iPad & DieHard

[ptonsparky]

I have a small battery pack that is charged via wall wart. The pack itself is designed to jump start vehicles with dead batteries.

My iPad was low on charge and, (left out unnecessary details), I used the packs tablet port to charge it. This morning the tablets charged but the pack is down to 15%.

I'm struggling with how the iPad can draw enough power to drain something that can start my car.

 

[wwhitney]

The only conclusion I can come to is that the low end capacity range of jump pack batteries overlaps the high end capacity range of portable electronics at about 30 Wh (using a half order if magnitude scale 10, 30, 100, etc.)

So what's impressive is that the jump pack battery, which may only have 30-100 Wh of energy, has been engineered to put out 300-1000A. I.e if C is discharge rate that depletes the battery in 1 hr, it's putting out on the order of 100C. Which would nominally deplete the battery from full in 36 seconds; but then again it doesn't usually take 36 seconds to start a car.

Cheers, Wayne

 

[jaggedben]

I'm struggling with how the iPad can draw enough power to drain something that can start my car.

It never drew enough power to start your car. But it drew much more energy than that.

The time factor in energy consumption can really stretch our intuitions. When the National Ingition Facility did a nuclear fusion test earlier this year the fusion reaction produced more power than the entire US grid. But because it was only for a nanosecond, the amount of energy was about the calories in a piece of toast.

 

[ruxton.stanislaw]

Think of it this way - in theory, you could deplete the battery of the iPad to charge a super capacitor and then use that to jump the car. It is a transfer of a certain amount of energy.

 

[LarryFine]

The difference is time.

 

[drcampbell]

... I'm struggling with how the iPad can draw enough power to drain something that can start my car.

Go back to your freshman physics book, review energy & power, (and the difference between the two) and Do the Math.

 

[ptonsparky]

No Physics book, but a search did the trick.