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Flashing LED a power sucker?

J

Jack

Jan 1, 1970
0
Hi.
Just recently, used a ~12volt integrated-flashing red LED as an indicator on
a simple open-door sensor: door opens, contacts send a ground to the LED,
completes the circuit to a common 9 volt alkaline battery.

Problem I'm running into is that the LED is a fast drain on the 9 volt
battery. I tried using a 500 ohm resistor to increase the resistance
without drastically diminishing the light intensity. That kinda works but
still only allows about 36 hours at a steady flash rate before the battery
is dead.

Any suggestions to improve the endurance is appreciated.
Jack
 
F

Fritz Wue

Jan 1, 1970
0
If you still can get one:
National Semiconductor LM3909N
Fritz
 
P

petrus bitbyter

Jan 1, 1970
0
Jack said:
Hi.
Just recently, used a ~12volt integrated-flashing red LED as an indicator
on a simple open-door sensor: door opens, contacts send a ground to the
LED, completes the circuit to a common 9 volt alkaline battery.

Problem I'm running into is that the LED is a fast drain on the 9 volt
battery. I tried using a 500 ohm resistor to increase the resistance
without drastically diminishing the light intensity. That kinda works but
still only allows about 36 hours at a steady flash rate before the battery
is dead.

Any suggestions to improve the endurance is appreciated.
Jack

Don't know what flasher you have but there is something inside that makes
the LED flash. If its meant for a 12V supply I may not be designed to run
on low power. So a part of the available power may be used to make the
flash. (Even then the flashing LED will be more economical then a continuous
powered LED but nevertheless too powerhungry for your applicaton.) The
resistor you mentioned will help to reduce powerconsumption but it will
reduce the lightproduction more. Other and better ways are using very low
power elecronics and reducing flashrate and -duration. As I doubt you can
modify the flasher at hand, you may as well dump it and build your own
flasher from scratch. It makes no sense to reinvent the - er - broom, so
google for "led flasher schematic" to find a bucket full of LED flasher
designs.

petrus bitbyter
 
J

Jack

Jan 1, 1970
0
Well, thanks.
Seems a shame to toss out the nifty little compact display packages I made.
How about using a 120 vac ~ 9 vdc plugin converter (the type used for toys,
radios, etc.)? Can I just substitute the 9 volt battery with the converter?
If so, are they usually regulated to prevent toasting the flasher led?
Anyway, I have bunch of those saying around home ..and there is an ac
outlet nearby.
Jack
 
P

petrus bitbyter

Jan 1, 1970
0
Jack said:
Well, thanks.
Seems a shame to toss out the nifty little compact display packages I
made. How about using a 120 vac ~ 9 vdc plugin converter (the type used
for toys, radios, etc.)? Can I just substitute the 9 volt battery with
the converter? If so, are they usually regulated to prevent toasting the
flasher led?
Anyway, I have bunch of those saying around home ..and there is an ac
outlet nearby.
Jack

Jack,

Had the impression you required a battery powered solution. If not, a
wallwart that produces let's say 8-12VDC will be all you need. That 9V
converter you mentioned will do fine and be cheaper on the (not so very)
long run. You wrote that the flasher(s) were meant to run on about 12V. Even
if the voltage is not exactly 9V, it will not give a problem. Only
unregulated power converters will have pretty high voltages when they feel
little or no load. If you have to use one you'd better add a series resistor
but I'd opt for a regulated one.

petrus bitbyter
 
N

nospam

Jan 1, 1970
0
Any suggestions to improve the endurance is appreciated.
Jack


If you want a battery to last longer you :-

Use a high efficiency LED and reduce the drive current as much as possible.

Turn the LED on for as little time as possible.

Waste as little energy as possible. A 9v battery driving a 2v LED means
7/9ths of the battery energy is wasted.

A LED running at 10mA and 5% duty cycle driven by a suitable micropower
pulsing circuit should last around 6 months on a pair of AA alkaline cells
for example.
 
J

Jack

Jan 1, 1970
0
Thanks.
A 9 volt battery supply would have been convenient but I can live with the
adaptor as a wall plug is near by.

My other indicator LED's are for a somewhat different app. They are used as
[fake] "alarm-activated" flashers mounted above an outside door in 2
locations, and wired in parallel back to a small switch also fed from a 9
volt battery hidden in a closet. That application is more important as the
LED has to flash continuously for up to 2 weeks when we leave for holidays,
etc. ..and of course it won't last that long.

So it sounds like I either have to use the suggestion of building a flasher
circuit with descrete components (to control the draw) _or_ find a way of
rewiring a lead from the same converter to supply this setup also _or_
simply find an electrical outlet nearby and wire another converter to the
"alarm" LED ???

BTW, the specs on the blinking LED's: 5~12vdc

Jack
 
P

petrus bitbyter

Jan 1, 1970
0
Jack said:
petrus bitbyter said:
Jack,

Had the impression you required a battery powered solution. If not, a
wallwart that produces let's say 8-12VDC will be all you need. That 9V
converter you mentioned will do fine and be cheaper on the (not so very)
long run. You wrote that the flasher(s) were meant to run on about 12V.
Even if the voltage is not exactly 9V, it will not give a problem. Only
unregulated power converters will have pretty high voltages when they
feel little or no load. If you have to use one you'd better add a series
resistor but I'd opt for a regulated one.

petrus bitbyter


Thanks.
A 9 volt battery supply would have been convenient but I can live with the
adaptor as a wall plug is near by.

My other indicator LED's are for a somewhat different app. They are used
as [fake] "alarm-activated" flashers mounted above an outside door in 2
locations, and wired in parallel back to a small switch also fed from a 9
volt battery hidden in a closet. That application is more important as
the LED has to flash continuously for up to 2 weeks when we leave for
holidays, etc. ..and of course it won't last that long.

So it sounds like I either have to use the suggestion of building a
flasher circuit with descrete components (to control the draw) _or_ find
a way of rewiring a lead from the same converter to supply this setup also
_or_ simply find an electrical outlet nearby and wire another converter to
the "alarm" LED ???

BTW, the specs on the blinking LED's: 5~12vdc

Jack

That blinking LED assemblies are apparently not designed with power savings
in mind. The only thing you can do is using a lower battery voltage. Let's
say 6V or four penlights in series. They contain more energy and waist less
then a 9V battery.

The better way is looking for LED flasher schematics on the net. Some
designs runs for months on one or two penlights. Check out
http://www.discovercircuits.com/PDF-FILES/ac14fls.pdf
for instance.

petrus bitbyter
 
D

Don Klipstein

Jan 1, 1970
0
If you want a battery to last longer you :-

Use a high efficiency LED and reduce the drive current as much as possible.

Turn the LED on for as little time as possible.

Waste as little energy as possible. A 9v battery driving a 2v LED means
7/9ths of the battery energy is wasted.

A LED running at 10mA and 5% duty cycle driven by a suitable micropower
pulsing circuit should last around 6 months on a pair of AA alkaline cells
for example.

If you need to use a battery rather than a wallwart, see if you can use
a bunch of AA's in series unless you need the compact size of the 9V.

Also, those InGaN high output green LEDs with a wavelength nominally
around 520 or 530 nm may well be bright enough at just a milliamp or half
a milliamp - all you need then is a flasher.
You can make a low current flasher with an LMC555 IC - use the
traditional astable circuit that uses pin 7 (as opposed to a somewhat less
common one that doesn't). Use high resistor values to minimize current
consumption through them, and make the duty cycle high. Have the LED (and
its droppong resistor) go from B+ to Pin 3, and you get a low duty cycle.
You can probably get the total current draw under .3 milliamp if you
really try, which should get the battery life to about 2,000 hours
(maybe somewhat more) witha 9V battery.

- Don Klipstein ([email protected])
 
W

Watson A.Name - \Watt Sun, the Dark Remover\

Jan 1, 1970
0
Jack said:
Hi.
Just recently, used a ~12volt integrated-flashing red LED as an indicator on
a simple open-door sensor: door opens, contacts send a ground to the LED,
completes the circuit to a common 9 volt alkaline battery.

Problem I'm running into is that the LED is a fast drain on the 9 volt
battery. I tried using a 500 ohm resistor to increase the resistance
without drastically diminishing the light intensity. That kinda works but
still only allows about 36 hours at a steady flash rate before the battery
is dead.

Any suggestions to improve the endurance is appreciated.
Jack

Here are some very low current flashers.

http://www.discovercircuits.com/L/lite-flash.htm

http://www.discovercircuits.com/PDF-FILES/3vledfs1.pdf
For a different flash rate, change 0.68 uF capacitor value.

http://www.discovercircuits.com/PDF-FILES/badgfls1.pdf
 
W

Watson A.Name - \Watt Sun, the Dark Remover\

Jan 1, 1970
0
Fritz Wue said:
If you still can get one:
National Semiconductor LM3909N
Fritz

They're no longer available. Besides, he wants it for 12V.
 
W

Watson A.Name - \Watt Sun, the Dark Remover\

Jan 1, 1970
0
Jack said:
Hi.
Just recently, used a ~12volt integrated-flashing red LED as an indicator on
a simple open-door sensor: door opens, contacts send a ground to the LED,
completes the circuit to a common 9 volt alkaline battery.

Problem I'm running into is that the LED is a fast drain on the 9 volt
battery. I tried using a 500 ohm resistor to increase the resistance
without drastically diminishing the light intensity. That kinda works but
still only allows about 36 hours at a steady flash rate before the battery
is dead.

Any suggestions to improve the endurance is appreciated.
Jack

This one will probably be less hassle since there's already a 12V
version.
http://ourworld.compuserve.com/homepages/Bill_Bowden/page5.htm#flash2.gi
f
 
T

Tim Shoppa

Jan 1, 1970
0
Jack said:
Hi.
Just recently, used a ~12volt integrated-flashing red LED as an indicator on
a simple open-door sensor: door opens, contacts send a ground to the LED,
completes the circuit to a common 9 volt alkaline battery.

Problem I'm running into is that the LED is a fast drain on the 9 volt
battery. I tried using a 500 ohm resistor to increase the resistance
without drastically diminishing the light intensity. That kinda works but
still only allows about 36 hours at a steady flash rate before the battery
is dead.

Who made the LED? I'm sure there's a datasheet specifying the current
drain.

Seeing as it's apparently a 12V unit, probably for some automotive
application, current drain could be 10 or 20 mA. 20mA * 36 hours = 720 mAH,
which is about the capacity of a 9V battery.

If you instead used a LM3909 type flasher, average current drain would
be measured at way less than a mA, and battery life on a alkaline D
cell would be measured in years. LM3909's aren't made anymore, but
a discrete de-integration is illustrated at

http://home.cogeco.ca/~rpaisley4/LM3909.html

Tim.
 
W

Watson A.Name - \Watt Sun, the Dark Remover\

Jan 1, 1970
0
nospam said:
If you want a battery to last longer you :-

Use a high efficiency LED and reduce the drive current as much as possible.

Turn the LED on for as little time as possible.

Waste as little energy as possible. A 9v battery driving a 2v LED means
7/9ths of the battery energy is wasted.

A LED running at 10mA and 5% duty cycle driven by a suitable micropower
pulsing circuit should last around 6 months on a pair of AA alkaline cells
for example.

And one thing that's important in this case is a system that's
independent from the AC power. If the thief decides to disable the
power, and sees that it also disables the alarms, then he's happy as can
be. If they keep working, then he may be deterred from breaking in.

I was just watching the local news, and they said that the city of L.A.
is going to start fining people $115 if they have a false alarm in their
security system. But you gan go to alarm 'traffic school' just like
when you get a traffic ticket. Sheesh.
 
J

Jack

Jan 1, 1970
0
Yes, probably. However, me thinks I could still use a plugin power
converter through a rechargeable battery that would latch when the power to
the converter is pulled..?
Jack
 
W

Watson A.Name - \Watt Sun, the Dark Remover\

Jan 1, 1970
0
Tim Shoppa said:
Who made the LED? I'm sure there's a datasheet specifying the current
drain.

Seeing as it's apparently a 12V unit, probably for some automotive
application, current drain could be 10 or 20 mA. 20mA * 36 hours = 720 mAH,
which is about the capacity of a 9V battery.

If you instead used a LM3909 type flasher, average current drain would
be measured at way less than a mA, and battery life on a alkaline D
cell would be measured in years. LM3909's aren't made anymore, but
a discrete de-integration is illustrated at

http://home.cogeco.ca/~rpaisley4/LM3909.html

There's no point in trying to 'build' a 3909 from scratch to gain its
advantages, because the low voltage advantage doesn't apply in this case
since the OP could use any battery he wants, including 9V.
 
T

Tim Shoppa

Jan 1, 1970
0
Watson A.Name - \"Watt Sun said:
There's no point in trying to 'build' a 3909 from scratch to gain its
advantages, because the low voltage advantage doesn't apply in this case
since the OP could use any battery he wants, including 9V.

In any event, a 9V battery is quite mismatched to the load in this case
(a LED with Vf around 1.5V). This guarantees an efficiency less
than 20%, because 80% of the power will go into heat in a current-
limiting resistor. Unless you do something funky like use a switching power
supply... If he could truly use any battery he wanted, he'd put in
a RTG and he wouldn't have any complaints about the battery lifetime!

(Note that a LM3909 is a switched-capacitor supply in itself...)

Tim.
 
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