Question about USB charging for batteries

[csziggy]

I've got a wall wart charger that connects by USB cable to my tablet to charge its battery. I've also got a pair of speakers for the tablet that charge by connecting via USB to the computer. Would it be safe to use the tablet wall wart to charge the speakers?

I know the USB standard should be the same but this method of charging built in batteries is new to me.

Thanks!

[MannyGoldstein]

1. Should be fine

USB supports charging. Some tablets come with weird USB chargers that won't fit into other USB ports, but in any case nothing should get hurt. Worst case is that something won't charge.

Good luck!

[liberal N proud]

2. Check the power ratings for both devices first.

They should match.

[MannyGoldstein]

3. Actually...

The voltage is always 5v for USB. The current rating of the charger (in amps, abbreviated A) indicates the max current that it *can* supply - the device drawing power can draw whatever current it needs up to that amount. If it tries to draw more, the worst that should happen is it won't charge.

[csziggy]

5. There is no information on the power requirement for the speakers

Or on the tablet. The wall wart says "50/60Hz - 0.5 mA" if I am reading the miniscule font correctly. The output from the wall wart is a standard USB cable on the end that plugs into the wall wart and a 30 pin plug (pretty much identical to an iPad plug) on the other end.

[pokerfan]

4. new power delivery spec for USB was announced yesterday

Since it's becoming a defacto standard for charging portable electronics (My cell phone, eReader and mp3 player all charge this way.)

100W Power Delivery Spec Approved For USB 2.0 And 3.0

[grok]

6. 100 watts seems like overkill over usb.

20 amps over a thin cable?

better stick to charging at a max of .5 amps(2.5 watts). charging should be safe.


I've had early laptops who's usb ports got fried by overtaxing too much.

[pokerfan]

7. It doesn't specify the cable

but rather just that the USB port itself be capable of providing 100W. It will be up to peripheral manufacturers to size the cables for their devices appropriately. For example, the cable for my eReader is fairly stout while my mp3 player's is quite light. I haven't dug into the technical details, but I expect that there will be the usual protections for shorts and other abnormal conditions. I welcome the standardization as it means that OEMs will have to treat it as a true power supply instead of as an afterthought. I've had PCs where the ports on the back weren't capable of powering an external hard drive while the front ports were just fine. That was just silly design.