atelier
Posts: 1
Joined: Mon Jul 30, 2012 7:05 pm

Exactly 5v?

Mon Jul 30, 2012 7:21 pm

Hi there, must the power supply for RPi be exactly 5v, if not what is the deviation? (I realise 'exactly' is impractical in real terms, I'm talking about what it's rated on the label =D) My supply is 5.2v and it's unlikely but I was wondering whether this would make any difference. My power supply is only 320mA so I'll need a new power supply (I'll have a Model B) anyway. Basically, I was just wondering about the safe min/max limits for the numbers given for power supplies (5v, 700mA, Model B)?

Thanks

calebzulawski
Posts: 46
Joined: Tue Jan 31, 2012 6:00 am

Re: Exactly 5v?

Mon Jul 30, 2012 8:07 pm

The acceptable variation is plus or minus 250mV (0.25 volts), so a 5.1V or 5.2V cell phone adapter is fine (and perhaps better than 4.8V? I'm not sure). The amount of current that your PSU can supply is much too low, as you have guessed.

JeremyF
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Re: Exactly 5v?

Mon Jul 30, 2012 8:18 pm

In theory, the Pi can run on 4.75-5.25V and anywhere from 500ma (I've been able to do it) or higher current. (However, when powering from micro USB socket, the most it can draw is 1000ma-1200ma, not sure exact number)
{sig} Setup: Original version Raspberry Pi (B, rev1, 256MB), Dell 2001FP monitor (1600x1200), 8GB Class 4 SD Card with Raspbian and XBMC, DD-WRT wireless bridge

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r4049zt
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Re: Exactly 5v?

Tue Jul 31, 2012 5:38 pm

Checking the voltage at D17 with a multimeter, 4.90 Volts across there is what I get running the pi off a micro-USB power supply from RS which was meant for the Pi.

At the same time, my PS2 old keyboard and PS2 old mouse work just fine from a single USB to PS2+PS2 adapter cable in the upper of two usb sockets.

The lower of the two USB sockets was insufficient to run four USB memory sticks plugged in via a usb to 7-way usb adapter. The power socket at the adapter showed less than 3 Volts. Switching its power-from-raspberry-pi to off, and connecting four NiCAD rechargeable batteries to the 7-way usb block, that got 5.1 Volts at the usb block, off a separate battery supply to the raspberry pi.

Like that, the raspberry pi Debian6 opened new file manager windows for each usb stick, and was able to read and write from each of them. It was able to move files from one usb stick to another.
Moving a GB of files got into problems with a flat battery and bad transfers when battery voltage at the 7-way block fell to about 4.4 or 4.3 volts. Rebooting and restarting, I got the other GB transferred with 5V power from another block of four AA 2000mAh NiCAD batteries. Those are all on charge now, from solar power.

I have also tried directly powering the rPi board from 5Volt off four more NiCad rechargeable batteries connected at D17. That did nothing so I'll keep trying more things.
Attachments
copying.jpg
debian6 finds external usb sticks.
More than 130GB of filespace for user documents so far and counting
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keymouse.jpg
example of old PS2 keyboard and PS2 mouse via one usb socket
keymouse.jpg (31.26 KiB) Viewed 2166 times
usb7.jpg
external 7-way usb with independent 5V supply
usb7.jpg (34.65 KiB) Viewed 2166 times

itimpi
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Re: Exactly 5v?

Tue Jul 31, 2012 9:47 pm

r4049zt wrote: The lower of the two USB sockets was insufficient to run four USB memory sticks plugged in via a usb to 7-way usb adapter. The power socket at the adapter showed less than 3 Volts. Switching its power-from-raspberry-pi to off, and connecting four NiCAD rechargeable batteries to the 7-way usb block, that got 5.1 Volts at the usb block, off a separate battery supply to the raspberry pi.
If that was an unpowered hub then I would not expect it to work. The Pi is not designed to have an unpowered hub plugged into it. If anything did work it would be by luck and would tend to be unreliable.

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