21

I looked for 20 minutes for a post similar to mines, and couldn't find one. Which is interesting to me, because I don't understand why people want to use the display to HDMI instead of using thunderbolt USB-c port natively instead. Before I get to this...I shall ask my question.

I plan on buying a MacBook Pro-2018 15 inch for my home-based business. I need to connect 3 monitors to this laptop. I understand the 15 inch MacBook Pro comes with 4 thunderbolts 3 ports. I plan to buy 3 24-27 inch monitors that are 4k display. Also, I understand that the charger for this laptop uses a Thunderbolt 3 port, which leaves me with 3 left. Will connecting 3 monitors that have Thunderbolt 3 ports leave me with performance issues? Will the refresh rate lower?

Finally, why do I see a lot of post with people using old 2.0 display port to HDMI; why they can use Thunderbolt 3 port natively?

12

I currently use 3 4k displays (Dell P2715Q) on a MacBook Pro 15" 2017 (GPU: Radeon Pro 560 4096 MB).

Two monitors are connected to the right side ports/bus and the third one (plus a dock for charging/USB/etc) are connected to left side ports/bus. The monitors are arranged in a "H-shape" with two monitors flipped 90 degrees.

I've had this setup for about 6 months now and while it is usable, I do face some issues from time to time, always after waking up the monitors after sleeping overnight:

  1. The orientation (90 degree rotation setting) tends to get messed up in two of the three monitors and I have to waste 1-2 minutes fixing it on System Preferences > Displays. The cause for this likely a software/compatibility issue on macOS and I have had this on a two monitor setup as well.
  2. Every now and then the ONE of the monitors connected to the right bus fails and I can't make BOTH work again without a system reboot. By repeatedly disconnecting/reconnecting the mDP cables I can get EITHER of them to work, but often not BOTH simultaneously, which is pretty annoying. I feel like this is a hardware issue, perhaps GPU memory issue, but more likely something to do with the Thunderbolt bus bandwidth as it always happens to the bus that has 2 monitors attached to it and never to the one that has only a single monitor attached to.

TL;DR: It is possible but be prepared for some minor issues and eventual monitor "loss" followed by a system reboot.

4
  • Thanks for the feedback. Its been a year since this post and I've been loving using a MacBook Pro since February of 2018; however, I noticed basic project management with Microsoft Office and other software is not the right move for me. However, when it comes to coding and basic web development the Mac platform is right for me. However, I think I' am going to migrate back to Windows OS, and only use my MacBook pro when it comes to web development only.
    – Predevsign
    Jan 14 '19 at 20:21
  • 2
    I have a 13" MBP with only two USB-C ports (cannot use 3 monitors), and I have the same issue with two external displays getting messed on re-connect, as well as one of them occasionally not displaying and requiring the reboot. The reboot issue is rare and I don't have a solution. For the orientation getting messed up I use github.com/jakehilborn/displayplacer. Each time you plug in a monitor it might be assigned a different ID (even though same cable is supposed to provide same ID). So I have two profiles to swap the position and orientation of the monitors and I just toggle it.
    – Jens Bodal
    Jan 23 '19 at 19:46
  • Update: I added a 4th monitor to my new MBP 16”. Two monitors are connected directly and the other two through a Caldigit dock (DisplayPort). After two months of usage I haven’t yet experienced the “dead monitor” issue, but the orientation issue is still there. Also, eventually 1-2 of the monitors (connected over the dock) don’t get recognized right away requiring turning it on/off or switching input source and then switching back. Jun 13 '20 at 8:39
  • @GustavoBezerra your not by chance using a Caldigit dock are you? Ive only ever had that issue with those model docs.
    – Ray
    Jul 12 '20 at 3:31
22

For anyone trying to do this using a dock that has multiple display outputs, the MacBook Pro 2018 only has two thunderbolt busses, but 4 ports (2 ports per bus), as a result, if you try to connect three external monitors, you will need to use different sides of the device.

If you try to connect all three monitors into two ports on one side, it won't work.

2
  • 8
    "If you try to connect all three monitors into two ports on one side, it won't work." <- This is the secret! Apr 15 '19 at 16:31
  • I think you just solved my problem, thanks! I had the power (PD) and external display plugged into the same, causing issues where the external display would not wake from sleep. I see similar info now confirmed in this Apple support post: support.apple.com/en-gb/HT201177#usbc Feb 9 '20 at 22:02
8

From the MacBook Pro Technical Specs page:

Simultaneously supports full native resolution on the built-in display at millions of colors and:

Up to two displays with 5120-by-2880 resolution at 60Hz at over a billion colors.

Up to four displays with 4096-by-2304 resolution at 60Hz at over a billion colors.

As per Apple, you should be fine with upto 4 4K display.

3

Yes, you can connect 3 x 4k-monitors to the 2018 15" MacBook Pro - and yes, you can use USB-C to DisplayPort cables to connect the monitors.

Doing it this way will take up 3 of the 4 ports, leaving one available for charging, as you describe.

You will not suffer from lower refresh rates, nor "performance issues" as such that are specifically related to connecting the 3 displays in this manner.

You'll often see people using docks or other adapters to allow connecting multiple displays to a single Thunderbolt 3 port - leaving more ports available for other things, and simplifying connecting the displays when docking/undocking. In this case, the docks often offer HDMI ports instead of DisplayPort.

2

Reading this guide may help you:

How To: Run External Displays with your USB-C/Thunderbolt 3 MacBook

It helped me a lot, although the guide is from a dockstation manufacturer, it's somehow neutral, and addresses in a practical way the different scenarios that we can face when we want to work with multiple screens in our MacBook Pro, either using a single cable solution or with the help of a dock station.

Mine is a 15" MacBook Pro w/TouchBar and I have three 4K connected screens, two using a single port each, and the third is using a tethered dock that even provides power to charge my laptop.

0

I just installed a driver from https://www.displaylink.com and plugged this recent Macbook Pro into a Dell D6000 docking station via a single USB C (not Thunderbolt) cable that my colleague is using for his Dell. All three monitors worked and the Macbook got power. I was able to drag a single window across the built-in display and the three monitors, one monitor at a time.

I didn't check anything else like resolution, refresh, etc. What's interesting, though, is that everything I've read indicates that a single USB C 3.1 or Thunderbolt port should drive only two monitors, but this does three. Weird.

** Note: The DisplayLink driver does not support Night Shift on macOS. **

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  • 1
    DisplayLink is to my understanding not a monitor seen from the computer (where you send a finished image from the GPU) but a graphics card to be programmed over the USB-C port. Feb 21 '19 at 22:59
  • DisplayLink is basically a low end USB graphics card. I have had horrible experiences with it in the past and wouldn’t recommend it to anyone, especially Mac users. Jun 13 '20 at 8:33

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