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I have a project that includes a RP3 and an Adafruit motor hat (https://www.adafruit.com/product/2348), with 2 5v stepper motors (https://www.adafruit.com/product/858).

In the guide they state the following:

Please note the HAT does not power the Raspberry Pi, and we strongly recommend having two seperate power supplies - one for the Pi and one for the motors, as motors can put a lot of noise onto a power supply and it could cause stability problems!

Currently I have two separate plugs going to two separate wall outlets. I want to use only a single plug but I'm not sure what's the right way to do it, and I'm pretty new to power and electricity.

My best plan now is to use a single 6V 3A plug and connect two buck converters (https://www.adafruit.com/product/1385) one for the RP3 and one for the Motor hat, in hope to eliminate the noise coming from the motors (?). Am I in the right direction and idea or tip on how can I use a single power supply for my project will be greatly appreciated!

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  • Welcome to Raspberry Pi! Please take the tour and visit the helpcenter to see how things work here. Could you please add the current required to drive the steppers? The driver supports up to 1.2 A (two channels) if the steppers use that much a 3 A supply will not be sufficient.
    – Ghanima ♦
    Commented Dec 9, 2018 at 19:50
  • thanks @Ghanima! this is the motor I'm using adafruit.com/product/858. Datasheet doesn't provide any clue on required current, my guess is that it varies on speed and torque so they don't provide it(??). I currently run it with a 5v 2.4a plug with no issue other than over heating of the motors.
    – user2810692
    Commented Dec 9, 2018 at 19:55
  • The power supply for digital things (like microcontrollers and single board computers) should be kept entirely seperate from the power supply for analog things (like servos, motors and relays). Failure to do that is likely to let the magic blue smoke escape as analog things have the nasty habit of dumping back emf into the circuit when a magnetic field collapses.
    – Dougie
    Commented Dec 9, 2018 at 19:57
  • Thanks @Dougie! Nothing is never entirely separated, everything is connected to the same grid, for example I can always use a power strip on the wall outlet side. I'm guess I'm asking how can I miniaturize it is a way it fits in my project and not as a chunky power strip.
    – user2810692
    Commented Dec 9, 2018 at 20:37
  • You need one DC supply for digital and an isolated (except for a common 0V line) DC supply for analog. The only other connection between analog and digital is the control signal (which is, ideally, open collector).
    – Dougie
    Commented Dec 9, 2018 at 20:45

2 Answers 2

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This is not really a Pi question.

However the issue of supplying power to the Pi is a common problem. "having two seperate(sic) power supplies" may be good advice, BUT a single well designed supply would be better than 2 plug-packs, which have minimal filtering.

The real issue with a single supply is to avoid common wiring - if you use 2 separate cables there should be minimal interference, and it is possible to add additional filtering if needed. Ideally the motor control circuitry should have separate connections for control and load.

The readily available supplies, sold for powering LED light strips, are well regulated. I use one of these to power several Pi.

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My best plan now is to use a single 6V 3A plug and connect two buck converters (https://www.adafruit.com/product/1385) one for the RP3 and one for the Motor hat, in hope to eliminate the noise coming from the motors (?).

This might work but I wouldn't recomend it. What is important with electronics and power is that you are supplying enough amperage on the correct voltage.

The recommended amperage for the Raspberry Pi 3 alone is 2.5A power supply at 5V. For each one of the stepper motors you plan on using, needs at least 1.5A per motor, so for two 3A total.

With the Power supply and Buck Converters you suggested in your question these would get you the correct Voltage. However, you would be lacking in the amperage area. It would only produce 2 amps per buck converter. According to the data sheet for those buck converters you need:

Iout    Vin   Iin   Vout
3A      7V    2.6A  5.0V

For this to work the way you are intending you will need to get a 7V 2.6 Amp power supply, to get the proper output of 5v 3A.

I would also suggest to put a diode in line with your power inputs for the stepper motors. That way they don't give any back signal to your buck converters or power supply.

Note: I can't confidently say that this solution would work either though. As I am not sure that the power supply could handle having two buck converters, this is something you would have to test with a multimeter.

May I suggest a Power supply like this, which takes a regular 110v or 240v Ac and converts it to 2 5v DC 12 Amp outputs. This would be more then enough power for your project. This would even give you room to add more stepper motors if you wanted to.

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