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I have a Huawei Matebook X Pro which I normally charge using the original charger provided by Huawei. I'm leaving on vacation tomorrow and want to pack as light as possible, so I was wondering if I could charge the latop using my Samsung charger for Galaxy S9?

Both the laptop and the phone charges via USB-C, but can lower voltage from the cell phone charger do anything bad to my Matebook?

What will be the effect of a lower voltage? I assume that it won't be as quick as the normal charger, but I can live with.

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  • 1
    what is the specified voltage/current for the laptop, and how much does the portable charger provide?
    – Albin
    Nov 14, 2018 at 18:03
  • Laptop will likely want 20 volts (as per USB C charging spec), most likely at 65 watts /(maybe 45watts)
    – davidgo
    Nov 14, 2018 at 18:52
  • @davidgo How much does charger provide?
    – Albin
    Nov 14, 2018 at 19:17
  • Found a link to specs - 65 watts - charger can output 20v @ 3.5 amp, and unit has 57.4Wh hour battery - consumer.huawei.com/us/tablets/matebook-x-pro/specs
    – davidgo
    Nov 14, 2018 at 19:37
  • @davidgo thanks, do you know does the S9 have a standard power supply (5V, 2A)?
    – Albin
    Nov 14, 2018 at 19:39

4 Answers 4

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Short answer:

If the power supply provides 5V (standard USB charger) and the device requires 20V (according to davidgo) it's very, very, very unlikely it will work (unless the laptop can handle a 5V power supply)!

But it will work the other way around, you can use you're laptop power supply to charge you're S9 according to those specs. (which I just saw davidgo already suggested in his answer)

Long answer:

In general lower voltage won't cause any damage within the device (laptop), but it might happen that the device won't charge and/or turn on at all. It depends on the specification and the tolerance of the on the power supply and the device.

But there is a chance that the power supply will be damaged if it doesn't have sufficient protection against loads that are too high. But this happens because of the current (if the device requires more current then the power supply can provide) not because of the voltage.

Regarding the charging duration, the current is the main factor here. Too little current might prolong the charging time or might cause the device not to charge at all depending (because high requirements on current will cause the voltage to break down in the power supply).

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  • I'm not convinced that current is the main factor (but it is very important). I'd be concerned that the voltage required to drive the battery pack is to low and could do damage - although I would expect voltage negotiation on the charger to mitigate that risk.
    – davidgo
    Nov 14, 2018 at 18:47
  • @davidgo I never heard of a case where too low voltage from the power damages supply in the realm of regular end consumer electronic devices but on the other hand I'm not a electronics professional? Do you have an example? I don't think the S9 will to a voltage "negotiation".
    – Albin
    Nov 14, 2018 at 21:00
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This will not work. The matebook wants a 65 watt charger, and has a USB C form factor port - this means it requires a voltage higher then a Samsung charger can provide and won't charge.

That said, you can do the reverse - the Samsung should negotiate the appropriate voltage off the Matebook charger, so you can use that device for both.

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  • I'd still feel uneasy using a 20V charger with a phone which requires 5V
    – undo
    Nov 14, 2018 at 19:38
  • @rahuldottech it's not a problem according to those specs the charger offers 5V if the device doesn't "negotiate" a specific power level.
    – Albin
    Nov 14, 2018 at 19:48
  • @rahultottech - no reason to - there is a standard (USB PD) for USBC charging which negotiates the standard - I'd rather have something intelligent working out what is required and then providing it (or failing back ) then a dumb charger from China which does not care if it is supplying voltage out of spec because it saved 10c on the unit cost.
    – davidgo
    Nov 14, 2018 at 19:49
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USB Power Delivery chargers are smart and will negotiate the correct voltage and amperage with the device as needed, so damage shouldn't occur under any conditions as long as the charger and laptop are designed properly (if something does go wrong, it's more likely to be the charger's fault). Furthermore, when evaluating USB PD chargers, you only need to compare wattage because the USB PD standard requires that a higher-wattage adapter support all output voltages that a lower-wattage adapter would support.

That said, it's unlikely the system will be able to properly charge with a charger that is substantially weaker than what the computer shipped with. At best, the system will discharge the battery more slowly when powered on. At worst, it'll charge only when off or in sleep (which is what my HP ENVY x360 does if I plug in a 15W USB PD charger), or refuse to charge altogether.

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Most laptops use batteries with 3 or 4 cells in series. That means a nominal battery voltage of around 11.1 or 14.8V and a maximum charge voltage of around 12.6V or 16.8V.

The charge controller inside the laptop is essentially a power converter, taking the voltage from the power brick and converting it to what is currently needed to charge the battery (this increases as the battery gets closer to full charge), it's much easier to design power converters that only reduce voltage or ones that only increase voltage than it is to design ones that do both. So generally charge controllers need the input voltage to be higher than the battery voltage.

Phones and phone-like tablets on the other hand tend to use single cell batteries, so can charge off 5V. Some modern phone chargers use higher voltages to allow faster charging without heating up the cables too much, but are still lower than laptops generally require.

So as a general rule you can't charge a laptop off a "phone charger".

You should however be able to charge a phone off a USB C "laptop charger" from a reputable laptop manufacturer. All compliant USB C power supplies are required to start at 5V and only raise to higher voltages when requested by the device.

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