I have two current source. Both are about 5 volts. I want to charge my phone with the highest current source out of the two, so if the highest current source (2.1 amps) is gone, it will switch to the lesser (1 amp) source.
The current setting:
I have my tablet in my car. The tablet is set to wake up, set the displayTimeout to 30 minutes, and start playing music when 2.1 amps is connected. When I turn my car on to ACC or ON, 2.1 A is sent. When the car is turned off, the tablet detects no current, stops playing music, turns screen off, and sets displayTimeout to 7 seconds.
What I noticed is my tablet barely drains battery when above 50%, but under that it drains to 0% so fast sometimes I go to my classes at College and when I drive home I see and big ugly 0% screen.
Future:
What I plan to do is either buy a rechargeable power bank that charges the tablet when the car is off, or just charge the tablet even when the car is off by connecting it straight to the battery. The only problem is the tablet cannot detect a change between car on and car off. It can only see if the current has been changed from 2.1 amp to 1 amp, so I want the tablet to stop music, turn off display etc when it detects 1 amps.
What I think might work:
I'm thinking if I splice the two current sources together, it will just add to 3.1 amps which isn't a problem for my tablet (right?) since it only draws what it needs.
I say current source, but it's just two basic usb cords that get's it electricity from car chargers, so it may not be a current source but a voltage source? I'm taking circuit analysis this semester so forgive me!
My question:
I don't want to use a physical switch to switch between them, but I may have to. What should I do that can have my tablet use the 2.1 amp by default, and switch to the 1 amp when the 2.1 amp cannot be detected. I think I read that diodes are required but they cause a voltage drop. Would my splicing idea work?
Best Answer
Amperage does not work the way that you are describing.
Basically, a power supply puts out a specific voltage, and then the device draws whatever amperage it is designed to draw (assuming the power supply can put out enough voltage). If a device takes 1 amp at 5 volts, you can use any 5 volt power supply as long as it supplies at least 1 amp of current.
My guess is that the 1 amp power supply is not powerful enough for the tablet to detect - it's likely that the voltage is sagging down below the voltage that the tablet needs. If that is true, then you can't charge the tablet with the 1 amp power supply.
You cannot hook two power supplies in parallel and get the sum of their outputs.
I would look to power the tablet directly from the battery with a power supply that puts out enough to drive it directly, and then come up with another way of detecting whether the car is running.
I would look