My Human-Powered Office
3 Nov 2019 - Jim Gregory - ~8 Minutes
I work from home, and have used a pedal-powered generator to power my office since 2009. (You can learn why here.) Since I can only generate about 50 W of electricity while working at my desk, I have needed to pick my equipment carefully to stay within the limits of my capacity.
Below is a description of the equipment I use in my office, as well as some issues to consider if you are thinking of setting up a similar office for yourself. (None of the links in this article are affiliate links, BTW.) I also describe what my typical workday is like for the curious.
My Office Equipment
In the past, I have used a 15” Dell Inspiron 3515” laptop or an 11” Acer C720 Chromebook with my desk. These laptops consumed about 25 W and 10 W, respectively, in use.
Both these laptops are now several years old. Newer laptops consume significantly less power. My father-in-law’s 11” Dell, for instance, is roughly comparable to the C720 and draws only 6 W, while a typical 13-15” laptop consumes 12-20 W. High-performance laptops may require more than this.
Note that all power consumption figures mentioned above assume the laptop’s battery is fully charged; if not, the power consumption will be far higher. Most laptops consume about 40-50 W while charging until the battery reaches 80%, then gradually taper off to their fully-charged power consumption level. If the laptop’s battery is fully depleted, charging can take 3 hours or more. Unless you are looking for a real workout, it’s best to use a fully-charged laptop with a pedal-powered generator.
You can save a few watts of power by powering a laptop using a DC-DC adapter instead of the manufacturer’s AC power adapter. That’s because a pedal generator normally produces DC electricity, and using an AC power adapter requires an extra DC-to-AC power conversion.
I currently use a Friendly Arm NanoPi M4 with 2G of RAM running Debian Linux as my main computer.
This small single-board computer is similar to a Raspberry Pi 4, but more powerful and (in my opinion) better designed (e.g., it only needs a heat sink to keep it cool, not a cooling fan). It consumes about 3 W of power under most circumstances, a few watts more when under heavy load. It is powered via a USB type C cable through a USB port built into the desk.
I have found this little computer perfectly adequate for typical desktop tasks like managing email, listening to streaming music, browsing the web, and watching occasional YouTube videos, as well as writing software, creating 3D CAD drawings, and processing images.
The NanoPi M4 only runs Linux, so it’s not a viable option for Windows or MacOS users. If you use Windows, an Intel NUC or other passively-cooled small computer would be a good alternative. Choose a model with the lowest TDP (Thermal Design Power) needed for your workload. This will minimize the power you need to generate.
I am not an expert on Apple computers, but I believe Apple has made some small-form-factor desktop computers that are fairly energy efficient that will run MacOS.
I use a Sceptre E165W 16” LED monitor. It draws 3 W in use.
The monitor is powered by a 12 V DC cable plugged directly into one of the four 12V DC sockets built into the desk, instead of using its AC power adapter. This saves a couple of watts of power by avoiding a round-trip DC-to-AC-to-DC conversion.
I am very satisfied with this monitor, but if you’re a developer more accustomed to a 27” screen or multiple side-by-side monitors, you will probably want something larger. If so, choose your monitor carefully, as some large monitors consume significant power.
I use an HP Envy 4500 3-in-1 multifunction inkjet printer, mostly for printing invoices and shipping labels. It draws about 1 W when idle and 13 W when printing. Other inkjet printer models seem to consume a similar amount of energy.
When the power switch is first turned on, this particular printer causes a 30 W power spike during initialization. The sudden drop in voltage this caused would sometimes cause glitches in my other equipment. I fixed this by adding extra filter capacitors to the pedal generator’s power supply system.
This printer is the only device in my office that does not have an external AC adapter, and therefore requires using a DC-to-AC inverter to power it. This adds 2.5 W to its power consumption.
If you want to use a laser printer with a pedal-powered generator, forget it. The heater used in laser printers to fuse the toner to the paper consume more power than you can reasonably supply yourself.
We use a Trendnet DSL modem router to provide internet service to our home office. Like the monitor, it’s powered by a 12 V DC power cable plugged into one of the desk’s power sockets.
While it only draws 3 W of power, it is the largest energy consumer of all the equipment in our office, because it operates 24 hours a day.
Our internet service is slow (12 Mbs). Higher-speed internet service may require a router with a faster processor, which may consume much more energy than ours.
Pedaling for long periods can make you very warm. To keep cool, I use a Cooler Guys 120 mm computer case fan. The fan is powered via a standard 3-pin computer case power cable off a header on my desk’s circuit board. It consumes about 6 W of power when on.
My desk has an Orange Pi PC+ which serves the dashboard controlling my pedal generator’s power system. Since I have it set up as a web server already, I decided to use it to serve this website over the internet. The web page you’re viewing now came off this computer.
Phones and Tablets
My wife and I recharge our phones using the desk’s built-in USB power sockets. The power consumed by a phone varies by phone model. My phone draws a maximum of 10 W when it is low, while my wife’s phone draws about 6 W.
If you have a quick-charging phone or tablet, you may not be able to charge it at its maximum charging rate. That’s because the USB power sockets are limited to a power output of 11 W.
AA/AAA Battery Charger
We use a lot of Ni-MH batteries and a few Li-ion around our home. I charge them while I work using one of two chargers, a basic Tenergy 12-bay charger and a more sophisticated Miboxer C8 8-bay charger.
The Tenergy charger is used most often because it can hold more batteries; the Miboxer is used to charge batteries that the Tenergy can’t. Both chargers are powered from one of the 12 V power sockets built into the desk.
Each charger consumes about 1 W per battery being charged. A depleted battery in good condition can be recharged in about 3 hours. Batteries in poor condition will draw less power when charging but take much more time to charge, due to their higher internal resistance.
We use most of the AA batteries mentioned above to power LED lights around our house. We often use these lights in lieu of standard desk lamps and ceiling lights. Many of them have motion-sensing abilities so they don’t have to be physically turned on or off when entering or leaving a room. They are an easy way to provide reliable, off-grid illumination.
Batteries in the most heavily-used lights are charged daily. Batteries in lights used less often are charged on a three day schedule.
The AAA batteries are used in smaller lights, like headlamps and bicycle taillights, that consume less power than the household lights. But, since the batteries have half the capacity of AA batteries, they have to be charged at approximately the same frequency as AA batteries.
I use a Remington R3000 electric shaver to shave each day.
According to the specs on the power adapter, it should only draw 0.4 W when charging, making it well-suited for charging off a USB port. Unfortunately, it has a non-standard charging voltage (4 V) and proprietary charging socket, so to charge it I’m forced to use it’s AC power adapter and a DC-to-AC inverter. This increases it’s power consumption 5x (2.5 W).
I generally work on my computer 2-2.5 hours before breakfast, responding to email, writing code, and working on CAD drawings. This is typically my most productive part of the day in terms of the total work (both office and physical) accomplished.
It is also the time of the day when I’m strongest. I can generally maintain an electrical power output of 50-55 W.
After breakfast, I generally work on my computer another 1-1.5 hours. The PedalPC stores any excess electricity produced in a storage battery, and by this time that battery is completely full. So, I usually stop at this point and start work in our shop.
By evening, the desk’s storage battery is partially depleted, having powered our internet gateway and the web server all afternoon. I usually spend another hour or so pedaling to recharge it.
I am also depleted by this time, too. My power output in the evening is usually about 10 W less than in the morning.
In total, I currently spend 4-5 hours a day pedaling at my desk and usually generate 200-250 Watt-hours a day. Most of the electricity generated goes to maintain our internet connection and keep this web site running around the clock.