5 ms·

Can somebody explain why it's so difficult to allocate the power dynamically per port? Apparently this charger (as well as all others I'm aware of) seem to hav

Can somebody explain why it's so difficult to allocate the power dynamically per port? Apparently this charger (as well as all others I'm aware of) seem to have hard limits depending on the number of devices connected. For example when all four ports are in use this charger outputs 50W + 30W + 20W + 20W. Now let's imagine I charge a notebook which could charge with more than 50W, but on one of the 20W ports I charge a smartphone which is only capable of charging with 5W. Why is it so difficult to allocate the remaining 15W to the port the notebook is connected to as well?

aappleby 5y ago
USB-C power delivery allows the device to request voltages other than 5v, up to 20v. Since the voltages differ, the ports cant all share one big 5v rail and need dedicated voltage converters. The power limits come from both the individual converters and the big master AC-DC converter upstream from them.
- Dunedan 5y ago
  But how can that be a limiting factor as long as the sum of power delivered to all ports is <=120W and the power delivered per port is less than what the rail for this port is capable of delivering? Why can't I charge devices on all ports with the power distributed like 65W, 30W, 20W, 5W for example?
  - gumby 5y ago
    The real issue is the chipsets; because of cost they spend essentially nothing on firmware. You can add your own controller to manage the issue but that adds to the BOM and requires finding a programmer who can handle embedded and is willing to write a very policy, but that adds cost too. I agree it’s not that hard, though figuring out a policy that won’t annoy people is hard (I’d implement of sorting devices by what they ask for, then go from high to low doing your best to satisfy them, with nobody getting less than the USB 2.1 baseline, though I know that would piss some people off). So in the end there is no economic incentive to do a good job.
    - Dunedan 5y ago
      > The real issue is the chipsets; because of cost they spend essentially nothing on firmware. You can add your own controller to manage the issue but that adds to the BOM and requires finding a programmer who can handle embedded AND is willing to write a very policy, but that adds cost too. Thanks, that sounds plausible to me, although it's a shame, because it'd make such chargers so much better. > I agree it’s not that hard, though figuring out a policy that won’t annoy people is hard (I’d implement of sorting devices by what they ask for, then go from high to low doing your best to satisfy them, with nobody getting less than the USB 2.1 baseline, though I know that would piss some people off). I mean right now there is already such a policy: Each device can only get as much as the port is rated for depending on how many and which ports are occupied. They could just leave the numbers as they are and label them as "minimum power provided by the port". If a device requires less power they can provide this surplus power to devices which request more, if the port is capable to handle that.
ksec 5y ago
What you are essentially asking is for the 50W port to support 65W, or every single port to support 120W if it needs to be. The answer isn't technical, but a question of BOM ( Bill of Material ) cost and go to market strategy.
- Dunedan 5y ago
  > What you are essentially asking is for the 50W port to support 65W, That 50W port already supports up to 100W when it's the only port occupied, so from my understanding the hardware is already capable of it. > or every single port to support 120W if it needs to be. That'd be perfect of course, but yes, that would significantly increase the BOM.
  - ksec 5y ago
    >That 50W port already supports up to 100W when it's the only port occupied, so from my understanding the hardware is already capable of it. You can think of these charger as two charger combined into one. It has one side with two port of combined 120W Max and the other side with 20+20W max. So you cant allocate the low power port over to high power port. The 20+20 are there as baseline. What you want is dynamic allocation of 120W between 4 port in an ultra intelligent manner, again a cost issue, UX issue and policy issue as mentioned by gummy's reply.
xiphias2 5y ago
I will stay with the 2 USB-C output power source for my travel, as I don't want to think about charging speed.

aappleby 5y ago

USB-C power delivery allows the device to request voltages other than 5v, up to 20v. Since the voltages differ, the ports cant all share one big 5v rail and need dedicated voltage converters. The power limits come from both the individual converters and the big master AC-DC converter upstream from them.

Dunedan 5y ago
But how can that be a limiting factor as long as the sum of power delivered to all ports is <=120W and the power delivered per port is less than what the rail for this port is capable of delivering? Why can't I charge devices on all ports with the power distributed like 65W, 30W, 20W, 5W for example?
- gumby 5y ago
  The real issue is the chipsets; because of cost they spend essentially nothing on firmware. You can add your own controller to manage the issue but that adds to the BOM and requires finding a programmer who can handle embedded and is willing to write a very policy, but that adds cost too. I agree it’s not that hard, though figuring out a policy that won’t annoy people is hard (I’d implement of sorting devices by what they ask for, then go from high to low doing your best to satisfy them, with nobody getting less than the USB 2.1 baseline, though I know that would piss some people off). So in the end there is no economic incentive to do a good job.
  - Dunedan 5y ago
    > The real issue is the chipsets; because of cost they spend essentially nothing on firmware. You can add your own controller to manage the issue but that adds to the BOM and requires finding a programmer who can handle embedded AND is willing to write a very policy, but that adds cost too. Thanks, that sounds plausible to me, although it's a shame, because it'd make such chargers so much better. > I agree it’s not that hard, though figuring out a policy that won’t annoy people is hard (I’d implement of sorting devices by what they ask for, then go from high to low doing your best to satisfy them, with nobody getting less than the USB 2.1 baseline, though I know that would piss some people off). I mean right now there is already such a policy: Each device can only get as much as the port is rated for depending on how many and which ports are occupied. They could just leave the numbers as they are and label them as "minimum power provided by the port". If a device requires less power they can provide this surplus power to devices which request more, if the port is capable to handle that.

ksec 5y ago

What you are essentially asking is for the 50W port to support 65W, or every single port to support 120W if it needs to be. The answer isn't technical, but a question of BOM ( Bill of Material ) cost and go to market strategy.

Dunedan 5y ago
> What you are essentially asking is for the 50W port to support 65W, That 50W port already supports up to 100W when it's the only port occupied, so from my understanding the hardware is already capable of it. > or every single port to support 120W if it needs to be. That'd be perfect of course, but yes, that would significantly increase the BOM.
- ksec 5y ago
  >That 50W port already supports up to 100W when it's the only port occupied, so from my understanding the hardware is already capable of it. You can think of these charger as two charger combined into one. It has one side with two port of combined 120W Max and the other side with 20+20W max. So you cant allocate the low power port over to high power port. The 20+20 are there as baseline. What you want is dynamic allocation of 120W between 4 port in an ultra intelligent manner, again a cost issue, UX issue and policy issue as mentioned by gummy's reply.

xiphias2 5y ago

I will stay with the 2 USB-C output power source for my travel, as I don't want to think about charging speed.