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I have a 2-cell LiPo battery, a RPi3, and a motor driver with 2 DC motors. I wanted to use the same LiPo for both, instead of a LiPo for the driver, and a Power Bank for the RPi3.

My idea was to use a Voltage Regulator connected as below:

schematic

simulate this circuit – Schematic created using CircuitLab

I'd use the microUSB port in the RPi3 to take advantage of all the protective circuitry they have in there, instead of directly connecting to the 5v pins.

Is this correct? Or am I burning something once I plug everything in and accelerate a little bit?

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  • \$\begingroup\$ There are schemes like this that could work, but success (or likely failure) is in details not covered. The motors may be noisy. Operating them may cause the voltage to sag below the regulator's dropout. Finding a regulator with low dropout that can source the pi's peak current demands will not be trivially simple. A pi isn't really the sort of computer that belongs on many projects that would have motors and battery power... most such systems use simpler computers with no file system state to worry about corrupting and no scheduler to slow responsiveness. \$\endgroup\$ – Chris Stratton Oct 8 '18 at 15:07
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I think it should work. One thing to note is that 7.4V is a nominal voltage for a 2-cell LiPo battery. The full range of the battery voltage (depending on its charge status) is something like 6.6V - 8.4V (3.3V - 4.2V per cell). So the voltage regulator you linked may not be appropriate - its spec list only 7V as an input.

You may want look for a low-dropout voltage regulator. Alternatively, you can try using a DC-DC converter for better efficiency. E.g.

https://www.pololu.com/product/2858

Also, you can look around for a 5V BEC (UBEC) (Battery Eliminator Circuit) used for RC models. E.g.

https://www.adafruit.com/product/1385
https://www.aliexpress.com/item/Hot-Sale-DC-DC-Converter-Step-Down-Module-UBEC-3A-5V-12V-BEC-For-RC-Airplane/32824894112.html
(many BECs on Amazon)

In any case, you do want to make sure that once you apply full power to DC motors, the battery voltage does not drop below the minimum regulator value.

DISCLAIMER: I never actually powered RPi3 or any Single-board computer this way: not providing any guarantees.

For the reference: When to use multiple batteries vs a UBEC

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