Hardware Reference
In-Depth Information
Solve Power Problems
Now that you've reviewed your power options, you have to figure out what to do when
things go awry.
When the power is too low (or the current is too low), the Raspberry Pi starts to act…
well, the technical term is “weird.” USB devices might not show up, or they might blink
in and out randomly. Software might not run reliably. Cats and dogs living together,
mass hysteria!
If things are just being “weird,” there's a good chance insufficient power is to blame.
There are two main reasons why this can happen, even when you think you've done
everything right: a subpar power supply or a faulty Micro USB cable.
Get a better power supply
It's the opposite of that power spiking problem mentioned in
“Think Twice Before
Using the GPIO to Power the Pi” on page 25
. It
says
“5 V,” but what it means is, “I might
consider delivering 5 V on my best day when all the stars are aligned and you perfectly
hum the
Doctor Who
theme song backward to appease my cranky nature.” But they
couldn't fit all those words on the plug, so they just put “5 V.” (Or at least that's our
theory.)
Sadly, this is a common scenario. A lot of cheap Micro USB cell phone chargers are
cheap for a good reason: they don't work very well. (Did you buy it at a dollar store?
That could be a clue it's a cheap one.)
When it's for your phone, it's no big deal. It just takes longer to charge your battery.
But the Raspberry Pi won't take so kindly to the drop in desired power.
The best way to avoid this is to buy a proven reliable power supply. For example, Ada-
fruit sells an excellent
5 V 1A power supply
that actually outputs 5.25, which makes up
for any voltage drop across the resistance of the USB cable between the power supply
and the Raspberry Pi.
Get a better micro USB cable
Your Micro USB cable is less likely to be subpar in quality than the power supply, but
it does happen. Cables have conductors in them that provide some resistance, but
that's usually irrelevant.
For example, at 5 ohms and 50 mA of current, the voltage drop across the cable might
be about 250 mV. Most devices are OK with that, because the USB specifications
require that they be tolerant of voltage drops of that amount. However, some devices,
like the Raspberry Pi, want more power (especially if you have some hungry USB
devices plugged directly into the Raspberry Pi's USB ports).
