Part 1： PN-910 testing
Part 2： 20000mAh powerbank testing
Part 3： Lithium-ion / polymer Li-Po （not 18650 type）
Part 4: Xiaomi Powerbank tested
Part 1: PN-910 testing
I had carried out a test, this powerbank had discharged for 7 hours 20 minutes（4.925V, 0.945A)
i use two 10ohm resistor in parallel , resulting total resistance of 5 ohm, resistance is enough low to get the output of 4.925V，0.945A.
two 10ohm resistor in parallel
display show a little of fluctuation，between 4.92-4.93V, 0.94-0.95A. on average, it is 4.925V，0.945A.
Inside the case contain four 18650 type battery, each one contain 2800mAh of capacity.
measurement taken by vernier calipers, diameter is around 19mm.
The powerbank in the current market are measured by mAh, of course the higher the better.
But, mAh cant reflect the real capacity of a powerbank, why?
Because most of the powerbank is using lithium ion battery, voltage is 3.7V, after fully charge is 4.2V.
When you are using it to charge other devices, its output voltage is at 5V. (USB device must be 5V)
This mean that the 3.7V should be converted into 5V before it can charge or operate other usb devices.
An example, for 11200mAh powerbank,
3.7V x 11200mAh = 41.44Wh = 5V 8288mAh
So we are more concern on 5V output, that is 8288mAh
The conversion is not 100%, there will be some losses about 10% or more.
just take 10% as losses, so we have 8288 x 90% = 7459.2mAh @ 5V
if your handphone battery is 1800mAh capacity, it mean that it can charge your handphone for about 4 times.
what i tested here, i am measuring using power and not mAh, which is accurate.
As you know, VXI= Power
Under 5ohm load, 4.93VX0.94A=4.6342Wh
Because of the measuring time is quite long, i take measurement on every half hour.
Total discharging time is 7 hours 20 minutes.
From calculation, i can get a total power dissipation of 34.13Wh,
the rated power is 41.44Wh ( 3.7V x 11200mAh)
34.13/41.44x100%= 82.36% is the real capacity
This is one kind of fake powerbank.
(shared on facebook, just for comparison)
Just avoid this type of powerbank, even inside is not filled with sand, its capacity is very much lower than the rated capacity.
My tested powerbank has 11200mAh capacity, HxWxL: 21.5mmx71mmx110mm
Each 18650 is around 18mm in diameter
length of 110mm can fit a capacity of 11200mAh, what is the length of powerbank to fit 20000mAh or 30000mAh? you can do the calculation.
Beware, there exists of fake powerbank which is same as what i tested. The one i tested is 100% original.
This post has been edited by x-treme: Jun 4 2014, 09:18 PM
What is the powerbank?, Updated with Xiaomi Powerbank