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Powering a portable monitor via USB-C

Powering a portable monitor via USB-C

Old Dec 21, 18, 1:33 am
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Powering a portable monitor via USB-C

I've got a Dell Precision 5520 laptop that has a Thunderbolt 3 port (USB-C form factor).

I'd like to get a portable monitor for it that is powered via a USB-C port. (Video is handled separately, via mini-DP or mini-HDMI... USB-C is only for power.) The power supply included with said monitor is rated for 12V 2A. I don't see any documentation on how much the display actually draws, so I am assuming near the full amount for the time being.

On Dell's Thunderbolt FAQ page here, it says "Type-C can supply 100 Watts of power charging for a 15W device."

I'm far from an electrical engineer, so can anyone help me understand this? A 15W device would only ever draw 15W, wouldn't it? So I don't understand what it means by supplying 100 watts of power charging for a 15W device. In a nutshell, I'm trying to figure out whether I can safely power this portable monitor, which in the absence of other documentation I assume to be 24W, via the laptop's port.
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Old Dec 21, 18, 1:54 am
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The USB-PD standard covers charging up to 100W (20V/5A) over a USB-C connection, but it's unlikely your laptop's ports can output anything other than 5V.

Dell's page appears to have some editing errors--my guess is that the sentence you quoted should say "can supply 100W of power for charging or power a 15W device"--but here's a graphic from the same page that makes more sense:



Thunderbolt 3 supports 100W input (i.e. for charging your laptop on those laptops that charge over USB-C), but can only output 15W (5V/3A) for charging or powering devices.

Unfortunately, that means you'll have to continue to use a brick to power the monitor if it needs 12V.

It looks like there are monitors available with a low enough power draw that they can run off nothing but a Thunderbolt 3 or USB-C displayport, e.g. a couple ASUS ZenScreens

Last edited by der_saeufer; Dec 21, 18 at 2:17 am
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Old Dec 21, 18, 3:21 am
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Thanks, that makes more sense. My key requirement in a portable monitor is that it matches my laptopís size and resolution (15Ē 4K). There are very limited offerings that do so - most are lower resolution such as 1080p or at most 2K. If I have to use the brick to be able to have 4K, then I have to use the brick.
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Old Dec 21, 18, 8:13 am
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Unfortunately, there appears to be only two portable 4K monitors on Amazon...and they ain't cheap. And they require power bricks. And one is 4K-lite (3200x1800). I'm happy with my 15.4" 1080p monitor (powered by USB 3.0).
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Old Dec 21, 18, 11:08 am
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Originally Posted by pseudoswede View Post
Unfortunately, there appears to be only two portable 4K monitors on Amazon...and they ain't cheap. And they require power bricks. And one is 4K-lite (3200x1800). I'm happy with my 15.4" 1080p monitor (powered by USB 3.0).
The one Iím looking at is a Sibolan S16b. They donít have it on Amazon, but it runs a little under $300 on eBay. 15Ē, true 4K. Iím one of those people who wants every pixel possible so I can see more on the screen (even if itís tiny), and it drives me nuts when I use multiple monitors that have different resolutions and the scaling never matches quite right. This one uses a charger that is more like a cell phone charger, so itís not really a brick like my laptopís, but I was hoping to eliminate the wall plug nonetheless.
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Old Dec 21, 18, 11:41 am
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USB C chargers providing 12V are rare. The Mu One tech specs, for example claims "Voltage: Variable 5-20 " but the actual device has the usual 5-9-15-20V printed on it, I will check with the One Mix Yoga 2S once I am home, I don't have a 12V USB C device here. However, if you are into saving space, the Maru & Masa kickstarter is right up your alley. However, even that only provides 12V on the main (45W) USB C port, the secondary only provides 5V and 9V.
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Old Jan 2, 19, 6:33 pm
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I ended up trying it anyway. Seeing that the included charger supplies 12V 2A, and they make a similar monitor with Thunderbolt input that explicitly supports Power Delivery and specifically mentions my Dell as a compatible device, I suspected that either 1) they might have included Power Delivery support in this monitor too, and 2) whether Power Delivery or just plain old USB-C, the monitor doesn't actually draw more than the 15W the Dell is capable of supplying. (I wanted a monitor that was broadly compatible even with older laptops, so I didn't pick the Thunderbolt model even though my Dell supports it.) I bought a USB-C cable that includes E-Markers, and the laptop and monitor seem to be playing well enough. No signs that the monitor is trying to draw too much power from the laptop, so fingers crossed I don't set my laptop (and house) on fire, but so far so good.

Last edited by javabytes; Jan 3, 19 at 1:34 am
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Old Jan 3, 19, 3:24 am
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Thanks for the update, and that's awesome! I wouldn't worry about setting your laptop on fire--it won't output more power than it's rated for; if the monitor needed more power than the laptop could provide it simply wouldn't work.

I wonder whether the monitor is in fact running on 5V or the laptop is capable of 9 or 12V output. My guess is the former, but I can't actually find any hard specs on Dell's Thunderbolt ports other than the page you linked in your first post that says they provide "up to 15W". That would imply 5V only because the lowest standard for anything else is 18W (9V/2A).
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Old Jan 4, 19, 12:31 am
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Could you perhaps buy (and then return ) an USB C power meter and see what's going on there? This really is strange.
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Old Jan 5, 19, 2:43 pm
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Not 4K, but I've got one of these: https://amzn.to/2LRn0yD and it works well with both my XPS 15 (9560, roughly the consumer version of your 5520) which has a TB3 port, and my work Latitude 5491 (which is USB-C only.) The manual shows it pulls about 7.5W (1.5A @ 5V)
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Old Jan 5, 19, 6:00 pm
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I hate not have having a second monitor when traveling, will have to look into some of these options now.
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Old Jan 7, 19, 8:41 pm
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Originally Posted by chx1975 View Post
Could you perhaps buy (and then return ) an USB C power meter and see what's going on there? This really is strange.
I have one on the way, I'll let you know.
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Old Jan 8, 19, 4:33 am
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portable monitor, powered by USB

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Old Jan 8, 19, 5:53 am
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Originally Posted by deniah View Post
portable monitor, powered by USB

https://www.youtube.com/watch?v=ps0Dn5l88Pg
That doesnít seem portable. If Iím understanding correctly, the USB-C port is on the bottom, meaning you have to use it with that bulky dock. Iím sure it saves space on a desk, but it doesnít look like itís meant for travel.
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Old Jan 8, 19, 9:37 am
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Originally Posted by javabytes View Post
That doesnít seem portable. If Iím understanding correctly, the USB-C port is on the bottom, meaning you have to use it with that bulky dock. Iím sure it saves space on a desk, but it doesnít look like itís meant for travel.
It's also a concept product. I imagine there would be additional things added to it before release (such as VESA or some other mounting capability on the back so that the dock isn't necessary).
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