A customer came to us asking for a way to power his monitor using his HDMI cable. It’s an interesting proposition and actually something like that isn’t really so far off.
What you can actually do with HDMI
Some TVs have a port labeled MHL. MHL is a technology that allows 5 volts of current to pass through an HDMI connector. In this way, devices like streaming sticks can be powered without an external USB connection. It’s pretty rare to see, but it’s out there if you look.
The idea of MHL is a good one but it’s never been really well implemented. People are generally fine with plugging their streaming sticks into a USB port on their TVs, especially if that USB port stays powered all the time. It’s just not a big deal. And for people who want a cleaner install, TVs with built-in smart features are certainly not that expensive.
What you could do…
We’re just beginning to see what USB-C is capable of. USB-C is more than just a better connector. Although, let’s be honest, it is a MUCH better connector, am I right? USB-C can carry power. Using the USB-PD standard, a USB connector can carry up to 100 watts of power. That’s enough for most laptops, even enough to power practically any monitor. At the same time, USB-C can carry video information. We’re talking about one wire that does it all.
Can you buy a USB-C monitor?
At this moment, as I write this in early 2020, there aren’t a lot of monitors that take advantage of this standard. There’s still a lot of work to be done here. HDMI has been the standard for monitors for over a decade and it’s going to stay for quite a while longer. Because HDMI can’t carry power, any monitor with an HDMI connection is going to need a separate power connector. This means if you want to have the monitor powered over USB-C, you would need two pathways for power. This would raise the price of the monitor.
You would also need to make sure the computer’s power supply was robust enough to supply the monitor. Gaming PCs and laptops have big power supplies, but smaller and older laptops don’t. It’s going to take some time to build computers that are designed to do this sort of thing.
What would happen if you tried to run power through an HDMI connector?
The HDMI cable itself is really built for a lot of different options. You could absolutely isolate two of the wires in an HDMI connection and start running current through them. This is what MHL does already. But you get a paltry amount: 5 volts at 250 milliamps. That’s barely enough to charge a phone. It’s not anywhere near enough to run a monitor.
If you somehow frankensteined this whole thing together, my guess is that it would last about a minute before the wires started to melt and the whole thing failed spectacularly. It might kill your monitor or your computer, or possibly both. Just, don’t do it. Just… don’t.