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is it possible to get a Battery to power A LED for a LONG time?

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shaunye

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I'm currently studying design at uni and don't have much electronics background. I would like to design something that requires battery (cant do powered to mains) and its an indoors item so i dont think solar would help.

Basicly the idea is to have a small LED light which is permanetly on. Is there any (small - was thinking button cell) batterys that would be able to power this for a long time, like months, hopefully a year? or is it just not possible?

thanks for any help
 
A good solution will be 2 alkaline AAA cells that powers an LED that is driven through a joule-thief circuit.

It'll surely last for many months(hopefully a year) I hope :)
 
Most definitely, LEDs typically don't use a lot of power. White LEDs are a bit more inefficient compared to those of a narrower spectrum. I have recently completed a DIY head tracking device that utilizes 3 high output IR LEDs. I'm running them off a standard 9v battery with a 120ohm current limiting resistor. The battery lasts for ages. Using 2 AA battery will also give you a nice run time. Here are a couple of very useful tools to help you out.

**broken link removed**
LED Resistor Calculator
 
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I second the joule-thief idea. Google for that circuit. I take all my flat batteries and run an LED night light in the garage (for the cat). I get a couple of days easy on a battery that would have normally went in the trash, and the D cells will impress you for sure.
 
Button cells come in capacities from about 45 to 100 mAh. So an LED drawing 1mA would last from 45 to 100 hours. Many LEDs are very dim at 1 mA.

According to Duracell, the standard CopperTop AA cell has a capacity of between 2000 and 3000 mAH depending on how it is used and how end of life is determined. If you use a Joule Thief and design it so it uses only 1 mA, a brand new AA might last 4 months.


I have a little single-AA flashlight with a Joule Thief type circuit that draws 15 mA. It should work for 5 to 8 days.
 
Joule-thief circuit is a very inefficient circuit at the best of times. I contacted the designer but they are not interested in improving the design, mainly because they have absolutely no idea how the circuit works.

The only way to power a LED for a long time is to flash it periodically or run it in pulse-mode and be prepared for a very low output in brightness.
 
Look at a low power microcontroller. Some can operate on microamps. Use the controller to set out a pulse, directly to the LED, and without a current limiting resistor. The pulse rate and width will define the LED brightness. The controller might be put to sleep between pulses to further reduce current draw.

The instantaneous current draw might exceed controller design limits. But you might still get away with it.

Look at the Microchip 10F200 for an example.
 
Hello there,


I have a refrigerator monitor that uses both a microcontroller and a tri color high power LED. It uses 2 AA alkaline cells, and the projected life for the two cells is 2 years.
How can this be possible using not only an ic chip but also a high power LED?
Well, the microcontroller is put to sleep between cycles, and the LED is pulsed for only a tiny bit of time so the power consumption is very very low. The average current is extremely low, somewhere around 100ua.
The problem with this however is that means the LED is not always on, but only comes on once in a while. The LED is very bright when it does come on but it doesnt stay on for very long and then turns off and doesnt come back on for another 10 minutes or so.

The problem with any LED circuit is that the LED is going to draw current from the battery, and that drains the battery down. For full brightness many of the LEDs require 20ma, and that would drain two alkalines down in around 100 hours which isnt very long really. Lower that current down to 2ma and you get around 1000 hours which is close to 42 days, but even that doesnt seem to be long enough for your application.
The only way around it then is to use more batteries, or run the LED at a very very low current level if you can accept very low brightness.
Some of the white LED's "first light" spec is somewhere around 10ua i think, but the brighness is very very low. At 100ua however you may find it is bright enough in the very darkest rooms, and at 200ua that might be enough and that will get you quite a long run time.

You have to choose, either more batteries or less brightness, or both. It doesnt matter what kind of circuit you use, it's always the same: more batteries or less brightness. In fact, any kind of circuit will just introduce more loss.

The nice thing about the white LED's is that their efficiency goes up as the current goes down. That means that if you use 10 LED's running so that they put out one-tenth the total light output of a single LED the whole thing will run longer than a single LED at the same total light output.
 
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My Ultra-bright Chaser projects run for months on two AA alkaline cells for RED LEDs and on four cells for blue, bright green and white LEDs at very high brightnesses. Of course the LEDs are pulsed so are turned off for most of the time and have a pause after chasing around a few times. The circuits use 74HCxxxx high speed Cmos that have a current drain of almost nothing while they work. The pulses are quite frequent but are short in duration.
 
Welcome to ETO, 101CIRCUITMAN101.

Never hurts to note the date(s) of prior posts.
 
Maybe Mr Circuit has to change batteries of his almanach...!:woot:

Welcome by the way! :)
 
And the refrigerator monitor is near useless. Mine similar. LED is used for an hour after alarm, that's it. Fridge/Freezer temps and alarm indication are always shown by LCD. problem is, it's the storage Freezer and for the lack of anything else to call the other one, "Medication refrigerator". The alarm will time the amount of time it's in alarm.

I have some other ideas for the system. Temperatures are useful. I did install a "children's lock" that may help. At least there is a positive indication of a door closure, but it won't prevent food falling and leaving a crack.
 
Hi,

Yes old thread, but what refrigerator monitor is useless?
Mine works pretty well. The one i had before that, a purchased item, was the more useless one :)
It had to have the two AA cells replaced every two months. This new one, every two years.

If you have trouble with the door opening unexpectedly, try using a bungee cord to keep it closed. If you can teach the kids to use it, that's good too.
If you have the option to PLUG IN your fridge monitor, you got it made. Then you can have it monitor and report every second. With mine, i use batteries so i have it report every 10 minutes to save battery power. Another thing you can do though is build in a faster report time if there is a fault. Mine does not do that because every 10 minutes is good enough for me, but you could do that if you want a faster indication that something is wrong, and also have a nice alarm.

If the problem is that the motor runs more when the door is cracked slightly, then you could monitor the motor run time and compare it with ambient temperature and inside temperature. You are smart enough to study the cooling cycles for various modes of operation such that you could come up with an algorithm to detect a true fault. Maybe calculating dT/dt or something would help for example.
 
Mr Al:

This https://www.thermoworks.com/products/alarm/rt8100.html is the thermometer I have.

The LED alert only shows for an hour. The LCD alert shows continuously.

The freezer is located in the basement in a way that's its hard to see if the door is open.

There is actually a 16 cuft freezer next to a 1950's refrigerator/freezer, so one probe is on each.

So, in a perfect world, it would be nice if I got an SMS as a door prop alarm. I investigated the door prop alarm. Too expensive for now.

No kids! But the latch is simple. If somehow the door wasn't shut properly because some food was sticking out too far, I'll know. If something fell and propped open the door, it would be open a small amount.

I had two instances this summer that required defrosting the freezer because the door was open. Not good at all.

I have two long-term plans:

1) A possible SMS from a door prop alarm. This probably won't happen.
2) an SMS from an over temperature alarm. I'd have to figure out how to tap into the LED signal on the fridge alarm.
3) Just turn on a light if overtemp occurred.

4) What actually seems the EASYIEST is to mount a "grabber catch" on the freezer. e.g. One of these: **broken link removed**

They come in 3, 5 and 10 lb pull forces. I got a 5 lb. I'll mount with double-stick tape. One on a flat Aluminum plate and another on an angle bracket.

Then I will use that to actually turn on a light, that really needs to be on anyway, so I kill two birds with one stone. Door prop could happen in a future iteration. So, could interfacing the freezer alarm.

Light on with the door open is higher on the priority list although I approached it from lots of angles. It may be possible to send an alarm from a UPS which isn't installed yet. It has inpus for water/temperature contact closures and can be network connected. Priorities are all over the place.

You blink an eye and the week is GONE!
 
Hi,

I put a simple magnet switch on mine, with an LED light and triple AA battery holder. The 3x AA cells lights up the LED without any switcher circuit, just a series resistor. It's easy to mount those little things, and a strong magnet on the door.

If you'd like to build your own temperature detector, a simple PIC based sensor is so easy to do, and because it is in 'sleep' most of the time there's very little battery power required.
But if you can plug in the thing and you trust the power line, you can use a wall wart and comparator. I've seen some of your ideas on here so i am sure you can come up with something that is a sure fail safe, but if you'd like to see mine i'll post some details. All it is really though is a PIC, a high value 50k thermistor, a 50k series resistor, an LED, a battery holder, and a switch for a quick instant measurement. The PIC measures the thermistor every 10 minutes and blinks the LED according to how much the temperature differs from about 40 degrees or something like that. Green if below, red if above (red is a warning that the temperature is above the optimum). It blinks once per degree C, above or below.
The unit is located outside of the fridge, with two wires running inside for the thermistor. The two wires are #32 AWG so the door closes easily even with the wires running inside, anywhere.
You could run an LED upstairs or wherever you normally stay, or trigger a small beeper.
 
With some of the modern LED's it is possible to get about a year out of a battery. I did some tests with a super bright white LED. With a standard Alkaline 9V battery and a 4.7k resistor in series with the LED, it was real bright and consumed a little over 1 mA of current. With a 9V battery having a capacity of 550mA it would last quite a while.
Another way I have learned to adjust brightness of LED's is with a PWM supply voltage. I use a 555 timer as approximate 6% to 94% adjustable PWM generator and use that to turn on a power mosfet. With that a whole lot of LED's can be dimmed to my needs. The PWM generator has a frequency of about 100Hz.
Doing this the Led's are actually blinking but the human eye cannot see the LED's blinking, as the human eye can see blinking up to about 20Hz.
 
Mr Al. Thanks for your offer.

For now, I solved the immediate problem. I now just need to curt and drill and mount the switch and see if it holds up mechanically A 9Vbattery and a LED would work perfect for a quick design.

When and, if I get the Ethernet Patch panel done, I could pass that indicator upstairs to the bedrroom which is not a bad idea either. The panel is mounted, but no connections yet. Thanks for that idea. I could even do that in addition. The LED in the BR is the lowest cost.

I bought the DIN rail parts for (power supply, a few isolated contacts and a contactor that would operate off of 12 V). I would also need to cut a lowvolateg cutout for the wiring. Turning on a 120 V lamp (standard wall switch) would be PERFECT, because the lamp needs to be on to peer into the freezer.

A UPB system is inn the works too for one light.

I do have lots of sensors that need monitoring, or at least lots I could come up with. I have a wireless water alarm, but there is again no external outputs. One water alarm sits on a towel and the other has battery monitoring and is wireless and sits in the "french drain" with the receiver in the bedroom. But it doesn't help if our not home.

The refrigerator has the old fashioned locking handle, but also has a curved door so mounting will be more difficult. The door being open is more likely than it being off. There is no defrost, but I have the fridge turning off one hour a day.

I just would love to have a decent SMS alarm system that doesn't cost an arm and a leg.
 
The PWM generator has a frequency of about 100Hz.
Doing this the Led's are actually blinking but the human eye cannot see the LED's blinking, as the human eye can see blinking up to about 20Hz.
20 Hz is visible to most people, most of the time. It is well inside the range that can trigger epileptic fits in those sensitive (https://www.epilepsysociety.org.uk/photosensitive-epilepsy#.VUSxT9pViko).
The mains supply here is 50 Hz, so many lights are modulated at 100 Hz which is OK a lot of the time, but if anything causes 50 Hz modulation, that can be visible. Personally, I won't have lights with significant 100 Hz modulation fitted in the house. In the days of CRT monitors, I was a lot more comfortable with 100 Hz ones that 75 Hz, and would sacrifice resolution to get higher refresh rate.
Sensitivity to flashing lights is quite variable and increases with:-
How far from the centre of vision (peripheral vision is more sensitive to flicker)
Tiredness
Movement
Contrast
Depth of modulation (how dark the off phase is compare to the on phase)
and some people are more sensitive that others, so if you are wide awake, and you look straight and steadily at a light that isn't much brighter than the background, that doesn't mean it's fine.
I've detected car tail lights as flashing at around 2 kHz. Obviously, that involves movement, high contrast, and 100% modulation depth and I seem to be more sensitive than most.
 
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