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hard-wire a tablet?


Aug 11, 2014
I'm trying to solve a charging issue for tablets in my cars. We need to leave the tablets in the cars all the time (this is for work) and the temperature in the cars in Phoenix reaches 120 easy. The tablets are fine, but the batteries hate it. We've figured out also that the lighter-chargers don't put out enough current to actually run the tablet, so the batteries run down, even when plugged in and charging. We'd like to hard-wire the tablets, primarily to get enough juice to keep the tablets charged. Ideally I'd find tablets without batteries and just run them always plugged in, but the reason tablets are affordable is that they're not custom. The hard-wire harnesses I see coming from China don't seem to have any images or notes about amperages on them, nor any notes regarding this issue.

Any advice?
Thanks John Bean. We'll try that one.
Kaat72 - we've tried a couple of different options, and when we looked into trying to bypass the batteries (after narrowing down the problem) learned that tablets (mostly the screen) use more power than most chargers put out - so unless you hard-wire them, you really need the batteries. The tablets will trickle charge overnight if they're left plugged in, but the 'lighter's' in our hybrids are powered down with the ignition. If we can find a charger that puts out enough power so that the battery is never relied on, we're fine - that's our goal.

Thank you!
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Most chargers that are meant for tablets (as opposed to those meant for phone but just happen to also fit the micro-usb connector found on tablets) will be able to put out the extra current needed by the larger display on a tablet. Look for a charger with a 2.1A output and you should be good.

By the way, what are the tablets being used for? Display + GPS + Bluetooth + Active Data Connection can add up to a lot of additional drain.
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Thanks. We got some budget 2.1A chargers that haven't done the trick. And yes - Display + Bluetooth + GPS + Data Plan all day long. The charger that John Bean recommended says 4A output - we'll try it.

I thought that might be the case, that's why I skipped the obvious cheap chargers (too cheap to be true in some cases) that claim 2.1A but probably have a much lower output.

I know the one I linked to is quite a bit more expensive but I also know it works well with high-demand tablets like my Nexus 7. Just make sure you use a good-quality short USB lead; I recommend a dedicated charge-only cable like the PortaPow cable or equivalent. The choice of cable really can make a big difference on high-current devices.
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John Bean - thank you. I passed your device recommendation over to my code guy. He says he's tried one similar - if we dim the display it keeps up with the load demand. Most drivers want the screen bright. I'll forward the cable choice as well - makes sense that a lot of current is dropped in those tiny stranded cables.

Kaat72 - we're a transportation network startup - rubyride.co. Part cab, part microbus. Thanks for asking.
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Certain vehicles, like Mercedes ML500 or Honda CRV has the 3 prong outlet build into the car, so you don't have to use a car charger, you can just plug your wall charger directly into it. I really like that concept, but my car doesn't have one. So instead of car charger, I bought a portable 3 prong wall outlet that plugs into my cigarette lighter. Which works great for me because now I don't have to worry about the incompatible car charger, now I can use my device's own charger in the car. There are people whom question my setup though, they said it is too much electric current conversion, and my car will eventually get a short circuit. But it's not like I'm plugging in a chain saw here, and it's only one extra converting when compared to the cigarette lighter charger. Plus I really don't think my wall plug converter is really converting 12v current from the battery to the 120v wall current. Plus most of mobile device charger usually only draws 9v ~ 12v current. Any way, that's my suggestion, if you can afford it, get a car with the outlet, otherwise, try a portable outlet.
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I'm glad this thread was mentioned in the Phandroid article. I've been searching for solutions that would truly give 2.1A charging, for the charging adapter that I purchased. I ran into these cables on Amazon:

6 foot cable (2.1A)
Amazon.com: 360 Mobile Solutions Smart!(TM) Micro USB LED Cable Powerful 2.1A Output Fast Sync Rapid Charge for Smartphones and Tablets - Retail Package (Black): Electronics

3 foot cable (2.1A)


And this is my car charger, which works great (only issue I've had is when all 4 are being used)

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Pizzamannetje gave good advice - get a USB voltage/current meter - they can be had for less than $10 from Amazon.

What I found is that my N7 (2012) will only draw so much current for charging the battery, even when when using "AC Mode". The amount of current drawn seems to vary based upon the level of charge of the battery, and perhaps the temperature and other factors. My 3.2a charging source charges at about the same rate as my 1a source and 2.1a sources.

Regardless of the charger amperage, my tablet will consume power at a much faster rate it will recharge. If I disable GPS and dim the display, it almost always keeps the tablet charging. But then that really limits the benefits of having a tablet in the car.
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Sorry if this is silly advice but what about s small “converter”..??

At one point the face plate of our radio got stolen and i end up setting up a home stereo for music and the Tini converter provide all the power we need

Something like this for just the tablet

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