# LED spotlight battery life?



## wandererrob (Aug 8, 2007)

Does anybody have a guess as to battery life?

9v battery, (2) 330ohm resistors in series tied to 5 LEDs in parallel.

So far they've got 30 hours on them. I have no idea how long they'll keep going. Honestly this is longer than I'd hoped for. Now I'm wondering how far ahead of Halloween I could put them out and just leave them on.

Thoughts?


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## heresjohnny (Feb 15, 2006)

I ran a 5 LED spot continously as a test one time, from what I remember is was still going at 24 hours but considerably dimmed at 36 hours.


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## dynoflyer (Oct 8, 2006)

I run lots of 5 and 6 LED spots and have started converting them from 9V batteries to run on wall warts because I got tired of having to go out every night to unplug the batteries. 

Save wall warts from old phones, answering machines, calculators, mp3 players, etc. Most put out 4.5V, 5V, 6V or 9V. I've hooked up to 4 9V LED spots to one 9V wall wart without any problems. 

I save a ton on batteries and use a timer to shut them off automatically so I can enjoy my Red Sox game in peace. Go Sox!


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## wandererrob (Aug 8, 2007)

dynoflyer said:


> I run lots of 5 and 6 LED spots and have started converting them from 9V batteries to run on wall warts because I got tired of having to go out every night to unplug the batteries.


The trouble for me is that my haunt is one night only and my setup makes hardwiring impractical anyway. Combine that with my one outside outlet being occupied already by my fogger and my shed setup... freestanding lights were somewhat of a necessity for me.

That being said, so far my 5-LED spots are out to 60 hours on one battery. I could set up my haunt tonight and with fresh batteries, it'd still be fully lit come Halloween night. I have no idea how much longer they'll go yet, but I'm still pushing them.


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## dynoflyer (Oct 8, 2006)

Last year I taped a 5mm Xtra Bright Green LED to a 3V 2032 medical battery and it ran continuously for 39 days ;-)

I'll put several of these into white helium filled balloons over the front yard this year. The next morning I'll take them apart and store the batteries for next year.


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## Zombie-F (Apr 12, 2004)

Really, the duration of battery life depends entirely on how much current your circuit is drawing. LEDs in parallel draw more current than in series. Why the parallel configuration? It would seem that with 5 LEDs, you could probably run them in series without any resistor, especially with a 9v battery.


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## heresjohnny (Feb 15, 2006)

Zombie-F said:


> Really, the duration of battery life depends entirely on how much current your circuit is drawing. LEDs in parallel draw more current than in series. Why the parallel configuration? It would seem that with 5 LEDs, you could probably run them in series without any resistor, especially with a 9v battery.


I'll take a shot at this, though I think others may be able to answer it better. For one thing, a 5 LED circuit with the calculator used in my how-to will typically provide a parallel circuit (3 branches) as the first choice. Second, (this is where I get myself into trouble :devil: ) my understanding is that LEDs have an operating range where they will draw a certain amount of current for a given forward voltage drop, so 5 LEDs will use the same amount of power when operating correctly, regardless of the circuit.

Now for Zombies point, you may be right, because resistors use a certain amount of power themselves (given off as heat), so using a series circuit would not use resistors, and therefore use less power. Hmm, I 'll have to check this out tonight on the calculator.

I guess I should update my how-to, after halloween of course


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## wandererrob (Aug 8, 2007)

Zombie-F said:


> Really, the duration of battery life depends entirely on how much current your circuit is drawing. LEDs in parallel draw more current than in series. Why the parallel configuration? It would seem that with 5 LEDs, you could probably run them in series without any resistor, especially with a 9v battery.


Well, mostly see Johnny's answer above. It was also for simplicity's sake. Folded all the (-) leads together, a drop of solder, reapeat for the (+) side, done.

And honestly, I'm just winging it and experimenting. LOL!

I'll have to give it a try in series on the next batch though and see what happens.

On a side note, Zombie: I had no idea you were in Pembroke. I was just in Plymouth a couple weeks ago and would've stopped to check out Unpleasant Street had I known sooner. LOL! I've spent a lot of time on your site. Great stuff! Thanks for sharing it with the community!


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## Vlad (Aug 2, 2005)

I've read that LEDs should never be run in parallel. Here's a quote off of the Wolfstone site as to why >>>>>>>>>>

"To make this parallel wiring scheme work, you calculate the resistor so that you get three times as much current running through the circuit. Then, each of the three LEDs consumes one third of the (triple) current, which is exactly what it needs. Neat. Simple. Wrong.

This scheme is predicated on the assumption that all of the LEDs need exactly the same amount of power. If this assumption is met, or fairly close to being met, this circuit will work.

If one of the three LEDs needs less power, the electricity will take the path of least resistance. That one "easy" LED will light brighter, and the other LEDs won't get enough power, and will be dim. Remember that you calculated the resistor for three times the current of a single LED. If the other LEDs don't take their fair share, the easy LED will get more power than it should."

Here's the page that quote is from >>>>>>>http://wolfstone.halloweenhost.com/Lighting/litlpo_PoweringLEDs.html#BasicCalculation


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## heresjohnny (Feb 15, 2006)

That is good advice Vlad, I read through that and they are talking about running LEDs in parallel using a single resistor. For example, Wolfstone himself says

"Of course, this kind of thing works often enough that you can often get away with it. But why not buy a couple more resistors and do it the right way? ".

And several of the quotes say the same thing, for example:

"LEDs in parallel need their own individual dropping resistors. Series strings can be paralleled if each string has its own dropping resistor."

So hooking LEDs in parallel is okay as long as each branch of the circuit has it's own resistor.


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## Vlad (Aug 2, 2005)

It seems to say that it's okay to run sets of series in parallel when you're running lots of LEDs. For smaller #s of LEDs, series is the way to go.


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