Homemade 6 volt lithium flashlight

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I picked up a little AA ruberized flashlight ($4.50)and two Duracell Ultra CR2 3 volt lithium batteries ($10.97 for a two pack) at Walmart today. I used a single white 5600mcd LED. Broke out the glass and soldered it in.
I had to file out the plastic ribs on the inside of the flashlight with a long file. After doing this I could just get the CR2 batteries to fit inside. With no resistor it ran at almost 200mA. I didn't think the LED could handle this for too long so I put in a 10 ohm resistor. Now it runs at a steady 100 mA. With a rating of 750 mAh this thing should run at least 7.5 hours, I think. Bright as hell and real light weight. I just wish I could have fit the 123 batteries in it for more run time but they just won't fit. Sorry no pictures, I took the digital camera back to work.

 

[Badbeams3]

Sounds neat. But I can see what you are saying about wishing you could get the 123`s in there. It will be an expensive light to run. Do you think it could be resistored down further without losing to much brightness?

 

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I guess the question is at what point in mA does the LED stop getting brighter. If I could figure this out I would just set it for that and get the most battery life possible. Anyone know this one?

I changed the light today. I just can't stop messing with something when it should be done. I keep trying to think of ways to improve on the thing. I took my 4 LED white 5600 bulb I made out of my Maglight. I'm using a home made resistor tube. This is sometimes better than soldering it into the bulb. I can try many different size resistors and keep fooling with it after the bulb is done without resoldering constantly.
I used a 33 ohm resistor. I put the meter on it and the whole thing is pulling 60mA.
It's wired in parallel with the 4 positive leads down the center and the 4 negative leads soldered to the sides.

Question: Does this mean that each LED is pulling 60mA or do you have to divide the number by four and each LED is only getting 15mA?

The thing is real bright now with the four LEDs in it. I think I'll leave it like this. I like the extra brightness in such a small flashlight. It's got a good reflector in it and will make a good trail light. Real light weight too. Would be good to take backpacking.

 

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Well, I changed it again. Now I'm using a 10 ohm resistor and it's pulling 150mA total. It is brighter now. I tried running it without a resistor. It was real bright but started to get hot so I turned it off quick. My meter only goes up to 250mA. I pegged it all the way over to the far right so I don't know what it was pulling. I'm going to stop off at Radio Shack after work tomorrow and pick up a pack of 5 ohm resistors and try one of those. I'll post the results soon.

 

[Chris M.]

Question: Does this mean that each LED is pulling 60mA or do you have to divide the number by four and each LED is only getting 15mA?

Connected in paralell (and all identical LEDs), then divide the current draw by the no. of LEDs, so at 60mA total each LED is getting 15mA. At 150mA each one is getting a little over 37mA, I reckon you could push them a little harder at a guess, but not so hard as one LED on its own- you have to watch out for overheating. I think I read somewhere else on these boards that someone had a similar LED bulb that melted together!

 

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Thanks Chris,

I will try the 5 ohm resistor soon. Well, I did some more with the round file tonight and finally got the lithium 123 batteries to fit in the thing. 1300 mAh instead of 750 mAh. This should help some with runtime.

It's bright now but I want to make it just a little bit brighter without blowing any of the LEDs.

How come a little 10 ohm resistor makes so much of a difference? The light pegged my meter with no resistor but only runs at 150mA with the 10 ohm resistor. It doesn't seem like 10 ohms would make so drastic a difference. Anyone know why this is?

 

[Chris M.]

How come a little 10 ohm resistor makes so much of a difference?

Are you familiar with Ohm`s Law V=IxR? Volts dropped accross the resitor equals current flowing through (in Amps) multiplied by its resistance. So at 150mA or 0.15A you would have 0.15x10= 1.5 volts dropped accross the resistor so the LEDs get the other 4.5 volts of the 6 volts from the batteries. That`s why it makes such a difference.


I like the idea of the multiturn pot. With one of them you could hook it up on the bench and experiment with it till you get a current draw and brightness you like, then just unhook it, measure its resistance and fit a normal resistor of that same amount (or a few in series to get the right value) in its place. Saves time soldering different fixed resistors. One thing to be careful of is those miniature pots can`t handle a large current. You may have problems with overheating if they`re left on for a while with a cluster of LEDs so if you can- get a larger one with a higher power rating, otherwise keep on-times short. I did some experimenting with one similar a while ago and partially melted it so the screw wouldn`t turn any more!

 

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Thanks for the help guys. Here are some pics. I just threw the flashlight and parts on my flatbed scanner so the light output doesn't show up too well but you get the idea.

 

[axolotls]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by KenBar:
He suggested that I use a 10 turn pot. I had never heard of such a thing so I went to the store and came home with a 15 turn 1k pot.
<HR></BLOCKQUOTE>

So this goes from zero to 1,000? Seems awful rough; but something I could've used. I just went and got a 0.47 Ohm resistor for my first LED flashlight/box. Wonder if this will make any bit of difference....

 

[jbechto]

Hi Guys,

I was the original poster of the 10 turn 1 K pot thing. I nearly melted it testing a 24 volt setup with 12 20,000 mcd yellows. {;-)

They are available in higher watt ratings which would be good for the test setup. I give you guys credit for using smaller ones in a light setup. Great idea! A pot mounted for external access would be fun! Then you could dial it to whatever you want each time you use it.

Soldering your LEDs to the PR base helps keep them cool. It acts as a heat sink. I'm running that quad bulb at 170 now and they seem to be holding up fine. I ran a couple higher, but the difference in brightness wasn't significant. After 40 mA or so, I think it's better to just add more LEDs. A law of diminishing returns, I think

John

 

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Radio shack didn't have any 5 ohm resistors so I bought a big pack of different sizes. I soldered two 2.2 ohm and a 1 ohm in series to get a 5.4 ohm resistor. I stuffed all this into a plastic tube and hot glued it together at the ends leaving the wires I wrapped around a washer I put at each end. I put the tube in the back end of the light by the tailcap. The light is running at a total of 225mA. Quite a bit brighter than with the 10 ohm resistor running at a total of 150mA. I screwed a little nut onto the soldered base of the bulb for a heat sink. I think it's working because it's getting pretty hot after about 15 mins. The bulb case is getting hot too. The LEDs are a little hot but not too bad. I wonder if this thing will last or I should go back to the 10 ohm resistor.
Oh well, it's the brightest light I have made so far. Those 123 batteries are expensive but they sure work well.