Is this statement true!?

lordraiden · Feb 5, 2015

Ran into this statement while researching, of all things, battery chargers. Does anyone know if this is true? It seems a little too simple to be right. Well, to me at least.

A battery's capacity in mAh is 10x a flashlight's run time in minutes.

The Math:
The bulb in a P700 or P703 flashlight draws 600mA, and there are 60 minutes per hour, so a battery's capacity in mAH is (run time in minutes)/(60 minutes per hour)*(600mA draw rate), which can be reduced to (runtime in minutes) * 10. A fully charged P103 running at full capacity should keep a flashlight lit for 1300mAH/(600mA)*(60 min/hr) = 130 minutes. If the flashlight stays lit for only 90 min, then the battery's capacity is (90 min)/(60 min/hr)*(600mA) = 900mAH.

Bear in mind that the bulb doesn't draw EXACTLY 600mA , but I bet the actual number is within 30mA. So this method should give a measurement of battery capacity to within 5%, which I'd say is pretty darned good.

yellow · Feb 5, 2015

in case of 600 mA draw, that is - just by accident - true.

Try it with 1000 mA draw
or with 500

better use the full (the non "reduced") one ...
(= current draw * runtime / 60)

AnAppleSnail · Feb 5, 2015

Runtime is just about equal to battery capacity divided by current draw.

3000 mAh / 1000 mA = 3 hours.

lordraiden · Feb 5, 2015

Ah, okay. Wasn't sure about that as I could quickly see this running into Peukert's law and being nullified, and based on what I'm reading it does to some degree.

openbolt1 · Feb 9, 2015

I always tried to simplify the formula in my head by using this example:

Light draws 1 amp (lets say).

Battery capacity is 1000mAh (let's say).

Answer: you have roughly one hour of use from that combo.

It's worked for me but I'm a simply man...

Sent from my iPad using Candlepowerforums

fivemega · Feb 9, 2015

openbolt1 said:
Light draws 1 amp (lets say).
Battery capacity is 1000mAh (let's say).
Answer: you have roughly one hour of use from that combo.

That is true for lower current draw but when current draw goes higher and higher, then some of battery energy wasted in form of heat.
Assuming all current draw of following examples are acceptable by battery manufacturer.
Example 1:
Light draws 2 amps (lets say).
Battery capacity is 1000mAh (let's say).
Answer: you have roughly 1/3 an hour (20 minutes) of use from that combo.

Example 2:
Light draws 4 amps (lets say).
Battery capacity is 1000mAh (let's say).
Answer: you have roughly 1/8 an hour (7.5 minutes) of use from that combo.

Is this statement true!?

lordraiden

Newly Enlightened

yellow

Flashlight Enthusiast

AnAppleSnail

Flashlight Enthusiast

lordraiden

Newly Enlightened

openbolt1

Enlightened

fivemega

Flashlight Enthusiast

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