How do I get 3 white LEDs to burn with 4AA? *Moved*

I have a 4AA flashlight that I would like to mod with a certain number of 5mm LEDs. About how many would I need to safely direct drive them?

Thanks!

Ps My appologies if this question is too novice!


*Edited to change Subject line.

The problem is, 4AA (6 volts nominal with alkalines 4.8 Volts nominal with rechargables) is right in the middle-

WAY too much voltage to direct drive a single LED and not enough voltage to drive two serial LEDs. (I'm assuming you mean white LEDs)

Your best bet is to use a single white LED in series with a ~67 ohm resistor for alkaline or C/Zn batteries. For use with rechargables (NiCd or NiMH) use a ~27 ohm resistor.

Or you could use multiple LEDS in parallel with each having a 67 ohm resistor in series.

If you are talking Red LEDS, it depends- you could get some that operate on 2.0 V and use three of them in series. Other colors other possibilities.

Yes, I was going to use white LEDs with alkaline batteries. I was WANTING to do like 3 or 4 white LEDs in serial, but I guess this can't be done without help from some sort of regulator?

Okay, if I wanted to use 3 LEDs with 4AA, what do I need to accomplish this?

Thanks!

As Silviron has said, 6 volts it too high to directly drive the 3 leds in parallel and not enough to drive them in series.

So connect a resistor to each LED (to prevent the 6 volts from cooking them) and then connect them in parallel to the 4 x aa batteries.

Maybe this thread should be moved to the Homemade and Modified Lights area.

Orion -
What kind of light are you going to be putting your LED's in?

And, I'm confused. How do you

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>]use multiple LEDS in parallel with each having a 67 ohm resistor in series.<HR></BLOCKQUOTE>

How do you do that? Also, probably a stupid question, but which lead do you connect the resistor to?

ChrisM, I'm using it in one of those lantern type lights you see at Walmart with the big clear top.

I guess the reason why I though that 3 white LEDs would work direct drive with 4AAs is because I bought a 3 white LED set on a screw base flange that was for 4 cell lights. I don't know, maybe there's some sort of resistor inside the flang part.

I'm SOOOOO new into this mod thing that I quickly learn that I'm way over my head! All the stuff like mA, Ohm, volts, etc. are a bit overwhelming.

Connect the resistor to the longer leg which is the positive one (ie. one side of the resistor to the long LED and the other side of the resistor to +ve). This will also be any easy way for you to identify the positive when it comes to hookup time.

Easy to experiment with. Get a 9 volt battery, get some resistors of varying values from 68 up wards and try the above. See how the brightness varies, feel the LED to make sure it's not getting hot, if so, increase resistor value. Remember that when you go live and you are running say 12v that you will need to make the resistor bigger than when running 9v.

Best way to test however is using an ammeter and to make sure that you keep the LED current around 20 to 30 mA.

See, that's what I'm talking about. I've heard people say to use a resistor, but I figured that you buy two resistors, one for each leg. Knowing that you put the resistor on the anode (is that the correct terminology?) only is very important to know. Thanks!

I have no measuring equipment of any type, so I can't test mA. How much are they (say, from Radio Shack)?

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