Looking for the right disposable batteries

orionlightlight

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Hi everyone. I'm working on building a flashlight. Are there any disposable batteries out there that can power this LED for 10-30 minutes and be under 25mm when stacked one on top of another? :

Nominal Wattage: 0.5 W
Rated Current: 150 mA
Forward Voltage: 3.0 - 3.4 V
Luminous Flux: 40-45 lm

Thanks in advance.
 

orionlightlight

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Thanks for the response.

These look too wide. I'm making a keychain flashlight. Do you know if button cell batteries would work?
 

HarryN

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Part of the fun of building a light is finding the battery that fits what you personally are trying to accomplish. The CR2 fit your request for 25mm long or less. :)

There are 3 volt coin cells on the market. Data sources like batterystation, everyready, energizer, etc are good places to look. Every battery has a data sheet - just look at the capacity and divide by 150ma to get a first order estimate or run time. Sometimes they even publish a curve of volts vs time at various currents.

In general it is a good idea to use a combination that can run for no less than 30 minutes, ideally closer to an hour, because if you run it so that it drains in 10 minutes, that is a great way to cause battery related problems.

A really simple light can be built using just the battery, a head, and some Al tape. Very light weight, a little bit challenging to turn off. ....
 

HarryN

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It is a bit tricky to tell exactly what will happen without looking at the data sheet for each cell.

As an example, look at the energizer web site for the CR2032 and CR2450.

These represent fairly state of the art Li coin cells and the general intended service for them as envisioned by the mfg.

At the bottom of the data sheet there are discharge curves - ranging from 0.2 - 6 ish ma for the 2032 and up to 9 ma for the 2450.

In general, that is the load you should expect a cell like that can sustain.

The good news is that you can probably purchase a 3 or 5mm LED with a built in reflector, skip any kind of driver or resistor at all and just wire it on with a simple on/off switch.

The battery will simply be unable to supply enough power to damage the LED but it will be enough to drive it with some light.

Also convenient - easy to bench test before actually building a light body.

For the LR44, I found data sheets on the energizer site -but really just safety sheets - no discharge curves. Assuming that they can delivery 10 ma or so, it would take 3 in series to make 4.5 volt (before the voltage sags under load).

I think at one time (early LED days) some companies would hand out free trinket flashlights at trade shows with 3 each LR44s in series running an LED. It is a pretty small battery and alkaline, so - just completely guessing, it might support 2 - 3 output. They are cheap enough to test and see what happens. - part of the hobby.

Maybe a 1/3N ?
 
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orionlightlight

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Cheers, that's exactly what I need - the 1/3N. I've been doing a ton of research. They're 3Vs each and I need to use 2 of them. That's 6Vs and the LED handles up to 3.2V, so I'll need a series resistor. Is this a practical thing to do for keychain flashlights?
 

Lynx_Arc

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I wouldn't call using hard to find batteries practical. If you can't find them locally then sooner or later you will shelve the light due to the cost of running it vs other lights. The problem with button and coin cell lights is finding batteries cheap and sometimes having to stock them to get them cheap enough and if you don't use them within a few years they go bad on you. The most practical is the 1AAA format either with a boost circuit for 1.5v batteries or a resistor for 10440 lithium ion batteries (rechargeable). I've tinkered with small lights even took a button cell light by rayovac and converted it to 1AAA using a drop in PR base LED bulb.
While it is fun to make your own the small size doesn't easily lend itself to practical options. Back long ago when there was no 1AAA boost circuit lights people were taking solitaire maglites (1AAA incan) and modding them for LED use either using button cells or a 10440 but when the first decent 1AAA LED light came out (dorcy) most of these lights got shelved in favor of it and since then you can get cheap boost circuit lights in the stores. They used to have 1AAA LED lights at Walmart for about $2-$3 you could rip one apart for the LED and boost circuit if you wanted to go that way.
 

HarryN

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Before you design the actual light, maybe buy a few batteries and LEDs to test.

I just mount stuff up on plywood to prototype. Brass screws / or nails can be reasonable heat spreaders to mount the LED on.

I would think that a single 1/3N could power it and if you need more run time, maybe 2 of them in parallel. You will be able to determine this from your proto testing.

If you are willing to use red or red/orange, (roughly 617 - 660nm range) the Vf is lower than for blue / white and that makes it all easier to do single cell.

Try to avoid thinking of the Vf is a "hard number", it is number selected from a curve of voltage vs current that corresponds to the mfg targeted current for that LED.

While I agree with Lynx Arc in some ways, who cares if it is practical? It is a DIY home made light built for fun / hobby / intellectual curiosity. Unless you are talking about attempting to sell them it doesn't matter much. I do agree that if you plan to use it a LOT, then battery cost can become an issue.

For a small light, a resistor is much easier to implement than a boost circuit and that saves considerably on cost, space, complexity, etc.

One word of warning - when I started playing with LEDs, they were not nearly as bright as they are now. You will be sitting very close to the LEDs, turning them on/off, most likely in moderate to low light conditions and there is a tendency to stare at how cool they are. Consider to have some sunglasses around.

As far as what package is "practical", I like CR2s but that might be too large for your goal.

In some ways, keychain lights are not needed much any more because that function is built into most cell phones. A tritium vial is bright enough for some uses and the phone on the higher demand side. Keychain lights are sort of squeezed out IMHO.
 
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orionlightlight

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Well, actually I am planning to sell them for a project I'm working on. I probably should have mentioned that earlier. I am planning to offer a early bird discount for the community. Flashlights are a lot more complex than I thought. I might have bitten off more than I can chew but it's too late to turn back now.

These are the designs I had made - https://imgur.com/a/Fw1mxfk

As you can see, a CR2 would not work with this although the power works.

It looks like I'll have to go with the 10280 rechargeable or the AAA. If I may ask, which one would you recommend?
 

HarryN

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Those look nice. Its fine to try to sell them - that is what this place is all about.

I made some prototypes of 2 lights that I liked, but the cost was quite high to really turn into items that could be sold, so finally after investing about $3-4K, I gave up. (with encouragement from my wife)

How do you plan to fabricate the hexagons? It seems like that will be challenging to make in a material that is thermally conductive.

For the small lights that I made, optics were the really hard challenge, as it took 2 stage optics to do what I wanted.

I agree with you, it is a non trivial matter to build a custom light, even for personal use, much less for sale. I learned a LOT in the process.

Don't be surprised if you end up with $200 cost per light in materials alone and $1-2K of NRE.
 

HarryN

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Well, actually I am planning to sell them for a project I'm working on. I probably should have mentioned that earlier. I am planning to offer a early bird discount for the community. Flashlights are a lot more complex than I thought. I might have bitten off more than I can chew but it's too late to turn back now.

These are the designs I had made - https://imgur.com/a/Fw1mxfk

As you can see, a CR2 would not work with this although the power works.

It looks like I'll have to go with the 10280 rechargeable or the AAA. If I may ask, which one would you recommend?

Probably I am the wrong person to ask about batteries for your custom light - I have more or less standardized on just a few battery sizes now and really would rather just use one size in the house if I could get away with it.
 
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