Battery Life with 1 LED

[oldmil]

Can anyone tell me how long a 9v battery will power a single white 5mm led (3.4v 20 mA)with ~330 ohm resistor?  I am making a nightlite and before I go any further I figure I better find out if it will last more than one night.

Thanks for your help

Oldmil

[ghurd]

About 45 hours with a quality alkaline battery.

A lot longer if you don't mind it being dim.

It would be worth it to increase the resistor to 475 ohms.

Not quite as bright in the beginning, but last a lot longer.

G-

[ghurd]

I should add a 9V isn't the best choice for battery life or cost per hour.

I made a pretty nice, small, portable, nightlight with 3 AAs in a 4 cell holder with a switch.

Rearranging the battery contacts for 3 cells is easy. The LED and 220 resistor are in the empty battery area.

Uses about 8ma. Not as bright as 20ma, but not as dim as it sounds.  Lasts a few hundred hours.

A good bright LED is the most importand part for long battery life.  Crappy LEDs make very little light.  Good LEDs make a lot more light with a lot less power.

G-

[Norm]

 I think Ghurd still sells his 2 cell flashlight

LEDs that I have used with regular cheap 'D' size

 batteries...used to use them about 6 hrs. a night

....a single set of batteries lasted for weeks..

Yes...Weeks!

 I also use at present LED lamps that he sells

that I use 4 AA rechargable in each of that I

recharge every few days with a small VW panel.

 A small 3 AAA battery powered tap 3LED light

from DollarTree for a buck will last for at

least one night I think they use about 20 Ma.

[mikeyduk]

Came across this :

http://stinet.dtic.mil/cgi-bin/GetTRDoc?AD=ADA469794&Location=U2&doc=GetTRDoc.pdf

courtesy of the military.

Mike

[ghurd]

The circuit is not very suited to white LEDs.

Good for red, maybe yellow.

A red nightlight isn't so great.

G-

[vtpeaknik]

For some "night light" purposes a motion-activated light may be suitable, and that may make the batteries last far longer.  I got a 1-LED motion-activated lamp from Harbor Freight for about $5.  It uses 4 AA batteries, rechargable ones work OK.  I got it with the intention of using it as a deer repellent device in the garden (perhaps with a small sound-making device (radio?) wired into the motion-activated circuit?) but currently use it as an as-needed light inside a deep dark kitchen cabinet.

[Madscientist267]

Hey I've been looking for something like that, but figured that the sense circuitry would use more than just burning the LED. Got some details on the guts and what kind of standby it uses?

Steve

[GlutealCleft]

Hopefully this will help a little bit.  My son wanted a nightlight, so I took a light from Ikea called Skina, Skiina, or something like that, which they don't seem to have any more.  They cost $4 each, if I recall, use 3 AAA batteries, and have a pleasant yellow-white light.

They're supposed to give 40 hours from a set of batteries, and my experience seemed about right.  But they were too bright for a nightlight.  I opened one up, and found three LEDs in parallel, and a 33-ohm resistor for current limiting.  I pulled the 33-ohm resistor out, and plopped in a 370.  Perfectly sufficient light, and in a couple of months, I've only changed the batteries twice - despite it getting left on all day and night fairly often.

Here we go.  The lamps were "Skina" lamps.  Ikea has no mention of them, but they look like this.  I used the white-colored lamp.  I have about five of them around the house, they're very useful.  If they carry them again in the summer, I'll probably buy ten of them.

[ghurd]

Amertac makes a nice (non-LED) unit, with a light sensor on top.

The sensor mostly disconnects the batteries from the circuit for day time.  Makes the batteries last a lot longer.

I put LED bulbs in them.

G-

[Madscientist267]

I was thinking more along the lines of motion sensing - CdS is easy enough to implement, but isn't useful for detecting motion at night. The idea here being that the light isn't on until it senses something move nearby, then turns on for a few minutes, and back off after no motion is detected for a while... PIR comes to mind, but all the circuits I know use 15 or 20 mA, which defeats the whole purpose; might as well just run the LED.

Steve

[ghurd]

The Amertac is a motion sensing light.  The 'sensing' part just uses a couple ma.

With a 3 LED bulb, 4 AAs last maybe 4 to 6 months.  

The CDS cell on top really helps.  It wouldn't help in a closet, but in an area that gets daylight it does.

Lowe's had them for about $14 with incandescent bulb. Square corners.

The rounded corner version they had for a short time was not as impressive.

They have them with LEDs now, but I don't know how good they are.

Only one I can find with square corners is from a place fitting a 1W LED in it.

http://www.theledlight.com/security.html

It isn't worth $60!

G-

[vtpeaknik]

OK, y'all convinced me to bother and measure the standby current of the Harbor Freight motion-sensing light I mentioned above.  If I did it right, and if my olde analog multimeter is right, the standby current is only about 1/4 of one mA.  With the LED on it's about 20 mA.  BTW this model also has a daylight sensor so it does not light up in the daytime even when motion is detected.

[Madscientist267]

I think I'm gonna have to jump on that.

.25 mA? Thats doable in almost any circumstance.

[vtpeaknik]

The also have a 6-LED model if you need brighter light.