Estimating (predicting) runtimes...

[beav]

I posted this at the flashlight electronics forum and got no action... So I'll try here!

I'm not too savvy in all things electrical... Have a quick question.

Is there a relatively accurate way to estimate runtime of a battery powered LED light?

I presume that I'll need to know the starting voltage, estimated current draw, and maH of the battery? Also the estimated efficiency of the circuit. Anything else I'll need?

Any help with formulas and theory is appreciated.

 

[nerdgineer]

I think there are too many variables for technically precise, broad base predictions. Best I know of (others more in the know please enlighten me..) are a bunch of rules of thumb which each apply to some type of light/battery running in some operational regime. But nothing general.

Rules of thumb are like, if you can measure the current draw and are using nimhs in a resistored direct drive LED light, calculate the time the nimh rating should supply that current level, and reduce by 30% to estimate how long the light will stay bright. If it's calculated to run real long (low current drain) you can reduce the 30% fudge factor.

Boosted/regulated LED lights vary all over the place because of the efficiency of the electronics. Higher currents reduce battery capacity, higher boost (like 1.2 V to 3.7+ V)reduce regulator efficiency, lower cost also tends to reduce regulator efficiency.

But a fun topic. Maybe we should have a place for all our collected rules of thumb.