Explorer pHat and 4 AA battery pack


#1

Hi,

I read the documentation of the explorer pHat, but I am not 100% sure: can I connect a 4 AA battery pack (~5 Volts) to the 5V input and the GND output to power my RPi Zero?

If not, what else could I use?
I am just building a small robot, but the portable phone charger I planned to use is not working as expected. The Pi freezes just about 1-2 seconds after I start the two motors (Pololu 50:1 High Power Micro). :-/

Thanks in advance!


#2

Some people have had success powering their Pi’s directly from AA batteries in this fashion, but it’s definitely not recommended. They only output 5v under ideal conditions and when fully charged, and the Pi may hang, crash, brownout or otherwise when the voltage dips too low.

I’m guessing your portable phone charger just can’t output enough current to supply both the Pi and motors. Does it have a rating (500mA 1.5A?) written on it anywhere?


#3

Thanks for your answer!

The phone charger has a 18650 battery with 3,7V, 30A and 2100mAh. It’s cheap China quality, so probably not the best idea to use it anyway… :-)

I also have the Zero-LiPo. Is this recommended for this kind of project? And what battery would I need?
I currently only have 1-2 LiPo battery packs with <= 500mAh. That’s probably not much?


#4

I think I’ve seen those motors draw 150-300mA quite easily at 5v, and more when they stall. That would mean that a 500mAh LiPo would be enough to run the motors for about an hour on their own.

I’d assumed 90% efficiency, so it’s (3.7v/5v) * 500mAh * 0.90 = 333mAh

So you should be able to run a robot for maybe half an hour on a 500mA battery. Whether you consider that “not much” or not, really depends on how quickly you get bored of trying to do little robot wheelies :D

I suspect my guess about your cheap china quality phone charger is probably right. Good enough to trickle-charge a phone, but just can’t handle the demands of two motors firing up.

You can always upgrade to a bigger LiPo later, but we’ve got robots built that run from 500mA and I think @CannonFodder uses them too with his infamous battling robots.


#5

I normally use the 1000mA and get about 2 to 3 hours intermittent use. I have just finished building a version of my MagPi robot ‘Tiny’ with the explorer P’hat, 4 x Micro metal gear motors and a zero LiPo, it uses one of the Pimoroni 2200mAh tube batteries


#6

Thank you both for your answers and the calculation!
I will buy a new battery once I know how much space I have left. The tube batteries are nice, but I think I will rather go fo a battery pack as it’s easier to mount it on the chassis.

Btw, very cool robot. This is one of the projects that inspired me to build my own robot. :-)


#7

Sorry for the long time in replying, glad Tiny has inspired you to build your own robot! :-)