LED Tape/Strip - Power from 1.5V AA

[Ste1070]

I have a small project where I would like to power 2 small say 6" strips of led tape (color not really relevant but possibly amber or red) but I need it to last as long as possible from a battery source. Was thinking AA's for ease of availability but am open to suggestions. Whilst more expensive, you can get CR123A style which are 3V of course but they may have a longer life with a lower draw?? Am open to suggestions. Where is best place to source tape from? Thanks

 

[Audioguru]

Most people who sell LED strips (Amazon, Home Depot and Walmart) know nothing about them so they list size and weight instead of voltage and current.

A red LED needs 1.8V to 2.2V plus some voltage across the current-limiting resistor. All LED strips already have current-limiting resistors so for each group 3 in series they operate from 9V, and 4 LEDs in series and with a resistor operate from 12V.
For 9V you need 6 AA alkaline cells in series and for 12V you need 8 AA cells. For 9V you need 3 CR123A batteries and for 12V you need 4 of them.
But the AA alkaline cells will power the LEDs for 1.7 times longer than the CR123A cells.

If you reduce the current then the batteries will last longer but the LEDs will be dimmer.

 

[Ste1070]

Would there be anything that could work on 3v (2x1.5aa's) to run a six inch led tape with say 3-4 LEDs on? Would circuitry to blink/flash be easy enough to incorporate?

 

[Audioguru]

Most LED strips work from 12V, not 3V. A single LED with a series current-limiting resistor will work poorly from 3V because it will get dimmer and dimmer as the battery runs down then the LED will stop lighting before the battery is dead.
An LED strip with 3 or 4 LEDs would have them in series and in series with a current-limiting resistor so they would be very dim when powered from 9V but would work well with 12V.

Many LED strips come with a controller that blinks/flashes/changes colors. I didn't notice if they are powered from mains AC or a battery, maybe both.

 

[kam1787]

Would there be anything that could work on 3v (2x1.5aa's) to run a six inch led tape with say 3-4 LEDs on? Would circuitry to blink/flash be easy enough to incorporate?

as said several times here, these strips/ropes/strings/etc are usually meant for use with 12V

you need a dc-to-dc [ie 3V to 12V] converter or similar. these are not very efficient, so battery drain is a concern

what is unknown is how much current is needed - typically 20mA per multiple of 3

there are multi-colored self flashing strips. as mentioned often controllers are an option

maybe if you mentioned the purpose, it would be more helpful

there are zillions of places to buy from - depends on your location / budget - google!

 

[Audioguru]

LED strips have A LOT of LEDs. I looked at one that has 36 LEDs per foot. A lot of LEDs use a lot of current.
They are probably in groups of 3 in series and with a series resistor so if each group uses 15mA then 36 of them in 12 groups use 180mA which is too high for battery operation because four expensive CR123A cells in series would last only 9 hours.
Each group might use 20mA then the battery will last only 4 hours.

 

[kam1787]

maybe if you mentioned the purpose, it would be more helpful

I think your stated objective is at odds with your actual goal and so is confusing the issue.

Forget the strips.

Do you really want to know how to make [2] groups of 3 LEDs [say Red] flash with a commercial or very simple circuit which is powered by the smallest batteries possible [2*AA is ok] yet for as long as possible?



Again, telling us the end purpose would let us help you better and faster. Trust me the NSA/CIA/KGB/Mi6/Mossad/ISIL/DGSE and corporate espionage types are not interested.

 

[Audioguru]

I have been repairing five of my solar garden lights getting them ready for Spring and Summer. They are cheap Chinese ones with transistors and LEDs rusting away because they have thin STEEL wires instead of normal thickness copper wires. The cheap Ni-Cad battery cells rusted away long ago and I have replaced them with Western made Ni-MH cells that come in a stainless steel case that does not corrode. I use CLR to clean the rust off the battery connector. The solar panels got sunburned (no kidding) so I polished them with VIM and gave them a couple of coats of water-based clear Varathane wood finish.

Most of the LEDs I salvaged from the garden lights are red-green-blue with an IC built inside that flashes the colors at different rates and with different sequences. One AA Ni-MH cell charges all day in the sun then powers a flashing LED all night long because the circuit steps up the 1.2V from the battery cell to 3.5V or more to operate the LED. Some people connected two LEDs in series and the voltage step up circuit goes that high.

I have seven LED chasers that I built 9 years ago. They flash all day and all night and are powered for months from 2 or 4 AA alkaline cells.

 

[Ste1070]

I think your stated objective is at odds with your actual goal and so is confusing the issue.

Forget the strips.

Do you really want to know how to make [2] groups of 3 LEDs [say Red] flash with a commercial or very simple circuit which is powered by the smallest batteries possible [2*AA is ok] yet for as long as possible?



Again, telling us the end purpose would let us help you better and faster. Trust me the NSA/CIA/KGB/Mi6/Mossad/ISIL/DGSE and corporate espionage types are not interested.

Hi, thanks for your help. It's for a warning indicator that I want to blink with say 3-4 LEDs. I want it to run from a battery source. Am just looking for thoughts and options really. I am more electrical than electronic so am just looking for inspiration. How could I make this run for max amount of time on a battery source that would be portable? Aa or similar? Thx

 

[Audioguru]

You might not see LEDs blinking a warning (?) in the daytime. For a daytime warning you need a bright light that uses a lot of current. A lot of current needs a pretty big battery. A warning light is useless if its battery is too small and becomes dead soon.

 

[kam1787]

There a number of dedicated ICs and modules for blinking/flashing LEDs. 'Google' will turn up dozens.

Anyone use LM3909 for multiple LEDs?

 

[Audioguru]

An LM3909 had an output current of 45mA but for a duration of only 6ms. A duration of less than 30ms looks dimmed so the LM3909 was good for only one LED.
Powered from a single 1.5V battery cell it flashed an LED that had a maximum forward voltage of 2.1V (only a red LED). A higher supply produced a higher output voltage to drive a blue, bright green or white LED.