Battery to power an LED for a LONG time?

[Mark JD]

I'm new here and wondered if someone here might know how I could battery power a small tac-flashlight, that now uses 3 AAA batteries for long period of time (it's for a 6 or 7 month show)...this is an art project I'm working on. The new fabricated battery pack needs to be approximately 2" x 6" (5cm x 14cm). It needs to fit through a 2" hole (wider 3" space once inside) of the object I've made and be completely reliable for at least that duration of time. Attached is an image that will give an idea of what I'm trying to do.

Any novice advice you could offer would be greatly appreciated.

 

[MikeMl]

Only by pulsing the LEDs with a very low duty cycle.

 

[Mark JD]

Only by pulsing the LEDs with a very low duty cycle.

Thanks Mike...how would do that and maybe also add additional batteries.

 

[MikeMl]

Thanks Mike...how would do that and maybe also add additional batteries.

What is your electronics building experience?

 

[Mark JD]

Very Limited...almost zero! However, I'm pretty handy, worked in high-end custom fabrication (metal & wood) for approx. 16 years.
I did do some elevator interiors and accompanying lighting fixtures.
No breadboard work experience.

 

[MikeMl]

Next question: Do you have a Multimeter for measuring voltage/current? Brand/Model?

 

[Mark JD]

Mike, there's a couple at work I could use...not sure of Brand/Model#s right now...I will have to answer that part your question on Monday afternoon.

 

[dr pepper]

If you google 'joule thief' that might give you some ideas.
The 'thief doesnt do anything special or overunity it just runs a battery down to a really low voltage.

 

[alec_t]

Looks like your artwork is on stands. Can't you put batteries inside the stands? They seem plenty roomy.

 

[ronsimpson]

Only by pulsing the LEDs with a very low duty cycle.

What do you call "duty cycle"? On or 0.5 second and off for 1 minute?

 

[MikeMl]

What do you call "duty cycle"? On or 0.5 second and off for 1 minute?

I was thinking more like on for 1 to 10ms; off for 20 to 50ms

 

[ronsimpson]

I was thinking more like on for 1 to 10ms; off for 20 to 50ms

With flashlights; they got dim. (mS rate) A 10% duty cycle uses less power but also produces less light.
Also; When you more your head fast, or move the flash light fast, you see the flashing.

 

[MikeMl]

If you google 'joule thief' that might give you some ideas.
The 'thief doesnt do anything special or overunity it just runs a battery down to a really low voltage.

A Joule thief circuit will only extend battery life by another 10% compared to not using one. The TS is looking for a 5000% extention.

 

[Beau Schwabe]

A couple of years ago I made a Halloween costume for one of my daughters with about 30 Blue LEDs powered from a couple of AA batteries, that throbbed or pulsated fading ON and then fading OFF ... I only expected a couple of hours out of it, just enough to last through Halloween. ... But I wanted to see just how long it would run... to my surprise it lasted until January. The PWM period was about 1kHz (I didn't want any weird flickering when she moved) and the duty cycle slid from 0% to 100% ... Her costume was "Toothless" from how to train your dragon.

 

[Externet]

Out of the box... If your thingy is displayed under flood/spot-lamp illumination, a baby solar panel can energize the LED during the show times forever. It would use the illumination to generate electricity turning it on. No battery.

 

[Mark JD]

Looks like your artwork is on stands. Can't you put batteries inside the stands? They seem plenty roomy.

Alec, here's some better photos....when I first made this "Flying Heads" pc. several years ago, I used Mag-Lites to illuminate the hard drive boards...that's one reason they were so tall. Also, I was just starting to learn about wood at that time and thought wood & tech might look nice together.

Anyway, I need to now update it for a european show, that runs from May thru November...I want it to stay lit that whole time, without people there having to fool around with it. Also, I prefer not to have a cord coming out of it.

I liked the idea of using a tac-lite to update it, because of the magnified lens and bright beam that would make the outside lighted element, be brightly lit. I'm open to other ideas too...like reworking the mag-lite itself, which part of it has to stay anyway (see images).

There is plenty room inside, but the only entry is the approx. 2" hole at the tops of the wood portions.

 

[Diver300]

There is plenty room inside, but the only entry is the approx. 2" hole at the tops of the wood portions.

I suggest you get a few of these:-
https://uk.rs-online.com/web/c/batt...atteries/?searchTerm=lithium thionyl chloride
Lithium Thionyl Chloride batteries in D-cell size are nominally around 18 Ah and 3.6 V, so one will run 4 mA for 7 months, with enough voltage to light an LED.

They are a bit over twice the voltage of an alkaline cell of the same size, so only 1 is needed to power an LED. The voltage of the Lithium Thionyl Chloride batteries stays nearly constant as the battery is discharged, which means that you don't have to worry about a varying voltage. If it works when new, and the current is low enough, it will work for 7 months. The voltage of an alkaline cell reduces as it discharges.

If you want a longer time or more current, put more in parallel.

You will need a resistor to limit the current. There are various calculators for the resistor value, and one is at https://mtrak.co.uk/led_calculator.html but you will need to know the LED voltage at the current you want, so you might end up adjusting the resistor up or down a bit for your particular LED, to get the current to the value that will allow the 7 months of use.

Lithium Thionyl Chloride batteries are really expensive, but as you are only making one or two of these, you could spend a lot of time designing and testing a circuit with cheaper batteries. Also the Lithium Thionyl Chloride batteries have a very good energy density and they are perfectly suited to low power loads. Alkaline batteries will be a lot bigger for the same energy, but would be better for high power loads like motors.

 

[Les Jones]

How about a proximity sensor so the light only comes on when someone is near it.

Les.

 

[Mark JD]

I suggest you get a few of these:-
https://uk.rs-online.com/web/c/batteries/non-rechargeable-batteries/d-batteries/?searchTerm=lithium thionyl chloride
Lithium Thionyl Chloride batteries in D-cell size are nominally around 18 Ah and 3.6 V, so one will run 4 mA for 7 months, with enough voltage to light an LED.

They are a bit over twice the voltage of an alkaline cell of the same size, so only 1 is needed to power an LED. The voltage of the Lithium Thionyl Chloride batteries stays nearly constant as the battery is discharged, which means that you don't have to worry about a varying voltage. If it works when new, and the current is low enough, it will work for 7 months. The voltage of an alkaline cell reduces as it discharges.

If you want a longer time or more current, put more in parallel.

You will need a resistor to limit the current. There are various calculators for the resistor value, and one is at https://mtrak.co.uk/led_calculator.html but you will need to know the LED voltage at the current you want, so you might end up adjusting the resistor up or down a bit for your particular LED, to get the current to the value that will allow the 7 months of use.

Lithium Thionyl Chloride batteries are really expensive, but as you are only making one or two of these, you could spend a lot of time designing and testing a circuit with cheaper batteries. Also the Lithium Thionyl Chloride batteries have a very good energy density and they are perfectly suited to low power loads. Alkaline batteries will be a lot bigger for the same energy, but would be better for high power loads like motors.

Diver, the Mag-Lites hold (3) D size batteries each (maybe someone makes a spacer if 3 of these is too many). Also, maybe there's a bright bulb that would work with them...attached are images of the standard Mag-Lite bulb (MAG3CELLHK 1E0).
So all I would have to do is get these Lithium Thionyl Chloride D size batteries and new, better bulbs that could handle these batteries.

 

[ronsimpson]

You want a LED replacement bulb. They use much less power. The ones I designed use a PWM. Most will work over a wide range of voltages. Many will have a spec of 2V to 30V or they will say 2 batteries to 5 batteries. (read the data!) Don't use a old type bulb.