How to calculate how many amps a given flashlight draws.

LED Flashlights – General Info
1

Sorry for the dumb question but how do I do that? I heard the Q8 for example will draw just over 4 amps per cell on turbo if 4 cells are used, but how does one actually calculate that? I want to know a formula so that I can figure it out for any flashlight I am interested in.

2

It might vary from meter to meter but heres the gist of it…
>Make sure your flashlight and meter have good batteries.
>Use GOOD meter lead probes
>Set meter to read DC amperes
>Configure the positive lead to the 10A port
>Touch black probe to the flashlight body contact
>Touch the red probe to the -Batt

The light will turn on and the meter will display the amperes passing through.

Side note… on my Fluke 179 I can use this configuration (set the knob to read AC Hz) measure the PWM frequency like a square AC wave.

3

Thanks Kramer. Any chance that method could cause problems for the battery in any way?

I just tried it on my cheap tac light for starters and DMM displayed 0.55. By doing your method, does it always go to max amps?

Edit: I posted too soon as I see every time I run the test, the mode changes each time.

4

Sure…
I have never damaged anything from doing this. Essentially the meter replaces the tailcap in the circuit. Just make sure you re-configure your meter back for measuring DC battery voltage… you’ll fry the meter if not properly fused, or at the very least pop its fuse.

5

I have a cheap meter. 10 amps is the max it will show I think as the labels on the side display 10A and then drop down to milli amp

6

Yeah it might automatically set its range depending on what it reads.

7

there are also those clamp meters used by others. I have no experience with those.

8

Better use a clamp meter to measure high currents.

9

Does one just clamp the clamp meter around the whole body of the Q8 and then turn on the Q8 to max to get an amp reading then?

10

My old article about measuring on a flashlight (and a bit more) may be useful: Measurement on Flashlight

11

Just what I was trying to search for, thank you HKJ.

12

Good point… FWIW my brightest lights only draw about 5~7 amps.

13

HKJ to the rescue