How it started
Maybe a year or two ago, I jotted an idea down for a portable workstation down in my digital notebook (Obsidian with Syncthing for the curious).
Isn’t that just a laptop you may wonder?
Pretty much except with all of the parts more modular, and I am not talking like Framework laptops.
I mean, take a mini PC, a portable monitor (with VESA compatibilty), a lightweight VESA mount, a keyboard, a mouse, and optionally although not really, a battery.
Why though?
- Laptop monitors being tethered to keyboards and touchpads is not great for your shoulders and neck
- Each part is swappable. There are many options for each component that goes into it
- Mini PCs are cheaper than many laptops for equal specs
- Fun project
I had all the parts sorted, from the Beelink SER5 mini PC to the HHKB Pro classic mech keyboard to the Kensington Trackball mouse along with some shitty cheap LCD monitor.
I picked out one cheap 1 monitor VESA mount to try which worked great.
I got a second one that could hold two monitors that needed some effort to mod to fit in my backpack.
Unfortunately I stripped a few of the bolts so that part is on hold, but the one monitor stand works fine.
I then neeed to pick out a battery.
I saw some interesting multi-device battery pack that advertized 250 W, 230 Wh with an AC outlet and a few USB-C ports.
Seemed a little overkill but would do the job.
Failure
I put all the pieces together, testing the battery powering all the devices.
After preparing my USB with a Linux distro (Arch btw), I started going through the installation procedure.
A few minutes in, the mini PC powered down randomly.
I noticed the USB-C powering the monitor was significantly chewed up by one of the cats so I replaced it and tried again.
I got a lot further this time but about 20 minutes in, the PC crashed again.
I was out of time for some plans with friends but I could not help wondering what was going wrong.
When I got back home I checked the specs of the battery pack on the device.
For the AC outlet, which the mini PC power adapter was plugged into, the specs read “120V ~0.83 A” meaning 110 Volts and 0.83 Amps.
I compared that to the specs on the power adapter which read “AC input, 100-240V 1.5A”.
So I was pretty sure something was off there.
I have not dealt with electriconics physics in a while so I had to some web searching.
Turns out, as I relearned, power (Watts) is volts * amps.
Watts is the unit measurement of power for electrical devices.
Then Watt hours, or Wh, is the power used (or provided by a battery) in an hour.
Back to the battery, with our equation power = volts * amps, 110 V * .83 A is 100 Watts.
That is a lot less than the advertized 250 W I saw before.
I went back to the web page and noticed that lower down there was a bullet that read charges a laptop 3 times, 100 W max fast charging.
100 W max fast charging?
I realized they must have meant each port was only capable of 100 W max and that 250 Watts was the total power capacity of the battery.
The vendor definetly could make the description more clear.
I setup a return for that battery pack and started looking for a new one.
Quest for the battery
I did some math this time around.
On the specs of the mini PC, I saw that it takes 19V DC at 3.7A.
That is 65 Watts max.
The monitor takes 5V 2A or 10 Watts which can be lowered further by dropping the frame rate, resolution, and brightness.
The other peripherals like mouse and keyboard would add maybe another 5 watts max.
At highest power consumption, 65 + 10 + 5 = 80 watts for the workstation.
Realistically if I was only programming with limited web browsing on a lightweight distro like Arch with XFCE, this would probably be closer to 50W.
I estimated that at a coffee shop I would want at least 2 hours of battery power before needing to find an outlet to be reasonable.
Therefore, I needed 50W * 2h = 100 Wh battery with 19V and >3.7A DC output and >80 Watts max.
Found a couple that met those specs and included barrel connector adapters to plug into the mini PC DC in.
The one I chose ended up specifying mAh (miliAmp hours) rather than Watts so I had to convert.
Lithium Ion batteries have an internal voltage of 3.7V.
Wh = 3.7 * I mAh / 1000.
The battery advertized 50000 mAh so 3.7 * 50000 / 1000 = 185 wH.
Worst case that gives me 2 hours of charge, average case more like 3.5 hours.
Not too shaby.
Bonus was that it only 2 lbs compared to the other one which was 5+ lbs and much larger.
Unforseen con of all of this is that none of these batteries are allowed on planes.
Thing I (re)learned
Power (Watts) = Volts (V) * Current (Amps)
- Wh = Watt hours = Watts * hours
- You need to make sure that batteries are capable of delivering enough watts for all the devices they are powering (sounds obvious but not relevant in most daily life as a programmer)
- Laptop batteries are crazy efficient for their size and safety compatibility
- Lithium Ion batteries operate at 3.7V
- Batteries need to be low Wh and watts to get on planes
- Buying a mini PC with a USB-C cable or 12V DC in would have been smarter for battery options
- When things go wrong, do some research
This ended up taking me 3 hours today so no update on gamedev or Vim.
Thanks for reading!
