how is battery life calculated?

[ixfd64]

Does anyone know how to calculate how long will a set of batteries last?

At first, it seemed that this was done by simply dividing the mAh rating by the current draw. However, something doesn't quite add up. For example, the current draw of Wicked's green pen-style lasers is 600 mA, so a set of two batteries should last over three hours, assuming that each battery has a capacity of 1,000 mAh. However, Wicked lists the battery life as 90 minutes.

Am I missing something?

 

[Jimmymcjimthejim]

Yes, as you have read in other threads and whatnot, most drivers (including the one in your laser) aren't 100% efficient. So all that power going into the laser, only some of it goes into the diode. I believe that readings from the multimeter show the current going into the diode, not the total current used.

 

[Things]

Batteries arent always up to spec, in fact, they rarely are!

 

[Helioplasma]

Battery mAh divided by the draining current in mA = possible turned "on" in hours
i.e WL executives : power consumption : 600mA ; average AAAs : 900mAh ; battaery lifetime = 900/600 = 1.5 = 1h30.
of course batts will never ever last 90 minutes in a green laser pointer so maybe I've been tricked by WL.

 

[Jimmymcjimthejim]

Does anyone know how to calculate how long will a set of batteries last?

At first, it seemed that this was done by simply dividing the mAh rating by the current draw. However, something doesn't quite add up. For example, the current draw of Wicked's green pen-style lasers is 600 mA, so a set of two batteries should last over three hours, assuming that each battery has a capacity of 1,000 mAh. However, Wicked lists the battery life as 90 minutes.

Am I missing something?

Oh and I missed something that I caught in Helioplasma's post.. The batteries are connected in series, which adds the voltage rather than the current. So if you have two 1000mAh batteries in series, then the batteries together have a capacity of 1000mAh, but with 3v instead of 1.5v.

 

[styropyro]

Yes, as you have read in other threads and whatnot, most drivers (including the one in your laser) aren't 100% efficient. So all that power going into the laser, only some of it goes into the diode. I believe that readings from the multimeter show the current going into the diode, not the total current used.

Efficiency of the laser has nothing to do with the current drawn, when you measure the total current draw of the laser by putting the multimeter leads in the tail cap and battery you get the total current being drawn, not just the current going into the laser diode. So if your laser draws 600mA and you have 900mAh batteries in series, the battery life of the laser will be 1.5 hours pretending the batteries don't sag under the high current draw. Of course that never happens so the battery life where the laser is actually useful and not dim/mode hopping is usually a lot lower.

 

[Jimmymcjimthejim]

[quote author=Jimmymcjimthejim link=1215581533/0#1 date=1215581837]Yes, as you have read in other threads and whatnot, most drivers (including the one in your laser) aren't 100% efficient. So all that power going into the laser, only some of it goes into the diode. I believe that readings from the multimeter show the current going into the diode, not the total current used.

Efficiency of the laser has nothing to do with the current drawn, when you measure the total current draw of the laser by putting the multimeter leads in the tail cap and battery you get the total current being drawn, not just the current going into the laser diode. So if your laser draws 600mA and you have 900mAh batteries in series, the battery life of the laser will be 1.5 hours pretending the batteries don't sag under the high current draw. Of course that never happens so the battery life where the laser is actually useful and not dim/mode hopping is usually a lot lower.[/quote]

Oh, thanks for correcting me