USB battery box EPCTEK 20000mAh
The box has a unknown number of batteries and two usb outputs.
The specifications are:
- LED Indication tell you how much power left
- Stylish Design with trim colour option
- Fully UK Compliant ROHS and CE Certified
- 2 USB Charging ports 2.1Amp and 1.0Amp
- Capacity 20000mAh
- Charge input: 5V 1A (Max).
- Includes USB cable for charging the powerbank
I bought the box from Ebay seller: eoutlet_uk
How does it look
The power bank is delivered in a white cardboard box without any markings.
It contains the power bank, a usb cable and a manual.
The two output connectors are placed on one side.
And the usb mini input connector on the other side.
On top of the power bank is a switch and a stipe with 4 leds. The leds show charge status.
The bottom has some labeling about capacity and current.
I do not know if the box contains 18650 cells or a Lithium polymer pack, but the above picture gives an idea about size and how many 18650 could be fitted.
Measurements
I could not open the box, i.e. there is no measurements directly from the battery, only from the input and output connectors.
- The leds are on when the output is on.
- The box has a overload protection, it will turn off the output and flash the leds.
- The two channels can deliver the same current, because they are in parallel.
- Both outputs are coded as USB charger DCP
- When charging the leds shows charge state.
- A short press on the button will turn on output and show the charge state.
- Output turns off after 20 seconds with load below 11mA.
- Output turns off when input power is connected.
The first test is a load sweep to get an idea about the performance. The two outputs looks identical and can both deliver 1.8A not the rated 2.1A.
The output looks very fine at 0.5A with about 9000mAh capacity, this is way to low for a 20000mAh box.
Note: Specifications always list battery capacity, output capacity will about 60% compared to that, due to the voltage difference between battery (3.7 volt) and output.
The output also look fine at 1.6A
But when look at the output with an oscillioscope, it does not look that fine. It has 120mV rms noise and 650mVpp noise at 1.6A.
At 0.5A the noise is down to 52mV rms and 221mVpp.
The specifications says the box need 1A when charging, as can be seen on the curve it can use up to 2.5A and the battery capacity looks to be about 15000mAh
It takes about 11 hours to fully charge the power bank with a usb power supply that can deliver 2.5A.
Adding some series resistance, equivalent to a long cable or a weak charger reduce the charge rate significantly and increases the charge time to 19 hours.
Conclusion
This box has a couple of smaller problems:
It cannot deliver the rated current.
Charging draws lots of current at the start, but reduces charge rate later on.
It has signigicantly less capacity than specified.
It has lot of noise/ripple in the output at higher loads.
Both outputs is coded as DCP (Why is the 2A not coded as Apple 2.1A).
None of these problems prevents the box from being used, but the total makes it considerable less than a ideal power bank.
Notes
Read more about how I test USB power supplies and chargers
