Overthinking USB charging

[iljitsch]

I don't like perpetual threads, but this one may become a long-lived one. Please add as appropriate.

In the past year, I got both a 100 W USB-C PD charger and a big USB-C power bank that can also deliver 100 W. The charger has four USB-C ports and one USB-A, the power bank two USB-C (one of which may be used to charge the power bank rather than discharge) and one USB-A.

The interesting thing here is that these need to distribute the available 100 W over the ports in use. Which requires a notion of "in use". As the charger is hidden behind the couch and thus doesn't allow for easy plugging/unplugging USB-C cables, I like to have cables connected and then simply plug them into devices to charge them. For USB-C cables/devices this works great, as when those are not plugged in, they are ignored for the purpose of distributing power.

This is not true for cables plugging into the USB-C ports but having a ~ USB-A destination. Here, just having the cable plugged it registers as in use, so they get their portion of the power, even if nothing plugged in.

This also applies to the Apple USB-C to MagSafe 3 cable included with my recently acquired MacBook Air. This is otherwise a completely perfect innovation, giving me the USB-C PD benefits but also the MagSafe benefits. My last computer before MagSafe was a PowerBook which was once flung across a room as someone stepped on the power cable. My first computer after MagSafe was a 2016 MacBook Pro with only USB-C ports where a USB-C cable was destroyed (but fortunately no damage to the computer) after someone stepped on the power cable. The Apple power cable is also thinner than equivalently rated USB-C power cables and of course doesn't take up a 40 Gbps port for just delivering power.

But there's also tons of stuff that only takes single digit Watts to charge. Like AirPods or other headphones. Or aTV remotes. Plugging those into a high capacity charger removes up to 60 W from the other ports, so that's pretty bad. But... what if you still have an old school USB-A multiport charger? I found one of those back in a closet not too long ago and it's now working nicely in my bedroom with an Apple lightning cable that can deliver 5 V 12 W as well as my Apple Watch magnetic connector and a 5 W iQ charger. With USB-A there are different rules for what counts as "in use" and a 60 W 5-port charger has fewer issues distributing the power. So this type of charger is really useful in certain circumstances.

What makes everything more complex is that I'm on a dynamic electricity pricing contract, where electricity prices are often very low during the afternoon when there is a lot of sun. When that happens, you want to charge power hungry devices quickly to take advantage. Slow charging stuff is then less interesting.

So: make sure your big USB-C PD chargers can do their thing quickly, and have slow-charging stuff on more modest USB-A multiport chargers.

 

[Paladin]

Every charger is a bit different so you just have to look at what fits your needs. Generally, the better models tell you how each port works under which conditions. Plug in one thing on USB-C 1 and you get up to 90W, connect a second thing and USB-C 1 drops to 65W and the second USB-C port does 30W tops. Stuff like that. Basically for me, I have nothing that I actually want to charge at top wattage except my laptop so I have a charger just for that and then a charger that does everything else very well. No confusion that way.

 

[Andrewcw]

With buying a charger hopefully it is something someone's reviewed and tested it before properly and then hope they didn't change it between then.

And then sometimes it's charge logic and what happens when things are plugged in. Such as charger from Brand A might negotiate a charge rate only once a product is plugged in. Leaving the remaining ports to fight for what's left. And Brand B might re-negotiate EVERYTHING any time anything is plugged in.

Here's a situation where Brand A Scenario is preferable. For example when charging an item with a 90% cutoffs hardware based logic which you can't get around and you're in the trickle charge state. When you plug in another device it doesn't cause a re-negotiation.

When Brand B with this same device. But with re-negotiation after every plugin. It will ask this 80% cutoff device how much power it needs and it goes Zero because its logic is not to charge if above 90% even though you never removed the plug and it was in the final trickle charge state.

The big thing with chargers that boast 120W. And you need 60W or above. Is how it treats ports. Like some 120W claimed chargers will only go 60W or above is NOTHING else is plugged in. As soon as something else is plugged it everything goes 30W max.
So on Amazon what you're looking for is the one star Red Flags. Where Verified buyers who hopefully aren't competition Shills. Explain how a device isn't working to spec.

 

[continuum]

Generally, the better models tell you how each port works under which conditions.

++;

But yeah, as said, doesn't hurt to verify. I find you can generally trust UGreen, Anker, Aukey, etc... aka the major brands.

Smaller brands are a different story. Been burned a few times, usually by random brands on Temu or Amazon or whatever that had good reviews-- one dual port USB-C car charger I picked up claimed 90W total, 45W + 45W each port... yeah no, neither port could deliver even 45W. -_-

 

[Shavano]

I don't like perpetual threads, but this one may become a long-lived one. Please add as appropriate.

In the past year, I got both a 100 W USB-C PD charger and a big USB-C power bank that can also deliver 100 W. The charger has four USB-C ports and one USB-A, the power bank two USB-C (one of which may be used to charge the power bank rather than discharge) and one USB-A.

The interesting thing here is that these need to distribute the available 100 W over the ports in use. Which requires a notion of "in use". As the charger is hidden behind the couch and thus doesn't allow for easy plugging/unplugging USB-C cables, I like to have cables connected and then simply plug them into devices to charge them. For USB-C cables/devices this works great, as when those are not plugged in, they are ignored for the purpose of distributing power.

This is not true for cables plugging into the USB-C ports but having a ~ USB-A destination. Here, just having the cable plugged it registers as in use, so they get their portion of the power, even if nothing plugged in.

This also applies to the Apple USB-C to MagSafe 3 cable included with my recently acquired MacBook Air. This is otherwise a completely perfect innovation, giving me the USB-C PD benefits but also the MagSafe benefits. My last computer before MagSafe was a PowerBook which was once flung across a room as someone stepped on the power cable. My first computer after MagSafe was a 2016 MacBook Pro with only USB-C ports where a USB-C cable was destroyed (but fortunately no damage to the computer) after someone stepped on the power cable. The Apple power cable is also thinner than equivalently rated USB-C power cables and of course doesn't take up a 40 Gbps port for just delivering power.

But there's also tons of stuff that only takes single digit Watts to charge. Like AirPods or other headphones. Or aTV remotes. Plugging those into a high capacity charger removes up to 60 W from the other ports, so that's pretty bad. But... what if you still have an old school USB-A multiport charger? I found one of those back in a closet not too long ago and it's now working nicely in my bedroom with an Apple lightning cable that can deliver 5 V 12 W as well as my Apple Watch magnetic connector and a 5 W iQ charger. With USB-A there are different rules for what counts as "in use" and a 60 W 5-port charger has fewer issues distributing the power. So this type of charger is really useful in certain circumstances.

What makes everything more complex is that I'm on a dynamic electricity pricing contract, where electricity prices are often very low during the afternoon when there is a lot of sun. When that happens, you want to charge power hungry devices quickly to take advantage. Slow charging stuff is then less interesting.

So: make sure your big USB-C PD chargers can do their thing quickly, and have slow-charging stuff on more modest USB-A multiport chargers.

To deal with the dynamic power pricing, there are simple and complex solutions. If it's pretty much repeatable day to day you could put things that have a heavy load on a dumb light timer. If it's more complicated than that you might need a power controller that's managed by some low power always-on computer.

 

[Ananke]

What makes everything more complex is that I'm on a dynamic electricity pricing contract, where electricity prices are often very low during the afternoon when there is a lot of sun. When that happens, you want to charge power hungry devices quickly to take advantage. Slow charging stuff is then less interesting.

Question: is yourt interest here economic, or rather is this stuff just really interesting to you? I'm not asking in judgement, but if it's the former, then I think you're wildly mis-matching the amount of brain-power to the magnitude of the problem: phones and even laptops just don't consume enough energy to be worth spending much effort on this kind of optimisation if it requires spending any money to do so.

Even given a maximum size laptop battery of 99Wh and a price delta of 30ct/kWh or so, for the price of a new 50€ charger you could charge your laptop 1650 times at the expensive electricity rate and still come out ahead - and my laptop from 2016 still hasn't cycled that many times; while USB power delivery standards have gone through at least 2 major evolutions since then (USB-C becoming ubiqitous vs a weird niche that only Apple supported; >100W PD becoming A Thing). That same Macbook Pro will still fully charge from 0-100% at 30W in 3.5 hours: how narrow are the zero or negative power price windows?

If this is not purely about the numbers, but more about a hobby-esque interest, then my hobby equivalent is that I have a dumb EVSE, and a bunch of dumb, thermostat-controlled, thermal loads, along with an interest (amounting to the spectacularly grand total of ~120kr/month) of keeping the peak power load for the house below 5kW. I've been batting a design back and forth in my head for years about trying to build a distributed control scheme to switch the EVSE and water heater on/off based on the total house usage (dominated by the other thermal loads) to keep peak usage down - but I'd be looking at a pay-back time of 5 years or so assuming everything went perfectly - and a WAF approaching zero because a single cold shower as a result of a bug in the control schema would be infinitely too many.

Even so, I've still got a bunch of circuit diagrams, half-assembled shopping lists on RS, and a most-complete test implementation in Python knocking about somewhere.

 

[Shavano]

Overthinking is in the thread title, so I'm guessing unnecessarily complex solutions aren't off the table.

 

[iljitsch]

To deal with the dynamic power pricing, there are simple and complex solutions. If it's pretty much repeatable day to day you could put things that have a heavy load on a dumb light timer.

Well, starting right about now in the year the early afternoon is usually a gimme because of solar power. But it all depends on the weather and demand a lot. So lots of wind can make the nights cheap, and typically sunday early afternoon is especially cheap as demand is low then. So a timer is better than nothing, but it's not great.

If it's more complicated than that you might need a power controller that's managed by some low power always-on computer.

Yeah I have a device that should do that: my AppleTV 4K! That's my Homekit controller. The trouble is that the thing is too stupid to let me trigger something every 15 minutes without me having to set up 96 separate automations.

I could use Homebridge on my Raspberry Pi but I hate having that thing use up 3 W 24/7 for that. My M4 MacBook Air uses less than that with the screen on!

So it's possible to use AppleScript to trigger shortcuts that interact with Homekit, so what I need to do is figure out if AppleScript can wake up my sleeping laptop on battery power at a time determined by a script.

What I plan to do is create charging profiles for the stuff that needs to be charged daily (so like my iPhone starting at 12 W trailing off to 4 W after 90 minutes) and then calculate the best time to start charging at night to be fully charged in the morning, or in the afternoon for a laptop to charge fully at lowest cost.

But then I need my smart outlets to turn on at the right times. Turning off is less critical. I already have for instance an automation that turns off juice to my Roomba when the motion sensor in the hallway triggers and the Roomba draws less than 8 W. (It will keep drawing 5 W even when the battery is full.)

Yes, I know, optimizing for single digit watts is not really worth it, but it's basically become a hobby. I got my apartment as low as 32 W at night with everything off at some point. Now it's more like 40. I hate that. Still 10 x better than the average home, I think.

 

[iljitsch]

Question: is yourt interest here economic, or rather is this stuff just really interesting to you? I'm not asking in judgement, but if it's the former, then I think you're wildly mis-matching the amount of brain-power to the magnitude of the problem: phones and even laptops just don't consume enough energy to be worth spending much effort on this kind of optimisation if it requires spending any money to do so.

Well, my shiftable power use is low enough that it doesn't really matter. I guess I could watch TV and cook dinner at noon or in the middle of the night to save power, but I'm not doing that. (Although through the actions of a certain politician energy here in somewhat northern Europe may become expensive enough the next winter to reconsider.)

And I even favor the convenience of Qi phone charging over wired charging over the much better efficiency of the latter. But I definitely like the idea of cheaper and more climate friendly charging. So I spend way too much brain power on that.

I'm guessing the only thing that really makes sense is running the washing machine and dish washer on sunday when the prices are lowest. And generally I only need these once a week so that works well.

Right now we have many afternoons with zero gross electricity prices, but with taxes and stuff I still pay 13 cents per kWh. The real fun starts when prices are actually negative and wasting power earns me money. It's actually quite a challenge to suck down more than 2000 W consistently.