# Voltage drop over a resistor?

#### NoFair

##### Flashlight Enthusiast
Anybody have an estimate of voltage drop over a 60 ohm resistor in series with led drop in using 2 cr123s?

I'm looking at the feasibility of using my C2 with 60 ohm 2-stage tailcap from the sandwich shoppe with 2 cr123s and a 3.7V LumensFactory led drop in. This would be emergency only and the light would normally be run using a 17670.

Discussed it briefly with Mark at LF, who said not to try it

Sverre

I think:

V= 2*3 - 3.7 = 2.3V

I = V / R = 2.3 / 60 = 0.03833A

What you need to know is the specs of the drop-in at lower currents. My estimate is that the current will be anything between 40 and 70mA. If anybody has that answer, you have your answer.

Mark at LumensFactory says not to try it, but I want to know a bit more since I have spare cr123s for emergencies both at work and at home..

Normally I'll run it on a 17670.

I'd think the voltage should drop and the current be severely limited.. Been awhile since my electronics courses in high school

Sverre

LED-Pro says 45 mA at 3.3V from 6V.
What you need to know is the specs of the drop-in at lower currents. My estimate is that the current will be anything between 40 and 70mA. If anybody has that answer, you have your answer.

LED-Pro says 45 mA at 3.3V from 6V.

Thank you :twothumbs

Will test a bit before I try (hopefully not fry:green

Sverre

Thank you :twothumbs

Will test a bit before I try (hopefully not fry:green

Sverre

You are usually safe with an inline resistor, especially as high as 60 ohm. Just remember that 45% of the power will be lost over the resistor. Keeping in mind other inefficiencies of the driver and you should be running less than 50% effective.

You are usually safe with an inline resistor, especially as high as 60 ohm. Just remember that 45% of the power will be lost over the resistor. Keeping in mind other inefficiencies of the driver and you should be running less than 50% effective.

This is for emergencies only.

It will normally run unresistored on a 3.7V 17670.

Sverre