Can you use a 12V USB-C phone charger on a 15V USB-C laptop?

euskalzabe

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I just bought a cheapo Lenovo S330 Chromebook to try it out. It comes with a 15V output USB-C charger. My Moto Z2 Play uses a 12V output USB-C charger. It occurred to me that I could forgo the laptop's bulkier power adapter, and just use my phone charger with it.

Obviously, you wouldn't want to send 15V power to a phone that expects a max of 12V (although technically it *should* just ask for 12V, but I'm not going to risk frying my phone). However, 12V going to the 15V that the laptop expects... that should be fine and just charge a bit slower, I'd guess?

It'd be great if while traveling I could forgo this:

upload_2019-8-17_14-52-6.png

And simply bring this tiny guy for both devices:

upload_2019-8-17_14-53-12.png

Granted, the Lenovo charger isn't huge, but if I can "downsize" to just 1 charger... it lightens my travel load even further. I charge the Z2 fully in less than 1h while I get ready in the morning, so even if the S330 took longer I could charge that overnight.
 
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Voltage is just a part of the power output equation. Total output power is measured in watts, which is calculated by voltage * current. Odds are your phone charger is 12V at 1 or 2 amps, or somewhere between 12 and 24 watts. Your chromebook charger probably puts out closer to 4 amps, so I'd guess anywhere from 30-60 watts.

Odds are your chromebook might charge while it's suspended or turned off, but would still drain slowly if turned on and plugged in.
 

euskalzabe

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It would just charge slower, no?

That's what I would think, but what do I know...

Voltage is just a part of the power output equation. Total output power is measured in watts, which is calculated by voltage * current. Odds are your phone charger is 12V at 1 or 2 amps, or somewhere between 12 and 24 watts. Your chromebook charger probably puts out closer to 4 amps, so I'd guess anywhere from 30-60 watts.

The Moto charger says it has 3 modes:

5V at 3a
9V at 1.6a
12V at 1.2a

So... would it charge the Chromebook at 5V? At 12V? I haven't received the S330 yet, but Lenovo's website says about the power adapter:

Input: 100 V to 240 V, 50 Hz to 60 Hz
Output: 15 V
Power: 45 W

Odds are your chromebook might charge while it's suspended or turned off, but would still drain slowly if turned on and plugged in.

As long as it's safe, it doesn't matter to me how long it takes to charge. The phone charges super fast which I can do in the morning before work, while the laptop could charge at night for hours. If using less power than it needs means I can't burn anything - that's what I'd figure - that's all I'm looking for :)
 

mjz_5

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If it helps. I charge all my devices with a 5w USB brick. The slower charge prevents devices from overheating. That could always be a good thing
 

mnewxcv

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I don't know enough about the USB standard, but not all laptops are smart enough to only ask for what the adapter can provide.
 
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The Moto charger says it has 3 modes:

5V at 3a
9V at 1.6a
12V at 1.2a

3*5=15, so 15 watts, this follows for the other voltage outputs.

So... would it charge the Chromebook at 5V? At 12V? I haven't received the S330 yet, but Lenovo's website says about the power adapter:

Input: 100 V to 240 V, 50 Hz to 60 Hz
Output: 15 V
Power: 45 W

The phone charger only puts out 1/3 the power of the laptop charger. Again, it may keep it running, but I doubt it'll charge during use, and odds are because of the additional current being drawn your charger's lifetime will be significantly shorter.

Think of electricity like a river. Wattage is the total flow of water, you can either have a slow, wide, deep river which would be the rough equivalent of a low voltage high current supply (5V at 3 amps) or something akin to rapids with a high velocity, but a smaller all around area for the water to flow through (12V at 1.2 amps).

Both are supplying the same amount of power, but in different ways. Your phone charger simply won't be able to keep up with the demands of a device drawing 3 times the power. There's a reason it's significantly smaller than the laptop power supply.
 

euskalzabe

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Think of electricity like a river. Wattage is the total flow of water, you can either have a slow, wide, deep river which would be the rough equivalent of a low voltage high current supply (5V at 3 amps) or something akin to rapids with a high velocity, but a smaller all around area for the water to flow through (12V at 1.2 amps).

That was the best explanation of electricity I've ever received, thanks a lot. I see now what you mean, and thinking about shortening the phone charger's life is an important consideration. Seeing the S330 charger is smaller than most laptops I've had until now, I'll just carry both. This was very helpful!
 
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That was how it was explained to me 15 years ago when I first started messing around with electronics. Really helped me visualize what was happening, even if it is a gross oversimplification. Glad I was able to help!
 

NattyKathy

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As long as charger and device are standard and behaving as expected, USB Type-C PD (Power Delivery) devices should ask the charger for the highest level of power they can accept based on the levels the charger has available and the charger should supply it. The PD standard defines multiple standard voltage levels- 5v, 9v, 12v, 14.5v, and 20v. However, some devices have a minimum voltage level they want or they won't accept power at all. For example the (3rd-party) iHome charger I use has 5v, 9v, 14.5v, and 20v available and will charge both my laptop (which is marked on the nameplate as taking 12v but is probably using the 14.5v level on this charger) and my phone (which uses up to the 9v level for fast-charging), but the charger that came with my phone, which has 5v and 9v levels, won't charge the laptop at all, in fact the laptop acts like it's not even plugged in when I tried it.

tl;dr there shouldn't be such thing as a USB-C PD charger that is too powerful for a device but depending on how picky the device is it's possible for a charger to not be powerful enough
 

NattyKathy

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Not that I'm doubting you, but could you elaborate on why?

a very poorly-behaved charger could just bang whatever voltage it wants across the USB port. This is why it's best to stick with USB-PD chargers that have the supported voltage levels clearly marked, and preferably ones with some reviews. If a device is actually USB-PD compliant there will be some "smarts" and it will be safe to use with other PD compliant devices.
 
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