Using a 9V bat for LS?

[pedalinbob]

i just tried a single 9V alkie to drive a nice white 1wLS. i resistored it down to theoretically draw 350ma.

any problems with this? i know it is better to be closer to the voltage requirements...but...it seems to run nicely, so far, and i like the small 9v form factor.

Bob

 

[OddOne]

It'll work, but not for a whole lot of time. 9 volt batteries are only good for 100 mA of draw continuously if you want 10 hours or more of usable life.

You might want to investigate step-down power supply ICs if you intend to use 9-volt batteries. Might give a longer lifespan to the battery. Plus, you could build the circuit and LED in such a way so as to snap right onto the battery.

oO

 

[pedalinbob]

interesting...that is what im looking for: small, pocketable size. i would love to be able to make it with adjustable brightness. if only i knew more about electronics.

well, i was thinking of keeping it as simple as possible...but an electronics guru could assist, im sure.

so, the battery cant supply more than 100ma continuous? i think im misinterpreting your point...because the LS seems to run very bright (i havent measured current flow). will i damage the battery somehow by forcing it to supply 350ma?

how would a 9v Li fare?

jeez, i have a ton of learning to do...but at least it is fun.

many thanks,
Bob

 

[star882]

I have seen someone driving a 5w LS directly from a alkaline 9v battery without resistor on CPF a long time ago.
Problem is, forget and install a lithium or Ni-MH 9v, and you blow an expensive LED.

 

[Deleted member 684]

Does that person happen to be electrolumens? /ubbthreads/images/graemlins/grin.gif

 

[x-ray]

Yeah, I think we're talking Pocket Zorch /ubbthreads/images/graemlins/smile.gif

 

[eluminator]

If the battery doesn't get hot, you won't hurt yourself. You can't be getting a lot of light for very long though, because the 9v battery doesn't have that much energy. It's made of 6 itty bitty 1.5 volt cells and is a rather inefficient way to supply power to a 3 volt LED. You are losing 2/3 of the energy in the resistor. But, if it works, use it.

You could get twice the light and the same runtime if you used two LS's in series, and a smaller resistor.

If you want a longer lasting or brighter light you could use 3 AAA cells in series. I think these hold considerably more energy than 1 9 volt battery, and you are only losing 1/3 of it in the resistor.

Now if you can get your hands on some DL123 cells cheap, that's another way to go. They put out 6 volts and should make quite a flashlight.

Edit-- I meant to say 223 cells not 123 cells.

 

[tonyb]

Do you mean something like this?

Top: 1-Watt Luxeon /Star-O with 98% Eff. Step-Down Regulator, 9-Volt Batt. 6 month old light only the 2nd battery, use this one alot, like to repair my car and hike at night in woods. I plan on making a bracket to use it on my mountain bike this summer.

Middle: Sky-Light rip-off 98% Eff. switchmode converter, fully dimmable,switchable between 2 white and 2 red leds, 9V Batt. 2yr old light only on the 2nd batt. the 1st batt. was used it lasted a long time. I use it to read at night sometimes I fall asleep with it on it draws practically nothing, about 10mA, when I read.

Bottom:1-Watt Amber pocket light 9-Volt snap on, really bright and small, direct drive, 8 super bright 5mm amber diodes.

I feel I get my moneys worth out of 9v batterys when you factor cost to size and efficiency. I plan on making more 9-volt lights in the future. I'd say go with 9-Volts !

 

[webley445]

click on the link in my sig. I've done the same but without using an LS, just a regular Nichia, maybe it will give you some ideas.

 

[ab]

Here's another approach to a 9V clip-light:

AB 9V mini-light, 2 @ white LEDs with reflectors...

/ubbthreads/images/graemlins/smile.gif

A.

 

[pedalinbob]

yes, many of those look similar to what i intend to build. i have to be patient, because i want a very fine balance of pocketability, brightness and runtime.

you were correct--the 9v with luxeon did not last long at all. in 60 minutes, it went from 85 lux to 9 lux. yikes!

i then tested 3aaa with 2 ohms resistance: went from a peak of 95 lux to 52 lux in one hour. the rate of decline appeared to be slowing.

therefore: if i go with a LS, i will use aaa or aa (possibly a 123?). if i use aa, i would prefer to use a step-up like a micropuck--but i dont think i will be able to dim the luxeon driven in this fashion. another possibility is direct driving with lithium aa.

if i go with nichia LEDs, i have a little more flexibility with my power source.

thanks again...back on with the thinking cap...

Bob

 

[eluminator]

I edited my previous post. I meant to say 223 cells not 123 cells. I guess a 223 is basically 2 123 cells bundled into one package. I hear you can buy a 223 a lot cheaper than you can buy 2 123's and it gives enough voltage to drive a white LED through a resistor.

 

[eluminator]

[ QUOTE ]
pedalinbob said:
i just tried a single 9V alkie to drive a nice white 1wLS. i resistored it down to theoretically draw 350ma.

any problems with this?

Bob

[/ QUOTE ]

It all depends on what theory you are using. If you aren't allowing for the internal resistance of the battery, you probably aren't getting the current you calculated. It would be interesting to know what voltage the 9 v battery is actually putting out when driving the LED. Of course you can easily determine the actual current through the LED by measuring the voltage across your resistor, and dividing by the resistance. As you probably already know, when dealing with resistors, V=IR, or to put it another way, I=V/R.