0

Newbie: LED/Battery help
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

Newbie: LED/Battery help

by carolyn_ on Fri Sep 24, 2021 5:10 am

Hello!

I'm a graphic design major currently working on my thesis on psychedelic mushrooms. I plan to craft some mushrooms that light up, so I ordered the Diffused 5mm Slow Fade Flashing RGB LEDs from AdaFruit (https://www.adafruit.com/product/679#technical-details) and the rest of the needed supplies from other places to make this happen. I really need to buy the batteries required for this but I seem stuck on which voltage amount to buy. If I were to wire up about 15 of these lights (disguised as mushrooms) across a driftwood plank, what voltage battery pack would I need to buy? and what type of resistors? any help? I need an answer as soon as possible so the time taken to answer would greatly be appreciated and I'll be super grateful!

Here are links to some references of the disguised mushrooms I've mentioned:
https://www.instagram.com/p/CN8Ie9Xs2fu ... _copy_link
https://www.idlights.com/wp-content/upl ... m-Lamp.jpg

carolyn_
 
Posts: 2
Joined: Mon Sep 20, 2021 2:19 am

Re: Newbie: LED/Battery help

by dastels on Fri Sep 24, 2021 9:36 am

15 LEDs. The should be wired in parallel for best results (with a resistor for each LED). So with each requiring up to 20mA will require 300mA. You could use a LiPo battery that would give you between 3.7v and 4.2v depending on its charge level.

4.2v - 3.4v (for the LED) leaves 0.8v for the resistor to account for. Ohm's Law tells us the R = V/i (resistance = voltage divided by current) R = 0.8/0.020 = 40 ohms. When the battery voltage drops to 3.7v the voltage for the LED (if it continues to consume 20mA) will be 2.9v which will probably still light them up, albeit dimmer.

What size battery? The biggest that will fit is generally my approach. The bigger the battery, the longer it will last. It sounds like you'll have room so a 6600mAh battery https://www.adafruit.com/product/353 will get last a dozen or more hours (educated guess) while a 2500mAh https://www.adafruit.com/product/328 is probably good for 5 or 6. It depends on how long you need it to last on a charge. See https://learn.adafruit.com/adafruit-microlipo-and-minilipo-battery-chargers for information on chargers.

Dave

dastels
 
Posts: 7543
Joined: Tue Oct 20, 2015 3:22 pm

Re: Newbie: LED/Battery help

by carolyn_ on Sat Sep 25, 2021 4:42 am

Thank you for your reply! I do understand it a bit better.
I do want to find a battery pack with a switch. Would something like this work? https://www.adafruit.com/product/727
When using alkalines, the output will range from 4.6V to 3.3V.
So would that mean 4.6V - 3.4V = 1.2v; ergo = 60 ohms for the resistors.
I'm still confused about figuring out how much it will last depending on the battery pack. How much would it last for the product above? And how many LEDs can I put on each pack ?

carolyn_
 
Posts: 2
Joined: Mon Sep 20, 2021 2:19 am

Please be positive and constructive with your questions and comments.