"1.5V AA" 3 months continuously night lamp

[madhippiescientist]

A little battery does not have much capacity so it will not last long.

It was simply another suggestion, and
those "camera" type batteries, I believe,
are NiMH and have a pretty good AH, for
their size.

 

[audioguru]

It was simply another suggestion, and
those "camera" type batteries, I believe,
are NiMH and have a pretty good AH, for
their size.

We are talking about primary alkaline battery cells that have the same capacity as a charged Ni-MH cell.

I don't think anybody uses an old carbon-zinc or a low capacity Ni-Cad battery anymore.

 

[MrAl]

Hi again,


I am still in favor of using two or three batteries rather than one with a converter.
I have done lots of tests with white LEDs and batteries and have found that there
are two ratings for a battery (this has been known for some time however)...
one rating for when the battery is used 'normally' under more typical uses like
flashlights and medium to high current draw, and another rating for VERY low
draw applications like what you would see with a white LED running with very
little current. The capacity actually comes out much higher when the current draw
is much much lower than 'normal' so the run time actually goes up again because
of that factor alone. That can get us more hours with the same battery.

If the LED is to be turned on and off in order to save even more power, then
another idea is to simply use three batteries in series and a circuit that is designed
just to turn it on and off rather than a converter. This can be made EXTREMELY
efficient, using a mosfet as the switch element of course and mosfet or lower power
microcontroller circuitry.
As an example, i have a temperature monitor using a uC chip and LED that can
run two years on two AA cells.

 

[mneary]

I agree with MrAl. Circuits which rely on parts to work properly at half their minimum voltage are curiosities. Maybe you build one and it sort of works but reproducing it is another matter.

Putting it on the web, to trap newbies and make them struggle, is just plain cruel.

 

[audioguru]

Nearly all solar garden lights use a single 1.25V Ni-Cad cell, a simple cheap voltage stepup circuit and a low voltage cheap solar panel.

Instead if they used three fairly expensive Ni-Cad cells and a much higher voltage solar panel then their cost would be too high.

 

[mneary]

Nearly all solar garden lights use a single 1.25V Ni-Cad cell, a simple cheap voltage stepup circuit and a low voltage cheap solar panel.

Instead if they used three fairly expensive Ni-Cad cells and a much higher voltage solar panel then their cost would be too high.

That's not my point. They don't use a 2 volt 555.

 

[audioguru]

National Semi guarantees that their LMC555 will work with a supply as low as 1.5V.

I made some LED chasers with 74HC4017 ICs that are guaranteed to work when their supply is as low as 2.0V. They all work perfectly when their supply is only 1.4V (but the red LEDs are very dim).

 

[karthiks]

current drawing is 500 micro amp

HELLO. Hey you say that the circuit consumes about 500 micro amps how did you come up with that number? well the led draws 20mA of current right? then how 500 micro amps

 

[karthiks]

Audioguru, would please help me out

 

[karthiks]

HELLO. Hey you say that the circuit consumes about 500 micro amps how did you come up with that number? well the led draws 20mA of current right? then how 500 micro amps

 

[karthiks]

National Semi guarantees that their LMC555 will work with a supply as low as 1.5V.

I made some LED chasers with 74HC4017 ICs that are guaranteed to work when their supply is as low as 2.0V. They all work perfectly when their supply is only 1.4V (but the red LEDs are very dim).

HELLO. Hey you say that the circuit consumes about 500 micro amps how did you come up with that number? well the led draws 20mA of current right? then how 500 micro amps

 

[audioguru]

HELLO. Hey you say that the circuit consumes about 500 micro amps how did you come up with that number? well the led draws 20mA of current right? then how 500 micro amps

The LED is turned off for most of the time. The Cmos 555 charges the capacitor slowly with an extremely low current then connects the capacitor in series with the battery to blink the LED with maybe 5mA for a moment until the capacitor has drained. Then the LED turns off and the capacitor charges slowly again.

The average current from the battery is 500uA.

My LED chasers blink each LED at a very bright 25mA for a moment. Their average battery current is about 200uA. The AA alkaline cells battery lasts for months.