[colug-432] RPi peripheral power consumption: Reduce by Using Switch Mode Regulators

[jep200404 at columbus.rr.com]

On Sat, 18 May 2013 12:40:17 -0400, Scott Merrill <skippy at skippy.net> wrote:

> I'm contemplating battery / solar power configurations, and want to
> minimize power consumption to prolong usage.

I understand. 

Empirical testing is the way to answer the original question. 
The resolution you likely want is finer that of typical 
power meters for AC input to your wall wart. 
So you will likely want to measure the USB power by using a 
small value resistor (like 1 ohm) in line with USB power 
and measuring the voltage drop across the resistor. 
Current = voltage / resistance
See the fancy altoidish way of doing so[2]. 
The Penguin Mints box was a very nice touch. 

The Pi itself takes 5 Volt input and uses linear regulators 
to create the lower voltages that it actually uses. 
Linear regulators waste power. 
See RG1, RG2, and RG3 on the schematic[1]. 
There is a note by RG2 about having enough copper to help 
dissipate the wasted power. 
Switch mode regulator (switchers) are more efficient, but have 
more parts, are more complicated, and cost more. 
The cost alone probably eliminated them from consideration. 
You can retrofit a switch mode regulator. 
You would remove a linear regulator and replace it with 
wires to a switch mode power supply. Look in the experimenter 
section of Micro Center for a kit for such. Another option 
with sufficient scrap electronics is to use the switch mode 
regulator from something else, like a dead ethernet switch 
or router. If you roll your own switch mode regulator, 
you'd likely use a buck[4] or SEPIC[5] converter. 
With a switch mode regulator, your Pi will use less power 
_and_ run cooler. There are many many correct solutions. 

Many other folks have been here[π]. 

[1] http://www.raspberrypi.org/wp-content/uploads/2012/10/Raspberry-Pi-R2.0-Schematics-Issue2.2_027.pdf
[2] http://www.ultramobilegeek.com/2007/02/measuring-power-on-peripherals-usb.html
[3] Switch mode power supplies are the electrical equivalent of 
    hydralic rams. 
    https://en.wikipedia.org/wiki/Hydraulic_ram
[4] https://en.wikipedia.org/wiki/Buck_converter
[5] https://en.wikipedia.org/wiki/SEPIC_converter

http://www.ti.com/ww/en/simple_switcher_dc_dc_converters/regulators.html
http://www.ti.com/ww/en/simple_switcher_dc_dc_converters/regulators_lm310x.html
http://www.ti.com/product/lm3100
http://www.digikey.com/product-search/en?pv7=2&FV=fff40027%2Cfff8029a&k=lm3100&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25
http://www.digikey.com/product-search/en/programmers-development-systems/eval-boards-dc-dc-ac-dc-off-line-smps/2622539?k=lm3100

[π] http://www.raspberrypi.org/phpBB3/viewtopic.php?f=63&t=12387
    http://www.seanet.com/~karllunt/RasPiRegulatorReplacement.html
    https://duckduckgo.com/html/?q=raspberry+pi+RG2+switch+mode+regulator