LED help please

[funkybozu]

hey guys. im perplexed about hooking up an LED to a battery mod.
im using the body of a flash light as minus and have the positive broken with a
swicth(between the batt and the atty conector). it works perfectly like this, no shorts ,good voltage going to the atty connector.
what i dont understand is when i hooked up a LED, the earth going to the body ans the positive going to the Atty side of the swicth.
it lights up as supposed to when i push the swicth , but when i check for current if i touch both sides of the swicth connectors (swicth off)i get a 1.9V??????
when i remove the LED i dont get it anymore

 

[kinabaloo]

You are completing the circuit with your meter. The 1.9v is the forward voltage of the LED.

The mod vapes correctly with the LED in place?

If not, you probably need a 100 ohm resistor in series with the LED.

 

[breakfastchef]

Think of the circuit as two loops. The outer loop provides power to the atomizer; the inner loop provides power to the LED. The LED is protected by as resistor to prevent it from burning out prematurely. See the below diagram I drew to help you visualize the two circuit paths.

secondson2929 (creator of Zi Moshi mods) recently posted about his choice for resistors depending upon the voltage of your device and the type of LED you are using. Maybe this will also be helpful to you.

Standard 3.6 volts (4.2v)
Green, blue, UV, white, Rainbow, Pink, Purple (3.2) = 60 ohm
Yellow, red, orange (2.0) = 120 ohm

Magnum 6 volts (7.2v)
Green, blue, UV, white, Rainbow, Pink, Purple (3.2) = 220 ohm
Yellow, red, orange (2.0) = 270 ohm

 

[funkybozu]

thanks guys. yeah it works as its supposed to. push on light, normal no light
theres is no current from the minus of the LED and the positive of the push swicth till i turn it on. so it seems ok.
if you look at ther model above i get a 1.9V with connect the multimeter from the + of the batt side of the connector to the + of the LED
is that normal?

 

[breakfastchef]

I never took a voltage measurement as you describe, but I would expect the voltage to be significantly lower to the LED. This resistor is there to protect the LED from burning out from the high voltage of the power source.

 

[kinabaloo]

You are completing the circuit with your meter. The 1.9v is the forward voltage of the LED.

The value is fixed and determined by the LED. It's normal

 

[funkybozu]

great thanks guys. at least i know whats what now