Gray
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Need advice on power supply

Mon Sep 16, 2013 3:08 pm

Hey everyone. I want to buy a RPi B and need a good PSU to safely power it, a keyboard, the ethernet and the HDMI port. Currently I have a Samsung 5V 700mA phone charger. If it's not sufficient Ican also get 5V 1200 mA micro-USB Nokia charger. Should I use my charger, buy the Nokia, or look for something else?

Sorry if it's the wrong place to ask.

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RaTTuS
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Re: Need advice on power supply

Mon Sep 16, 2013 3:30 pm

personally I'd use a Powered USB adpater to run the RPi and your peripherals
see PiHub
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W. H. Heydt
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Re: Need advice on power supply

Mon Sep 16, 2013 5:28 pm

If you're in the US, try the Adafruit power supply. It's 5.25v at 1A. The higher voltage is to compensate for low quality power cables and still be within spec for good power cables.

chilinski
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Re: Need advice on power supply

Mon Sep 16, 2013 8:21 pm

Almost all power supplies will list the amperage they can provided. Of course, they can lie, too. But anything less than 1 amp is probably going to cause you frustration down the road. Something else you probably ought to know...if you buy an ac adapter with two usb ports and it says it outputs 2.1 amps, that generally means you get 1.05 amps on one port and 1.05 on the other. You don't get two amps out of each port separately. I've run this one with a 4.3 LCD screen (adapted to run 5V) and Raspberry Pi with no issues whatsoever. http://www.amazon.com/RCA-PCHUSB2R-Port ... B004WK3U9W

W. H. Heydt
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Re: Need advice on power supply

Tue Sep 17, 2013 4:37 am

chilinski wrote:Almost all power supplies will list the amperage they can provided. Of course, they can lie, too. But anything less than 1 amp is probably going to cause you frustration down the road. Something else you probably ought to know...if you buy an ac adapter with two usb ports and it says it outputs 2.1 amps, that generally means you get 1.05 amps on one port and 1.05 on the other. You don't get two amps out of each port separately. I've run this one with a 4.3 LCD screen (adapted to run 5V) and Raspberry Pi with no issues whatsoever. http://www.amazon.com/RCA-PCHUSB2R-Port ... B004WK3U9W
That varies quite a bit. If you read the fine print, many such devices will claim that you can get 2.1A on a single port if you only connect one device.

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FTrevorGowen
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Re: Need advice on power supply

Tue Sep 17, 2013 7:15 am

W. H. Heydt wrote:
chilinski wrote:Almost all power supplies will list the amperage they can provided. Of course, they can lie, too. But anything less than 1 amp is probably going to cause you frustration down the road. Something else you probably ought to know...if you buy an ac adapter with two usb ports and it says it outputs 2.1 amps, that generally means you get 1.05 amps on one port and 1.05 on the other. You don't get two amps out of each port separately. I've run this one with a 4.3 LCD screen (adapted to run 5V) and Raspberry Pi with no issues whatsoever. http://www.amazon.com/RCA-PCHUSB2R-Port ... B004WK3U9W
That varies quite a bit. If you read the fine print, many such devices will claim that you can get 2.1A on a single port if you only connect one device.
On the basis of the two (different) PSU's "of this type" I have (measured load curves can be found within my webpages) I suspect that most (if not all) simply have their output ports/cables "in parallel" and hence "2A" (or whatever the spec. says) is the maximum total the PSU can supply (but not necessarily at 5V!) whether that's shared between two ports or just one is in use. Low-to-medium cost powered hubs seem to use the same method, but are spec'd at 500mA per port (ie. a 4-port hub would be supplied with, if you're lucky, a 2A PSU - at least one such hub PSU I've tested actually had a ~500mA current limit).
Trev.
Still running Raspbian Jessie or Stretch on some older Pi's (an A, B1, B2, B+, P2B, 3xP0, P0W, 2xP3A+, P3B+, P3B, B+, A+ and a B2) but Buster on the P4B's. See: https://www.cpmspectrepi.uk/raspberry_pi/raspiidx.htm

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