Battery Packs for the Pi

[Roo_027]

Hi everyone

I would like to know if it is safe to use 4 AA (non-rechargeable) batteries in a battery pack to power the Pi as well as 2 motors. Each one obviously supplies the usual 1.5V so this is 6V in total. I read in a few articles that the Pi only needs 5V of power to run and that if more is supplied that the Pi could get fried.

I would like to know if I need to buy a voltage regulator of some sort? I have connected the battery pack to my motor controller board's terminal which is then connected to the Pi's GPIO pins.

My confusion is that I have also seen evidence of the opposite taking place - namely that people have connected these 4 AA batteries to the Pi and the motors run just fine. So I am not sure who to believe? Below is some of the contradicting information I have found (there is more but this is just to show you what has confused me):

The battery packs work:

https://projects.raspberrypi.org/en/pro ... -a-buggy/2
https://www.youtube.com/watch?v=pbCdNh0TiUo

Using the 4 AA batteries not being safe:

https://www.reddit.com/r/raspberry_pi/c ... with_4_aa/

I do not want to have to go and buy a USB power bank if possible.

Thank you in advance for your explanations.

[pootle]

4 AA alkaline batteries is definitely a NO https://www.raspberrypi.org/help/faqs/#powerBatteries

But why do it this way when you could so easily just use a small power bank fot the pi and the motors. I would strongly recommend though that you add a couple of small capacitors close to the motors unless you are already using a driver for the motors that includes decoupling.

For small motors (e.g. small servos or micrometal) I typically add something like 10uF electrolytic plus 10nF as close as possible to the motors. Without these you can easily get glitches and crashes.

I can run a pi-zero plus a couple of micrometal motors for a couple of hours using one of these, and it is easily recharged using a normal mobile phone charger

[pcmanbob]

NO it is not safe to power a pi from 4x AA batteries at 6V you will destroy your pi.

In the 2 examples you posted of people doing this your are wrong they are not supplying the pi directly from the 4X AA batteries.

Example 1 https://projects.raspberrypi.org/en/pro ... -a-buggy/2

clearly shows a 5v power pack being used to power pi via the micro usb port, white cable in this picture goes from 5v battery to pi micro usb port.




Example 2 https://www.youtube.com/watch?v=pbCdNh0TiUo

The motor board being used in this example has its own on board 5V regulator witch is being used to feed the pi 5V via its gpio pins, which in its self is a bad thing for a beginner as it by passes the on board protection on the pi micro usb power port.



if you listen to the commentary on the video he actually says he is using the 5v supply from this regulator to power the pi via the 5V and ground pins on the gpio header.

[Roo_027]

Hi there - thank you for the replies.

I am a little confused - are you saying that if you connect the 4 AA battery pack to the motor board then it will be ok (it will not blow)? Since is that not what Sendtex did in the Youtube video - or am I completely wrong? Does the motor board controller that I connected to the Pi GPIO pins regulate the 6V from the battery pack automatically and bring it down to the 5V the Pi only needs?

I understand that connecting the battery pack directly to the Pi is a big mistake - that is not what I have done.

I am not sure what you mean about using electrolytic plus on my motors - I will read up on that.

The rechargeable usb battery pack looks like a good investment - but until I get that I would like to figure out how these other people have used their AA batteries to power the motors.

[pcmanbob]

I am a little confused - are you saying that if you connect the 4 AA battery pack to the motor board then it will be ok (it will not blow)? Since is that not what Sendtex did in the Youtube video - or am I completely wrong? Does the motor board controller that I connected to the Pi GPIO pins regulate the 6V from the battery pack automatically and bring it down to the 5V the Pi only needs?

OK in the video they connected the 6v battery to the motor control board using the power input terminals that are used to connect the battery for the motors use, depending on the board this input could be up to 12 or 24V.

now the electronics on this board works at 5V so it has its own on board voltage regulator the produces 5V from the 12 or 24V used for the motor.
in the video example this 5V was used to power the pi also ( but probably wont work with a pi2 or pi2 ).

now when you connect you gpio pins to the control pins on the motor board there is no voltage coming out of them you send voltage in to them to control the motor board so to signal a low command you send 0V to signal a high command you send 3.3V. So connecting your gpio to the motor board will not damage it if you connect it to the motor board control pins.



** for the experts out there I know saying you send voltage in to some thing is not strictly correct but trying to explain in terms OP will understand **

[Roo_027]

Thank you pcmanbob

I come from a financial background and the last time I studied electronics was quite a number of years ago - so please excuse me until the lightbulb eventually comes on for me.

now when you connect you gpio pins to the control pins on the motor board there is no voltage coming out of them you send voltage in to them to control the motor board so to signal a low command you send 0V to signal a high command you send 3.3V.

So from the above I understand that when I connected my AA battery pack to the motor controller board's terminal and switched the ON switch, NO POWER is reaching the Pi, am I correct? The electricity is only travelling within the motor controller board? This is actually another question I wanted to ask - why was nothing happening when I turn the battery pack ON?

If the above is correct, then does that mean I am forced to buy a usb rechargeable battery pack to connect directly to the Pi itself - otherwise how else can I power it if nothing is reaching it from the motor controller board circuit?

[pcmanbob]

What were you expecting to happen when you power the motor driver board ? As it has no control inputs at that point nothing will happen.

The 5V regulator on the motor board will only be rated at 1A and some of that will be used by the board it's self , the pi 2 or pi 3 requires at least a 2A supply .
In the video they are using an original pi B that would boot on a 1A power supply and they are back feeding the 5V from the motor board to the pi.

Yes it's recommended that you use a separate battery for your pi, but at the end of the day it's your hardware you can do it how ever you want but don't come crying if it all goes wrong.

[Roo_027]

Thank you for the explanation - it makes quite a bit of sense!

What were you expecting to happen when you power the motor driver board ? As it has no control inputs at that point nothing will happen.

The way I saw it in my mind is that by connecting the motor controller board to the Pi, there is one big circuit. So when I turn on the AA Battery pack that is connected to the motor controller board terminal, the electricity will move through the motor controller board AS WELL AS the Pi. But clearly I was wrong as you are saying the current within the motor controller board is not enough to operate the PI which needs 2A not the 1A there is in the motor controller board.

Thank you very much once again! I will be sure to buy a rechargeable battery pack in that case.