This may be interesting for those of you who read my post regarding the power supply problem with the Samsung Tablet being used in the Isuzu 4WD as a vehicle GPS.
To recap; the tablet battery was discharging faster than the vehicle usb port could recharge it. After identifying this as the issue I ordered from eBay China a 12V to 5V converter rated at 3 Amps. It arrived today.
I’ve started making a wiring loom. However before I fit the converter to the vehicle there is something important I need to check. I’m not sure if this is something unique to Samsung, so let me explain.
The tablet can either be connected to a usb port on a laptop or a 240V wall charger. When connected to a laptop the tablet might be transferring data. Moreover the tablet knows it shouldn’t draw too much recharging power from the laptop as the laptop may be damaged. Therefore, when connected to a laptop or other usb data capable port, the tablet is designed to recharge slowly at a low amperage.
If the tablet us connected to a 240V charger with a usb port it knows the charging rate can be much higher as the charger can provide plenty of power.
How does the tablet know when it’s connected to a mains charger verses a laptop port? The usb plug has four pins.
The outer two pins (red arrows) are the 5V positive and negative terminals for powering the tablet. The inner two pins (blue arrows) are the data connections.
A Samsung 240V charger shorts out the two inner (data) pins. The tablet identifies the pins are shorted and will accept a higher rate of charge.
One of my first steps has been to place my multimeter across the two inner pins to check whether they were shorted out. If they weren’t I would have to modify the usb plug. Fortunately they were shorted.
Accordingly, my new converter should provide maximum power to the GPS tablet.
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