Calculating battery discharge time

[dnglos]

According to my Ohm's Law calculator, running a 2.0 ohm coil at 4.0 volts produces 8 watts of power with a current of 2000 milliamps.

To calculate how long a fully charged battery would take to fully discharge I figured you'd use the formula mAh/mA, but for 900mAh that gives 900/2000 = 0.45 hours - which is clearly not right.

What am I doing wrong? Anyone?

 

[zapped]

move your decimal place over... 4.5 hours sounds about right. I get 8-10 hours off a 2000mAH 18650 running 3 ohms at 5.2 volts.

 

[Rader2146]

It means if you were to hold the button down without letting up, it would take .45 hours for your battery to be completely drained.

Since we only hold the button down a couple seconds at a time, it all depends on your vaping pace. A chain vaper might drain a battery in 3 hours where a light vaper might take 8 hours.

There are more variables too, like usable capacity vs rated capacity, but that is really getting down to the brass tacks.

 

[Switched]

0.45hrs = 1620 secs. An average toot 5 secs = 324 puffs Rule of thumb 1-1.5hr per 100mAh. YMMV

 

[proteckt3d]

Cool, I just confirmed my hunch that a charge will hold more on a battery when you draw less amps or current. Just wanted to highlight this, maybe there are many of us who presume that less volts will give you more vape time.

 

[Switched]

^^what he said^^

 

[WillyB]

This may help put things into perspective.

Even at a rather paltry .8A drain we see that the 900mAh cell is only 592mAh and at a constant drain it lasted 44min.

All mAh ratings have to taken with a grain of salt, Panasonic with it's Li-Ions uses a 2.5V cut-off, not appropriate for our use. With their gray high drain they use a measly 430mA drain to establish the 2250mAh rating.

 

[dnglos]

Thanks to everyone for taking the time to respond. I'm starting to think the '1 hour per 100 mAh' rule is a bit of a myth - unless you're a very light vaper. I don't consider myself a particularly heavy vaper (I get through about 30ml of juice per week), but for me a single 18350 battery lasts a couple of hours at best before it needs recharching.