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Comment by hanche | Hacker News Reader

I have a food thermometer with a builtin rechargeable battery. It charges via usb-c, but so far I have not managed to charge it from a usb-c charger. It will only charge with the supplied usb-a to usb-c cable. I would love to understand why. But at least, they had the good sense to not supply their own charger.

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USB-A ports output 5V as long as the device is on. But with most USB-C ports, to save power no power is supplied until the device requests what voltage it wants. Requesting 5V is very simple, just two resistors which cost fractions of a cent, but somehow a lot of cheap devices forget to include them.

It might need a low amp device to charge. My vape does not charge with my good chargers but it does with older ones and the usb port on my laptop.

Doesn't USB-C have a "basic mode"? As in, if it's unable to negotiate some kind of high-power PD mode, it will just deliver the basic USB2 5V/0.5A?

I can charge my Sony headphones with anything from an old USB2 only PC, old Samsung USB-A phone charger to my 65 W HP USB-C power adapter.

I don't think they have any kind of PD mode, I think they just expect regular 5V. The specs on the site say "USB charge" and the charging duration is 3 hours. They come with a USB-A to C cable.

usbc chargers are not supposed to even have 5V output until a device requests it. For 5V at various currents, “charge configuration” resistors can be used at the device. For higher voltages an active negotiation is required. Cheap devices based on old products often omit the 2 resistors (literally worth under $0.01 each) and this only charge when connected to a usb-a charger, which always has 5v output. Depending on the device, it can be anywhere from easy to impossible to hack in your own resistors.

> usbc chargers are not supposed to even have 5V output until a device requests it.

I did not know that, thanks. I was expecting USB-C chargers to work in "dumb 5V mode" by default. I guess that could be to avoid problems if you connect two chargers together?

I think that is why usb-a (male) to usb-c (female) adapters are not supposed to exist. They might let you connect two usb-a chargers together using a usb-c cable, and they are not designed to tolerate that.

Have you tried a different USB-A charger? Some smaller devices have problems with USB-C to USB-C. I don't know why this is the case, though. It's just something I have observed with different devices.

I have a Philips toothbrush like that too, at least it works with any A-C cable, just not C-C

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