jets
Posts: 58
Joined: Mon May 06, 2013 9:40 am

Is this good 12V power source for Pi?

Fri Nov 22, 2013 3:33 pm

I recently came to conclusion, that I should power up my Pi-server at my off-grid-cabin directly from my battery bank, instead of getting power through inverter and then again through transformer.

So, I ordered this:
http://www.ebay.co.uk/itm/DC-12V-to-5V- ... 1266538422

Specs say:
Input voltage: 12V
Output voltage: 5V
Output Current: 3A
Output Power: 15W
Conversion efficiency: up to 96%
Soft-start time: 500mS
Output ripple: 50mV (MAX) 20M-bandwidth
Dynamic response speed: 5% 200uS
Size: 46x26x14mm

But honestly, I am unsure if such a step-down PSU is a best choice. I would like to get your comments on this.

And if this is not the best choice (price is cheap!), then what would be?

Dilligaf
Posts: 283
Joined: Wed May 23, 2012 6:48 pm

Re: Is this good 12V power source for Pi?

Fri Nov 22, 2013 5:15 pm

I use these http://www.ebay.com/itm/Hot-LM2596-DC-B ... 1c367bf788
Being adjustable they allow you to adjust the voltage up to 5.25V at the TPs ensuring stability. Of course you need a voltmeter, also make sure you adjust them to 5V BEFORE connecting to the PI then fine tune after connecting.

jets
Posts: 58
Joined: Mon May 06, 2013 9:40 am

Re: Is this good 12V power source for Pi?

Fri Nov 22, 2013 7:20 pm

Dilligaf wrote:I use these http://www.ebay.com/itm/Hot-LM2596-DC-B ... 1c367bf788
Being adjustable they allow you to adjust the voltage up to 5.25V at the TPs ensuring stability. Of course you need a voltmeter, also make sure you adjust them to 5V BEFORE connecting to the PI then fine tune after connecting.
Ahaa.. what exactly do you power with that? Just the RPi alone? I need to power USB camera and 3g dongle as well plus a RF transmitter to control electrical 230v RC sockets, 1-wire and RS232.

How much experience you have of those? They are inexpensive too, but they seem to require some soldering/tinkering to get power to USB. The item I ordered, just requires USB cable, which I happen to have lying around.

But your option seems very viable too.. have you measured its efficiency? And how much does it consume when Rpi and other peripherals are "off"?

Dilligaf
Posts: 283
Joined: Wed May 23, 2012 6:48 pm

Re: Is this good 12V power source for Pi?

Fri Nov 22, 2013 9:09 pm

I power the PI through the gpio pins bypassing the polyfuse so full current is available to the usb ports, I put an inline 2A fuse in the wiring to the PI. I have used many usb devices including cameras with led lights and non powered hard drives without issues other than hotplugging. I have not looked at efficiency but they use a switching regulator so should be in line with other such devices. The listing claims up to 92% efficiency.

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joan
Posts: 15272
Joined: Thu Jul 05, 2012 5:09 pm
Location: UK

Re: Is this good 12V power source for Pi?

Fri Nov 22, 2013 9:17 pm

Looks OK to me. I'd have no problem connecting that to my Pi. Personally I use a UBEC as it supports a wide range of input voltages (6V-26V) for the 3A 5V output.

jets
Posts: 58
Joined: Mon May 06, 2013 9:40 am

Re: Is this good 12V power source for Pi?

Fri Nov 22, 2013 9:31 pm

Dilligaf wrote:I power the PI through the gpio pins bypassing the polyfuse so full current is available to the usb ports, I put an inline 2A fuse in the wiring to the PI. I have used many usb devices including cameras with led lights and non powered hard drives without issues other than hotplugging. I have not looked at efficiency but they use a switching regulator so should be in line with other such devices. The listing claims up to 92% efficiency.
Interesting! Can you give me more details, like a sketch or maybe even step-by-step-howto-amateuridiot-apecandoit-type of instructions/documentation? Not even the polyfuse rings my bell..

I have one 2.1A 230V PSU, but it seems to be unreliable with my Inverter. So at the moment I am using 1A PSU for Rpi and 1A additional PSU for USB Hub that runs the dongle, but camera is attached directly to Rpi.

How much power does the Rpi actually let go through to the USB? Is it only matter of how many amps the PSU can do if the Hub is not using separate PSU?

Dilligaf
Posts: 283
Joined: Wed May 23, 2012 6:48 pm

Re: Is this good 12V power source for Pi?

Fri Nov 22, 2013 9:46 pm

It's really simple, you put the 5V and ground into the gpio pins, pinout here http://elinux.org/File:GPIOs.png this powers the PI after the input polyfuse bypassing its volt drop, current limit and protection. You put a 2A inline fuse in the wiring between the PI and source to provide short protection. The traces on the PI should be able to handle 2A the limit of what is supplied to the usb ports is what your power supply is capable of outputting or 2A. On very early PI they had 140mA usb fuses so this wouldn't apply to them unless you bypassed the usb fuses.

A UBEC works fine but doesn't allow fine tuning the voltage, the linked converter also supports a wide range of input voltage like the UBEC does.

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