The Efficient Cabin, RV or Van Computer

Efficient 12 volt computing. Can you spot the PC in the photo?

This backcountry cabin computer project isn’t so much about saving the planet (though perhaps it helps) as it is about avoiding the expense of PV system battery replacements and larger solar panels — expensive any way you cut it — as well as increasing our “no-sun” use time.

The numbers prove out nicely. My Amazon sourced efficient computing system demands a rough average of 0.42 amps, while my former system, based on a tiny old Acer netbook optimized as much as possible, still demands a full 3 amps. That’s nearly SEVEN times the power! What is more, we had our Hughes Net satellite internet upgraded to the latest version, which also draws surprisingly less power. Prior to all this I only got a few hours of non-sunshine online computer time out of the system. I now enjoy an astounding six or so battery powered hours with zero sunlight on our panels!

I’m excited, mostly because of the huge increase in no-sunlight use time. But more, knocking down our power demand will easily get us another year or more out of our cabin batteries. Those cost about $1,000 to swap out, on average every 5 years, thus costing $200/year. If I can squeeze another year out of them I’ll thus drop that to $167.00/year, or bump it up to 7 years at $143.00/year. As listed below, my component built system cost at most $156.00 (and about 6 hours of my time obtaining parts and customizing connectors for our cabin system), so the payback time on that in terms of increased battery lifespan is a couple of years. Not fantastic in one sense, but delaying a $1,000 expense by a few years has value, not to mention delaying the physical process of swapping and re-wiring big heavy batteries.

I’ve come to the understanding that literally hundreds of thousands of people, worldwide, constantly mess with attempting to do low power computing on 12 volt PV systems. Hopefully some of these ideas will help. Check out the components and how they fit together.

First step in this was finding an inexpensive computer that ran off 12 volts. I wasn’t as successful in this as I’d have liked, as nearly every system I found with a 12v input was expensive or had problems running Linux. However, I did find the affordable “computer stick” genre that runs off USB power (5 volts), and thus can be powered fairly efficiently from a “buck” type solid state voltage reducer hooked up to a 12 volt PV system.

By using a lean version of Linux (Lubuntu), not only do I save the OS cost premium added to any Windows PC, but end up with less software overhead, thus enabling the use of a minimalist computer. For now, my choice is the Intel Compute Stick STCK1A8LFCR. Works fine for internet based work, light word processing and photo editing. Available memory can be easily increased by popping a USB stick into connected USB hub. (Warning, if you’ve never used Linux you will need some time to do the installs and learn the ropes, allow at least half a day, and know that many of these “mini computers” claim to be “Linux compatible” but actually are not due to Linux not having the correct drivers for components such as wireless and audio.)

Not every 12 to 5 volt “USB” converter will run or charge a given item. The simple solution, or so I thought, was to find a 12 volt powered USB hub with “high power charging” slots and and use one of those slots to power the Compute Stick. That was a fail. For what reason I do not know, the Stick just sat there with power indicator light flashing, but never booted up. Luckily I have a variety of voltage converters sitting around from other projects; a sweet little CPT Agile-Shop DC Converter Buck Module did the trick. This little thing is well engineered. When connected and under zero demand my amp meter shows it as requiring zero current, the CPT then appears to only demand whatever current is needed by connected items. Efficient, though ideally you want to run every item directly off 12 volts, without converters.

Metering the new system. It seems to average out at about 0.42 amps. This is incredibly efficient for a full-on desktop style PC. As a basis of comparison, I could indeed do some of this work on my Samsung Galaxy smartphone, when hooked up to charger it draws an average of about 0.47 amps — nearly the same as my larger screen system with full keyboard and mouse.

Next challenge, an efficient monitor that runs directly off a 12 volt source. Not many suitable choices in this. You can find plenty of automotive LCD and LED panels but most are small and often expensive. After much searching I found the Sceptre E165W-1600HC E 16″ Screen LED-Lit Monitor. I cobbled up a direct 12 volt connector lead, yep, runs fine on cabin electricity. Sixteen inches isn’t particularly great in terms of size, but it’s usable and being LED does sip rather than gulp electrons. Another advantage of this screen is it does not have speakers, which I’d guess are an extra power drain even when not in use. Instead, it’s got an audio-out jack that pulls sound from the HDMI connection and works fine with headphones or external speakers if you so desire.

Compute sticks don’t have a keyboard (nor any other peripheral for that matter). While the Intel does have Bluetooth connectivity, rather than fiddling with that unknown I opted to the simple solution: cordless keyboard and mouse that connect via USB dongle. Nothing crazy here, though both keyboard and mouse require AA batteries, which are said to last for years but should be noted as an expense if you get picky.

Other items:

An inexpensive USB hub is necessary, as most of my work is creative output and is always backed up one way or another, so I just pop a thumb drive into the hub and backup to that. Incidentally, the model of Compute Stick I used is USB-2, USB-3 is much nicer, but later versions of tiny computers that boast USB-3 are likely to have wireless and audio that may be difficult to get working under Linux. (For anyone reading this and running into Linux challenges with built-in wireless and audio, rather than spending hours if not days trying to get things working, the probable best solution is to cut bait and just use tiny inexpensive USB wireless and audio adapters that Linux recognizes.)

Most of our cabin electrical connects with either standard automotive “cigarette lighter” plugs or “Anderson power pole” connectors. I happen to have the Anderson crimping tool and a variety of connectors, so I converted everything to the Andersons. Cost of doing so was minimal.

In all, this is an exciting little bit of computer hardware. Incredibly inexpensive, sips power and is easily hooked up to a 12 volt photovoltaic system.

— Sceptre E165W-1600HC E 16″ Screen LED-Lit Monitor, True Black (E165W-1600HC) $66.00
— Intel Corp. BOXSTCK1A8LFC Compute Stick STCK1A8LFC $39.00
— Cordless keyboard/mouse Logitech Wireless Combo MK360 – $21.00
— USB 2.0 hub – $12.00
— USB power supply for Compute Stick: Agile-Shop DC Converter Buck Module 12V convert to 5V USB Output Power Adapter $8.00
— Various electrical connectors etc. – $10.00
Total system cost – $156.00

Following are a few power demand demand measurements normalized for what they draw when I hook them up at home on grid power, measured with a watt meter at the 110v source. Calculations illustrate how little any of my computer systems cost using grid power (based on 325 days use, 6 hours a day). What this shows is just how incredibly expensive PV power with battery storage actually is compared to being on the grid at around ten cents a kilowatt hour. In other words, spending money on an efficient computer will save insignificant cash when calculated on the basis of grid power — but reduce power use on a PV battery system and the numbers are much better due to cost of battery replacements or adding extra PV panel capacity. (Electrical engineers, please help if my math is wrong.)

— Office computer system, 73 watts, x 6 hours = 438 watt-hours per day, x 325 days = 142,350 divide by 1,000 for kilowatt hours = 142 x $0.10 = $14.20 per year

— Laptop, 28 watts, x 6 hours = 168 watt-hours per day, x 325 days = 54,600 divide by 1,000 for kilowatt hours = 55 x $ .10 per = $5.50 per year

— Cabin super efficient system, 7 watts, x 6 hours = 42 watt-hours per day, x 325 days = 13,650 divide by 1,000 for kilowatt hours = 14 x $0.10 per = $1.40 per year