couple of thoughts on recharging batteries in tablets etc

[e9999]

I have been playing with my new tablet (love it, Note 10.1, squashes ipads). A couple of observations come to mind. perhaps useful to other prehistoric dummies like myself.

-it is really useful to have a battery monitoring app, especially with logging features. To check usage by various apps when on and to figure out recharging capabilities.
-I was surprised to see how much slower the tablet would recharge from a regular USB port rather than with the OEM USB brick with a USB outlet. No doubt due to the relatively low half amp rating of regular USB ports. For example, my brick is rated at 2 amps, 4 x more. Sure enough, when I did some charging tests, it took 4 x longer to recharge from a regular USB port. Interestingly, at first I even thought that the tablet was incapable of recharging from a regular USB port, as it would show a no charge symbol on the screen when connected to a regular USB port. Furthermore, when recharging off a regular USB outlet with tablet on, the recharging can barely if at all keep up with power consumption. But of course better than nothing when on the road and using a 12 volt USB adapter. For that application, you may want to check carefully the specs of the adapter.
- also surprisingly perhaps at first glance, putting a short extension cable on the USB OEM cable from brick to computer cut down the power to charge the battery by about half, as a quick look at a wiring diagram confirmed. In other words, put an extension cable of equal length and resistance and it will take twice as long to charge your battery. Kind of counterintuitive, as one might expect that the cable resistance is negligible. Well, not in this case. This is probably 1 of the main reasons why the OEM power brick comes with a very short cable.

 

[hey you]

12 volt USB adapter

What would you recommend for a 12 volt USB adapter? My wife likes to charge (or leave it plugged in) her Ipad when we travel. Her older adapter didn't provide a charge for the Ipad but works well for the Iphone.

 

[badlander]

Very good info, thanks.
Sorry, but, I have to ask what is probably a dumb question.....
What's the OEM power brick? I have a 2002. I don't think I have any bricks in my truck!

 

[hey you]

Glad you asked... Just kidding. I'm curious as well. My question regarding the USB adapter should have included the brick question. I just bought a new InCase (EC20041) Dual USB charger. They say it will charge two devices at once, Ipad and Iphone.

 

[lumpy70]

Get a 12V USB charger that delivers 2.1A...that's the magic number for tablets including ipads. It'll charge at a regular rate in your truck that way.

A Google search for 2.1A charger gets you zillions of results, pick your poison (Radio Shack, Best Buy, Cruchfield etc).

Craig.

 

[e9999]

sorry, wasn't clear. By OEM brick I meant the 120V to USB-female charging adapter from Samsung. Actually quite a bit smaller than the old style outlet bricks. That one is 2A as said earlier. And by "regular USB" I meant a USB outlet on a computer etc, which is normally rated at 1/2A max.

Unfortunately, my current (ah!) 12V to USB adapter is only 1/2 A. When I got it way back I thought it'd be fine since it's the standard. From HF IIRC, but was only like $2. Will have to get a 2A. (Probably better not to go over that since I imagine that's the design charging rate of the battery. I think it's a 7Ah battery in that tablet, amazing when you think that some big lead acid car batteries are under 100 IIRC...)

I would suggest that if you do get a "2A"adapter, to check that it's really 2A per USB outlet or for at least one, if it has more than one.


OTOH, and probably worth stating, I have no idea what a 2A USB outlet would do to a non-battery gizmo like a drive etc. Probably best to avoid getting mixed up with those...

 

[tclark]

This is what you need; got a couple in my boat and they're great:

http://www.starmarinedepot.com/Blue...ght+Cap.html?gclid=CLqBnt7xlrYCFVCRPAodc20AkQ

 

[george_tlc]

...
Will have to get a 2A. (Probably better not to go over that since I imagine that's the design charging rate of the battery. I think it's a 7Ah battery in that tablet, amazing when you think that some big lead acid car batteries are under 100 IIRC...)

I would suggest that if you do get a "2A"adapter, to check that it's really 2A per USB outlet or for at least one, if it has more than one.


OTOH, and probably worth stating, I have no idea what a 2A USB outlet would do to a non-battery gizmo like a drive etc. Probably best to avoid getting mixed up with those...

Do you realize that there IS a charger inside the tablet and any other USB powered/charged device?

So, whether the 12V USB adapter is 2A or 3A or 4A doesn't mean that you'll overcharge the device you plug in. I personally would get something in the 3A range to cover future higher current requiring devices.

The only concern is having a USB adapter that can't provide enough current for the device you are plugging in to charge.

Also, some USB devices are smart enough to detect that they are plugged into a computer and will then draw less current since they know that a computer can only provide at most 500mA (as part of the USB spec). That allows the USB device to still charge (albeit slower) without the risk of drawing too much current and causing the computer to shut down that USB port.

cheers,
george.

 

[Bogo]

While there is a charger that will control voltage, it may not have an over current limit. Don't hook your device up to a USB port with more Amps than the charger that is provided with it outputs. I've read repots of some phones batteries being destroyed when hooked up to 2.1Amp USB ports. I think most smart phones and tablets are now designed for that rate or at least have some current limiting, but some of the older ones couldn't deal with it.

While my HP Touchpad works nicely with this (http://www.amazon.com/gp/product/B005XRDB92/?tag=ihco-20) 2.1A/1A dual port USB car power supply. My Samsung Galaxy Tab 10.1 didn't like it and would only charge at the 500mA rate. Check others comments on which ones work and don't work with the devices you have.

 

[george_tlc]

While there is a charger that will control voltage, it may not have an over current limit. Don't hook your device up to a USB port with more Amps than the charger that is provided with it outputs. I've read repots of some phones batteries being destroyed when hooked up to 2.1Amp USB ports. I think most smart phones and tablets are now designed for that rate or at least have some current limiting, but some of the older ones couldn't deal with it.

Any device that uses a charging chip WILL regulate current. That IS a requirement of charging li-ion cells, the charger chips will do a current limited initial charge phase and then transition to constant voltage while monitoring charging current. When that charging current drops far enough the charger chip deems the battery charged and will indicate it as such either via a status LED or through the devices UI.

This charging profile has been the case since charging chips came out for li-ion cells many many years ago (more than 10).

The 'repots' you've heard are typical hearsay or other uneducated responses to device failures or idiots plugging things into higher voltage sources.

Standard USB to single li-ion charging chips are linear devices that take the 5V and drop it down to the appropriate charging voltage (internally current limiting in the charger chip). So, sure, if you had say 6 or 7 or ... volts coming out of your 5V USB then you will potentially overheat the charging chip.

Oh, and the only 'current' limiting that goes on in a 12V USB charger is that the switcher IC inside can't provide more than a certain amount of current before it limits, either by design or by lack of current delivering ability - in the later case it will be quite stressed and possibly fail.

Anyhow, as a EE who has designed a few li-ion chargers I personally don't have any issues whatsoever plugging any of my USB charged devices into a 3A USB outlet...

cheers,
george.