Alternative power supplies

[jmknapp]

If you remove the four plastic "feet" and remove the corresponding screws, the plug splits into two halves, one of which contains the main power supply and the other the main circuit boards. Here's the power supply side:



It's just a simple 5V supply with a 4-pin connector, the two red leads being 5V (actually 5.25V measured) and the two black leads being ground.

The circuit board side has the female power connector J3:



A closer view:



The pins have a 0.1" (2.5mm) spacing.

So to run the plug on, say, a battery or solar panel just requires feeding 5V to J3. The schematic shows that the two power pins and the two ground pins are tied together:



Here's a proof of concept with an 18W solar panel and small battery (to bridge cloudy intervals):



The solar panel produces 18V @ 1A in full sunlight. That feeds into a 12V charging regulator which then goes into a 5V regulator and then to J3. The plug runs fine with this setup, including the USB hub (Targus Bend-A-Hub) which has an 802.11g USB adapter as well as a 16GB USB memory stick attached in the photo. The plug draws about 800ma @ 5V normally, up to 1000ma depending on cpu activity. The 802.11g dongle bumps the current up to about 1100ma.

Here's a laptop vnc'ed into the plug, showing the gnome desktop:



Joe

[jlpoole]

Sweet, I was musing over what it would take in terms of solar power to sustain one of these.

What made you decide on 18 watts?  Availability of components?

For the components:

Component	Brand	Cost
Solar Panel
12 volt charging Regulator
5 volt Regulator
12 volt battery (what brand/ type?)

Do you have a preferred supplier of solar components and regulators?

How long does the battery hold a charge?
What were your calculations for sustained use in sizing the battery?

[jmknapp]

Availability of components was the main thing--I bought the solar panel and 12V charging regulator at the Dayton Hamvention over 10 years ago! But I figured that at 18W (in full sun anyway) it should handle a 5W load including inefficiencies.

Sizing would depend on the application... if 24-hour uptime was desired on an "average" day, I think more than 18W would be needed at least around these parts. The battery in the picture is only 1.2 amp-hours at 12V (i.e., about 15 watt-hours) & so by itself only powers the 5W plug for about 3 hours, actually a bit less since the 5V regulator has 85% efficiency. So to get through the night or a long cloudy stretch would require more battery. Then there would have to be enough solar panel to keep that battery charged. The 18W panel might suffice on a good day (and succeeding night)--will have to test that. Probably more would help when the weather is like it is right now--pretty much overcast. Suddenly a 5W draw doesn't seem very parsimonious.

Another application though could just be for the plug to wake up at certain intervals, say, to take webcam shots of glaciers --then the power budget is much easier to meet. Is the plug capable of going into and resuming from sleep modes?

Joe

[jlpoole]

Availability of components was the main thing--I bought the solar panel and 12V charging regulator at the Dayton Hamvention over 10 years ago! But I figured that at 18W (in full sun anyway) it should handle a 5W load including inefficiencies.
...

Here's some rough results or a quick search on the web:

Looks like solar panels run in the $7-13/watt category when sized for a low wattage application, e.g. 10 watts.  For reference, the large panels used for home/commercial installations are about $3.50/watt when purchased in bulk, e.g. $15,000 worth.

A little refresher on Ohm's law: 
     Watts = Volts x Amperes
SheevaPlug + some other stuff ~ 10 watts = 5 volts x 2 Amps


For instance, a BP Solar XS-310M 10 watt panel (16.57" x 10.59" x 0.90" ) has:
Electrical Characteristics
Maximum Power: 10 Watts
Voltage at Pmax: 16.8V
Current at Pmax: 0.59A
Warranted minimum Pmax: 9 Watts
Short-circuit current: 0.69A
Open-circuit voltage: 21.0V

and sells for $94.00 + $25 shipping.  Probably need at least four (peak .69A x 4 =~ 2.8 A, but remember that's peak and probably means a noon day sun in August) for say $400.



See also:
SOLAR,POWERFILM,MPT4.8-150 [@Jameco]
4.8V,100MA,94mm X 150mm  at $24, so 20 of these might meet a projected peak load demand of 2As.  That's ~$500 not including regulators &etc.



I guess if you can lay your hands on a free used/discarded solar panel, it might be not too $$ to explore.  But remember, solar panels can be similar to batteries in terms of degradation -- the older they are, they less performance, so if it's used, you're going to be at a lower power output.

[dattaway]

I've been thinking about this.

Curious what your 18 watt panel will put out during a dim, cloudy day.  That would give me an idea what size I should go with.

[jmknapp]

jlpoole:
> ~$500 not including regulators &etc.

Oy! Who knew 5W could loom so large? What the world needs is a good half-watt computer.

dattaway:
> Curious what your 18 watt panel will put out during a dim, cloudy day.

Thick cloud cover is about all I've had for three straight days & I can verify that it's likely to deliver only 2W under those conditions.

Joe

[scruss]

I don't think it would be as much as $500 - the single 15W Eliminator panel you can get in many hardware stores is $100 or less. It includes a reverse-current protection diode.

I used to install a lot of small solar for powering remote wind monitoring equipment. A number of the manufacturers have (or used to have) really good application guides for sizing panels against load, with maps of solar radiation.

This is fairly awesome that we can run a Linux box from a small sized panel. The weather stations I used to install ran single-digit megahertz 8-bit microcontrollers, and used the same size of panel.

[jlpoole]

I don't think it would be as much as $500 - the single 15W Eliminator panel you can get in many hardware stores is $100 or less. It includes a reverse-current protection diode.

Here's one for $180
http://www.4lots.com/browseproducts/Pro-Kit-15W-with-Charge-Controller.html


Hmmm.... if you are running a business from your computer, e.g. a commercial web site, then one might consider whether the commercial tax credit for solar power would apply -- that, plus other government incentives, might bring solar power back into the realm of not seeming so expensive.

[Rabeeh Khoury]

If you are able to build your own kernel then you can get the cpuidle patch from Marvell git.
This will lower the power consumption when the system is idle.

http://git.marvell.com/?p=orion.git;a=summary

Look for the cpuidle and peripherals clock gating patches.

[jmknapp]

If you are able to build your own kernel then you can get the cpuidle patch from Marvell git

I just gave it a try on a Fedora box:

- installed ARM cross-compiling tools from codesourcery

#git clone git://git.marvell.com/orion.git
#make ARCH=arm mrproper
#make ARCH=arm kirkwood_defconfig
#make ARCH=arm menuconfig
#make ARCH=arm -j1 CROSS_COMPILE=/usr/local/bin/codesourcery/bin/arm-none-linux-gnueabi uImage

The compilation seemed to go OK, but the resulting uImage doesn't boot, giving this output:

Code:

d 1:0:0:0: [sdb] Attached SCSI disk
kjournald starting.  Commit interval 5 seconds
mmc0: unhandled error status 0x4000
mmcblk0: error -42 sending read/write command, response 0x900, card status 0xd00
end_request: I/O error, dev mmcblk0, sector 8192
Buffer I/O error on device mmcblk0p1, logical block 0
lost page write due to I/O error on mmcblk0p1
EXT3 FS on mmcblk0p1, internal journal
EXT3-fs: mounted filesystem with writeback data mode.
VFS: Mounted root (ext3 filesystem) on device 179:1.
Freeing init memory: 112K
mmcblk0: retrying using single block read
mmcblk0: error -110 sending read/write command, response 0xc20, card status 0x400d00
end_request: I/O error, dev mmcblk0, sector 20064
mmcblk0: error -110 sending read/write command, response 0x400d00, card status 0x400d00
end_request: I/O error, dev mmcblk0, sector 20065
mmcblk0: error -110 sending read/write command, response 0x400d00, card status 0x400d00
end_request: I/O error, dev mmcblk0, sector 20066
mmcblk0: error -110 sending read/write command, response 0x400d00, card status 0x400d00
end_request: I/O error, dev mmcblk0, sector 20067
...

So it looks like it isn't able to read the root filesystem from the SD card (/dev/mmcblk0). I am able to boot kernels from http://sheeva.with-linux.com/sheeva/

Maybe something needs to be configured in menuconfig?

EDIT: After some searching it looked like I might need a patch discussed in other threads, mvsdio.patch. Sure enough, I applied that patch and the kernel boots--will make some power measurements to see what effect cpuidle has. I do notice that of the two idle states listed in /sys/devices/system/cpu/cpu0/cpuidle and the plug basically idle, state1 is active about 90% of the time and state0 10%, based on the 'time' files in those directories (given in microseconds).

Joe

[Rabeeh Khoury]

You need a patch for the SDIO support (called mvsdio.patch).

Refer to either for sources and binaries -

http://openplug.org/plugforum/index.php?topic=265.0

or

http://openplug.org/plugforum/index.php?topic=92.0

[jmknapp]

Thanks, Rabeeh. I tried cpuidle and posted some results here:

http://openplug.org/plugforum/index.php?topic=272.0

joe

[Manic]

Awesome and very informative post, im also thinking of alternative power solutions for the plug.. this will give me a starting point!

[tvrusso]

I'm very curious about what 5V regulator you're using that can handle the current draw of the Sheeva and the USB dongles you've got on it.

I'm not so much interested in powering the sheevaplug with solar, but my primary use for the SheevaPlug will be to handle some of my amateur radio applications --- which means it's working in an area where I have lots of 12V supplies available including some batteries.  It would be nice to power the Sheeva from the 12V athat's all over the shack rather than AC.

So far, all the DC/DC converters I've seen that can do 12V-5V at the current levels needed are almost as expensive as the SheevaPlug itself.

[jmknapp]

I'm very curious about what 5V regulator you're using that can handle the current draw of the Sheeva and the USB dongles you've got on it.

I got a relatively cheap one on eBay from a guy in Hong Kong:

Step Down DC /DC Converter Charger Regulator Controller:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWNX:IT&item=230338695225

It converts 12VDC to 5V with 93% efficiency and max current of 3 amps! It was only $4 but the $10 shipping is the kicker. I think they were pulled off some other assembly line. There's even a little trimpot to adjust the voltage.

It made me think--what about those car cigarette lighter adapters that provide USB power? Maybe just cannibalize one of those.

Joe