Captive vs separate USB-C power supplies

[brianl703]

How can you even charge a laptop through USB? All the ones I've owned have a connector for a dedicated charging plug.

My Lenovo laptops, both my personal one and my work one, have a USB C port that can either be used to charge the laptop or as a regular USB C port for peripherals (like Klein Tools Ideal boroscope camera, which doesn't work with their app on my Android phone, but works just fine plugged into my laptop and using VLC to display the video).

The power supply/charger for these laptops has a cord with USB C plug at the end.

USB C can supply power at several standard voltages, 5V, 9V, 15V, and 20V. But when you convert a USB A port to USB C with an adapter or cable, 5V charging is all you get.

I have a USB A to USB C cable I use to charge my phone, because I have a wall outlet with USB A charging ports on it, but it does nothing when plugged into my laptop. Laptop will not charge off 5V.

 

[brianl703]

This is the one I use. It was on sale for $12.50 when I got it, cable included:

https://www.amazon.com/gp/product/B0B4N4WKTB

Is that thing UL-listed with the correct creepage distances between the input and output?

 

[bunnspecial]

What do you mean not compliant or unsafe? I'm using one right now to connect my new external drive to the computer.

USB-A female ports are intended to be able to supply power. A male USB-A should never have power applied to it, and doing so is likely to fry something.

The USB-C standard allows for bi-directional power. A port can either be used to deliver power(quite a bit of power) to a device or it can be used to charge a device. I think the limit is something like 95W. Some laptops, like most Macs from 2016-2021, charge only by USB-C and a lot have the option now even if there's another way to charge them.

Those adapters could allow a power delivery USB-C device, like a dock or even just a regular USB-C charger, to be plugged into a USB-A port. That's a bad thing, which is why it's not compliant with the standard. It's sort of a computer equivalent to a male-to-male household cord.

If you have a USB-C only peripheral, it should be connected to a USB-C port. USB-C ports can be adapted to USB type A, but not the other way around. You won't find a reputable brand(Anker, Belkin, Apple, etc) making an adapter that allows a USB-C device to be plugged into a type A port, although all make simple and inexpensive adapters to plug a type A device into a C port.

In practice will it likely cause a problem to connect a low power draw USB-C peripheral to a type A port? Probably not, but bear in mind it might not work as type A ports officially are limited to 5W.

 

[atikovi]

If you have a USB-C only peripheral, it should be connected to a USB-C port. USB-C ports can be adapted to USB type A, but not the other way around.

So how would you connect the USB-C cable external drive to a computer with USB-A port other than with what I linked to? It seems to work fine as far as I can tell.

 

[LDM]

How can you even charge a laptop through USB? All the ones I've owned have a connector for a dedicated charging plug.

Most laptops use a USB C port for charging and docking stations these days. They no longer have a "dedicated charging plug" which was typically the old barrel connectors.

As for the device you linked, its fin3 for low power devices. It would not work with anything charging over 5V.

 

[y_p_w]

I like the Apple way of replacing the cheap cable rather than the expensive brick. The Belkin one I’m using now(on an Apple brick) seems to be holding up well.

Of course I still prefer MagSafe, which my first gen M1 MBP doesn’t have. Thankfully the current MagSafe implementation allows just the cable to be replaced too.

MagSafe 3 cables are really expensive though. I have charged a MagSafe 3 equipped Mac with just a normal USB-C to USB-C cable. If mine failed, I might just go that route permanently. I've gotten Monoprice 5A USB-C cables for less than $10.

 

[y_p_w]

That device wouldn't work to even try to charge a laptop because it can only output 5V, and a 45w laptop won't charge on 5V. Probably needs 15V or 20V.

The remarkable thing about USB-C is that it will accept 5V. I've done it with Macs and that Lenovo (a ThinkPad X1 Carbon). I've used a combination of a USB-C to USB-A cable and a 1A USB-A power adapter, and my Mac reported that it had 5W. But basically all it's going to do is slow down the charge drop or charge excruciatingly slow while in sleep mode. My newer Chromebook is USB-C too.

The Macs I've tried don't give any warnings. I previously started a discussion on plugging two USB-C ports on the same Mac together and it displayed that it was charging. But the Chromebook and Lenovo give various warnings if they're connected to a "low power" source. The Chromebook indicates that in the charging info. The Lenovo does that with a non-Windows text screen when it's powered on or maybe when it wakes up from sleep. Not sure if it displays a message in the power info in Windows.

 

[brianl703]

The remarkable thing about USB-C is that it will accept 5V. I've done it with Macs and that Lenovo (a ThinkPad X1 Carbon).

Neither my work Lenovo nor my Lenovo laptop will acknowledge that it's getting any power when I try using the same USB C cable that charges my phone with them.

On those, 5V isn't enough.

 

[y_p_w]

My Lenovo laptops, both my personal one and my work one, have a USB C port that can either be used to charge the laptop or as a regular USB C port for peripherals (like Klein Tools Ideal boroscope camera, which doesn't work with their app on my Android phone, but works just fine plugged into my laptop and using VLC to display the video).

The power supply/charger for these laptops has a cord with USB C plug at the end.

USB C can supply power at several standard voltages, 5V, 9V, 15V, and 20V. But when you convert a USB A port to USB C with an adapter or cable, 5V charging is all you get.

I have a USB A to USB C cable I use to charge my phone, because I have a wall outlet with USB A charging ports on it, but it does nothing when plugged into my laptop. Laptop will not charge off 5V.

Lenovo laptops with USB-C that I've seen won't accept 5V, but it's not because it's not feasible. Macs can do it. So does my Acer Chromebook. I'm trying it right now in my Chromebook and I get a popup message - "Low power charger connected - Your Chromebook may not charge while it is turned on". In the power info part of the panel I get "Battery charging may be unreliable". It's just going to use whatever it can for direct power to the electronics, and maybe if there's something left over it goes to charging the battery. And of course if I power it down it should be able to charge the battery, albeit really slowly.

The electronics will do whatever voltage conversion is needed to power and charge.

 

[Quattro Pete]

Lenovo laptops with USB-C that I've seen won't accept 5V, but it's not because it's not feasible.

It's not feasible on most laptops. All USB chargers I've seen are limited to 3A of current at 5V, which results in 15W of max power. A typical laptop probably needs 30W to operate. CPU itself needs 15W unless you restrict it to some lower power mode maybe.

 

[y_p_w]

Most laptops use a USB C port for charging and docking stations these days. They no longer have a "dedicated charging plug" which was typically the old barrel connectors.

As for the device you linked, its fin3 for low power devices. It would not work with anything charging over 5V.

I've got a USB-A power adapter with a 12V output. Not sure exactly what can use it. It's this one (combination USB-C and USB-A):

Anker 725 Charger (Nano II 65W)

Universal High Speed - From iPhone to Samsung to USB-C laptops and more, Anker’s signature PowerIQ 3.0 technology provides high-speed charging to virtually any mobile device. One for All - Compatible with virtually any device that can be charged via USB; with a USB-C PowerIQ 3.0 port and a USB-A...

www.anker.com

Specs​

​

Total Wattage: 60W​

​

Input: 100 - 240V ~ 1.8A 50 - 60Hz​

​

PIQ 3.0 (USB-C Port): 5V ⎓ 2.4A / 9V ⎓ 3A / 15V ⎓ 3A / 20V ⎓ 2.25A (Up to 45W)​

​

PIQ 2.0 (USB-A Port): 5V ⎓ 2.4A / 9V ⎓ 1.66A / 12V ⎓ 1.25A​

 

[y_p_w]

It's not feasible on most laptops. All USB chargers I've seen are limited to 3A of current at 5V, which results in 15W of max power. A typical laptop probably needs 30W to operate. CPU itself needs 15W unless you restrict it to some lower power mode maybe.

I meant feasible in that it could accept power and use it, although obviously it might not be enough to provide power to the electronics and charge the battery at the same time. USB-C is flexible enough that an OEM can decide whether or not to allow 5V input power. Lenovo laptops don't accept 5V, but others may. That was just a design choice.

 

[brianl703]

I meant feasible in that it could accept power and use it, although obviously it might not be enough to provide power to the electronics and charge the battery at the same time. USB-C is flexible enough that an OEM can decide whether or not to allow 5V input power. Lenovo laptops don't accept 5V, but others may. That was just a design choice.

How do you know that it's actually using the 5V as opposed to just popping up a courtesy message saying that the charger isn't enough?

Lenovo probably figured that most users would come to the same conclusion when the light next to the charge port doesn't turn on.

 

[y_p_w]

How do you know that it's actually using the 5V as opposed to just popping up a courtesy message saying that the charger isn't enough?

Lenovo probably figured that most users would come to the same conclusion when the light next to the charge port doesn't turn on.

I suppose the best way would be to use a USB monitor for charge and voltage. There are probably tools to access the internal power system to see what it’s doing.

With Macs I can see the power rating in System Report. I’ve specifically seen it listed as 5W when connected to a 1A USB-A power adapter. I can also use coconutBattery to get access to the internals listing charge or discharge current. However, that’s usually at the native voltage of the battery or charging system. A 5V source would need to step up the voltage.

 

[LDM]

I meant feasible in that it could accept power and use it, although obviously it might not be enough to provide power to the electronics and charge the battery at the same time. USB-C is flexible enough that an OEM can decide whether or not to allow 5V input power. Lenovo laptops don't accept 5V, but others may. That was just a design choice.

I don't know about Macs but Lenovo and Dells will not charge at all if there isn't enough power. Dells will give a message after POST about not having enough power, Lenovos generally give the message inside Windows, both state they will not charge due to not having XX watt power supply attached. Doesn't matter on either if it is a dedicated power supply or a docking station that uses USB C. Its also highly variable on the computer, we have Lenovos at work that go as low as 45 Watt supplies and some that require 135 Watt supplies.

 

[y_p_w]

I don't know about Macs but Lenovo and Dells will not charge at all if there isn't enough power. Dells will give a message after POST about not having enough power, Lenovos generally give the message inside Windows, both state they will not charge due to not having XX watt power supply attached. Doesn't matter on either if it is a dedicated power supply or a docking station that uses USB C. Its also highly variable on the computer, we have Lenovos at work that go as low as 45 Watt supplies and some that require 135 Watt supplies.

I've used a 30W Apple USB-C power adapter with a Lenovo ThinkPad X1 Carbon, where the OE was a captive cable 45W power adapter. I get the lower power message, but that clearly charges the battery. My kid primarily uses it and the battery always stays fully charged. I don't know what the cutoff point is where it just won't use it.

Heck - I've used several 20W (some max 9V [Apple] or 12W) USB-C power adapters with that Lenovo. This is the message I get on power-on with that or the 30W power adapter:

The connected AC adapter has a lower wattage than the recommended AC adapter which was shipped with the system. To use AC power, please connect the AC adapter which was shape with the system.​

Press the ESC key to continue.​

But I've left it connected for a week (away on vacation) with the 20W power adapter in sleep mode and it woke up just fine, so obviously it can charge the battery. Obviously it's not ideal, but it seems to do something.

I experimented a little with a 12W USB-A power adapter and a USB-A to USB-C cable. I get the same message on power on, but not any indicator that it's charging, like the little LED on the side nor the charging icon in the information panel. It starts normally if it's not connected to power at all.

 

[bunnspecial]

FWIW, my MBP specs a 45W charger. I use a 30W charger at work as would come with an M1 MBA.

I don't get any complaints from it. When I'm using it, usually it will show a plug over the battery in the menu bar, which is supposed to indicate that it's running off the power adapter but not charging. In reality I usually can see it creep up 1-2% an hour. Sleeping and plugged in, it still charges decently on this charger.

I've not tried an iPhone/iPad 21W charger, which I don't have. I'd be curious as to how it would charge a Mac. I do somewhat often charge my phone off the TB3/USB C ports on my laptop, and my iPhone 12 does charge ridiculously fast compared to a 5W type A brick or a 7.5W wireless charger.

 

[y_p_w]

I've not tried an iPhone/iPad 21W charger, which I don't have. I'd be curious as to how it would charge a Mac. I do somewhat often charge my phone off the TB3/USB C ports on my laptop, and my iPhone 12 does charge ridiculously fast compared to a 5W type A brick or a 7.5W wireless charger.

I think those are spec'ed as 5V/9V. Not sure how that affects the conversion to the charging/operating voltage. Or at least I'm thinking you mean the 20W because I can't find anything from Apple that's 21W. I've got a couple of the 20W that came with a 9th gen iPad and with an iPad Mini 6. Mine are labeled as Salcomp and Flextronics. But it should look like this:

 

[FishFry]

Those magnetic adapters working great for me - up to 5A charging.

https://www.aliexpress.com/item/1005004971580228.html

 

[y_p_w]

I found the old captive cable power adapter for that Lenovo ThinkPad X1 Carbon. It’s actually rated for 65W. I guess captive cabling helps since most cables are only rated at 3A, where 20V is common. The laptop says 20V at 2.25/3.25V, but that could just be the battery rating. But I’ve gotten it to charge on 9V or 12V.

And strangely enough I plugged it in and it’s working. Not sure why it stopped working previously. So it doesn’t give that power up warning on 45W input which I’ve tried.