Powerbank Charging Efficiency Estimation Test

kosPap

Flashlight Enthusiast
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Mar 1, 2007
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Naoussa Greece
hi all!
I would like to help me verify my efficiency estimation of powerbank charging one's phone.

I made a series of tests using my phone, several powerbanks, and two USB meters.
By and large charging efficiency I foudn it to be 50%!

Data:


  • Xiaomi 4X phone with Li-Po 4100mAh 3.85/4.4V battery
  • KCX-017 and OLED USB meters
  • Replaceable 18650 batteries Powerbanks
  • NCR18650A & B batteries with capacity measured with the Opus charger
  • I assumed a steady 5V USB voltage across the meter, and 3.6V 18650 battery and 3.85V Xiaomi battery voltages for Wattage calculations

Results

PowerbankEvaluation.png


What do you think?
 

parametrek

Enlightened
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Apr 3, 2013
Messages
578
Assuming constant voltages for the batteries will probably throw off the efficiency calculations. Logging the voltages takes a bit of effort. The 18650 is kind of easy since the powerbank is modular. All it needs is a meter that can send data back to a computer. The phone of course can't be opened as easily but there are plenty of battery level loggers. FDroid has 3 I think.
 

kosPap

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Mar 1, 2007
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Naoussa Greece
I can somehow get your point on the variable cell voltage. It requires a different kind of measurement.

on the other hand we have the watts passed through the USB meter as given.
So a NCR1650A starts fl with an energy of 10+ watts (10.415 @ 1A discharge per HKJ measurements)
and then we have only 7.7 watts passing through the meter (stable voltage and an accurate meter per HKJ).
So how can such an efficiency estimation can be wrong?

At the moment I am running another test.
I am discharging a 2x18650 in parralel powerbank.
After this one battery will be charged in the same powerbank and the other in the Opus charger.
 

Lynx_Arc

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Oct 1, 2004
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Tulsa,OK
If you are measuring how much power the phone registers charging its battery from a power bank then it isn't truly total efficiency of the power bank output but also the loss in power of the phone charging system also.
I've told people who buy power banks to charge phones that they are about 50% efficient due to both batteries are 3.6-4.2v in use and require 5v to transfer power thus requiring both a voltage booster and voltage buck circuit.
 
Last edited:

kosPap

Flashlight Enthusiast
Joined
Mar 1, 2007
Messages
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Location
Naoussa Greece
If you are measuring how much power the phone registers charging its battery from a power bank then it isn't truly total efficiency of the power bank output but also the loss in power of the phone charging system also.
indeed....but I am kinda disappointed that each voltage conversion consumes about 20-25%. I expected efficiency to be better.

power banks to charge phones that they are about 50% efficient
And my tests seem to fall right into that range.

Next tests will be with 4 bare AA NiMhs. And see if there are any efficiency gains in "field" use.
 
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