Limiting how much the FW16 asks from the Power Brick

Framework Laptop 16
1

Hi.

This is a bit of a rare request, but I have a 100W car 12V charger.
When I plug the FW16 into it, it happily asks for 100W and gets it.
The problem is that I have other things plugged into other car 12V sockets and the car is limited in the total amount of W it can supply to all the car 12V sockets in the car.
When the laptop gets 100W, other bits of equipment plugged into other car 12V sockets switch off, and I wish them to stay on.
So, I wish the FW16 to only ask for a max of 40W from the 100W capable car 12V socket.
My normal use of the laptop only takes about 20-30W, so limiting the FW16 to 40W charging should be OK.
Does anyone know any way to limit what power the FW16 asks for?
I will need it to be configurable.

  1. Car mode - 40W from 12V socket.
  2. Office mode - 180W from FW Power brick.

The car 12V charger is this:

So, it is compatible with the FW16 as it correctly supplies the power to the FW16.

2

I think the simplest solution will be to get a 40W 12v adapter that you can use for in your car.

2 Likes
3

Yeah, I have to agree on just getting a 40W 12v USB-PD charger.

If it’s possible to have the FWL16 request less on it’s end, you’d very likely have to get into modifying the EC (Embedded controller) code to do it. It’s yet another place where the USB-PD spec should be improved imo, requiring such control to be available to the user where it’s practical to do so.

4

There’s also things they can do on the software side to simply consume less power that I neglected to mention, such as using ryzenadj to set power limits on the cpu (if they’re using linux), using battery saving features, and etc., but this isn’t as good of a solution IMO as the charger simply being capped at 40W.

1 Like
5

I have a theory of something that might solve my problem.
USB-PD needs cables with a small chip in them to tell USB-PD how much power the cable can handle. So, in theory I could get a cable that says it is only 40W and that should solve my problem. Can anyone see a problem with my cunning plan?

6

If you can find a cable like that, I don’t see a reason not to try it.

8

Good idea!
But I’m afraid you probably can’t get 40W that easy and cheap.

USB-PD only requires cables with chips in them, called eMarker cables, for PD over 3A. Non-eMarker cables will limit your charge current, but only to 3A, minus any cable losses. If your charger can do 20v then that gives you a limit of 60W (20v * 3A = 60W). EMarker cables may also be listed as e-marker, eMarked, e-marked, or simply by the current or wattage, eg 5A, 100W, 140W, etc.

9

I found something odd about the UGREEN 130W car 12V socket adapter.
If I use the FW16 180W power brick cable with it, the FW16 actually asks and gets 180W (CL: p1 s0 i5000 v36000]) from the UGREEN adapter.
The UGREEN adapter gets a little too hot doing this !!!
So, I will need to make sure I only use 100W cables or less with the UGREEN adapter.
Unfortunately, the EC console logs don’t give any details regarding the USB-PD negotiation, so I don’t know what the UGREEN advertised it could do, but something has gone wrong with the CC negotiations.

10

I don’t think that tells you what it’s actually getting, probably just what it thinks it successfully negotiated for. Who knows what it’s actually getting. A real measurement wouldn’t give exactly round numbers like that.

11

You are right about the 20V * 3A = 60W. If I use a cable that I know has no chip in it, the FW16 gets 60W.

12

True. The CL: line only gives what is negotiated or something like that.
When the battery is fully charged and the FW16 power brick only needs to supply 20W, it does not print out any EC console messages saying it is asking for less that 180W, even when I know it is only asking for 20W (Using a power meter on the AC side of the power brick)