Hello, I'm thinking of buying this product, LM2596 Dual USB DC-DC Step-Down Buck Converter Board.
It is advertise to supply 5v 3a (out 1 = 1a, output 2= 2a). I am using it for an Arduino gsm setup.
Will the out_2a be able to power the gsm shield? Is the output_1a will be able to power the Arduino or is it too much?
Power source: Car battery (12v connected to a solar source)
The power supply must be able to supply more than the maximum current draw of the rest of the circuit. Does the GSM module draw more than 2A?
"Too much" is not a worry.
It is important that the voltage to the Uno not exceed 5.5V. The Arduino will pull the current that it needs, no more. Same goes for the Arduino gsm setup. If you have a regulated 5V make sure to connect to the 5V pin not the power plug or Vin.
it'll be going to the usb of the arduino.
In which case, given a UNO, you are strictly limited to a total of 500 mA for the operation of the UNO and anything connected to it.
does this mean we can't use the out_1a for the arduino?
Don't know. How much current does the GSM shield require?
2a at load they say
Well, you clearly cannot supply that through the unnamed Arduino.
You need to connect the power supply - best by simply soldering to the connections under the USB jack - to "5V" and ground on the Arduino, and in parallel to your GSM module. You need to keep all the wiring bundled together from one device to the next so it does not form any open loops.
However because of a limitation of a UNO (but not a Nano) you need to disconnect (just) "5V" whenever you plug the USB into a PC.
The converter is probably quite suitable for this job. We are always just a trifle suspicious of these Chinese sellers. OK, it is virtually all made in China, but part of paying a lot more for local vendors is the expectation that they have checked out and rejected the junk. 
To clarify, I am trying to power the arduino in out_1a then the gsm shield will be powered using the out_2a not arduino to gsm shield
I am powering it using a solar panel so it's best to use a dual USB than buy 2 separate 5v 3a converters. I am from the Philippines and these Chinese vendors are the only ones selling it.
Hi,
Do you have battery storage?
The PV panels themselves will not be suitable.
What are the votlage/current/power rating of the PV cells?
Can you post a diagram of your project please?
Thanks.. Tom.... 
I am using a solar panel connected to a solar charger going to a car battery (12v) then going to converter then going to arduino and gsm
I doubt the GSM "shield" - whatever that is - has a USB connector. Plugging things together using pieces of USB cables is completely inappropriate. The USB sockets on that particular board are an unfortunate inconvenience; you would really need to solder wires to the underside. A module with the same specification but proper solder pads or screw terminals would be far more appropriate.
If you are interfacing a GSM module to the Arduino, the power connections need to run alongside the data connections, not separately.
How about this item?
If you are interfacing a GSM module to the Arduino, the power connections need to run alongside the data connections, not separately.
wait I don't get this part. Isn't it that I connect the rx/tx of arduino and gsm module, then power it using an outside source
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