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I have an raspberry pi 3B I want to use as the brains for a robot car. In my initial setup I used a power bank for the Pi and a powered the motors using a seperate pack of two 18650 batteries in series. I want to combine the two power sources and see if I can power the entire device off a single power source.

I was looking at using a an LM2596 buck converter to bring the voltage down to 5V and a set of capacitors to smooth any fluctuations caused by the motor. I would then connect directly to the 5v and gnd pins. Is this setup possible, or am I just inviting more problems? what else should I add to make sure the PI runs stable?

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You can find a lot of small switching regulators on Aliexpress, Ebay etc. The LM2596 should give you plenty of power, and has a decent efficiency.

For a more general answer, look for small switching voltage regulators with an output of at least 2 Amps. Don't go linear regulator, it will fry.

Be advised these module have often a variable voltage Output you may have to set before powering the Raspberry.

EDIT: If you run your motors from the batteries directly, and not from the voltage regulator there is no need for extra capacitors. If you buy a LML2596 board it will have the required filter at the output.

Powering the PI via his USB power input is considered a best practice has it is protected.

From a previous answer from @Joan powering via the USB power input provide:

  1. a polyfuse which limits current flow and offers some protection to the Pi.
  2. transient voltage spike protection which stops transient overvoltages from damaging the Pi.
  3. the socket design ensures that if you use a standard lead you don't mix up +ve and -ve.

But if you still want to power the PI via the GPIOs you may consider adding one of the protections above.

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  • Thanks, that was the buck converter I was looking at. What about the second part of my question? Any other aspects I should consider?
    – Marc Wagner
    Commented Jun 15, 2020 at 17:21
  • thank you very much. this is an excellent answer. just one additional question: to protect from overvoltage, I am considering a 25V / 100uF and a 25V / 4.7uF cap to protect from overvoltage spikes. Am I correct in doing this?
    – Marc Wagner
    Commented Jun 17, 2020 at 7:29
  • This will not protect from survoltage surges. It's not the purpose of capacitors.
    – Wireless Learning
    Commented Jun 23, 2020 at 16:59
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Yes, this should be feasible. The 3B will consume about 1A maximum and this module will be able to handle that uncooled. If you need more current (f.e. for USB devices) cooling the device will allow you to go to 3 A.

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