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Do any tabs charge via USB??

25K views 19 replies 19 participants last post by  mTab 
#1 ·
as the title says, im after a new tablet, 8 - 10" ips, 1 GB ram but im finding it rather difficult to find one that says you can charge via USB
do any exist?
i like the sound of the cube u9gt2 or the onda vi40 as both fall into my price bracket but neither seem to do what i really need. is it too much to ask?
any recommendations much appreciated but only if you can guarantee USB charging
 
#3 ·
Hi,
The Zenithink ZT282 C71 Upgrade charges by USB, it also has 1Ghz Ram.
The is a Forum here for the Zenithinks you will find it in the Cortex 9 section
Regards Granny1
 
#4 ·
Unfortunately the C71 Upgrade (1GB RAM) is only 7" and does not have an IPS screen, so it's not really what the OP is asking for....
 
#8 ·
The 8" 4:3 format Teclast P85 dual core (RK3066) charges via usb (microUSB). Don't know how fast as not got mine here yet (hopefully delivery today).

Most RK3066 devices don't seem to charge via usb though (and I think there was an issue with an early P85 firmware, if the battery was low and you tried to charge via a laptop without enough amps from the usb port - could be it was people using non-charging ports though, and I can check with my Asus Netbook that does have charging ports).

I have a known good Samsung microUSB charger that delivers 0.7 amps, so I'll probably start with that (probably useful to have plugged in when using the tablet close to a power source as well), then probably use a car charger driven by my 12v 40ah gel cell powertank (built for astronomy use) from then on.
 
#11 ·
Charging a Tablet via USB is a very slow process, special if that Tablet is running on 7.4V (charger is 9V in that case).

Fact is that the max charge via USB is 500mA! That power in reality you'll hardly get As example, I use an P90 9.7" with IPS screen running on 3.7V (charger is 5V 2A) and if I charge via USB the real max charge delivered to thew Tablet is 270mA and on one computer as low as 190mA! The charging power will also be lower if some other device as the Tablet is connected to the same Computer's MB.

Said that, it's really recommended to use an external Charger who delivers 2A or even more. But you always have to be carefully not to "overcharge" the Tablet which will shorten the lifetime of the Batteries. Most of the chargers which you get with the Tablet didn't having a protection which cut's the charging power after the battery is full they will just continue to charge until you disconnect that charger. And on the cheap chinese batteries, the internal protection circuit is just a joke!
 
#16 · (Edited by Moderator)
There's a bit of misinformation here. I suggest reading this.

Fact is that the max charge via USB is 500mA!
That's not true. 500mA is the maximum for a USB2 data connection. On a USB3 port, it's 900mA. But then there are charging ports (just power, no data connection) which can provide even more. To quote the relevant part from the wikipedia article:
"A dedicated charge port may have a rated current between 0.5 and 1.5 A. There is no upper limit for the rated current of a charging downstream port, as long as the connector can handle the current (standard USB 2.0 A-connectors are rated at 1.5 A)."

Said that, it's really recommended to use an external Charger who delivers 2A or even more.
Yes, for a tablet, a good 5V charger with 2-3A is recommended over charging via USB.

But you always have to be carefully not to "overcharge" the Tablet which will shorten the lifetime of the Batteries. Most of the chargers which you get with the Tablet didn't having a protection which cut's the charging power after the battery is full they will just continue to charge until you disconnect that charger. And on the cheap chinese batteries, the internal protection circuit is just a joke!
Charging the battery and taking care that it isn't overcharged is not the job of an external charger! It's the job of the power management chip inside of the tablet. The external power supply provides power to the management chip, which then decides what to do with it. First priority will probably be to power the system, and then if any power is left, it'll be used to charge the battery. That's why it's a good idea to turn off a device while charging it, especially when using a relatively weak power supply. That way, all power can go to the battery and it'll be charged faster than if the system were running.

How do I know this? I've recently done some research on the power management chip used by most if not all Ainol Amlogic tablets. That chip doesn't care whether the external power comes from an AC/DC charger or from an USB connection - with one important exception. It has a current limit setting for USB. Depending on how the system software or driver configures the chip, it will limit the current taken from a USB connection to 100mA, 500mA or 900mA (these familiar values again). But it also has an "unlimited" setting where it'll take as much as it can get. And this "unlimited" setting is the default, on my tablet at least. I've connected it to a powered USB hub and seen that it happily drew 1000mA and more over USB.

Anyway, I think most tablets nowadays support charging via USB, and with more than just 500mA (if you use a dedicated USB charger, not a USB data connection). Nevertheless, I recommend using a good AC/DC power supply, if the tablet supports it.
 
#20 ·
Teclast and Pipo tablets often have MicroUSB charge ports.

My Pipo U8 can charge from a computer (quite quickly) or using the mains USB charger that came with it (2A). It does not charge at all using 700mA wall chargers. Many computers now supply plenty of power over USB.
 
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