Make it anywhere, part 4: Mobile lab systems
By Steven K. Roberts
This is the conclusion of our mobile lab series (please see the Introduction for background). At the end of our third installment, we found ourselves with a trailer filled with work surfaces and inventory stowage fixtures. We now have one final step to complete before calling the rig “done” and using it to work on real projects, whatever those may be.
In my case, this is a way to park my workspace at the marina where I’m geeking-out a 44-foot steel sailboat with a network of Arduino nodes and an embedded Linux server, a built-in lab with wrap-around consoles, and significant upgrades to ship systems. It’s hard to even imagine such a project without nearby workspace, and a mobile lab was my only option. But portable facilities like this have lots of interesting applications: working effectively at client sites using familiar tools, surviving a move with minimal creative disruption, installing a stealthy shop away from domestic distractions but without running afoul of building-codes, showing up at Maker Faires and other events in full hack-mode, or setting yourself up to be a geek hero in the aftermath of a disaster.
Regardless of the application, any mobile lab has some fundamental requirements for power, lighting, communications, security, and Internet access. This final article addresses such “systems” issues, so let’s start with the basics…
My installation was shaped by equipment I had on hand (and a general preference for marine hardware), and is by no means cast in stone. In fact, a minimum configuration may be all that’s needed if you’re creating an alternative to a traditional outbuilding: just run a cable to a dedicated outlet on your house and distribute power internally with a generic breaker box. At this level, “big box store” resources are all you need, and there’s no reason to get fancy unless you need to survive power failures. If I were installing a lab in a shipping container, then having it dropped on a pad wherever I happen to live, this is probably what I would do.
Otherwise, a mobile workspace calls for batteries, an inverter/charger, and at least one primary energy source. Here’s a photo of my “power wall”:
The control panels are mounted on a door that I cut into the nose of the trailer, which was easy since it has an aerodynamic “nose cone” that renders that area conveniently hollow for wiring. In most installations, a power panel like this would require either an additional enclosure or repurposing existing cabinetry (as in an RV). From upper-left to lower-right in the photo, the access door carries:
- DC circuit breaker panel (lights, embedded systems, and auxiliary jack)
- Control panel for ProSine 2.0 inverter/charger
- Analog AC voltmeter directly connected to main bus
- Link 10 battery monitor (fuel gauge)
- AC circuit breaker panel (main switch, lighting, desk, forward benches, machine tools)
- Control panel for Trace C40 solar charge manager
- Indicating fuse socket for loads connected directly to shore power
To the left is a water bottle in a cage, which is actually a pack of Lithium-Ion batteries. The charger for this is local, providing a quick handful of portable, isolated DC when needed (complete with a kit of adapters for all coaxial power connector sizes).
Below the door is a GFCI outlet and light switch, both protected by a stand-alone fuse. This may seem redundant, given that gorgeous marine-grade AC breaker panel with two unused positions, but I felt it worthwhile to provide a power source that is connected directly to shore power upstream of the whole inverter/charger environment (in case of system failure).
To the right of that is a 12-volt DC “cigarette lighter” outlet. That is an ugly and anachronistic connector standard, but it’s handy for appliances like hand-held spotlights and other automotive-grade stuff.
Continuing down, we see the two big boxes: a 2-kilowatt inverter/charger and the solar charge controller. Neither of these would be my first choice in a new installation, but they were lying around the lab; the ProSine is inefficient and noisy, and the Trace is nice but has long since been superseded by more efficient MPPT (maximum power point tracking) solar charge controllers from a number of vendors. If you venture into this territory, I recommend Home Power Magazine as an excellent information resource.
The heavy red and black battery wiring is next: a main disconnect switch, 300-amp fuse block, a shunt for current measurement… then the cables (2/0 size) disappear into a steel cabinet where they are connected to a bank of AGM deep-cycle marine batteries. The small gray wire heading the same direction goes to a temperature sensor that is used by the ProSine to fine-tune its charge parameters.
Behind the access door, it’s the usual rat’s nest of power wiring (I’ll spare you the graphic details <grin>). The key bits of advice here are to provide a generous hinge loop to minimize focused wire flexion, use stranded wire only, and make sure cables are well clamped before they are terminated (to prevent breakage at the stress-riser of a crimp).
This may look like a crazy amount of power-related hardware, but consider the capabilities, starting with the 30-amp marine shore power connector:
This is the outside of the nose cone mentioned above, so it’s a very short cable run to the main breaker. Normally, I have this standard marine cordset running to a nearby building (house, lab, or marina), with a pigtail adapter on the other end that converts it to the 3-blade RV standard. This keeps the hardware interoperable with my boat stuff.
If the rig is not at one of its standard parking spots, I have a couple of AC options. First, if needs are modest (lighting and office equipment, not machine tools), I use another adapter that converts to a 15-amp household-style plug and go sniffing for an outlet with a regular orange outdoor extension cord in hand. Failing that, the pigtail adapter is long enough to plug into a quiet little Honda eu2000i generator (2 kilowatts) that rests neatly on a shelf mounted just below the nose cone.
Regardless of the AC source, the internal path is the same: a 30-amp main circuit breaker directly feeds the inverter/charger, and its output returns to the panel and feeds all the branch breakers. When AC is present, this keeps the battery bank charged, but if shore/generator power disappears, then it immediately switches over to inverter mode and continues to provide AC. In other words, the whole thing is just a big UPS (uninterruptible power supply), and the change-over is so quick that I barely detect a flicker.
Meanwhile, DC loads are derived directly from the battery bank. For maximum efficiency, when off-grid I try to avoid AC loads entirely… but of course that’s not always possible. Depending on activity (computers, lighting, soldering, test equipment, ham radio, power tools, compressor, etc) I can get anywhere from a day to over a week of routine operation from four AGM 110 amp-hour batteries. I’m based in the Pacific Northwest, so sun can be a little iffy at times… but the system is also set up to handle a large solar array on the roof (on hand, but not yet installed).
All current in and out of the battery bank passes through a shunt on the ground side, which generates a proportional voltage drop (50 millivolts per 500 amps). This, along with terminal voltage, is monitored by the Link 10 (harvested from my boat when I pulled out the legacy stuff and installed new Outback power management gear). Displaying real-time volts and amps, along with an amp-hour tally, fuel gauge, and extrapolated time-to-empty, it goes nicely with my retro AC voltmeter:
As you’ve probably noted from some of my comments, there are many ways to put together a system like this. If I were starting fresh with a healthy budget, I would use all Outback equipment. From what I’ve observed on the boat, their gear is remarkably quiet (in both RF and acoustic domains, unlike the ProSine) and able to withstand random insults like shore-power glitches without pathological side effects. All their hardware talks Ethernet, so a suitable system for a mobile lab of this scale would consist of an inverter/charger, solar charge controller, battery monitor, and network hub… plus a “MATE” display to serve as the single user interface to all of it. Conveniently, this device has a serial port, allowing easy data logging and remote access.
OK, we have power, light, and AC/DC distribution to all the benches. What else do we need? Let’s take a brief look at the other infrastructure category…
One of my first discoveries upon actually starting to work in my mobile lab (named Polaris) was that wi-fi was a challenge… even when parked near my house with a couple of parabolic reflectors on the router’s phased-array antenna pair. This was not good; I knew the trailer was mostly sheathed in steel, but the whole back door is plywood and the nose cone is fiberglass. Alas, those RF-transparent surfaces were not enough to establish a reliable Fresnel zone in all parking orientations ‘twixt the already range-challenged MacBook Pro and my hotspot.
I fiddled ineffectually with crude antenna hacks, but after growing tired of standing at the worktable in the stern to check email, decided to do something a bit more proactive. I picked up a Pepwave Surf, which just… works. I’ll need this anyway to allow the boat’s router to fail-over between EVDO and wi-fi on the WAN side, so it was an easy decision… and the antenna is remotable with a standard RP-SMA cable when the environment becomes a little more challenging than my own backyard.
That blue cable is Ethernet to the laptop, but it could of course go to a router or anything else aboard… including the Axis IP network camera for security. (Further details about monitoring systems are redacted for obvious reasons, but I recommend both perimeter and motion sensors as well as 0-lux video with off-site archiving via wi-fi, all well-hidden and powered in a way that can’t be conveniently disconnected.)
Voice communications are easier for most folks these days, though my home base is an RF black hole with almost no cellular coverage. That would explain the clunky cordless phone in the first photo above… a temporary solution.
Ham radio, however, is an important part of this rig; I use the venerable Icom 706mkIIg for VHF and UHF with a permanently mounted Larsen dual-band whip antenna, as well as occasional HF with the external tripod-mounted Buddipole. The latter conveniently supports an Arrow dual-band yagi for weak-signal or DX work with the old “Yaesu twins,” (290 and 790). One of the key applications of this whole lash-up is a back channel for packet-radio telemetry from the boat, so the radio gear is more than just casual fun.
The nutshell summary is that Polaris was created to be a distillation of the huge, sloppy lab that I have used for 12 years, inconveniently located in the middle of a forest on an island with no moorage. That setup did not make for efficient nautical projects (except perhaps for tiny boats, which were the original intent), so now I’m downshifting and hauling the lab to the project instead of the other way around.
Polaris is a compact but robust toolset with over 900 inventory drawers, oscilloscope, stereo microscope, Metcal soldering station, a good array of power and hand tools, drill press, sander/grinder, table saw, air compressor, small wirefeed MIG welder, brazing outfit, dedicated computer, Sirius/iPod marine stereo, security system, and a full suite of office equipment. A blank spot on a machine table is reserved for a small CNC router (Fireball V90) for console front panels and circuit boards; this will have its own computer with touchscreen.
Once I’ve bootstrapped the boat project, disconnected from home base, and made the long-awaited transition to a full-time life aboard, the mobile lab will become a backup facility parked at a friend’s house… in regular contact with the ship, holding a stock of spare parts, and serving as shoreside shop and office whenever needed.
And this is what it’s all about (photo taken over Montague Harbour in the Gulf Islands of British Columbia, 2 years ago):
Cheers and fair winds from Nomadness!