Given drogon's recent re-location, it is obvious that drogon has moved further from a power station and is therefore incurring more voltage drop. More seriously, drogon demonstrates that the 5V from USB looks convenient but it should be treated with the same suspicion as a 9V power jack.
I share the general consensus that USB power negotiation is generally mis-guided. In all of my bodging, I've never mixed power and data. I am horrified that a device, colloquially known as a USB condom, acts as a packet filter to allow power negotiation while (hopefully) blocking all other communication. This allows convenient public charging, such as in an airport, to occur without a device sharing its address book, calendar, passwords, crypto wallets and cached files.
In the good old days - when gasoline cost 30 cent per gallon and an efficient vehicle obtained 15 miles per gallon - unregulated 12V was stepped down to 5V with vast inefficiency; typically less than 50%. Furthermore, in the NMOS era, an idle chip consumed a minimum of 20mW and the scale of integration was such that 80 chips or more were common. For example, many of Acorn's designs. That's 5W to do nothing.
I am not impressed with modern design but I see hope of improvement while protocols become less hostile to amateurs - or at least people who have not paid for a proprietary specification.
One of Dave L. Jones' thousands of videos (probably somewhere from 800 to 1100) is an investigation into the root cause of an Apple laptop failure. In a quest to make smaller, lighter devices, Apple used an internal connector which is like a Centronics connector except that it is approximately 2mm thick and the pins are approximately 1mm apart. This is not the cause of failure. The design process within Apple had become stratified to the extent that it was not obvious to any individual that 100V electro-luminescent back-lighting was 1mm from an unbuffered processor signal line. Surprisingly, this meets international safety standards and works in ordinary conditions. Unfortunately, a stray cup of coffee is enough to destroy the processor. Attempt to replace the processor may invoke a processor power regulation flaw which was copied over from the previous design iteration. Specifically, inadvertent solder reflow of the surrounding circuitry may cause an intermittent power problem which looks like the processor was not replaced correctly. Erroneous attempts to make further component substitutions are likely to worsen the situation. It looks like a particularly underhanded example of planned obsolescence but Apple's deficiencies with power supply go back to Apple II where
outdated switched mode designs were often copied across design iterations.
We have a situation where V = IR and P = IV = I^2R. Power, P, increases because people want fast charging. Resistance, R, also increases because people buy increasingly shoddy cables on the open market. The only way to avoid the square effect of coulomb heating is to only allow official cables, enforce safety features such as moisture detection, make power negotiation ridiculously complicated and/or increase voltage, V. Unfortunately, parties like Apple have burned their goodwill with leads. For example, does anyone remember Apple's 5*6 laptop SCSI connector or the RCA/phono power connector? It is also less well known that Apple Desktop Bus patents were part of the foundation patent pool for USB implementation. When Apple's 6502 products ceased funding Apple Macintosh development, Apple was a failing company. And then Apple magically bounced back with iMac and top-tier USB support. Forget all of the management drama. Apple made money from every USB device whether or not it worked with Apple products. And that came from a patent which allowed 512 word PIC microcontrollers to send data to a 6502/65816 host over a common bus.
Anyhow, we are likely to see USB power negotiation rise to 50V (the limit established for exposed telco wiring) or 100V (approximate air breakdown voltage for USB C pin spacing). We are also likely to see a corresponding round or two of exploding phones and similar. At 100V, only require 10mA to deliver 1W power and it is too tempting to ignore. I briefly considered the (hopefully) facetious suggestion to interleave pulse charging and Gigabit Ethernet. I thought "Can I get my
cell networking to do that? What am I thinking? No, that's a stupid idea." It violates the constraint to separate power and data. Unfortunately, someone, somewhere may not reach the same conclusion.
I am also concerned that protocol checksums are weak or absent - and approximately nothing uses two phase commit. This creates a situation where increasingly complex attempts to stay within safe limits invoke bit error and cause the unsafe conditions which are trivially averted. We will also have the situation where moment-by-moment monitoring will be entirely in software with no hardware interlocks. And said software is not written to any safety standard.
Nokia, another company sustained by patents, commonly implemented a safety feature where absolute humidity and temperature sensor input is used to determine relative humidity. If a limit is exceeded, the radio interface is not powered. This type of safety feature may be introduced to each end of a USB cable; possibly adjacent to registers for active signal dampening. There is also the possibility that larger connectors may allow charging to exceed 1kV.
This is where it converges with data-centers (and hobbyists). To increase energy efficiency, data-centers increasingly use 380VAC to the rack, 12VDC across the board and then local Buck and linear regulation adjacent to each subsystem. With the pre-condition of using 5V signalling as an interchange standard, this gets back to 1970s practice of 12V unregulated power stepped down to 5V where needed. However, it is now possible to do this with 96% efficiency while also inter-operating with 0.95V GPU cores and FPGA, 3.3V OLED, 3.7V exploding lithium batteries, drogon's suggestion of
4.6V undervolted 6502/65816, 5V USB and 12V UART.
So, don't despair. Protocols, such as
65SIB (with unregulated 12V and signalling at 5V) are the vanguard of common sense.
As a workaround to drogon's immediate problem, I recommend a Buck/Boost via 3V or 7V and then to good 5V. I also thank drogon for the cautionary tale that 5V USB is not consistent even across ports of one host.
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