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I'm working on a project that requieres a lot of current. I'm using 6 servos, and 4 DC motors (all of them plugged to an Arduino, ontrolled by the Raspberry).

I've seen a battery of 6V 4.5A, and connect it to the micro usb power supply. Is it safe?

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    No it's not safe. It'll most likely just blow the fuse but I wouldn't try it. 4.75-5.25 is what you should look for – ElefantPhace Sep 30 '16 at 1:53
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    It may do far more than blow the fuse. It will likely fry the PI. – Steve Robillard Sep 30 '16 at 1:59
  • And what if I use a 7805? or a Zener diode? – XanderCraz Sep 30 '16 at 2:02
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A 6V Power supply can be used for your Pi, but not directly. You mention two options (7805 and Zener diode) in comments, and they both won't work:

The best bet you have is to find an LDO regulator. Googling should give you both product names and reference schematics.

  • Thank you! I've looked in some forums about LDO regulators. i some of them they suggested to use diodes in series to reduce voltage, guess t is not safe :P I think I'm gonna use LT1529-5 LDO regulator :) – XanderCraz Oct 1 '16 at 2:36
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No.

A 6V 4.5 amp power supply via the microUSB is neither safe nor useful.

  1. It's likely to be far more than 6V when the batteries are fresh. 6 volts or more will destroy a Pi.
  2. The Pi3B has a 2.5 amp polyfuse on the microUSB input so even if the voltage was safe (which it isn't) the polyfuse would trip once you tried to draw more than 2.5 amps from the battery.

You need to power your servos and DC motors externally to the Pi.

There is no reason they can't be controlled from the Pi. The pi is just as capable of sending control signals to the servos and motor driver boards as an Arduino.

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No, it exceeds the normal power range for USB. Just above 6V, circuit protection in the Pi will kick in.

What's most likely to happen is the overvoltage condition will cause the TVS Diode to start shunting power to ground. This short condition will in turn make the current draw increase dramatically, which will cause the polyfuse to open, thereby cutting off power completely. This is a quasi-crowbar circuit protection solution, and it's rather clever.

Stick with a 5V supply for USB. If your motors are only controlled by the Pi, they can be powered separately.

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The specs say the input voltage needs to be between 4.75 and 5.25 volts. Part of this is because of the logic voltage levels, esp for the GPIO pins.

Adding more voltage will not help anything. It may very well cause damage to the Rpi3 board. The board has a built-in regulator, and the spec is very clear about the voltage it expects to work with.

Using a power supply capable of higher amps is no problem, since the Pi3 will use whatever it needs and no more. Recommended is 2 to 2.5 Amps and 5V. One popular power supply for the Rpi3 is a plug-in module with a USB port and a switch in the USB line so you can power down your Rpi3 without punplugging the USB port itself.

If you need more amps from the Rpi USB ports you do have the option of adding a directive max_usb_current=1 in the /boot/config.txt file. Output from the USB ports is 5 volts, regulated on the board. Default amps is 600 ma for all ports combined. If you use this directive it doubles the amount of power you can draw, to a total of 1200 ma (1.2 Amps) for all the USB ports, combined.

For running servos and such, consider using this: https://www.adafruit.com/product/2327 You can have multiple boards so you can run a lot of servos. Plus it is more precise than generating the proper pulses in your software. It gives a lot of flexibility for a reasonable price.

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