Understanding USB charging standards

MrM · 2025-01-29T20:09:29+0000

Long story short I have recently bought a new portable wifi scanner that will only charge when connected to a computer USB port. I knew this ahead of time; all the negative reviews are around the lack of ability to charge from a wall plug. I’ve tried a variety, as have others online, with no luck.

The charging cable is a USB 3.0 A (the slightly funny looking figure of 8 ish shape). Prior to purchase I thought it was something to do with the current output of the port and anticipated being able to get around this with a similarly low output (<750ma) USB plug but to no avail. I am now wondering, and assuming that it is something to do with a data handshake or similar that is absent when connecting to a wall plug.

Despite a lot of trawling online, my efforts have larger drawn a blank. One individual got around this using a “u disk mp3 decoder” where the device is powered by a mini USB connection and seems to get around the issue. Again I have not the knowledge to understand why this works. Whilst it’s an inexpensive solution, it’s not convenient.

Bottom line is I’m hoping to find a wall charger that I can purchase that will get around my issue.

Can someone kindly enlighten me as to what is likely going on here please?

5abr3 · 2025-01-29T21:52:10+0000

Not 100% sure what's causing that but the USB charging standard is supposed to start at the lowest possible charge level (5V @100mA from memory) and then the devices negotiate upwards.

If I had to guess I would think they've not implemented the USB charging standard (by skipping a resistor across the data lines for initial handshake) and all chargers stay at 100mA; I would also guess their charger just shoves out a high current regardless of what's attached to it so I wouldn't risk using it to charge anything else.

MrM · 2025-01-30T05:21:25+0000

Sorry, perhaps I’ve not explained the situation well enough. The scanner is made by Brother. They supply just a cable, saying the device can only be charged via a computer. And it seems this is true; it won’t charge when connected to a generic wall plug socket (they do not supply one). I am trying to understand why I can’t charge it from the wall.

WARburton · 2025-01-30T06:43:34+0000

make and model?

MrM · 2025-01-30T10:53:10+0000

Brother DS-940DW

WARburton · 2025-01-30T11:21:10+0000

lol yer no reason given at all but as stated by Brother it will only charge from a pc.

when you charge it dose it open an app or sync in some way so it can monitor the battery and stop over charge/damage

WARburton · 2025-01-30T11:24:50+0000

i found this comment on readit

Huh, I guess it was because of the links... What I did was use a "mp3 lossless decoder with u disk" module (google it). Connect it to power, and then plug the scanner to the USB port. It'll get tricked into charging!