Power source for RaspPi

The "official" RasPi voltage spec is same as USB: 5.0V +/- 5% = 4.75V to 5.25V.  Most USB chargers / power supplies are rated at 5.1V, which is excellent since there will be a small voltage drop across the Micro USB cable and RasPi's polyfuse F3.  So while a 5.25V supply would work provided that it doesn't go above 5.25V, a 5.0V or 5.1V supply should be fine provided that you have a good Micro USB cable.

Thanks,

I have a Griffin usb charger which is rated at 5.2v @ 1000mA.  Would they leave off anything after the 5.2 i.e. 5.2x where x is some other number?

Cheers

David

David Harrison wrote:

 

I have a Griffin usb charger which is rated at 5.2v @ 1000mA.  Would they leave off anything after the 5.2 i.e. 5.2x where x is some other number?

Voltage regulators are built from real circuit components, and real circuit components have tolerances on their values which vary from one manufacturing lot to the next, and across the specified temperature range of operation.  In my experience, a good voltage regulator typically regulates within 2% of spec, i.e., +/- 0.1V for a 5.0V regulator.  So there's no point in adding a 0.01V digit unless you're designing a precision voltage supply and charging hundreds or thousands of dollars.

5.2V @ 1000 mA should work with a RasPi.  The caveat with all RasPi power supplies is that the actual manufacturer may not be as careful meeting the written spec as one would like.  For example, a poorly-regulated supply might supply too high a voltage under a light load, possibly damaging RasPi, or drop to a much lower voltage as it approaches its current limit causing RasPi to misbehave.  Such supplies may work as cell phone chargers but not provide a clean, well-regulated 5.1V across the entire current range.  If you're unsure, check the power supply with a voltmeter (or better yet, an oscilloscope) before plugging in your RasPi.

There's a long list of working RasPi power supplies at the RasPi hardware wiki http://elinux.org/RPi_VerifiedPeripherals#Power_adapters, including two Griffins.  There's only bad supply listed, which is not a Griffin.  So your odds are good, though the Wiki only includes devices that people have bothered to add.

Thanks, I found my iPad charger and Griffin charger (one of which isn't listed).     I'll test it like you said to be sure but so far so good.  Now if I can find a list for Powered USB Hub.

David Harrison wrote:

 

Thanks, I found my iPad charger and Griffin charger (one of which isn't listed).     I'll test it like you said to be sure but so far so good.  Now if I can find a list for Powered USB Hub.

Same RasPi Wiki page.  You just need to scroll up to http://elinux.org/RPi_VerifiedPeripherals#Powered_USB_Hubs

Seems like if I use a Powered USB Hub that is known to work then I can use it as the power source and not have to use any additional chargers.

Cheers

David

David Harrison wrote:

 

Seems like if I use a Powered USB Hub that is known to work then I can use it as the power source and not have to use any additional chargers.

It can work, but it depends on the hub.  A cheap hub generally connects its 5V external power directly to all the downstream ports, which works.  An expensive hub may limit the current to each port under software control so a bad USB device doesn't take down the rest of them.  I don't know if any actually do this.

I currently use a cheap powered hub in this way and it works pretty well, except for one thing.  It has a 3.5 mm barrel power jack, which doesn't always make good center pin contact so sometimes my RasPi voltage drops too low and the DVI-D monitor blanks out.  A 5.5 mm barrel power jack is a lot better, especially if the power plug has wiping contacts for the center pin.

Thanks

To use the hub I'm guessing that one USB port connects to the Pi and then whatever else you want to use (wifi adapter) connects to one the remaining USB ports.  And of course the one that powers the Pi will also connect to one of the free ports.  I chose one of the CyberPower High Speed 7 port hub.  This was listed as a verified peripheral so cross my fingers.  But I see you point and agree, I am going to keep my power separate from the hub.

cheers

David

Updating this thread by developer request, to check date sorting.