Just a quick status report video

[Letalis Sonus]

Well you could limit the current using a transistor and a resistor

Many FET drivers have a current sensing input pin for Amperage limitations. Switching power supplies have an impressive range of regulation possibilities with a much higher efficiency than "conventional" circuity. Add the battery as a buffer and you're good to go - Using a too weak power supply? The battery will simply discharge slowly instead of being charged.

If you're using a higher sensitivity than commonly used for overcurrent protection you can even actively approach the power limit of the power supply by monitoring the voltage drop. The controllers of switching power supplies already are monitoring the voltage drop on the output side to stabilize the voltage depending on the current load.

 

[levi]

Yeah, maybe the phone or whatever you're charging will watch for the voltage drop and scale back on the current draw, because I guess that's what happens with a real 1.5A supply. Good point.

 

[Djoga'Ro]

Please correct me if I'm wrong, but isn't there some communication taking place between host and device about how much power may be drawn? If so, why not allow me to tell the host to not offer more than .8 or 1.5 A (I'd want to put little wear on big batteries also) or let it work with it's given capabilities (sometimes I need quicker charging or the device is running at the time and is a power hog).

 

[HelenF]

I'm not up-to-date on the state of things with USB C, but before that, yes? sometimes? inconsistently? With a computer connection, they communicated via the USB signal, but chargers tended not to (particularly as computer connection was only rated up to 500mA). Many chargers did things with different signalling resistors connected to the data lines, without everyone quite managing to standardise on that. Devices may also have detected a voltage drop and scaled back their current draw. If this doesn't work out right, supplying less current than the device is trying to pull isn't a great situation. A charger that's rated too low could overheat. A charger that's actually enforcing a current limit can only physically do it by dropping the voltage or cutting off entirely.

 

[Letalis Sonus]

Yeah, maybe the phone or whatever you're charging will watch for the voltage drop and scale back on the current draw

I was actually referring to the switching power supply within the device itself. You don't feed the input voltage directly to anything.

I'm not up-to-date on the state of things with USB C

As far as I can tell the USB-C related Power Delivery standard includes active negotiation of power modes, so no more dumb resistors. Switching to a higher voltage requires that the device tells the power supply to change to it first, after all, else you risk destroying other devices with it.

 

[levi]

I was actually referring to the switching power supply within the device itself. You don't feed the input voltage directly to anything.

Are you referring the buck convertors as switching mode power supplies?

As far as I can tell the USB-C related Power Delivery standard includes active negotiation of power modes, so no more dumb resistors. Switching to a higher voltage requires that the device tells the power supply to change to it first, after all, else you risk destroying other devices with it.

USB PD came in late in the USB2 era, mostly too late to change any device using USB2, but it was there from the beginning more or less from USB3.0. It's probably evolved since that first drop, but that's when you stopped merely patching a resistor across D- and D+ to set your limit.

I suspect the old resistor across the twisted pair works still though, so maybe patching a resistor into your cables across the data lines will actually give you the control you desire.

 

[Letalis Sonus]

Are you referring the buck convertors as switching mode power supplies?

Well, Wikipedia explicitly classifies buck convertors as a type of switch-mode power supplies.

 

[logen]

Please correct me if I'm wrong, but isn't there some communication taking place between host and device about how much power may be drawn? If so, why not allow me to tell the host to not offer more than .8 or 1.5 A (I'd want to put little wear on big batteries also) or let it work with it's given capabilities (sometimes I need quicker charging or the device is running at the time and is a power hog).

I do believe this can be done with ThinkPads. At least older ones.

I know you can do percentage cut offs, but I'm pretty sure you can enforce a slow charge mode as well.

So, perhaps? I don't see why we couldn't have a controllable charge controller.

 

[Djoga'Ro]

So, perhaps?

I was rather thinking of less smart devices, stuff with some MC. Most probably the internal circuitry isn't adjusted to cap itself to conservative charging rates. So I'd expect the builtin battery to be rather useless after at most 3 years - with luck.

I don't see why we couldn't have a controllable charge controller.

The manufacturers see no demand. A few years ago there still were multiport chargers with ports limited to different currents, but It looks like this was just a technical limitation. It seems rather to be about providing the highest power output they can muster on every port.

I guess I should take good care of my old Sony Ericsson USB-charger, which cannot do more than .8 A