Xiaomi 3 USB Power Strip

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Official specifications
I bought this from Banggood

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The charger/power strip was in a long box.

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It contained the charger/power strip and a instruction page in probably Chinese and Chinese 3 pin plug.

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The mains socket can mate with EU / US 2 pin plugs.

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Measurements


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The output voltage drops slightly when loaded and then stays fairly stable. There is overload protection at 3.3A.

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Same on this socket.

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Running all 3 socket in parallel shows that the overload protection is common for all 3 socket, i.e. the total current is 3.3A before the protection kicks in. This means you have to be careful with what devices are connected to the usb power too stay below 3.3A.

Xiaomi%203%20USB%20Power%20Strip%20load%20test

One hour with 3.1A load is not a problem.
The temperature photos below are taken between 30 minutes and 60 minutes into the 1 hour test.

Temp2140

HS1: 67,6C
HS1 must be the mains transformer.

Temp2141

M1: 48,2C, M2: 38,8C, M3: 38,0C, HS1: 56,6C
Here HS1 looks to be the mains switch transistor.

Temp2142

M1: 57,8C, M2: 45,1C, HS1: 63,3C
M1 is the rectifier IC.

Temp2143

M1: 49,1C, HS1: 49,9C

Temp2144

M1: 48,0C, M2: 49,7C, HS1: 71,8C
HS1 is the mains transformer.

10ohm

At 0.5A the noise is 12mV rms and 280mVpp, this is fairly low.

5ohm

At 1A the noise is 13mV rms and 207mVpp

1.6ohm

At 3.1A the noise is 25mV rms and 390mVpp, even at full load the noise is acceptable.



A short look at the power strip

The specifications says it has overload protection, is that correct?

Overload40A

The answer is yes, with 40A current it trips in about 1 seconds.

Overload20A

With 20A it is about 10 seconds.

Overload13A

And at 13A it is about 4 minutes. These trips times looks very resonable.

All test was done with a low DC voltage.



Tear down

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Beneath the feets was four screws, but that was not enough to open it. Around the edge was a lot of locks that had to be opened.

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On this side there is a input fuse, a common mode coil, a inductor and the mains switch transistor on the mains side. There is a safety capacitor between mains and low volt side, but nothing of interest on the low volt side.

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On this side we have the mains rectifier bridge (BD1) and the mains switcher controller (U1). On the low volt side there is two chips to handle the automatic coding of usb (U3 & U4), but there is no rectifier diode. Instead there is a synchronous rectifier chip (U2).

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On this side is the fuse (Brown block) and the safety capacity (Blue).

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The common mode coil and the transformer are mounted at the ends.

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The mains switch transistor and the inductor can be seen here.

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The black box is the switch with the automatic fuse. All connections inside and the sockets are done with unisolated metal.

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There is done a lot for safety in this power strip/usb power supply. The first part is the cutout and plastic shield in the circuit board, that handles nearly all creepage distances, including a good safety margin.

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At the end of the cutout, there is also enough distance.

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On the other side there is the distance from the mains switch transistor to the usb connector, it must be 4mm and is just about that. Note: The plastic shield is also present in the top part of the power strip and will keep the transistor away from the usb connector.



Testing the mains input with 2500 volt and 5000 volt between mains and low volt side, did not show any safety problems.



Conclusion

Just about everything looks fairly good on this power strip, but I have a few complains:
3A is not much current to share between 3 usb sockets, especially not when they all will report 2.1A capacity.
I would have liked if it could handle earthed connections for EU plugs, but that would probably spoil the versatility for other plugs.

If you can live with the limited usb power and the accepted mains plugs I believe it is a good power strip/usb charger, but it will probably be a good idea to replace the mains plug with one for your area.



Notes

Index of all tested USB power supplies/chargers
Read more about how I test USB power supplies/charger