2 AA 5 mm LED basic wiring

tsask

Flashlight Enthusiast
Joined
Oct 6, 2005
Messages
1,759
not sure where to place this post ...
I would like to run a single 3mm, 5 mm LED off a ONE or TWO AA batteries. from what I have learned from my ARC AAA, it takes a "special" circut/boost to run off a single AAA or AA. therfore it looks like I would be better off using TWO AAs. Can I run a single LED 5000 mcd off 2 AA's without using or needing a resistor or boost????
 

carrot

Flashaholic
Joined
Dec 6, 2005
Messages
9,236
Location
New York City
You can direct drive a 5mm LED on 2x AAs no problem. I tried sticking a normal 5mm LED into the socket of my Maglite Mini and it works fine.
 

Lynx_Arc

Flashaholic
Joined
Oct 1, 2004
Messages
11,212
Location
Tulsa,OK
Most 5mm LEDs the VF is a little above that of alkaline batteries to run at the rated current which means you will be underdriving them. If you use lithiums they are very close to vf of most 5mm LEDs if you use a pair of them for about 3.4v.
The MJLEDs have a vf I think about 3.2v or less and run well off 2 alkalines and may actually be overdriven by lithiums to the point of frying them.
I have tried regular white LEDs off 2AA alkalines and you get about 2-10ma drive current off new batteries which can be dimmer than expected and possibly... unuseful for all but a nightlight.
Unless you are opting for an MJLED you will probably have to resort to using a boost circuit of some type to drive a white LED at near Vf for useful light output.
 

DUQ

Flashlight Enthusiast
Joined
Jun 22, 2005
Messages
1,824
Location
Ottawa, Ontario, Canada
If you need more voltage, you can use three N cells for a Vin of around 4.2-4.5v. You will need a resistor if your only driving one LED.
 

tsask

Flashlight Enthusiast
Joined
Oct 6, 2005
Messages
1,759
thanks for the info. looks like I should try THREE AA's??
 

eebowler

Flashlight Enthusiast
Joined
Dec 18, 2003
Messages
1,735
Location
Trinidad and Tobago.
Three AA cells will fry your single LED very quickly. Even three AAA cells will kill a single LED. You NEED a resistor if using three cells. If you have to use two cells Lithium cells will work best.
 

cratz2

Flashlight Enthusiast
Joined
Apr 6, 2003
Messages
3,947
Location
Central IN
Honestly, KevinL's 35K LEDs on 2 alkaline cells is very decent and will give CRAZY long runtime. The MJLEDs, esp on Lithiums, will be brighter of course, but pull more current so will have less runtime.

THe Nichia CS LEDs are capable of being brighter than the 35K LEDs, but if both are driven directly on 2 AA cells, the 35Ks certainly look a bit brighter to me. The Peak Sno29 LEDs are another option and generally are whiter, but again, the 35Ks look brighter to me than the Snows or CSs if all three are direct driven on 2 alkaline cells.

Another nice thing about direct drive is that while there will be some dimming, the runtime is absolutely UNBELIEVABLE! I can't even guess how long without my current measurements in front of me, but it will be a VERY LONG TIME! Much longer than if it had a voltage boost.
 

tsask

Flashlight Enthusiast
Joined
Oct 6, 2005
Messages
1,759
cratz2 said:
Honestly, KevinL's 35K LEDs on 2 alkaline cells is very decent and will give CRAZY long runtime. The MJLEDs, esp on Lithiums, will be brighter of course, but pull more current so will have less runtime.

THe Nichia CS LEDs are capable of being brighter than the 35K LEDs, but if both are driven directly on 2 AA cells, the 35Ks certainly look a bit brighter to me. The Peak Sno29 LEDs are another option and generally are whiter, but again, the 35Ks look brighter to me than the Snows or CSs if all three are direct driven on 2 alkaline cells.

Another nice thing about direct drive is that while there will be some dimming, the runtime is absolutely UNBELIEVABLE! I can't even guess how long without my current measurements in front of me, but it will be a VERY LONG TIME! Much longer than if it had a voltage boost.

Wow thanks for the post! those MJLEDS look great what about those 35k leds? I'll search CPF to see where I can get them
this info is greatly appreciated
any ideas on the regulator???
thanks!
 
Top