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Posted: 7/23/2010 1:15:27 PM EDT
I am building a little electronics experiment. I am using a 3.7v dc power source and have an led and 480ohm resistor. How much voltage do I lose with the resistor?
Link Posted: 7/23/2010 1:17:31 PM EDT



Originally Posted By Toemoss:


I am building a little electronics experiment. I am using a 3.7v dc power source and have an led and 480ohm resistor. How much voltage do I lose with the resistor?






 
lose in compared to what, it not being there?  V=IR.
Link Posted: 7/23/2010 1:17:44 PM EDT
[Last Edit: 7/23/2010 1:18:29 PM EDT by AR4U]
It depends on the current through the LED.  





It's a tough question because diodes have exponential I/V curves, and even two LEDs from the same box will usually behave differently.



ETA:  what exactly are you trying to do?

Link Posted: 7/23/2010 1:19:13 PM EDT
Depends on teh voltage drop on the LED.  Usually diodes are approximated to 0.7 volts.  So in your situation....3V approx.
Link Posted: 7/23/2010 1:23:16 PM EDT
[Last Edit: 7/23/2010 1:26:42 PM EDT by Toemoss]
Scroll down to the 3rd post. I am doing this
Nicostick

But adding this to it:
LED and resistor

My goal is to stay as close to the 3.7 volts as possible. I am not so sure the LED needs the resistor at that voltage because there are others built up to 7 volts.

ETA fixing links
Link Posted: 7/23/2010 1:23:17 PM EDT
3 volts
You drop .7 volts across the led, unless they are in parallel.  

Not Ohms, Kirchoff.
Link Posted: 7/23/2010 1:26:03 PM EDT
[Last Edit: 7/23/2010 1:26:31 PM EDT by VRMN8R]




Originally Posted By 338winmag:

3 volts

You drop .7 volts across the led, unless they are in parallel.



Not Ohms, Kirchoff.


First link no worky.



http://www.e-cigarette-forum.com/forum/battery-mods/18409-how-build-nicostick.html



ETA: You just fixed it.
Link Posted: 7/23/2010 1:26:48 PM EDT
fixed
Link Posted: 7/23/2010 1:36:45 PM EDT
[Last Edit: 7/23/2010 1:39:32 PM EDT by xwarp]
is this a "build your own e-cig"?



i'm guessing that the resistor is wired in series with the led, in which case, is limiting the current flow through the led so you don't short it out.



keeping the resistor in is not going to affect the atomizer from working properly.




 
Link Posted: 7/23/2010 1:58:25 PM EDT
Thats kinda what I was looking for. Most 3.7volt e-cig mods don't seem to have an led in them so I was thinking it was taking up too much power.
Link Posted: 7/23/2010 2:08:52 PM EDT



Originally Posted By Toemoss:


Thats kinda what I was looking for. Most 3.7volt e-cig mods don't seem to have an led in them so I was thinking it was taking up too much power.


Extra 5-10mA draw on the battery, not much compared to other components, but it does add up.



V = Vsupply - Vled  (Voltage drop on white LEDs is around 3V, 2.7 for blue, and from 1.7-2.5 for other colors)

I = V / R   R = 380 Ohms, which limits the current, as the LED is a short circuit once lit.



 
Link Posted: 7/23/2010 2:56:57 PM EDT
forgot to add that led's typically require 1.5 to 3 volts to forward bias. white/blue led's 3-4, some lower.



most led's run about 20-40 ma current.



in that mod, dude is using a 900mah battery, meaning that battery theoretically can delivery 9/10ths of an amp in one hour time.



so, 2 to 4/100ths of an amp for the short duration that the led will be on when you take that puff, is pretty much null in that case.
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