sort, for a long period of time. I would like them to last for the matter of 36 hours or so. (My main use of them will be to have them on during model shows.)

The LED's are small chip LED, which I believe to be 3v each with a 20maH each. If I want to run 12 LED, will I need a power source of at least 36v? or does the power source just need to equal the voltage requirement for an individual LED (3v) regardless of how many there are?

I believe the calculation for a SINGLE LED would be to find out the battery capacity, which for an AA is about 2400maH and divide that by the draw of the battery (20ma)?

so, if I run 10 LED for a total of 200ma being drawn, would the calculation be correct for 2 AA batteries to run 10 LED (3v) for about 24 hours total?

From my magre electric knowledge -and faded with time, if you need 3v for each led you must connect them in parallel. That is, all positives directly to the positive and all negatives to the negative (opposed to a serial connection, in which you have a "chain").

As for how long it will last, I have no idea. But I would look for a way to allow easy replacement of batteries...

ah yes, I forgot about the series and parallel thing.

That answers the voltage part. however, what i really need to know is the length of time now.

Head over to http://www.modeltrainsoftware.com Theyre great for helping figure out what you want to do, and have some tiny LEDs and multiple power source options to boot,

Ive already been there but it since they dont tell u how long the lights will stay lit. They can tell you how many lights you can connect to one source, but thats all

This is not a direct answer but may help
https://learn.adafruit.com/battery-power-for-led-pixels-and-strips/estimating-running-time

Paul

Hi Jesse,
"Electronics engineer to the rescue"...
Your capacity calculation is correct, for a set-up of batteries connected in parallel.
You don´t want to install batteries inside a model, I suppose.
Regards
Nacho

Hi Jesse,

Your calculations are correct. Theoretically, with two batteries each with a capacity of 2400 mAh, your 10 LEDs should be lit for 24 hours. Practically, this time would slightly vary as your batteries might not be factory new (stored in shop for how long?) and there is also some variance in the production. Still, a minimum of 20 hours should be achievable with batteries fresh from the packaging.

Although, the LEDs are labeled to be 3V@20mA there is a variance here as well so you'll also need a series resistor of a few Ohm (50-100 Ohm) connected in series to each LED then have these groups connected in parallel to each other.

Hope this helps! Let us know how your project turns out!