Calculating charge potencial

[kristofk]

Hi,

 

I have an external batter that is 56Wh @ 18v and 3.1Ah.

A standard iPhone 6s battery is 1715mAh (6.9Wh) according to gsmarena.

 

Now according to my calculations this battery can charge up my iPhone

1. ~ 8x

56 ÷ 6.9 = 8.12

 

2. ~ 1.8x

converting battery Wh int mAh -> 56 × 1000 ÷ 18 = 3111.11

3111 ÷ 1715 = 1.8

I assume that the first calculation is correct because the battery isn't small. But how could I get so different results?

[Linus_torvalds]

That does not work that way. 8000 mah mobile external charger charged galaxy s6 (2550 mah) from 0% to 100% only 2 times.

[vorticalbox]

it's different. the 56Wh is calculated @ 18v where as the iphone Mah is calculated @ 5 volts.

[kristofk]

9 minutes ago, mate_mate91 said:

That does not work that way. 8000 mah mobile external charger charged galaxy s6 (2550 mah) from 0% to 100% only 2 times.

Well yeah because the internal resistance and the cable's resistance and than the phone's resistance are all factors that I'm not taking into account.

4 minutes ago, vorticalbox said:

it's different. the 56Wh is calculated @ 18v where as the iphone Mah is calculated @ 5 volts.

You are right!

So expanding on my 2nd calculation: 

 

iPhone battery voltage -> 

Wh = mAh × V / 1000

6.9 = 1715 × V / 1000

4.02 = V

V = ~4

 

external battery V ÷ iPhone V

18 ÷ 4 = 4.5

 

1.8 × 4.5 = 8.1

 

So now it all makes sense!

[Sors]

Also a lot of that energy is wasted in the charging process.

 

A 1000 mah battery can not charge a 1000 mah phone to 100%.  You could need 1200 mah to account for the energy that the charging circuits in both the battery and the phone use.

[kristofk]

2 minutes ago, Sors said:

Also a lot of that energy is wasted in the charging process.

 

A 1000 mah battery can not charge a 1000 mah phone to 100%.  You could need 1200 mah to account for the energy that the charging circuits in both the battery and the phone use.

Well yes because the of the resistance energy is wasted, the battery, cable and phone will heat up as a result, which creates more waste... but I don't have tools to measure resistance so I just leave it and imagine a perfect world. ??

[Bleedingyamato]

11 hours ago, InfinityCaptain said:

Well yes because the of the resistance energy is wasted, the battery, cable and phone will heat up as a result, which creates more waste... but I don't have tools to measure resistance so I just leave it and imagine a perfect world. ??

Safe bet is assume the battery will get about 75-80% of the mAh it's rated for.