Category Trail

Blue hybrid electric van

Being a mathematician, I love calculating numbers, especially useful ones that matter.

We've already detailed the Vansion modes of use and principal design goals, which has given us a really good mental picture of the layout. Now it's time to make some major decisions on how to actually build the damn thing, detailing specifics of its construction. Let's begin with our known constraints and then optimize over them, outlining some big choices and their inherent tradeoffs. We'll start with our ideal dream configuration, then plan a more realistic version once we have all the facts.

Being a mathematician, I love calculating numbers, especially useful ones that matter.

We've already detailed the Vansion modes of use and principal design goals, which has given us a really good mental picture of the layout. Now it's time to make some major decisions on how to actually build the damn thing, detailing specifics of its construction. Let's begin with our known constraints and then optimize over them, outlining some big choices and their inherent tradeoffs. We'll start with our ideal dream configuration, then plan a more realistic version once we have all the facts.

Minimum Figures of Merit

Here's are the numbers we should keep in mind for the Vansion. I'm showing how to do the calculations so that you can apply them to your own van conversion.

Size is 66"W x 156"L x 70"H

This comes directly from the queen size bed size + 3" walls, and the hallway layout. Optimally, you'd want the interior cargo height to be 5" greater than the tallest expected passenger, but unfortunately vertical height is the hardest attribute to find in a van, and often entails installing a higher custom roof.

Energy Storage is 3.6 kWh

Here's how to calculate your coach electrical system requirements:

1) Energy Storage

First calculate how much energy we need to store in the batteries. I need to run a four hour role-playing game session using 250W of electronics and 50W of fans: 300W x 4h = 1,200Wh = 1.2kWh. We never want to drain the batteries dry, but instead target a percentage depth of discharge (DOD). If you have regular supplemental power, multiply by at least 2 (50% DOD); for optimal battery life x5 (20% DOD) is a generous figure. Assuming solar 33% DOD is reasonable, giving a factor of x3, so we need to store 1,200Wh x3 = 3,600Wh = 3.6kWh total. Storage should also be at least 4 times your fixed daily load; your refrigerator (500Wh) and standby electronics (100Wh) are the big culprits here.

We need a deep cycle battery for the coach system, and lead acid is the de factor standard. I want no muss so I'll be using a sealed AGM VLRA battery.  Flooded batteries last longer but require too much careful maintenance, are more prone to corrosion, and emit noxious fumes. 

2) Battery Capacity

Next convert the kWh into Ah, which just means dividing by the system voltage. Most coach systems are 12V, so this means 3,600Wh / 12V = 300Ah of batteries. This capacity is called C and is often used in heuristics, on battery labels, and in specifications. C is unitless; we tack on the right metric unit as needed. For example, the maximum charge amperage is usually C / 3, which would be 300 / 3 = 100A in our case. Since 100A is around what a typical van alternator puts out, this is a great base figure to work from. It makes our system much simpler, since we can forego regulation circuits and just rely on the alternator itself when charging from the engine.

3) Solar Wattage

{2C in Watts} is good rule of thumb for solar. So we want 300 x2 = 600W of solar panels. Then divide by voltage 600W / 12V = 50A to determine the minimum controller size. This is half the max charge amperage, so it's safe. We might be concerned about running the alternator at the same time (since 150A is too high); fortunately, solar charging controllers are built intelligently to back off when other current is applied. That's one of the things charge controllers do: ensure safety in all circumstances. They also optimize charging for the battery type and extend battery life.

4) Inverter Wattage

Choose the wattage of a pure sine wave inverter based on peak load. Here's some rough figures on big draws:

  • 1.5kW
    Hair Dryer
  • 1.3kW
    Laundry Machine
  • ~1kW
    Microwave
  • 1kW
    Movie Watching
    500W projector + 250W audio + 250W computer
  • 1kW
    Air Conditioning
    {Divide BTU by 5} 5000BTU AC = 1,000W

Choose your peak based on what your worst case scenario would be. For me, I might want to watch a movie on a hot night, so I'd need at least a 2kW inverter. I'll just have to remember to be careful while doing the laundry.

5) Battery Bank

Determine the number of batteries based on peak amps, which is found by dividing by system voltage. Our peak amps is 2,000W / 12V = 167A. Each battery has a rating called its maximum discharge amperage; you can find it online or in its spec sheet. Make sure you use enough batteries to exceed that figure. For example, if each battery had a 75A max discharge, you need three, whereas if each had 50A you'd need four. For most typical setups 2-4 batteries wired in parallel is the sweet spot. If you find you need more than 6, try to reduce your peak load or find better batteries. Banks with many batteries can be done, but call for more sophisticated techniques than we'll cover here.

Designing to peak is simple but incurs extra cost because of excessive over-design. You can often reduce cost by changing your pattern of usage. For example, watching a movie at 2kW for 2 hours is 4kWh and well exceeds our battery storage. Thus, we must have supplementary power or dramatically enlarge our storage (12kWh). If we commit to only watching a movie while the engine is running, then we can use the van AC and get 1kW from the alternator, which means we'd break even power-wise and this is no longer our peak scenario.

6) Amps and Gauge

Match the wiring gauge, breaker, and fuse to max amps using this chart. The "maximum amps for power transmission" of each wire must exceed the "max discharge amps" of each battery. For example, if the battery had a max discharge of 100A we'd need Gauge 1 wire rated at 119 A, whereas an 80A battery could use Gauge 2 wire rated at 94A. Expect these to be big fat honkin' beasties; they are nothing like household power cords. They'll connect directly to the inverter and we want them as short as humanly possible, so plan your layout accordingly.

Put a fuse rated right above your wire gauge amps on each battery wire. The inverter has a built in breaker and can handle typical power faults. We then feed the inverter 120V output into a junction box and split it into separate circuits with breakers rated at 15A (1,260W), 20A (1,680W), 25A (2,100W), or 30A (2,520W), using wires of Gauge 10, 9, 8, and 7, respectively. It's a good idea to give major appliances their own circuit with a breaker around 15% greater than their listed max amp load. My power requirement is so small it makes sense to standardize on Gauge 8 for all wiring, even the 15A and 20A appliance circuits.

Note that the final electrical system will be much more sophisticated than this because we want to extract energy from a variety of sources:

Van Alternator
uses an isolator and a super big fat wire to charge the batteries, effectively turning the engine into a 1kW power generator
Grid Power
requires a combination inverter / charger; a line conditioning surge protector is a good idea if you regularly use RV stations. I'll forego both the latter and a 240V hookup, since I don't need them
Solar Power
will need a charger that plays well with the other chargers, like an MPPT

Payload is 3,300 - 4,550 lbs

Here are the (ahem) heavy hitters, with {useful conversions}:

  • 900lbs
    Water
    90gal {9 lbs / gal}, tanks
  • 500lbs
    Garden
    4 ft3 soil {100lbs / ft3}, potting, irrigation
  • 400lbs
    Passengers
  • 300lbs
    Bed
    mattress, frame, jacks
  • 300lbs
    Plumbing
    sink, shower, water wall, treatment, pipes
  • 300lbs
    Electrical
    battery {lbs / 12 Wh}, inverter, wiring
  • 250lbs
    Electronics
    computer, home theatre
  • 200lbs
    Laundry
  • 200lbs
    Cabin
    walls, insulation, decor, storage, mounts
  • 200lbs
    Appliances
    fridge, microwave, cooking, food
  • 150lbs
    Tools
  • 100lbs
    Projection
    projector, screens, exterior speakers
  • 100lbs
    Solar
    panels, controller, mounts
  • 100lbs
    Clothing
  • 100lbs
    Venting
    ducting, fixtures, fans
  • 100lbs
    Vehicle Related
  • 200lbs
    Outdoor Gear
  • 150lbs
    Assorted Junk

If you are over your vehicle weight capacity, the first thing to consider dropping is the laundry machine. It's the least used function and easy to find publically. Even compensating with 50lbs of extra clothing, you save 150lbs. You can then reduce your water tank by 10G, saving another 100lbs. I'm actually on the fence about whether I'll put one in my own Vansion; given how often I visit friends, it's difficult for me to envision a scenario where I'd be without laundry access for more than two weeks. A laundry machine has the most utility in off-grid living and extended boondocking.

The next good area for weight reduction is electronics. Changing the computer to a laptop gains 100lbs with only a modest reduction of stats. Choosing cheaper audio equipment can gain you another 75lbs. Removing all advanced multimedia (projection, speakers, amplifier) and relying solely on the laptop gains another 150lbs. If you still need to reduce weight while still keeping functionality, start shaving everything. A smaller garden, fewer gallons of water, less outdoor gear, etc. will add up. Probably the least weight you could get the essential Vansion is around 3,300lbs. After that, the only way to get more reduction is redesign, say via dropping a major system like the garden, bed leveling, or plumbing / tanks.

Conversion Materials Cost $21k

All figures here are deliberate over-estimates to account for shipping, accessories, etc. We're only looking for a conservative ballpark number here. Where I've linked to [specific units] those are options I'm considering actually using. Other links are just reasonable equivalents for comparison.

Your cost may be significantly different than mine. I've omitted stuff I already have, which includes tools, some vehicular gear, emergency supplies, etc. This can easily run over a thousand dollars if you are starting from scratch. I'm also supplying my own do-it-yourself labor. Expect many thousands of dollars for professional help; full conversion labor is usually $10k-$20k. And, of course, your configuration could be much different, with more or less expensive components, or including / excluding entire systems. But we're in the right ballpark: converting to a Vansion is around one-year's worth of mortgage or rent.

Vehicle and Chassis

We prefer two choices for a base vehicle: a van or a truck. Those meet our size and payload constraints in the typical 3500 model, which has the longer wheelbase chassis, high roof, and extended length cargo space. The newer wave of cargo vans can get near 20 mpg, while most other choices will be somewhere in the teens. Other vehicles don't meet our constraints well enough: minivans and smaller can't handle the payload and size, while larger vehicles fail too badly on mileage.

Driving with a full payload is a significant concern. Even for rated vehicles, modifications to improve safety make sense: like better tires, a beefier spring and suspension, and improved braking. Any 3500 van on this list can be made into a Vansion, though some must have the aforementioned modifications. Any of these three vans are good choices because of their high payload and attractive geometry. They have almost square box cargo spaces and the hard to find vertical height as a stock option. Each can be found nearly new for $40k-$50k and well used but still in good condition for around half that. However, there is a clear winner as only one van meets all our constraints:

  • 4,648 lb
    Mercedes Sprinter Cargo Van 3500
    20mpg $50k

Other choices bear mention. A 17' U-Haul Box Truck in good condition goes for $11k. While it has an abysmal 10mpg, it also has a whopping 5,930 lb payload and an amazing geometry. In fact, it is so spacious that the Vansion layout could be redone to include a lounge area, meditation garden, and a beautiful front door and mud room. This is an excellent option if you mostly plan on living in your conversion with infrequent travel. In that case, the low mpg doesn't matter as much as the improved room, livability, and beauty. The same argument applies to step vans, bigger trucks, buses, and other large vehicles. With some bargain hunting, you can find big vehicles in good condition for around $5k. I've decided on a cargo van for my Vansion (hence the name) but your selection may differ.

Power Choices

A significant decision is whether to incorporate propane as a base system. The three usual reasons to do so are for cooking, refrigeration, and heating. Propane enables much wider cooking options, including barbecue, broiling, range-top, and grilling. Using propane for the fridge significantly reduces battery drain and is usually quiet. For an RV, propane is hands down the cheapest pure heating solution per BTU, both for space and water. In my own Vansion I've decided to forego propane as a coach system, mainly because I'm a snowbird. The only reason why I'd consider including it is water heating, but I expect the solar roof loop combined with an electric faucet will more than meet my needs. Note that in cold climates propane is a must; your first hot shower in a snowstorm will convince you installing all that gas piping was definitely worth it!

If you have money to burn, there is an expensive but incredible new option available for a Vansion: to build it atop a hybrid electric plugin van. The Via ERev Hybrid Van costs $70k but gets an astounding 35+ mpg! Let's glance at some other impressive figures:

  • 23kWh
    Battery Storage
    6 times the 3.6 kWh I need!
  • 100kW
    Generator
    dwarfing the standard 1-2kW alternator
  • 14.4kW
    Exportable Power
    enough for 3 average family homes

The payload is only 2,800lb and a Vansion wouldn't seem feasible even shaved down to 3,300lb. But the abundant available power means the Vansion could be radically redesigned. First, the entire electrical system can be dropped for 300lb. Second, HVAC can be done thermoelectrically, which not only materializes another 100lb, it means whisper quiet operation. Third, exterior jacks leveling the whole van could be used (another $5k, btw), for a net 50lb gain. Fourth, several minor exchanges can eke out the remaining 50lb, like using UV irradiation for water treatment, etc.

Relying on the hybrid batteries for coach electricity works phenomenally for several reasons. Lead acid batteries are most effective at long slow discharge and recharge, making them good partners with solar panels. So even though an alternator provides enough power to quickly recharge a battery bank, it still takes hours because lead acid is slow, especially when capacity and usage are comparable.

Lithium ion is around 5-6 times faster than lead acid, making it well suited to burst applications. Combine that with the huge disparity between usage and capacity, and a daily charge effectively only takes minutes. Moreover, the auto manufacturer has optimized the battery charging cycle automatically far more efficiently than we could ever do. You could still put on a solar array for environmental reasons. From an engineering and cost perspective, it makes more sense to enlarge the gas tank, which has the added benefit of extending your driving range.

Building from a hybrid electric motor would create a true Van Mansion: a luxurious home on wheels with better gas mileage than most cars! Since we have 100% up-time power, we could use more power hungry units to improve quality across the board. I desperately want to make one of these, but alas, it's currently a fool's errand. Via Motors sells to fleets and not individuals; even if they did, they are already backlogged almost a year. But once hybrid electric vans do come on the consumer market, converting one becomes a moral imperative. :-)

Aesthetic Vision

Last but certainly not least, the overall cohesive feel of the interior is important and usually very personal. Everyone has their own opinions about what ambiance they want to evoke, and how to go about doing that. In my Vansion, the centerpiece I want to play up is the I2I. So I'm going for a modern mirror clear and white vibe. Once people open the door they should feel like they are stepping onto the sky. Mirrors help open the space visually and create nifty optical illusions like infinity and shadowing effects. I'll probably further exploit the mirroring with color pulsing LED strips and other funky lighting like prisms. Because, c'mon, rainbows. :-)

There are many fashion aspects that are determined by function. In addition to those already mentioned:

Large Sealed Molding
This serves double duty as a raceway for wiring and duct-work for the exterior vents, which does both sound baffling and thermal exchange

As a closing note, I feel like we are about to enter a new era of alternate living spaces. The rising expense of traditional property is making people seek other solutions. We are at a convergence of tiny homes, freedom from materialism, mobile living, couch-surfing etc. reaching mainstream awareness and significant adoption. That, combined with the increase in technologies and solutions available has created something of a perfect storm. I believe living in the Vansion is superior to being confined in a building. It encourages us to be healthier, more active and social, and to consume less resources, which ultimately results in a happier and more prosperous lifestyle. And, of course, it can be tons of fun!

We now have everything we need to actually engineer the Vansion. Onward!

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