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I got a Jemma 20,000mah battery pack from Amazon the other day and I have been doing some testing on it. In a Youtube video they explained charging inefficiencies and how the actually available mah is less than the rated mah. And this was the formula they used for a 20,000mah battery bank.
20ah * 3.7volts (assuming it's a 3.7v lithium battery) = 74 watt hours available
74 watts / 5volt output = 14.8amp hours available on the output
Assuming the charging circuits are 80% efficient, then: 14.8 * 0.8 = 11.84 amp hours available for actual use
So using 2 different USB doctors here are my results for charging and discharging the powerbank:
USB doctor brand Discharge mah Charge mah
Drok 8835 13361
Drok 8768 8768 (oddball result)
USB Safety Tester 8723 14710
As you can see for charging I get a bit more mah out of the powerbank, but for discharging I get quite a bit less than expected (8800 mah). Why the big difference between charging and discharging? Is it because the discharge circuit is booster 3.7vdc to 5vdc for the USB port? Or is it something else?
Thank you. I'm trying to learn something new here.
20ah * 3.7volts (assuming it's a 3.7v lithium battery) = 74 watt hours available
74 watts / 5volt output = 14.8amp hours available on the output
Assuming the charging circuits are 80% efficient, then: 14.8 * 0.8 = 11.84 amp hours available for actual use
So using 2 different USB doctors here are my results for charging and discharging the powerbank:
USB doctor brand Discharge mah Charge mah
Drok 8835 13361
Drok 8768 8768 (oddball result)
USB Safety Tester 8723 14710
As you can see for charging I get a bit more mah out of the powerbank, but for discharging I get quite a bit less than expected (8800 mah). Why the big difference between charging and discharging? Is it because the discharge circuit is booster 3.7vdc to 5vdc for the USB port? Or is it something else?
Thank you. I'm trying to learn something new here.
