Since I’m on the way to USB-C all the things, I missed a portable electron pump, err power supply. Newer models soon reach the power levels of old power tools. 45 Watts should be enough, I thought. I chose a manufacturer that has a reputation to lose, in the hope that this would prevent me from getting a device that would set fire to my home. So I chose the Xiaomi Power Bank 3, model: PLM07ZM.

It arrived discharged and when I charged it on my 45 Watts power supply, I was stunned to see that the unit took 45 Watts steadily. On my thermal imaging camera, I saw could clearly see the connectors and the electronics of the power bank get warm. But you don’t need a thermal camera: It gets warm enough so that you can surely feel it.

When I tested the power bank more thoroughly, I found a lot of smaller issues and one thing that really disturbed me: The power bank gets incredible hot. Not outside, but inside. The plastic case seems to insulate it well. Maybe too well. I discovered this by chance when I drew the specified 45 Watts at 15 Volts via USB-C/USB-PD. The power bank turned off multiple times when I tried this at 20 Volts, see below. So I switched to 15 Volts and wanted to take a peek at which parts get warm. About five minutes later, at the right moment, when the power bank switched off, I had my thermal imaging camera ready and couldn’t believe what I saw: The USB-A ports were glowing at 96°C. I made the following pictures later and also incorporated my Pt100 thermometer that I stuck into the USB-A port, since a thermal imaging camera can be off quite a bit, depending on the material you point it at. Both temperatures match to a few degrees. To be clear: This won’t immediately set the device on fire, but I wonder if it won’t hamper longevity and how warm the Lithium cells will get. I seriously hope that they are not impacted by this massive internal heat buildup. Honestly, I’m concerned about this device.

Compared with this, the other findings are just unimportant details, I’d say:

• USB-PD: What’s a few Watts more between friends
  

  

  Via USB-PD at 20 Volts, the power bank happily supplies 53 Watts without triggering an over-power/over-current limit. Just to be clear: According to the specification, the power bank is limited to 40 Watts at 20 Volts! That’s strange, the over-current limit should kick in much sooner.
• USB-PD: Little juice until the end
  Just above, I wrote that the power bank would supply more power than specified. But this is only true when it is more than half full. If not, the continuous power you can draw drops to less than 35 Watts at 20 Volts. Err, this is now less than the specification. This is in addition to the overtemperature issue outlined above.
• Switch and voltage switching interrupt output
  The power bank has a switch. If pressed, LEDs light up and show the charge level. Also, all outputs are switched off for half a second and reenabled. This is weird if you’re charging your phone and it makes noises or turns its display on to tell you that a new charging cycle started. The same happens if you connect the first device to the power bank that supports a different voltage than 5 Volts. Why? I suspect that the ports share their power regulators, see below. Or it’s a clever way to detect if there is a loop between two ports, which would “self-charge” the power supply since it allows being charged while supplying current to its USB-A ports. Interrupting the power supply could enable detecting such a loop and not activate the output in this case. At least in effect, plugging two ports together doesn’t cause “self-charging”.
• Charge multiple devices: Yes, but not quickly
  If I connect a device to the USB-C port that supports USB-PD, the USB-A ports switch down to 5 Volts, regardless of which voltage you negotiate via USB-PD. So, yes, you may use all ports in parallel, but not with more than 5 Volts.
• Huawei P20: USB-A faster than USB-C?
  My Huawei P20 supports its proprietary charging standard (SCP, Gen. 1), USB-PD and others. Strangely, it charges neither with USB-PD nur SCP on the USB-C port. Instead, it charges really slowly. This is indicated by a single lightning symbol on the phone. If connected to USB-A, two lightning symbols appear, indicating a faster charging mode. I would have hoped for this with USB-C, too…
• Samsung Galaxy Tab S2: Not the best
  The power bank also charges my Galaxy Tab S2 more slowly than my old Anker PowerCore 20100 does. Another oddity.
• Big and heavy
  The power bank weights 436 g, which is 22% more than my Anker PowerCore 20100 (358 g). Strangly, the Xiaomi power bank only has 2% more capacity. Where does the additional volume and weight come from, I wonder.
• Laser engraving: Dark brown on shiny black
  Maybe that’s a must for a power bank, since my Anker model also features unreadable print. Xiaomi make it even better, choosing to put the text on shiny plastic with a really thin font. It’s barely readable, even at the most favourable angle.

All in all, I enjoy the power bank as a mobile source of power for my electronics gadgets. Charging at 45 Watts is definitely a step up from my Anker power bank that took almost a day to fill. Nonetheless, there are many smaller issues with regards to the voltage negotiation and a big one: I fear that it catches fire. I will not use the power bank unless I have to. Xiaomi replied as followed.

Non-Replies from Xiaomi

1st reply from Xiaomi

Q: Why does the power bank behave as described? (I omitted the overheating issue, since I didn’t know about this when I asked the questions)

Paraphrased reply from Xiaomi:

Sorry, but we don’t sell this product internationally. Please refer to the dealer who sold you the product.

2nd reply from Xiaomi

Q: OK, but I can buy the product worldwide via AliExpress. Anyway. What about the overheating issue?

Paraphrased reply from Xiaomi: Exactly the same as the first time.

So, I learnt my lesson: Xiaomi isn’t interested in customer satisfaction.