How much power for Raspberry Pi?

[japonophile]

Hi,

I have build the Dagu 2WD robot and could successfully run it when connected to a power cord.
However, when I use the 6xAA battery holder, my WiFi drops very quickly (forcing me to restart).

I am guessing the Raspberry Pi requires a certain power that the batteries cannot provide.
(I should mention that I also connected a little speaker to the Pi. I am using the Pi from KANO.)

I was wondering: is there a way to determine how much power must be supplied to the Pi + mini driver, especially when starting to connect a bunch of sensors or peripheral stuff?

This is a very general question, so the answer is probably to take a basic electronics class and do the maths, but I was wondering if there are guidelines to figure it out.

Thanks,
Antoine

[Alan]

Hi Antoine,

Are you using rechargeable (NiMh) or non-rechargeable (alkaline) batteries? The kit doesn't work very well on Alkaline batteries unfortunately as they're not able to provide enough current. NiMh batteries have a lower voltage but should be able to supply more current.

Usually it's best to just measure current usage rather than try to calculate it, as especially with the Pi, it can vary depending upon what it's doing and on how hard the GPU is working. You should be able to do this with the current measurement function of a multimeter or alternatively, if you have access to a benchtop power supply, a lot of them have a display showing the amount of current being drawn.

Regards

Alan

[japonophile]

Hi Alan,

Yes, I am using rechargeable batteries.

I see, this is when the multimeter comes into play!
If my 6xAA batteries cannot supply enough current,
- how will I know from my multimeter how much current I need?
- would the Power Bank be able to provide more?

Thanks,
Antoine

[Alan]

Hi Antoine,

If you can give me info about the Pi you're using (is it an original Model B if from the Kano?) and the WiFi dongle you have plugged in, then I could try to recreate your setup here and tell you how much of a current draw I'm seeing, and whether my batteries can handle it. I use Duracell 2400mAH batteries which seem to work well in most situations.

The Model B Pi draws more current than the B+ and Pi 2, and if your WiFi dongle is not the EW7811Un then this may cause problems as well as other dongles seem to have a higher current draw.

Roughly, I would say that you should need the ability to supply 2A to confidently run the system, although you should be able to get away with less. It's not necessarily just the ability to supply the required current at some point in time though, the supply also needs to be able to respond quickly enough to cope with a sudden demand for more current. If a supply can't supply enough current, or can't supply it quickly enough then the voltage will sag, and this may cause the Pi to brownout.

A USB powerbank may work for you here, although not all powerbanks are the same and when looking for a powerbank to sell I found a number that couldn't keep up.

Regards

Alan