Dual USB-PD sources?

[D.H]

Hello all. Awaiting my batch 5 i5 DIY, and thinking through how I’m going to rearrange my desk, cables, etc.

I plan to have an eGPU that supplies 20v (87 or 100w) over USB-PD plugged into the framework most of the time.

I also have a USB 3 + displaylink (not thunderbolt) dock that can also pass 20v USB-PD (80w IIRC). I would like to have this connected to the framework occasionally, and it does not work reliably when powered only from a laptop, so it would get its own USB-C/PD source.

Can the Framework elegantly handle two offered USB-PD options, if they are the same voltage, different voltage, etc? If so, is it better to put both into the the same side of the chassis, or one on each side, or doesn’t matter for power supply?

I know the two ports on the same side share the same controller and bandwidth, so that’s a minor factor in getting the best eGPU performance. I mostly just want to make sure I’m not going to mess anything up by presenting two power sources…

[GhostLegion]

I could be wrong but I’m pretty sure I read somewhere on the forum that it only takes one power source, no dual pd possible

Could be mistaken tho

[D.H]

@GhostLegion

no dual pd possible

Right, I’m neither asking if it can, nor expecting that it should be able to draw power from two sources at once. I’m asking if it’s going to mess anything up to present two USB-PD sources simultaneously.

[Nich_Trimble]

I’m pretty sure that it will only negotiate and draw from one USB-PD device at a time- previously Framework staff have confirmed that you can’t charge from 3 15W PD sources, for example, and that it’ll just choose the first one that was plugged in to draw from, iirc.

[GhostLegion]

@Nich_Trimble

it’ll just choose the first one that was plugged in to draw from

I think it would be more likely it’ll check which source can provide the highest wattage and run with that

[Richard_Lees]

Without really thinking too deeply or really knowing much about this at all, I wouldn’t think plugging in two power supplies would really make a difference. The power supplies are voltage sources, not current supplies and hooking up two of them in parallel really wouldn’t hurt much – you’d just get 1/2 the current through each channel, I would expect.

[D.H]

Thanks for everyone’s input, but I would love to hear from @nrp , @Kieran_Levin , or @FrameworkSupport with a definitive answer also.

[dkt01]

@Richard_Lees

I wouldn’t think plugging in two power supplies would really make a difference. The power supplies are voltage sources, not current supplies and hooking up two of them in parallel really wouldn’t hurt much – you’d just get 1/2 the current through each channel, I would expect.

Having two independent power supplies directly powering a device is a bad idea unless the device is designed for that. USB-PD can deliver various voltages and even two supplies that claim the same voltage won’t be exactly the same. Even small differences could lead to weird current loops between supplies. If all the ports have independent voltage conversion, this is less of an issue.

That said, USB-PD device-supply negotiation should protect the device by only charging from one source at a time.

[Brad_J]

@D.H Here’s the quote you’re looking for:

@Kieran_Levin

the laptop will only charge from one port at a time. It chooses the port with the highest available power.
This is due to a hardware limitation, as we only have one charge controller, and charging from multiple ports would require per port load balancing. I do not think many, if any laptops would support this feature.

[taeyeon]

Some high-performance gaming laptops support charging from 2 chargers, but not over USB-C. This is probably one of the reasons why the next version of USB PD will support 240 W at 48 V.

I concur with @dkt01 - you could encounter weird problems if this was not explicitly accounted for during design but still permitted charging from 2+ ports.

[D.H]

@Brad_J

Here’s the quote you’re looking for:

Thanks for digging that up.

But I think @dkt01 makes a good point. I’ll probably run the USB 3 hub through a type A port to cancel it’s ability to present USB-PD if my eGPU is connected / on.