Having trouble finding a good power supply for the raspberry pi 2

You are telling the 'pi to allow 0.5A or even 1A towards the downstream USB port with the hard disk attached.

With the pi itself requiring roughly 0.7A,  you should be looking at a power supply able to provide at least 1.2A. So the 0.7 and 0.8A adapters that don't work, are no surprise to me.

USB ports on TVs or computers are sometimes not "fused" or "current limited", like they are on the 'pi. So the port will be able to supply more than what the USB-2 specs require (or maybe even "allow"). On the other hand, IIRC, USB3 ports are able to / required to provide more than the old 500mA....

I have tested a few cheap power supplies. I have one that claims 2A, but is actually capable of 1.2A, so that one should work, even though it provides less than advertised.

i have two differing approaches:

1. Buy a multiple USB ported reliable power supply. I have a RavPower with 4 ports. 2 are 1A and 2 are 2.1A so long as the total wattage is less than 30W. See RAVPower 4-Port USB Charging Station USB Wall Charger Travel Charger USB Adapter. Shopping around can save a some scratch.
2. Buy a powered hub with say 4-6 ports and a good 2.1 A 5 volt cord. Then I power the Pi 2 off the hub and connect all other devices on the hub. This is what I am doing now and have had good success. If you plug too much off the hub, move the Pi 2 on its own separate supply/wall plug.

     From what I see, HDD, WiFi, and DVB's seem to need more current than keyboards, mice(wired), and solid state USB sticks.

Cheers,

Clem

You did not specify but it needs to be  a 2.5" hard drive. The biggest problem with supplying a hard drive with power is when you

first turn it on. It takes a lot more current to "spin up" the disks in the drive than it does to keep them spinning. I have a 160 GB 2.5"

hard drive that takes 1.1 A to start up and about 400 mA (0.4 A) when reading or writing to give you some idea of the difference.

Another very common problem when using USB chargers that require a separate USB "data" cable to supply the power is that the

cable does not use wire that will carry that much current without dropping voltage due to the resistance of the wire. Most USB

cables I have seen use 26 or 28 gauge wire (the smaller the gauge number the thicker the wire, this is usually printed on the cable

but it may also be only on the packaging) and it seems fairly constant that longer cables (6') use the thinner wire and short cables (3')

use the thicker wire.

If you are in the states I have found that MCM electronics has a 5V 2A power supply for the Raspberry Pi that uses 22 gauge wire

for $4.99 that works fine with the previously mentioned 160 GB hard drive.

@Clem

A USB keyboard should use less that 80 mA (0.08A) and a mouse probably about the same. I'm not sure how much current is needed

for wireless keyboards and mice but it should not be much more.

Would this one work? 5V 2A Power Supply w/ 20AWG 6' MicroUSB Cable - International ID: 2297 - $14.95 : Adafruit Industries, Unique & fun DIY …

It's a little expensive but it should work just fine. I have bought several items from Adafruit and have found them to be good quality products.

Sounds to me like a good choice. Let us know when you get it working. TY

Thank you guys so much. I've tried to get question answered on reddit and many other places after doing extensive research. People just don't like noobs apparently. After the responses I got, I didn't expect to get such helpful responses.

I'll be buying and trying this out next month. Thanks. I'll let you guys know if this worked or not when I get the chance.

I agree with all the other replies, but there is one other issue. If you are using a USB power cable of 1 metre or longer then you will have problems. Use a 500mm cable and you will be able to run a Pi2 with a mouse/keyboard and a wifi dongle without any problems.

You might get away with running the external hard drive with a 250mm USB PSU cable, but I have doubts. If you can find very short USB cables, you might run it successfully.

The problem is not likely to be the power supply, even at 750mA, but the voltage drop down the connecting USB power cable. Even USB cables sold as 'phone charger' cables have too high a resistance at 1m in length or greater.

I covered all of this in my first post. The power supply I mentioned in that post and the one Christopher is going to buy are essentially dedicated power supplies for single board

computers with built in "USB" cables that use wire gauges capable of supplying the current needed with minimum voltage drop even with a 4' (22 AWG for the one from MCM) to

6' (20 AWG for the one from Adafruit) cable length.