# Noob Question - Single Power Supply for multiple devices with varying voltages?

Status
Not open for further replies.

#### L. Scott Hudson

Joined May 27, 2020
2
I'm not an EE; I'm a software engineer. I want to build a mobile robotics platform. Here is the question- very simply, I'd like to have one power supply, something like a 7.5v pack of six rechargeable AA batteries.

Let's say that the components are
1) Two 7.5v DC motors
2) One 5~6v motor controller
3) 5v Arduino
4) 5v Raspberry Pi

Is there any way to engineer this so that all components are powered by the same 7.5v pack? A quick google search suggests that the parts required would add up to less than a value meal, I just have no idea how to do it.

What about a 12v rechargeable battery? They are easily obtainable by searching recycle ads for discarded children's toys, and six AAs won't last very long powering an Arduino + Raspberry Pi simultaneously.

~ L

#### ericgibbs

Joined Jan 29, 2010
15,353
hi LSH,
Welcome to AAC.
What is the required operating duration of the robotics platform.?
It would be advisable to power the two motors from their own 7.5V supply

There are low drop out voltage regulators that will give 5V from a 7.5V supply.
E

#### WBahn

Joined Mar 31, 2012
26,398
I would imagine that the motors are going to be a significantly heavier drain on your batteries than you Arduino and the Pi are. But you need to supply numbers to know if that's the case or not.

Determine how much current each of the components you need to power will draw under realistic conditions. That's your starting point. Not much point going any further until that's done.

#### sparky 1

Joined Nov 3, 2018
703
It is very common to have different or variable different voltages.
The power has a 12V terminal. Following the data sheet for setting an LM317 find the correct resistor value.
The LM317 is set to 7.5V next the variable is called a PWM module. It operates the motors speed very nicely.

#### Janis59

Joined Aug 21, 2017
1,383
We call such method the "Ukrainian school of power supplies". Most soviet epoch Ukraine produced electronics used a stacked in series PS ideology. For ilustration, one PS produce the 10kV, other makes those kV dovn to 9988 Volts, then next makes a half down, next makes a 5 Volt upper etc etc etc. Normal constructors would not economy but use an independent (floating) PS for each device, may be except those filament down from cakode High Voltage when Anode is gnd.

Last edited:

#### L. Scott Hudson

Joined May 27, 2020
2
Thanks guys,

I've been going at it intermittently for about eight years now.

From what I could decipher reading EE manuals and tutorials, in theory it seemed like not much more than a few parallel circuits, with resistors to change the voltage. However I didn't feel too confident with that, and everything has just been battery packs on top of battery packs.

The one you see in my profile pic is controlled entirely by a desktop PC with a USB Serial Port to a Basic Stamp. I eventually bought a laptop with a 6 hour battery life and attempted to build a motor assembly with some power wheels motors + battery that I bought off of Craigslist, and a hobby motor controller that I bought at Fry's. I followed those instructions to a T and ended up with a small, unexpected fire in my living room.

My next/current iteration is the Raspberry PI plus this guy.

As far as operation duration, 10-20 minutes, or long enough to just record a few demos with a camera phone, should be enough to start......

#### ci139

Joined Jul 11, 2016
1,799
there are loads of various electric motors avail : technology old ... new , power low ... high , speed .... , voltage ... , etc. ...

there might be also ready made mechanical momentum translators (some of which may be directly mountabe to some motor types)

$$\uparrow$$ makes a mess to chose from ... is likely the slowest part of your development work $$\uparrow$$

however you likely don't want to save on battery (the brand does not matter that much - as that it's new)

unexpected fire
. . . is trivial TEST result with HV or high power workings . . . you never know the actual device response in advance too accurately . . . so such must be tested out ...
... but be ready for such and everything = DO USE fuses and/or current limits and/or thermal shutdown (the latter ones are more complex to implement) ... and your head

there are more hints about the inholds

Last edited:

#### alex.will

Joined Jan 13, 2021
16
The input should high ampere to drive multiple devices and use buck-boost converter to use multiple applications

Joined Jan 15, 2015
6,536
Your 7.5 volt motors likely won't need any regulation so just a 7.5 volt battery pack should suffice.
It would be advisable to power the two motors from their own 7.5V supply
Motors inherently have noise and back emf on their power lines. Micro-controllers and Redberry Pi modules really hate noise on their power lines. You can try decoupling, filtering and other tips and tricks but when all is said and done I would do as Eric suggest. Power the motors separately on their own battery supply. Next for your 5 volt power buck boost converters are very inexpensive and 5 volt out at a few amps are very common. That should be plenty adequate for an Arduino uC and a Raspberry Pi. That is likely how I would go about it. Run the motors directly off a battery and use another battery & regulation (buck boost converter) for your sensitive electronics.

Ron

Status
Not open for further replies.