Power - Raspberry Pi Hardware Reference - page 6

The 3.5 W represents a minimum requirement, so we should overprovision this by an
additional 50%:

P = 3.5 × 1.50

= 5.25 W

The additional 50% yields a power requirement of 5.25 W.

■ allow 50% extra capacity for your power supply. a power supply gone bad may
cause damage or many other problems. one common power-related problem for the pi is
loss of data on the SD card.

Tip

Current Requirement
Since the power supply being sought produces one output voltage (5 V), you'll likely see
adapters with advertised current ratings instead of power. In this case, you can simply
factor a 50% additional current instead:

I supply = I Pi × 1.50
= 0.700 × 1.50

= 1.05 A

To double-check our work, let's see whether this agrees with the power rating we
computed earlier:

P = V × I

= 5 × 1.05

= 5.25 W

The result does agree. You can conclude this section knowing that you minimally
need a 5 V supply that produces one of the following:

• 5.25 W or more

• 1.05 A or more (ignoring peripherals)

Supplies that can meet either requirement, should be sufficient. However, you
should be aware that not all advertised ratings are what they seem. Cheap supplies often
fail to meet their own claims, so an additional margin must always be factored in.