Charging at 12v while the battery is running at 7.4v

I've got a portable speaker Bose SoundLink Mini. What I don't get is that the output voltage of its charger is over 12v while the battery at its 100 % capacity only reads 7.4v (also on its label)!

Have you ever seen similar situation? Charging battery at way higher voltage that the battery is actually never gonna approach?

Why I am asking this:

I would like to charge the speaker via a travel charger from USB, which would require this:

http://www.ebay.com/itm/USB-DC-5V-t...679272?hash=item43e45671a8:g:MN4AAOSw~bFWJLkk

So if I have a power bank with output 5v USB, and connect in it the advertised cable (see above), would it charge the speaker with no harm?

Thank you a lot.

It probably has two LiFePO4 cells in series, as well as a charging module inside. The charger needs a 12v input, like most other 12v chargers that charge up standard Li-Co/Li-Mn/Li-Fe chemistry cells. They're ubiquitous.

A 5v USB power source probably won't work.

There are some power banks that will have adjustable voltages, up to 12v-18v, so seek out one of them that's of quality manufacture.

Chris

There is probably also a buck circuit inside the speaker to bring the 12v down to the 8.4v two cells in series would need. Like USB chargers, 12v wall warts are somewhat ubiquitous, so it is much cheaper to design the input for 12v and use readily available parts to make the wall wart, then design one for 8.4v and have to do more custom work.

Does the speaker work while it is charging? If it doesn't, it is quite possible that they are bucking the voltage down to 4.2 and charging the cells in parallel to help keep them balanced. Although, then they probably would have speced a USB charger instead. Whatever.

ArminVanBuuren said:

I've got a portable speaker Bose SoundLink Mini. What I don't get is that the output voltage of its charger is over 12v while the battery at its 100 % capacity only reads 7.4v (also on its label)!

Have you ever seen similar situation? Charging battery at way higher voltage that the battery is actually never gonna approach?

Click to expand...

No problem with that at all. There are electronics in the charger that transfer energy from the 12v source to the batteries. It's not a direct connection. 12v is a standard by which there is many sources such as in vehicles, etc.

I would not trust that DC-DC converter as shown on Ebay. For one thing its only $2.15 and so it can't be all that good. The other is that its not very big......thus there can't be much to it. If you have a power bank that has 5v and have a decent DC-DC converter (5v USB to 12v), then I see no problem with using it. I should point out though, that if you're boosting up the 5v to 12v in some type of DC to DC converter, that current coming out of the 5v USB power bank will be at least 12v/5v = 2.4 times higher than that which is being drawn by the 12v going into the charger. It's a power relationship with the conservation of energy principle.

Thank you all for your peaces of advice. To answer this:

Timothybil said:

Does the speaker work while it is charging? If it doesn't, it is quite possible that they are bucking the voltage down to 4.2 and charging the cells in parallel to help keep them balanced. Although, then they
probably would have speced a USB charger instead. Whatever.

Click to expand...

Yes, it does work. It is quite strange.

A am probably gonna try and buy it, its just 2 bucks, and just try it whether or not its gonna work.