86Views8Replies

Author Options:

Basic LED art question re: batteries!! Answered

Uhh, hi everyone.

I have a super basic question, and I'm going to appeal for help because I'm running low on time for this project.

I have a signpost I want to light up with about 100 3volt LEDs. What kind of power source should I be looking at? Would 4 AA batteries suffice?

I've seen online calculators for determining resistors, but not for an ideal power source. Do I just wire up as many batteries as I want and get the proper resistors? I'd like this thing to light for at least eight hours on a full charge, so I can swap batteries daily.

Thank you in advance! I'm dumb!

Comments

The forums are retiring in 2021 and are now closed for new topics and comments.
0
rickharris
rickharris

7 years ago

Your LEDS will have a data sheet you need to look at the required voltage for the LEDs - it varies -

The maximum current they can dissipate. this allows you to work out how your going to connect them and what current limiting resistors your going to need.

There are a lot of variables here. Much depends on your exact application. For example from Amazon you can buy one of these
http://www.amazon.co.uk/OXLUX-Floodlight-SILVER--Replacement-Halogen/dp/B004AA6KQE/ref=sr_1_4?ie=UTF8&qid=1370550965&sr=8-4&keywords=LED+security+light

Although rated at 10 watts I have one above my garage and guess it is roughly  equivalent to 60 to 100 watts of illumination. Runs off mains electricity less problem.

If your bound to battery power how long do the lights need to be on for.

You can flash LEDs on and off so fast they appear to be on all the time to your eye BUt they are using less power because for some of the time they are actually functionally off.

At night even low level lighting is surprisingly bright and eye catching.

If your LED needs 2 volts to illuminate - draws 10 Ma then your going to runt it from dry cells or rechargeable  for a few hours,  From a car battery for several days,

0
caarntedd
caarntedd

Answer 7 years ago

+1. Old car batteries are easy to get (most peoole find them a pain to dispose of properly). A battery that wont start a car can still be used for LEDs and other projects. One old car battery to light up the LEDs while a second one sits on the charger.

0
luxstar
luxstar

Answer 7 years ago

Uses for dead car batteries:

https://www.instructables.com/id/Uses-For-Dead-Car-Batteries-And-Sealed-Lead-Acid-B/?ALLSTEPS

0
mpilchfamily
mpilchfamily

7 years ago

Play around with the calculators. Make note of the power draw. 4AA batteries won't last very long with 1A being drawn from them. The more power you can give the circuit the better off you'll be. If you can give it 8AA batteries for a total of 12V then the system will be much easier to manage. Also the more voltage you supply it the less current the circuit draws and the longer the batteries will last. Not to mention the more voltage you have the more LEDs can go in each series string and the fewer resistors you'll have to use. Thus lowering the cost of the project. Not that the resistors will set you back all that much.

0
bicycle_samurai
bicycle_samurai

Answer 7 years ago

Okay, higher voltage battery = good. Unfortunately it's going to have to be something I can recharge during the day, so I'm kinda boned with AAs or whatever. I think they have pretty massive AA packs at my supply store, but 36 rechargables is gonna be insanely expensive at retail prices. Wow. I'm boned either way. Ugh.

0
verence
verence

7 years ago

Look like spam, but I'm bored, so I'll bite...

Let's do some basic math:

100 LEDs (let's say 20mA each), 3V, depending on the LED that is not very bright.

100*3V*0.02A = 6 W

8 hours of operation: 6W * 8h = 48Wh

Checking Wikipedia for how much power is in an AA cell:
Let's say 2500mAh for NiMH and Alkaline  = 2.5Ah (at 1.5V)
That are 2.5Ah*1.5V = 3.75Wh

So, you would need 48Wh / 3.75Wh = 13 cells
If ... well IF you can get a _perfect_ buck/boost voltage regulator. Which you can't. So you may get 75% efficiency (and that's very positive thinking). You may need (a bit more realistically) about 13 / 75% = 18 cells.

If you really want to do it, go for a lead accumulator (e.g. car battery) and a efficient step down converter or wire the LEDs so that they can use the 14V directly.

0
bicycle_samurai
bicycle_samurai

Answer 7 years ago

I'm not spam, and thank you thank you!!!