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I have a Raspberry Pi 3 Model B, and I wish to make a tablet with it. I am using the WaveShare 7inch touchscreen, the pi camera V1, a USB hub and an external CD/DVD drive. But when I got everything ready and started the Pi, I got a message saying something about "low voltage", and there was a yellow lightning sign at the top right, and the pi got unresponsive a lot. It is because of all those power hungry hardware.
So I was wondering if anyone could help me with the power consumption and how I should power the pi (boost converters and all; somebody would have to explain from the beginning, I'm really naive!).

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The official Raspberry Pi power supply will be good in most cases as the Pi requires 2.5 Amps, this can be purchased for about $9-$15 online. If you are powering more power hungry devices an external power supply for that individual device is recommended. Hope this helped :)

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I’d definitely follow Conor’s recommendation on a decent power supply, however the Pi generally doesn’t need 2.5A on its own, it probably the devices you have attached causing it to struggle.

I have the same Waveshare screen and haven’t had a problem, I suspect the CD/DVD drive is causing the issue and is drawing a lot of current, try unplugging it and seeing if the low power issue goes away.

I have an inline usb voltage and current monitor that I use to see how much power is being drawn by devices, really helpful thing to have handy. There are quite a few variants on amazon or eBay, only a few pounds.

Something like one of these:

https://www.amazon.co.uk/dp/B00ZPT6E1A/ref=cm_sw_r_cp_tai_i_YZ1aBbHDADBQT

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  • I removed the CD/DVD drive and everything else (there was nothing except the raspberry pi connected to the display). Still, I am getting the error and the lightning sign. I want the tablet to have its own rechargeable battery...
    – overwerk
    Commented May 26, 2018 at 6:21
  • By the way, I am using a power bank with output [email protected] (or so it claims). What power source are you using?
    – overwerk
    Commented May 26, 2018 at 6:23
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Few things you can consider here are:

Power supply:

  • For extreme conditions suggested power supply is with +5.1V 2.5A output. (Link: example)

Power cable:

  • Trim power cable size. (Example: 2 inches length is best.)

External drives:

  • Use self powered external drive so it doesn't drain power from your Pi. (Link: example)

USB Hub

  • (or) Use an external powered hub to connect external drives. (Link: example)

This should be enough to overcome Pi's low power warning.

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I think the other answers ignored the tablet part. It's been a while since the question was asked, but my answer may help someone.

This is the right time to mention that I am not responsible for any damage you cause. I have a degree at Electrical and Computer Engineering, but I have not experience (at the time) outside the University. So consider my suggestions with caution, we all make mistakes.

As the other answers mentioned The Raspberry Pi 3 requires a 5V/2.5A power supply, which means that the maximum current that your Pi should draw is 2.5 amps.

Since you are planing to use a USB hub (and plug more USB devices), ideally, you should get a USB hub that supports (external) power supply, and connect it to the same power source with the Raspberry (since it may be portable). This means that your power supply should now be able to output more than 2.5 amps (you should check the USB hub's rating and sum the max amps with Raspberry's). For example, some 4 port USB 3.0 hubs come with a 5V/2.5A, thus if you were to used such a hub, your power supply should be able to output 5amps, thus have a rating above 5amps.

Considering that you want to build a tablet, I guess you would like to add a battery too. You may salvage a battery from a broken tablet or old laptop, most likely a lipo battery. To connect the battery you will first need a charge control board so that you can safely charge it and discharge it (it may also features additional protection circuits). Then you should connect it to a boost converter that will be able to output 5V and more than 2.5amp.

To minimize the soldering and board search, you may search for a power bank that can output above 4 amps and connect there the USB hub power and the Raspberry power.

Some extra things to consider:

You may not be able to charge the tablet while you use it, for example, if our power source needs 1 amp for charging and your tablet consumes 2.5 amp, the charging power supply should output 3.5 amp. But all that depends on the ratings and the boards.

If you use for the Raspberry a power source more than 2.5 amps, you should avoid drawing more power.

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