# Calculating resistance of a flashlight switch

Discussion in 'Homework Help' started by sinner, Jun 12, 2014.

1. ### sinner Thread Starter New Member

Jun 12, 2014
2
0
Howdy,

I need to know how I can calculate the resistance of a flashlight switch.

Here is what I am reading.

According to my calculations it is 5.7mOhms but I think it is a bit too low and I am pretty sure my calculations are way off.

Any help would be appreciated.

Sep 17, 2013
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3. ### gerty AAC Fanatic!

Aug 30, 2007
1,182
319
Are you sure about the current? 2.8a seems a little high for a flashlight, battery life would be very short.

4. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,976
617
You connected voltmeter in parallel with the switch. You know the voltage across the switch, V=16.2 mV.

Now connect the ammeter in series with the switch. That will give you current through the switch, I=?.

When you have voltage across and current through, you can now use Ohm's Law: V=IR. V is known, I is known. Solve for R.

5. ### sinner Thread Starter New Member

Jun 12, 2014
2
0
Thank You guys for the replies, appreciate it.

Yes the LED is a 10W Gen.2 XML2 , there are people running it as high as 7-8amps in direct drive mode, the batteries are high drain Panasonic NCR18650PD 2900mAh (10A max discharge)

Secondly the circuit is a CC LDO AMC7135 based with 8x parallel chips (350ma each) that gives a constant output up untill the battery voltage drops below 3.8V

My multimeter unfortunately isnt the most ideal one to measure the current accross as it has some resistance of its own and measures about 0.8Ohms without any resistance attached in 200Ohms mode, I hope i am making sense.