12V Long Life LED ???

OK here is the scenario ... a remote wilderness cabin with 12volt electrical system consisting of your basic deep cycle auto battery needs some LED illumination. Months pass (often in cold temps)between maintanence other than a small solar panel that sees limited daylight. A small (1-3 LED) porch light is required that must be extremely efficient because it will be left on continuously. Long life and efficiency are definite sacrifices to brightness in this situation. An added bonus feature would be a convenient switch to go from an extremelly dim always on to a usable brightness for time when the cabin is occupied.

Any brilliant suggestions on any combinations of LED's and resistors etc... that would yield this type of light would be much appreciated.

Without thinking about it that much,
i would first say:

1. Get the biggest darn solar panel you can
possibly afford.
2. Get the most efficient batteries you can find.

Also, you might want to keep in mind the
study on the "half life" of white LED's
that was posted in this forum not too long
ago.

Summarizing that study and listed
in order of current followed by
1/2 brightness life:

50ma, 2100 hours (3 months)
20ma, 6500 hours (9 months)
10ma, 9500 hours (13 months)
5ma, 11500 hours (16 months)

This represents the life of the white LED
at the time it reaches a light output of
50% of its initial value (half as bright
as it was when it was new).
From that table you can see the harder the
LED is driven the lower its life. This is
for the white LED's only.

--Al

Hmm....i have been told that red is the most efficient color in ledlights. A good idea is to get a multifunction led-light. When you're away, set the light in flashing mode to preserve battery and when you need more light, switch to constant beam. I know a bicycle light that lasts at least 800-1000 hours on flashing mode and 300 hours on constant beam. It's run by 6(!) AA batteries. You can also get this light as a small lantern (even though it's too dim to be a true lantern). It's run by 6 C batteries! and has 2 modes like the bicycle light. Imagine the burntime on this lantern! 2 leds run by 6 C!
A friend of mine had this light, so i will ask him for the name and where to get it, if you're interested.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:

Also, you might want to keep in mind the
study on the "half life" of white LED's
that was posted in this forum not too long
ago.
<HR></BLOCKQUOTE>

If the ambient temperture is cold enough, then the life of the LED is greatly prolonged.

Assuming that you have a clear view of the sky, what you want should be easily possible. This is assuming that a lead-acid battery will function at cold temperatures.

For best efficiency, you should use a switching power supply. However, these regulators are TERRIBLE for use by a beginner. They are difficult to get right. Therefore, I would recommend a linear regulator. Using 12V, you should be able to run 3 or 4 LEDs in series, which would minimize the voltage drop across the regulator. You would sacrifice a little efficiency, but the simplicity would be worth it.

If you have more money to drop, visit www.techass.com. The VersaLux module is wonderful, but expensive. It could provide some great interior light. Just wire directly to 12V. If you even wanted the simplest solution, use a VersaLight for your exterior light, and crank the light output to its minimum.

However, these things are expensive. They are not too bright if they are gone when you get back.


If you want to use a linear regulator, e-mail me at [email protected], and I can feed you the part numbers and math.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by akwormy:
... a remote wilderness cabin with 12volt electrical system consisting of your basic deep cycle auto battery needs some LED illumination.
<HR></BLOCKQUOTE>

Either you have an auto or a deep cycle battery. For your application, a deep cycle battery is good.
Also think about wind generators.
Or, as mentioned above, try to get as much solar panel area as you can afford.

But even a few mW of LED light is enough for simple tasks. Or learn to live in darkness, but this is apparently the wrong answer in a flashaholics forum .-)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
2. Get the most efficient batteries you can find.
<HR></BLOCKQUOTE>
Al, can you tell us what the most efficent battery is?

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by recercare:
Hmm....i have been told that red is the most efficient color in ledlights
<HR></BLOCKQUOTE>

The most effective LED (prototype) is an orange one with slightly above 100 lm/W.
Commercially available are amber or orange ones for the Lumileds and green/turquoise for Nichia LEDs.
With new developments this data may change.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR> Originally posted by PeLu:
Originally posted by MrAl:
2. Get the most efficient batteries you can find.
--------------------------------------------
Al, can you tell us what the most efficent battery is? <HR></BLOCKQUOTE>

--------------------------------------------
How much do you want to spend? Need ISO 9001?
Under $100, Under $300, or several thousand...assuming 12 volt system..??
Here are a few modest priced ones..

Try this first... http://www.hawker.invensys.com/pdf/dco705g0300.pdf
---------------------------------------------------------------------------------------

Hawker Energy
Phone. 800-964-2387, 660-429-6437 http://www.hepi.com

Wow, great info guys I will pass all the suggestions right along. I knew I would get some good ideas from everyone here.

Thanks

Maybe think about the outdoor solar charged 'path lights' you can get at hardware stores.
Advantages: self charging, turn themselves off during the day, no need to run wires to them and possibly discharge your main battery, fairly low cost.

Coherence makes a good point. If that is the only thing you want the system for a solar lawn light would be the way to go. That would be far cheaper. I also remember seeing a 12v halogen motion sensing outdoor light with its own solar panel and battery. It was about $100, but would be much brighter. I can't remember where I saw it, maybe jademountain.com ?

I would suggest 2 Trojan T105's and at least a 55w panel or larger with a charge controller. But if you already are set on that part of the system I would suggest a 3 LED light to get it in a standard medium base housing like one from http://theledlight.com/120-VAC-LEDbulbs.html
I have the AC3 one it is about as bright as a 10w incandescent lamp.

I would strongly suggest an Intermatic timer switch. It runs on a single AA battery with a LCD clock and 6 on/off times. That way you can just run the LED at night, you wouldn't see it in the day anyway. It switches a latching relay so it takes no external power and can switch any load on/off up to 15 amps I believe. It also fits in a regular single gang box, but does stick out just a bit. http://www.intermatic.com/consumer/ss7c.htm

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by PeLu:

Al, can you tell us what the most efficent battery is?

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<HR></BLOCKQUOTE>

PeLu, please let me politely yodel that there is only one *Al*.

The gentleman you are referring to is *MrAl*, (a darn knowledgeable chap of many good qualities I'm sure, but still) not the *Alastair Windler* who signs off as *Al*

Don't nobody confuse my CPF name neither, for I am *something ridiculous

lightlover

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<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Al, can you tell us what the most efficient battery is?<HR></BLOCKQUOTE>

Basically the thicker the plates are in a battery the more efficient it will be and the longer it will last. Most Marine or automotive batteries have very thin plates, which makes them much cheaper to manufacture. A Trojan T105 has plates about 4 times thicker then a standard automotive battery. Some of the more expensive batteries like Surette have plates about 12 times thicker. Also most true deep cycle batteries have deeper cells so if the acid levels drops the plates aren't exposed as soon, which is VERY bad for a battery. I could go on for hours about this, but those are the basics.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Brock:
I would strongly suggest an Intermatic timer switch. It runs on a single AA battery with a LCD clock and 6 on/off times. That way you can just run the LED at night, you wouldn't see it in the day anyway. It switches a latching relay so it takes no external power and can switch any load on/off up to 15 amps I believe. It also fits in a regular single gang box, but does stick out just a bit. http://www.intermatic.com/consumer/ss7c.htm<HR></BLOCKQUOTE>

Brock, I'm just curious to see if you verified that this timer doesn't use any AC power to run the timer circuitry. The web site says it has a battery "backup" which implies that it is normally powered by the AC lines. I have a Radio Shack digital timer and it takes a couple watts to run the timer. I've always thought that was a waste of electricity.

Thanks, Mike.

I am sure it doesn't use any AC since I have one set up on a 12vdc LED light. I also have one switching a outside speaker on and off, just broke the line. It is just a switch on the wires. I like it because you can just push the front to turn it on/off and then it will shut itself off later if I don't remember to turn it off.

Brock

Thanks Brock! That sounds ideal. I'll see if I can find them locally for a decent price. The cheapest price I found on a web search was $26 + shipping.

Oh, I should mention I got mine at Home Depot on sale for $21.95 each on sale. I have also seen them at Menards, another local home store.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Brock:
Basically the thicker the plates are in a battery the more <HR></BLOCKQUOTE>

You assume a lead acid battery. But waht I was pointing at is that also the recharge scheme has a big influence on battery efficiency (defining efficiency as the power out/power in ratio). NiXX have around 70% , lead acid ~80% current efficiency. But there are charging methods which bring NiCd up to almost 90%. So there is just no 'most efficent battery' withoout the proper charger. Capacitors will outperform all of them.
Anyway, I don't think this is really an issue for this application. You may add another solar panel for much less money than caring about battery efficiency.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by KenBar:

PeLu:
Anyway, I don't think this is really an issue for this application. You may add another solar panel for much less money than caring about battery efficiency.<HR></BLOCKQUOTE>
=======================================
I agree.
I use a UNISOLAR Solar Electric Modulel US-64
It performs well on a snowy overcast day...
It is a 64 watt 16.5 volt 3.88 amp
I get 1.5 amp on these types of days.
My Siemens barely gets .1 amp in same situation. The trick is the tri mode operation. It is a continuous film and impervious to hail, partial shade etc.

I also use a Trace C12 Charge/Load/Lighting Controller. It turns on and off automatically at dusk and controls charging current etc...HVD,HVR,LVR,LVD,NightLight, easily adjustable with digital multimeter.
It treats batteries gently. I have been using the same battery 2 years now and it performs like new.

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