I have a external hard drive that has written on it "5V ⎓ 1A". Both power and data transfer happen over a single USB. I have been reading about powering this hard drive with the USB ports on my Raspberry Pi 3 B+, but I want to make sure I'm thinking about this correctly. I have a 5V ⎓ 2.5A micro-USB power cord for the Raspberry Pi, the Pi itself, the hard drive, HDMI output to a screen, and a USB receiver for my wireless mouse/keyboard. I calculate it like this:
Total USB current needed (Raspberry Pi 3 B+ can supply 5V ⎓ 1.2A via its USB ports):
1A (external hard drive)
+ <0.05A (my best guess for USB receiver for wireless keyboard + mouse, from here)
= ~1.05A total USB current needed
Then, to make sure the power cord is sufficient:
2.5A (my micro-USB power cord)
- 0.5A (typical current draw of the Raspberry Pi itself)
- ~0.05A (HDMI output)
- 1.05A (USB current needed, shown above)
= ~0.9A leftover.
From my understanding, this seems to be acceptable. I've even tried it a handful of times and was able to access the drive. However, from some sources (see answers in How Can My Raspberry Pi 3 B+ Power All My Devices? and Powering hard drives without a powered USB hub?, and also the Raspberry Pi forum), it seems like there might be surges in the current that the hard drive needs that aren't accounted for on the "5V ⎓ 1A" label. Is this true—will it sometimes require more current than the label suggests? Will I ruin this drive if I don't use a powered USB hub? Thank you for any help you can give!