I Yam What I Yam

Wait, what’s a potato battery got to do with Popeye?  Wrong vegetable Marcel.

Popeye, I yam what I yam

It could be that our unflappable wonky eyed protagonist got his power from a vegetable or it could be that I couldn’t resist the “yam” gag.  Can I claim a little of both?  Bad jokes aside, let’s get right into squeezing all the power I can from this.

Raspberry Pi Power requirements.
0.01amp at 240volt, not bad.

I know I want to power a small computer with this battery and I’m a little lazy getting out the multimeter lately, so I took my old Raspberry Pi (B model) plugged that into a 5volt dc adaptor and backed the lot off an old power meter.  Initially it didn’t work at all but I remembered the old B models had an issue where the SDCard slot would start to get hot and basically bake the solder on it until it became unusable.  No big deal, I just threw it into a case and mashed some paper between the SDCard and casing to apply constant pressure to the socket.

Ummm..hello?  Do you run off love or something?
Ummm..hello? Do you run off love or something?

Next up I threw a Raspberry Pi model A onto the meter and…well…I saw it peak at 0.01amp for a moment, but then it settled back down to free energy (don’t tell the government/oil companies).  I am still undecided which to use (model A or model B).  The model A was known for low power usage and I didn’t have an SDCard in there so I’d need to accommodate storage power too.  Which leads me to ask the question, “Which storage, available to use for the operating system, uses the least power?”  Unfortunately the Raspberry Pis have no onboard storage which I can leverage for this (easily), so I’m forced to use either some form of SDCard or USB drive.


MicroSD for the win!  Forget about USB as that’s way too much power, but it turns out there’s almost 100mA of difference between the full size and MicroSD.  It doesn’t sound like much, but when you’re using a potato for power, you take every mA you can get.  Which brings me to my next trick.

The battery vampire
The Vampire of The battery World

That little schematic above is what we call a Joule Thief.  Technical bits aside, this little oscillator rig has a knack for squeezing every last drop of life out of a battery.  The only problem here is that you end up with an unfiltered power supply.  No need to worry about any chips getting fried though.  The Raspberry Pi has some nice onboard voltage regulators that are quite forgiving.  Speaking of chips, let’s see what can be done in that area.

Who needs Speedy?  Senior Slowpoke will do fine.
Who needs Speedy? Senior Slowpoke will do fine.

If you haven’t guessed from the above image, we don’t really need to run the Raspberry Pi at full speed.  Some extra power savings can be had by underclocking the thing.  You do this a lot like overclocking but maybe throw some negative multipliers on the voltage config. 😛

Bite down on this...
Bite down on this…

Alright, considering this is the part that I start carving chunks out of the Raspberry Pis brain that I don’t need, I was going to have a lobotomy picture up there.  They were a bit unsettling, so just bite down on this while we offline some chunks o’ brain.  Now, you can carve the LAN chip off the model B and lose a USB port or 2 in the process by physically removing the chip from the board (and the associated power rails), but if you’re not using the LAN or USB you can save yourself the hassle and just not power it up in software.

E.g. edit the following:


You know what?  While we’re at it, let’s offline the HDMI.

sudo /opt/vc/bin/tvservice -o





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