Hi All,
I just wanted to share my experiences with setting up a Gigabyte GTX 750 TI eGPU powered only by the PCI slot in the Akitio.
My setup:
- 2014 Macbook Pro 13", 8GB RAM, 500GB SSD, running OS X 10.10 with Win 8.1 installed via boot camp (EFI)
- Gigabyte GTX 750 TI - the slim one with the single fan
- Akitio Thunder 2
- 120W Power brick from Trust
- external monitor
This looked like a really attractive solution to me, since it's as close to plug-and-play as it gets with a cool running GPU which fits tidily in the case and can be closed.
I don't recommend that power brick though, it says "automatic voltage selection" on it which is a bit bogus. The thing has a shunt regulator in it, so "automatically selecting" the voltage means choosing the correct plug (which has a built-in resistor) to fit on the end which regulates the voltage, and the correct plug for 12v was NOT included in the packaging (for me at least). So I cut the barrel plug off the Akitio and soldered that along with a 400k potentiometer which I used to regulate the voltage down from 19v to 12.3v (note, this is not the same as simply wiring in a resistor in series, a shunt regulator has a feedback line and the resistor goes between V+ and the feedback).
First off, there seemed to be some lack of clarity as to whether simply adding a 120W power brick and powering the whole thing through the barrel plug actually worked in practice. Turns out it works. I was playing the Witcher 3 on high settings at 1080p all evening yesterday.
Initially I tried to get it running on my newer 2015 13" MBP 16GB RAM + 1TB SSD running Win 8.1/El Capitan, and I couldn't get it to boot reliably (had to do the hot-plug-after-chime rain dance, and racing a fast SSD was really hit and miss), and most of the time I'd get a black screen or get to watch the pretty spinning dots for hours.
I noticed, though, that rebooting worked more frequently than a cold start, so I disconnected the Akitio fan as I suspected that the torque when it starts up might cause a voltage drop which puts the card in a funny state.
I then switched to my older 2014 MBP13" (the one on which this all works now), and installed Win 8.1 via boot camp. I also installed the Optimus EFI goodies from here which may have had the effect of inserting a tiny delay via the chain loading from GRUB and could have helped (the theory being that the card needs power a little BEFORE the PCI scan at boot time, but only gets power when the thunderbolt signal comes up, and that there's a race).
Once I had it booting reliably without any weird rituals, I had stability issues the first few days, where I couldn't run a game for more than a minute without the card crashing in various interesting ways. I noticed using GPU-Z that the power consumption was spiking as high as 115% TDP and was getting a lot of "PerfCap Reason" "Pwr" notices, so I underclocked it so that it doesn't go over ~98% TDP. And that was the key to getting it stable. After some experimentation, I ended up with both the core and memory clock speeds reduced by 150mhz (I used MSI AfterBurner). Did that, and now it works like a charm
Summary:
- get a 120W power brick and a GTX 750TI without additional power connectors
- disable the Akitio built-in fan by unplugging it from the board (the GPU runs very cool anyway, haven't gotten it over 62 deg. C yet)
- install Win 8.1 via boot camp
- write the OPTIMUS.dmg to the EFI partition (speculative)
- install latest NVIDIA web drivers
- underclock the card until stable
Thanks for all your advice and discussions. Couldn't have done it without y'all.