Multiple Power Supplies

Hardware
1

Is it possible/safe to have more than one power supply connected to Core2-ROS with RPi 3?
Background: I want to connect my RPi3 to PowerBank to avoid problems with missing shutdowns etc. The Core2 needs the battery pack for the motors and hardware, and the Core2 is also connected via USB to a computer to develop programs.
So the question is could there be a problem e.g. with the batteries because they may get power via USB or something like that?

2

Hi MichaelT,

if you connect the power directly to the 5V line, all parts of CORE2 powered from 3.3V and 5V should work, but I have to add some notes:

  • it has not been tested in this mode
  • the voltage from 5V line will cause the current flow back to the V_in line (6…16V) and the voltage on this line will be about 4.4V
  • you should not use motors, servos or USB host port as long as the main power is not provided
  • you can provide 5V voltage using “+5V” and “GND” pins on hMotor port - don’t use 5V pins from hExt or hSens connector,
  • also don’t use USB host port to supply CORE2
  • the on-board DC/DC converter will be still working sometimes
  • you shall use ONLY regulated power supply, with 5V, ±5% output voltage - the powerbank should meet this requirement
  • the USB serial (micro USB port) on CORE2 has a separate power line and using the USB serial does not affect the possibility of providing power supply in unusual way.
3

Hi
There seems to be a missunderstanding. I don’t want to add power directly, but I want to use the micro USB port at Core2 to upload programs from a PC, a PowerBank to the micro USB of the RPi (to prevent uncontrolled power loss) and a battery pack at the DC In of Core2 to power motors and additional hardware.
What I see is that using one them (USB of Core2, USB of Raspberry, DC In) all components are working (except motors in case of USB).
So the question is, whether it is safe (for the hardware/batteries) to use more than one of the power inputs?

4

Ok, now I understand better.

It is possible to use two power sources at one time but a little less safe - because the power distribution is less controlled. In case of any damage or short circuit, the consequences can be much higher, so you have to be careful. It also can increase EMC emission, so we can’t take responsibility of that :slight_smile:

Also the fuse on the RPi is more loaded and you have to think about the maximum load on the 5V line. The CORE2 itself will draw maximum 0.2A on the 5V line, so it all depends on other circuits connected to the CORE2.
Motors and USB host can be used only with DC IN connected. It would be preferred to check the DC IN voltage in your program code and allow to use motors only if the DC IN is greater than ~7V.

My notes in the previous post are still valid, because powering RPi from its own USB is almost like connecting power supply to the internal 5V power line in CORE2. Not recommended, but I would not except any problems if the powerbank will stay longer than main DC IN power supply; or if two supplies work simultaneously.