Newbie... 4,000 hours battery for LED?

Ok maybe this is a really ridiculous question...

but I am very new to LED's and battery life.



I was wondering if there is any kinda battery that would allow me

to get at least 4,000+ hours of run time on a white LED that would be

used with a photosensor?



Is this any where near possible???



just a newbie,

-chelsea

There is a little light available (Pal Light) that uses a standard 9 volt battery and is able to keep it's LED glowing for over one year. But, this is very dim and not useful except for locating the light or extreme close-up work. In order to power a white LED with the electronics to produce a reasonable, but still quite dim, level for 4,000 hrs I would think at least a 6 volt lantern battery would be necessary. To power a light good enough to see the immediate surroundings well or light up an entrance seems like you might need a car battery. Please wait for the experts to chime in.

Geoff

You have to give people more information. What kind of LED and what size constraints?

10 feet by 10 feet of nicads will definitely work. Or a stack of http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=2754 .

Assuming you want to run it at a mid-range current of 20mA:
20mA = 0.02 A
0.02 A * 4000 h = 80 Ah

a normal to large size car battery has this capacity (such as this one: http://www.planetbattery.com/details.asp?id=905 ). of course it will be necessary to use a converter or simply a current limiting resistor to give the LED the voltage it wants. then you need to worry about efficiency losses in the converter, but it may balance out because the battery will perform better than expected at such a low discharge rate.

I think Saft makes a 3.0V lithium D cell with a 21,000mAH capacity (I think)

Get a Luxeon and drive it at say 20mA at 2.8V (UWAJ?) and that would be 0.056 watt hours with the battery being 63 watt hours (3V x 21AH) it would give 1,125 hours of light. Figure converter losses in and 1,000 hours can be had. Take four of those batteries and you would have 4,000 hours of light.

The problem with car batteries is self-discharge. Thundersky makes a LiFePO4 lithium-ion with a rating over 100AH on a single 3.2V cell. The cells are basically $2 per amp hour so make sure you are dedicated to what you want. Any idea if a solar cell could assist the battery charge?

Re: Newbie... 4,000 hours battery for LED? You guys are great!

Hey you guys are GREAT! Just GREAT I tell you.

Thank you so much for your feedback. It's so great
there are people out there like you that help us confused
ones.

I don't need a strong light....only shine about 5-8 feet.
It doesn't have to be very strong light.
the "Pal Light" is kinda what I am looking for and a 9volt or even 2 9 volt batteries would work perfect.

If i had two 9 volt batteries...would it shine for 2 years?

How do I figure out how long a light will work for with what type of battery?
Do I measure the amps?

You guys are great. All your advice is so appreciated!!!

Thanks for helping this silly girl out!

-cheers to all! :twothumbs
-chelsea

I'm afraid the Pal Light in its "stand-by" mode is not as bright as you want. It really is not strong enough to lightup stuff 5-8 feet away. You would be able to see it shining at that distance, but that's why it has this mode, for finding the light. It also would not be possible, without doing some electronic work, to make it function using two 9 volt batteries.

Welcome to CPF, by the way.

Geoff

Re: Newbie... 4,000 hours battery for LED? You guys are great!

Chelsea378 said:

How do I figure out how long a light will work for with what type of battery?
Do I measure the amps?

Click to expand...

That's a good first step, but you have to consider the current draw of your whole setup, not just the LED itself. For instance, if you have an LED with a resistor to limit the current through the LED - that resistor will be converting some of the electricity to heat, and that energy loss needs to be taken into account as well as what the LED itself uses.

These things can really surprise you, one way or the other. As someone has already mentioned in passing - the more slowly you drain a battery, the more energy you actually get out of it - and that can change your runtime calculations. For instance, a CR2032 coin cell is rated at about 200 milliAmp-hours; theoretically, that would run an LED at 20mA for 10 hours, or at 5mA for 40 hours - but I've had an LED running with useful brightness off of one of those cells for over 100 hours!

I don't know how efficient the circuitry in the PAL light is, but the closer your battery voltage is to what the LED requires (most white LEDs will light up at something under 3v, though most are rated to have a "forward voltage" of about 3.2-3.6) the less energy you have to waste with a simple resistor in order to properly drive the LED.

For example - to run an LED with a Vf of 3.2 volts at 20mA from a 4.5v source (say, 3 AA cells), you'd need a 68 ohm resistor. In this case, according to the calculator over at LuxeonStar.com, the LED would dissipate 61 milliwatts of power, the resistor 25mw.

To use a 9v source, you'd need a 300 ohm resistor - and the LED would put out 62 milliwatts - but the resistor would burn up 112mw - nearly twice as much as the LED itself!

Given your stated wish to have an LED run for 4000+ hours, you'd need to minimize energy waste, and avoid batteries that tend to self-discharge - unless there's some way to incorporate a solar panel or some such to recharge the cells.

Is there a particular reason you need a setup to run that long (nearly 6 months) unattended? If you could explain the purpose a bit more, people might be able to make more directly useful suggestions.

Boy oh boy do you guys know your stuff!!!
Thanks again for helping me and walking me though the basics, as it's a little overwhelming.

wow, I had no idea that the resistors can burn up so much energy!
I'm defintaly learning alot today.

I was thinking the bigger the battery the better...more energy. Geeze it would take alot of AAcells to achieve what I want to do huh!

Even if I could make it run for just 2,000 hours.... I like the idea of the "always on" that Pal Light makes. But I want it a little brighter.

I did not think of solar panels... i will look into that some too.

I will try and figure out how many mA my LED light uses.

I know that Lithium batteries are better than alkaline batteries...but not powerful enough for what I need huh?









e2® Lithium batteries

I've been thinking about this. It's a fun problem!

According to Energizer's datasheets, D alks have around 20Ah. At 25mA, they'd be able to make use of most of that capacity, and would run for about a month. If you found an emitter with a low Vf, you might be able to run it on 2 D cells in series, but you'd probably need 3 D cells in series with the appropriate (68Ohm, apparently) resistor. If you put a group of D cells in a series-parallel configuration, it might last for a few months.

TigerhawkT3 said:

I've been thinking about this. It's a fun problem!

According to Energizer's datasheets, D alks have around 20Ah. At 25mA, they'd be able to make use of most of that capacity, and would run for about a month. If you found an emitter with a low Vf, you might be able to run it on 2 D cells in series, but you'd probably need 3 D cells in series with the appropriate (68Ohm, apparently) resistor. If you put a group of D cells in a series-parallel configuration, it might last for a few months.

Click to expand...

I've had a single 5mm LED run for weeks on a CR123A! Not at maximum brightness, of course - but that doesn't sound like the goal here. I have some LEDs that technically have a Vf of about 3.4 volts - but they still light up from a lithium cell putting out less than that, down to about 2.8v. I really should check the current levels - but I wouldn't be surprised if it's 5mA or less, and yet they're still putting out a useful amount of light. At that level of drain, any decent battery will be an "overachiever" in terms of run time.

The real issue here is determining what level of light Chelsea378 needs, and then figuring out the most efficient way to provide it.

a nichia CS led running direct drive from a CR123 is fairly bright. it takes a bit less than 20ma, and I guess CR123's are around 1500mah. I guess each cr123 could run the led for around 15 hours. If you got around 300 CR123's and wired them in parallel, this would work... I'm not sure how safe this would be tho.

I don't think that this is what CR123As are "for" - it seems a perfect fit for alks. Using 300 CR123As would be around $300, too.

I've done a lot of experimenting with PWMing LEDs. Using cheap Nichia white 5mm LEDs, there's very little visible difference between 30mA at 10% duty cycle and 20mA solid on.

Basically PWM means you're stobing the LED on and off much faster than the human eye can see. It looks like it's on solidly. If you measure the total light output it will be much lower, but to use it for illumination, the eye doesn't see the difference.

If you take that 3V 21aH battery lithium D-cell that BentHeadTX was talking about, you can PWM the LED at a 15% on-time and get over 4000 hours even allowing overhead for your controller.

In the kids room I have 4 D cells connected to a PAL head set to it's "LOW" setting. I am using 4 9000 mA NiMH D cells and I charge them once a month. I bet this setup would run at least 4 months on 4 D alkaline cells. As Biker said the light would just slowly loose intensity over time. I am sure it would still be making light after a year, but probably not much over the "forever on" level.

I did have another kids toy that had a blue LED in it and ran on three AA cells. I added a 3 D cell pack to that as well that lasted a LONG time, but I didn't like the blue color so I went to the PAL.

MikeHunt79 said:

a nichia CS led running direct drive from a CR123 is fairly bright. it takes a bit less than 20ma, and I guess CR123's are around 1500mah. I guess each cr123 could run the led for around 15 hours. If you got around 300 CR123's and wired them in parallel, this would work... I'm not sure how safe this would be tho.

Click to expand...

Keep in mind that the cell's internal resistance and such matters. A white LED I had on hand powered by a CR2032 (2.98v) was pulling about 1.5mA; connected to a CR123A (3.12v), it pulled about 9.5mA and was significantly brighter (duh! . Still, even at 1.5mA - it put out a decent amount of light, especially considering how little current that is. [This kinda helps explain why I've been getting such long runtimes off of some white LEDs driven directly by 3v lithium batteries....]

At the moment, CR2032 coin cells (25 cents each) and CR123A's (a "mismatch" lot from Battery station - 60 cents each) are a lot cheaper to "play" with than lithium AA's - even CheapBatteries.com's house brand are $1.25/ea. Still, maybe I should burn $2.50 to find out how long two of those will run a single white LED.

Chelsea378 said:

I will try and figure out how many mA my LED light uses.

I know that Lithium batteries are better than alkaline batteries...but not powerful enough for what I need huh?









e2® Lithium batteries

Click to expand...

The e2 lithium offers almost no advantage over alkalines at a current draw this small

Buy one of these
http://www.dorcy.com/products.aspx?p=412498
take the bulb out and put it in one of these
http://www.dorcy.com/products.aspx?p=411015
you would get a minimum of 700 hours on fresh alkalines.
If you include moon mode you might get up to double that.

Oh my Gosh, I can't believe all the posts you have all made to help me out!
I'll have to send you all something for helping me out.

I think I'm learning by leaps and bounds...I've tried to look up the things you are
talking about. I will have to send you guys something for helping this girl out.
I will try and play with some LED lights this weekend so I can maybe give you more information and maybe that would help you help me more....sorry, I'm just learning all this stuff and thanks for your patience.

I did find Oracle's comments on the PWMing LED's... would that work? If the human eye wouldn't notice it flickering...that would be cool...but how many 3V 21aH battery lithium D-cells would that take????

I had no idea this would be this difficult...there is defintaly alot to know. I sure do appreciate your comments and suggetions!!!!

-christy!!!!!