USB battery box 4x18650

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This usb box is from ebay and without a name (Look at photos of front panel and electronic to reconize it).
Specifications:



How does it look

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No fancy packing for this unit.

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Every control and connector is place in one end of the box.

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The placement is not strictly logical, I would have prefered the charging led, next to the charging connector and load indicator next to the output connectors.
To charge this box a charger/cable with a DC connector is needed (none is supplied).

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Two screws must be removed to open the box.

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Up to four 18659 batteries can be mounted in the box, it will work with both button top and flat top batteries, but not longer than 67.8 mm. This is fine for unprotected batteries.

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When replacing the batteries the "reconnect" button must be pressed or a charger connected.

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Looking at the PCB, there is a few interesting details.

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The bottom side is just connections, no components.

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Measurements


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The sweep shows that the box can supply up to 2.8A, before turning off.

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Running a test with 2.5A load does work, but only for 40 minutes.

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Reducing the load to 2.0A works much better, here the output is stable for 2.5 hours and the box has a efficiency between 70% and 90%.

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Going down to 1.7A increases the output time to 3.7 hours and the box has a efficiency above 80% most of the time.

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At 0.5A load the efficiency is well above 90% and it can run for 15 hour.
The box will discharge to about 2.9 volt, this puts some restrictions on what LiIon batteries can be used, but works very well with 2900/3100/3400mAh batteries.

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A single 3400mAh battery.

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A single 3100mAh battery.

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A single 2600mAh battery.

2ohm

There is some noise in the output at 2.5 A (About 57mV rms).

10ohm

Reducing the load to 0.5A will eliminate most of the noise (About 14mV rms).

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Charging 4 3100mAh batteries takes 20 hours. The charge chip is low on cooling and cannot deliver full charge current.

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Due to the higher voltage of the 2600mAh battery the charge current is higher and it is charged faster.



Conclusion

This box is very good up to about 2A, with low noise in the output, but I am not happy with the charge connector and I have no use for the round output connector.
The long charge time due to the "low" charge current means that it can be used with weaker power supplies, but a more constant 900mA charge current would have been faster and also work with smaller supplies.
With the impressive low idle current, there is no problem with forgetting to turn the box off.


Notes

Read more about how I test USB power supplies and chargers