How long will my battery last?

[ghh3rd]

I am building a mod with a 1600 mah battery that will run a .5 ohm coil.  I figure that I'll be using about 25 watts.  Is there a way to calculate about how long the battery will last before I need to recharge it?

Thanks,

Randy

[CraigHB]

Yes you can. Caclulate energy required then take it back to battery capacity. 

For example, if you vape with 25W and you take 3 second hits, that's 75 Joules per hit.  Watts are Joules per second so 25W for 3 seconds is 75 Joules. 

Battery capacity is measured in Amp-hours, but Watt-hours are simply Amp-hours times nominal battery voltage, in this case 1.6Ah times 3.7V for 5.92 Watt hours.  In terms of Joules that's 5.92 Joules per second for 3600 seconds which is 21,312 Joules.  Divide that by 75 Joules per hit and you get 284 hits on a charge.

That's about the best anyone can do since variables like how many hits you take in a time period and how long those hits determines length of time  That being the case it's not impossible to say how long a battery will last without specifying that data.

[ghh3rd]

Interesting - I've entered it to my "Calculations" Excel worksheet to play with.

Thanks!

[CraigHB]

Welcome.

You can do the same thing with current demand if you know the draw on the battery.

For example if you have a 5A demand on the battery and hits are 3 seconds that's 15 Coulombs per hit.  Amps are Coulombs per second so 5 Coulombs per second for 3 seconds is 15 Coulombs.

Battery capacity is Amps times hours so a 1.6Ah battery has 1.6A times 3600 seconds or 5760 Coulombs.  Divide that by 15 Coulombs per hit and you get 384 hits on a charge.