Trying to get a better grasp of LEDs

[PropDad]

I have recently got into making props for my daughter but also looking at selling if popular. Some of these props need to be lit and have a small power source. As you all already know LEDs should work for this.

My first prop needed a single light source. I did a little research and for the power source I went with on of those 3 AAA battery holders that can be found in some mini flashlights. The reason I went with this was because it was pretty much the biggest power source I could find that would fit. I then went to superbrightleds and ordered a light bulb with a base that matched the voltage. This has worked okay for me for know but felt I could have possible gotten more light by using individual LEDs, resitors, and what not.

Our next prop was a sword (acrylic) that needed to be lit up all the way down. This time I went with an LED strip that was rated for 12 volts. The handle had a very limited and specific shape to be able to hold batteries. There was just enough room for two 9 volt batteries. Since 18 volts would have been too much and 9 too low I decided to wire them in series to get 18 and then connected a small voltage regulator from Radio Shack that brings it down to 12. This has worked for awhile but something odd has recently happened. After just a few minutes of being at full brightness they suddenly dim down. Not a gradual but like a sudden voltage drop. I thought maybe there was something wrong with the regulator but after changing it out twice it is still doing it.

Our most recent prop is a sword as well but this time only the edge was supposed to glow in just a few spots/not all even. For this one I wired 6 blue LEDs rated for 3.5 volts max, at least that is what it said on the website. After picking them up I saw the package said they were rated for 3.8 volts max. I ended up using a 2032 battery which is 3.6 volts figuring it would be safe since it was lower. No problems so far but not sure how long one of those small batteries is going to power 6 LEDs.

For the last project I am going to bring up for now is a dress my wife made for our daughter that has LEDs in it. This time we went with a string of LED lights that had 3 AA battery pack attached. We went with the string since it was all prewired and perfect amount of lights for the project.

And now for the questions.

1) For the first item is there anything I can do to get a brighter light source with the same battery pack than what I mentioned?

2) Do you think there is anything I can do different to the acrylic sword that make it perform better with the current LED strip? Different battery? Something other than the voltage regulator? Would 18 volts directly damage it?

3) The sword with the blue LEDs has an even smaller space is why I went with the 2032 battery. Is there anything I might be able to do to make it last longer? Maybe even a different single battery?

4) For the dress the concern is the size of the battery pack. We have been able to hide it but not comfortably. Any suggestions as to what we might be able to do differently?

I know this is a lot all at once but any help or pointing my in the right directions to resources would be greatly appreciated. So far my process has been seeing what room I have for batteries and trying to figure out what might work for it.

 

[tim]

First off, awesome props! As an engineer, I'll give a few off-the-top-of-my head thoughts that I hope are helpful.

1) For the first item is there anything I can do to get a brighter light source with the same battery pack than what I mentioned?

Cree (and probably other manufacturers) make some high-brightness single LEDs that might work for your purpose. The spec sheet for the LEDs should list a brightness rating in mcd, so you can use that to compare them.

2) Do you think there is anything I can do different to the acrylic sword that make it perform better with the current LED strip? Different battery? Something other than the voltage regulator? Would 18 volts directly damage it?

Without seeing the electronics myself, I'm not sure what's causing your problem. Perhaps you're exceeding the maximum current rating for the voltage regulator. Does the chip get hot after operating for a while? Also, 9V batteries don't have a large capacity, so they will run down pretty quickly. I would not use 18V directly on the LED strip. Perhaps you can look into some lithium ion rechargeable packs that you could fit in the handle?

3) The sword with the blue LEDs has an even smaller space is why I went with the 2032 battery. Is there anything I might be able to do to make it last longer? Maybe even a different single battery?

That coin cell won't last for long running 6 blue LEDs (especially since the blue LEDs can draw more current than the typical red, green, or yellow LEDs). Is there room to connect two of the batteries in parallel?

4) For the dress the concern is the size of the battery pack. We have been able to hide it but not comfortably. Any suggestions as to what we might be able to do differently?

Perhaps make a belt pack? You could also try looking into lithium ion rechargeables as well.

I know this is a lot all at once but any help or pointing my in the right directions to resources would be greatly appreciated. So far my process has been seeing what room I have for batteries and trying to figure out what might work for it.[/QUOTE]

 

[PropDad]

First off, awesome props! As an engineer, I'll give a few off-the-top-of-my head thoughts that I hope are helpful.

Cree (and probably other manufacturers) make some high-brightness single LEDs that might work for your purpose. The spec sheet for the LEDs should list a brightness rating in mcd, so you can use that to compare them.

So since I am using 3 AAA batteries which equals 4.5 volts should I be looking at an LED that is rated for that or something rated lower and use a resistor or even something else.

Without seeing the electronics myself, I'm not sure what's causing your problem. Perhaps you're exceeding the maximum current rating for the voltage regulator. Does the chip get hot after operating for a while? Also, 9V batteries don't have a large capacity, so they will run down pretty quickly. I would not use 18V directly on the LED strip. Perhaps you can look into some lithium ion rechargeable packs that you could fit in the handle?

With all the work I put into links in my post you think I would have included that :/ I am using a simple 7812 12 volt regulator rated for 1 amp. It does not even get warm to the touch. Thanks for the idea of the rechargeable batteries though. I have 4 10440 batteries rated at 3.7 each (630mAh) for a total of 14.8 volts in series. I would think this might be safe as this is closer to automotive voltage range and not the 18 volts I suggested. The batteries are the same size as AAA and with a holder should be able to fit.

That coin cell won't last for long running 6 blue LEDs (especially since the blue LEDs can draw more current than the typical red, green, or yellow LEDs). Is there room to connect two of the batteries in parallel?

Unfortunately there is not much more room than this. Not even a single 10440 battery I mentioned above will fit.

Perhaps make a belt pack? You could also try looking into lithium ion rechargeables as well.

This one is not a high priority at the moment but would be nice to get done sometime.

I know this is a lot all at once but any help or pointing my in the right directions to resources would be greatly appreciated. So far my process has been seeing what room I have for batteries and trying to figure out what might work for it.

Thanks for the tips. Every little bit helps. Also thanks for the compliments. It's always nice when some one recognizes the work that has been put into something.

 

[tim]

So since I am using 3 AAA batteries which equals 4.5 volts should I be looking at an LED that is rated for that or something rated lower and use a resistor or even something else.

I would use a resistor, as you won't find an LED that will operate at that voltage, unless it's a module with built-in electronics. Use Ohm's law to calculate the resistor value you need to get the voltage drop you need; you'll need to know the forward operating current of the LED.

 

[13doctorwho]

I work in electronics product development for a living, and I have designed many light boards for my props.

Although LED's have a voltage rating, their brightness is more a function of current. I never, ever power an LED with out a current limiting resistor.

1) The blue LED dimming problem. While two nine volt batteries provide a lot of voltage you need to look at how much current the circuit draws. I have seen this phenomenon before. The LED's start out bright because when the circiut is turned on the LEDs draw to much current, at first the batteries and regulator can source it, but the batteries power sags. It is also possible the regulator is folding back. Some regulators have a feature where if they see excessive current for a given time it "folds back" limiting the current to protect the regulator.

2) I would look for a 12volt battery. We tend to think 9V, AAA, and AA but there are million types of battery out there. There are regular disposable and of coarse rechargeable. The thing to watch out for is the AMP-HOURS. An AMP-HOUR is how many hours a battery can run a one amp circuit. 1 AMP-HOUR can run a 0.5 Amp load 2 hours.

3) I have used a "lighter" battery in some of my small devices. They have them in 6 and 12 volt and the are smaller than a AA.

4) It depends how the LED's are wired and how much current they draw. I know Hobby Lobby sells a flashing light kit for t-shirts that runs on 4 button cells. In that case only one LED is on at a time.

Oh, by the way... Usually a 12 volt "LED" is one of two things. It is either a couple low voltage LED's strung together, or a single LED with a large resistor. It is usually cheaper (and you have better brightness control) if you construct it your self. For instance, you could use 5 2volt LEDs and a resistor. since brightness is controlled by current different resistors will give more or less brightness.

Well I hope something here helps. Feel free to PM me if you have specific questions.