144 HR 2fer: two people, two bikes, two kayaks


I have learned a lot from so many of build threads on this site, which means it is time to start giving back. If you are expecting another amazing build (or build thread), well this isn’t likely to be it.

Our 2019 RWD 144” HR sprinter arrived in May, and the build has started as it will go on: slowly.

Most things in our dream come in twos: two people, two mountain bikes, two folding kayaks, two burner stove. The most notable exception is that we can’t really do trips with just two pairs of skis.

If our design doesn’t suit your needs, don’t worry, it suits us.

I stole more from traipsingabout.com than anywhere else, but a lot of you on this forum will see your ideas borrowed, re-purposed, twisted, or otherwise used without adequate thanks. I owe you for sharing what went right and, often more usefully, what went wrong.

Our core layout is the now-common garage style with two sliders. Fresh and hot water tanks will be near the centreline in the garage so they don’t freeze in winter mode. The tanks will be framed-in, partly to support the bed, but also to protect bikes from loose payload. The original idea was to have a big open garage, but we slowly realized that dividing the space would let us carry more gear. Imagine traipsing about with tanks under the central storage unit.

A small fridge, storage, and a bench/head will go on the windowless port side, and a storage cabinet/sink/workspace will block the aft half of the door. More port-side storage on the bed platform will make the bed narrower and eliminate the need for upper cabinets.

Because I studied engineering way back when, the build will be complex. After 15 years with a small sailboat, I have experience in cramming life into small spaces and a lot of nautical terminology to add confusion to conversations.

You have been warned.


Step one of the build was taping out the plan and checking the design inside the actual van.

Step two is insulating the garage area, so we can start building the two most essential elements: a bed and a bike rack.

This US built van came with anti-vibration material (like rattletrap, fatmax, etc) in the critical places. Of the four 2019 cargo vans I have been inside, this one has much more of this material than the others combined. First noise reduction task complete, with no labour from me.

We chose thinsulate SM600-L (thanks Hein) because it does a good job with sound deadening and it should be adequate for winter glamping.

After sitting in an empty van in full sunlight on a 32C day, it became clear that the metal ribs transfer heat past the insulation, which makes me believe I don’t need to go crazy here.

The steel shell is fairly conductive, but nothing compared to the aluminum L track. Before insulating, the steel and aluminum got too hot to touch. After insulating half the van walls, both steel and aluminum were slightly better.

As many people have said, a thermal break between the van and the 8020 aluminum structure is essential. My first idea of using PVC (aka vinyl flooring) as a thermal break may not work as as PVC flows at about 70C. Don’t tell the beautiful one, but I will be sneaking the spare cooking thermometer down to the van to measure just how hot the metal gets.

It will take an age to insulate the whole van, as the sections that need glue have to be done early in the morning while the sheet metal is cool enough for 3M 90. We got the walls of the back half of the van done in four hours working time. The second side took only an hour as we had learned some tricks by then. We should be good at this by the time we never need to do this again.

We are not insulating the floor, as the van is reasonably quiet already. We will eventually add decorative (and mildly insulating) flooring to the parts of the floor that are exposed, but that is far in the future.

We are using reflectix and magnets for temporary window and skylight covers, but don’t see a need to use it as a vapour barrier in the walls and ceiling.

I took more photos of the thinsulate in place and they look just everyone else’s photos. Here is the loadable wheel arch, which is new.


The bed platform is in!

Well, temporarily, as this was my first experience with 8020 and I learned some things. We will get the bike mounts in (without the slider for now) and do some practice glamping to see how well the bed layout suits us. I have only 2.5” head clearance sitting fully upright in bed: once the ceiling and mattress are in, that may not be ideal. The top of the plywood is currently 39” above the factory wooden floor.

The 1010 (1”) aluminum is definitely strong enough for a van conversion. There are 1030 pieces to provide stiffness around heavy items (fridge, water tanks, batteries. The big downside of 1010 is the limited connector selection. I didn’t think the inability to slide in carriage bolts would become inconvenient this early in the build. And I definitely should have ordered some roll in t nuts, as I had to disassemble sections and remake them more often than I expected.

Most commercial RV’s have been built to current government safety standards (none!), but as a person who has used up eight lives already, I am hoping to get close to passenger car safety standards. My van, my choice.

You can see red nylon climbing slings around the bed posts. The bed frame is only lightly attached to the walls to allow the van to flex. Basically about 2000lbf forward will break the bed free along with the forward floor cabinets that are ‘suspended’ from the 1030 cross bar. At this force level, the van is no longer drivable, possibly totalled, so the focus changes to protecting passengers.

The slings will gently bring all the payload to rest, by stretching about 6” in a head-on collision. That extra stopping distance will reduce the peak load in the van walls, which should allow them to absorb enough energy to keep heavy items away from humans. Think of it as a crumple zone for payload, except inside out.

The central bed supports are going to be the frame for floor level water tanks (with storage above), and there is more 1030 on the floor to ensure the plastic tanks will travel directly forward and not upwards into the bed platform. By having a central support, I was able to make the bed platform out of 1/2” plywood. The tank frames will also protect the bikes (eventually on a sliding tray on the port side) from stray cargo. The folding kayaks will be on a starboard side slider. The installation of the sliders will be tricky, so that has to wait until we confirm that the bed height and shape will work. I only want to do that install twice!

I will definitively reshape the corners of the bed platform during the next reassembly. The corners are a bruise hazard and it is difficult for my partner to open the back door from the bed (I can reach around the plywood, her arms are shorter).


I have road tested the bed platform and partial insulation.

Adding thinsulate to the aft walls and the wheel covers has definitely made the van quieter. Road testing on clay, gravel, and coarse pavement shows a big gain in aural comfort.

There is still an annoying loud spray noise from the starboard side on wet roads and puddles. My guess is that it is coming from the aft edge of the side door step, which is bare metal on both sides.

I also hear occasional loud pings from gravel, but these aren’t from the wheel wells, which now make a muffled thud noise. Not sure where the pings are coming from, but with luck I will eventually insulate the right spot.

Loosely covering the skylights with reflectix makes the van much cooler inside. I will attach the magnets properly as the painters tape experiment won’t last long; the magnets are on the back side of the reflectix so they don’t scratch the van or grip too hard.

It seems like the bed platform is not interfering with the flexing of the van on bumps. Fingers crossed that I got this right.


We did a mini-roadtrip to test the half-insulated van.

Driving is vastly quieter with the bed mattress installed. Previously, sound was bouncing between the bare metal ceiling and the plywood bed platform, enhancing every noise.

Insulating the lower walls made a dramatic sound difference, but adding the bed mattress is probably equally effective.

In terms of heat on a sunny day, the roof is going to be the big influence. Even with the skylights covered, I can feel the heat radiating down from the bare metal ceiling, which is too hot to touch. It is very obvious which wall sections are insulated and which aren’t, but this is a minor effect on a sunny day.

Covering the glass is the biggest heat effect so far, maybe five times more effective than the wall insulation. Doing anything at all to the ceiling will probably be as dramatic as covering the windows.

We are really looking forward to getting the vent holes done, as this will let us cool our rolling greenhouse down.


The bike slider is done!

Well, version 0.9 is in and it works. It came out slightly narrower than designed after I learned a new way to make mistakes with a jigsaw, but the bikes still fit nicely.

We stole the core idea from Traipsing About, and then stole some tweaks from at least ten other people who built on their ideas.

The tray is 0.5” malaysian birch plywood, with steel corner braces and glue used to attach the sides to the base. It feels a bit flexible on its own, but is suitably rigid once bolted to the sliders. The corner braces work well enough that I was able to leave the front and back walls off the box.

The sliders are the extra-heavy duty Knape and Vogt 9208 locking version and are rattle free (so far) when locked closed. Expensive, but worth it. The lock on one side is a bit finicky to release, but with luck will wear into happiness.

The sliders are mounted to two 1030 aluminum rails (1”x3” 8020). These are ridiculously over-strength for the purpose, but the adjustability makes it worth the cost. Installing was painless: preload five bolts on a slider, push it into the 8020 t slot from the end, and tighten where it needs to be.

When the wood tray came out too narrow, I loosened two bolts, slid one rail outboard to perfectly fit a very imperfect tray, and tightened in place. The photo shows a sheet of 1/4” plywood stuck in the gap, which is temporary to test fit.

The first (outboard) bike faces forward, with the forks turned to make the bars fit. The block angles the fork mount to lean that bike inboard, which keeps the pedal from overhanging the wheel arch too much, and also makes a bigger space to store the loose front wheel.

The fork mounts are RockyMounts DriveShaft HM. They are not cheap, but eliminate the challenge of holding the bike still while sliding a thru-axle into position. Open the mount, drop the fork with pre-installed axle in the slot, and flip the lever shut: magic. As a bonus, I no longer need clearance space to slide the axle in.

The forward facing bike has a visible lean, which keeps the pedal from stealing too much of the storage space in the wheel arch.

The door clearance can be adjusted by sliding the 1030 rails forward or backwards. Bikes are getting longer every year, and we don’t want a major van rebuild when we get our next bikes.

The second bike has the fork mount raised to get the bars as high as possible, which means the overhanging bar blocks less of the central storage area.

We could have used 1020 rails and got all of the adjustability at lower cost, but the extra inch of height makes a relatively flat surface beside the tray. When we are using it for transporting anything other than bikes, that flat area will be convenient. The rails take up a lot of horizontal space (2” total), but we needed width for pedal clearance anyway. The loose wood block in the photo will be used to raise the rear tire of the first bike, improving the clearance from the second bike’s fork crown.

We used the bke tray as a test for the polyurethane we selected for our (future) birch plywood cabinet faces. I can definitely say the cabinets will be finished differently, but I am not sure if we picked the wrong polyurethane or just applied it wrong.

We are using chunks of a pool noodle (cheap, stiff, closed cell foam) to keep the rear wheels and loose front wheels from moving around. These will be replaced by a more permanent solution after a testing period.

It’s a long weekend, so time to start testing!


We got a chance to drive up the hill and camp in a friend’s driveway for a test of the build so far. We had a high of 28C in the valley where we live and a low of 8C overnight. Summer went for a holiday without us, apparently, but it was good to get April conditions to test in.

The milliard folding mattress was very comfortable, by our standards. It folds in three, which has been very convenient while working on the van. It is only 4” thick, which lets me sit up in bed with reasonable clearance. The platform is 39” above the stock floor, and I am 5’8”. More mattress detail here: https://www.milliardbedding.com/pro...ft-removable-cover-with-non-slip-bottom-full/
This mattress was cheaper than buying foam to make a custom solution. The cover unzips so we can cut away some foam to improve the fit.

Our choice of a summer weight duvet did not go well at 8C, so we added a sleeping bag on top. The beautiful one was curious why I chose a duvet that is less warm than what we use in the house, and I didn’t have a good answer.

We need to come up with some bedside storage as well. Headlamps, phones, and clothes need to be accessible while we sleep. There is lots of space beside the full (74”x52”) mattress, but we need to do something with it. There are about 20 major projects higher on the priority list, including a step to get up into the bed.

The factory floor was uncomfortably cold, even with socks on. The original plan was to add a foam, rubber, or pvc layer to the 10 square feet of floor that will be exposed. We are now thinking of upping the insulation a bit.

The bike tray worked very well. No rattles, the bikes stay still on bumpy roads, and it is quick to load/unload. The brilliant idea of leaving off the end walls of the tray makes it very easy to clean the mud off the tray at the end of the weekend. It also allows mud to drip out of the tray onto the van floor, where it is much harder to clean up. Oops.

It is amazingly convenient to have a private changing area at the end of the ride. It is also nice to have the bikes securely out of sight in a locked and alarmed van while we made a stop for some post-ride pain au chocolat.

The basic bed layout is now final. Next up, building cabinets.


After ten hours assembling 8020 cabinet frames (it would be a lot faster if I didn’t make mistakes and have to redo so much), my new car stereo was waiting in the mailbox.

This is a beoplay A1, and looks remarkably like an overgrown hockey puck.

The sound is better than any car stereo I have owned, but I have never had a car that sounded remotely like the home stereo. In the car, I usually choose music that sounds okay distorted and leave the jazz/classical/opera for home use.

Testing at home, the A1 is able to get louder than I want in a large room. I can’t say if it distorts at max volume because 70% was as loud as I was prepared to test.

The A1 speaker is fairly musical. My favourite test song is ‘The Last Time’, recorded by Marsalis and Clapton at the Lincoln Center jazz night. This is 1920s style jazz, with a lot of polyphonic melodies. (Not a music geek? The first 30 seconds of ‘Layla’ from the same album is a pretty good example of ‘polyphonic’.)

I was surprised to find the sound was fairly good. It was easy to follow the clarinet playing against the trumpet or trombone, but the two trumpets just get lost in each other. This is a song that is incoherent in my subaru, becoming monophonic, but it is still possible to identify solo instruments. Using MBUX, even solo instruments are not recognizable. The A1 isn’t perfect, but I wasn’t scrambling for the next song button like I do in the car.

While the A1 is not going to compete with the home system, I am pretty happy with what I got for $220 Canadian.

The big downside so far is that you seem to have to wake the speaker up with a button press. It saves battery power by sleeping if you don’t use it for a bit.


I finally cut a hole in my brand new sprinter!

Six weeks of mental preparation, and it was so easy that it was a bit of a let down.

I decided to do the floor vents in the face of the sliding door step. It is accessible, and well separated from the future heater exhaust and toilet vent.

Because it is easy to grow holes, but difficult to shrink them, I decided on 2.25” holes, with three expected to give me the target flow rate. If I come up short on flow rate, I can join two into a large oval.

I did one hole, and then paused for some testing.

I drilled a very small hole to confirm the location, then used that as a pilot hole for the hole saw. It took about two minutes to drill both holes. You can see the rustoleum paint (sprayed into a container and painted on with a q tip) isn’t a perfect colour match. It took much, much longer to collect all the steel shavings with a magnet.

The hole(s) will be covered by a mouse screen and a mosquito screen. Soon.

On the test drive, it was like I had undone all the sound insulation work. The transmission whine was now audible all the time at lower speeds, but a higher speeds the whine was almost drowned out by wind noises and tire noise.

The hole faces bare metal with a third metal end wall, which is great for echo effects and enhancing noise.

For test two, I put a heavy beach towel in the step well.

This knocked down the noise dramatically, pretty much equal with the ‘before’ sound level. The transmission whine and tire noise just vanished, but some wind noise was still heard.

For test three, I taped a piece of flexible PVC over the hole and left the towel in place. This was the quietest drive yet in the van.

Removing the towel and leaving the PVC cover on for test four was indistinguishable from the ‘before’ level, as expected. The transmission whine returned and tire noise was audible, with no wind noise.

Overall, test two and four were similar noise level, but different noises.

Dust came in on gravel roads, so I will need a way to close this vent.

The next step is to build a box around the holes and install a computer fan (0.1A at full speed) to encourage airflow.

The scary final step remains: cut a 3” diameter hole in the roof and install my marine grade exhaust vent. I just need a day with no rain, cool weather suitable for painting the bare metal and continued cool weather to give the silicone sealant a long enough working time. That weather will probably happen a few times before I am emotionally ready [emoji6]



Roof vent, marine style.

I decided that I wanted skylights more than I wanted an combined emergency exit and roof vent. Based on sailing experience, this tiny 3” diameter vent should be enough for the van. The Vetus Scirocco is intended for high flow, but we will be installing a small 37cu ft/min intake fan on the floor vents.

A quick fan test showed decent airflow, with cool air flowing into the van. Too bad I don’t have the house battery installed yet.

These vents are designed for marine use, so they are pretty effective at keeping water out. There is a raised ring inside the vent, which is very effective in rainstorms and moderate wave impacts.

The installation went fairly well until the moment of putting the vent on the roof. The sun came out just as I started the silicone bead, which reduced the working time to five minutes. It didn’t help that it was already 29C (a cool and mostly cloudy day!). The final result looks nasty from the bottom, and I didn’t get time to wiggle the alignment for the slightly misplaced 6th bolt. I drilled a tiny pilot hole (slightly scary moment), and then spent what is hopefully the most frightening two minutes of this entire build cutting a 3” hole with the hole saw. As before, rustoleum in an almost matching colour should slow the growth of rust.

I have decided that the mismatched rustoleum colour is actually a good thing, as it is easier to see what was been coated.

This install won’t pass ABYC, but as it will never experience a wave impact, five bolts should be enough.

The approach is wildly different than a normal RV set up, but my experience in sailing suggests that the HVAC calculations are correct and this will be effective.

Theory is great, but real life testing is coming soon. Watch this space.


We went for a week long glamping trip to test the first build steps. We stayed at serviced campsites (showers, toilets, drinking water, picnic table) as our van is a long way short of finished.

On the first day we installed our temporary mozzie screens (https://www.amazon.ca/gp/product/B0756K7CMM/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1). If you order from these (very helpful) people, they email you a discount coupon for your next order. Construction and stitching is surprisingly good for the price, and much better than the similar products we found at home depot and Rona.

We chose the 60”Lx86” size for the sliding door, which hangs about four inches too tall, but worked very well at keeping flying insects out. The back door is 64”Lx86”, and it is about 8” too tall.

The magnetic closure works surprisingly well, despite the weights at the bottom dragging and the lowest magnets snapping to the van exterior.

We got these as a temporary solution, but we are now planning to resew the bottom hem to fix the height issue and keep them permanently.

I have to say that loading the bikes requires pulling the curtain off the velcro, which can be a pain in buggy Alberta. We also discovered that the mozzie screen lets a lot of water through if a hail storm hits halfway through loading the bikes. Oops.

Other lessons from a week on the road:
1) The tiny vents are, as expected, insufficient without a fan. The interior was 7C warmer than the sunbaked parking lot in Drumheller after two hours with the doors closed. No shade, no wind, and two hours to preheat. It won’t hurt when we finish the insulation (which, like the fans, is waiting on an electrical system).
2) Hand sanitizer is NOT a substitute for being able to wash your hands.
3) The option to pee in the van is even more attractive after a midnight stroll through a mosquito festival.
4) Nothing beats the joy of sleeping dry during heavy rain! Watching the stars from bed after the storm ends is pretty close though.
5) Fuel economy was decent, by RV standards anyway. We got 10.0l/100km actual, with 10.1l/100km reported by MBUX. This will probably be typical for us, with two major passes each way and two headwind days on the prairies. This is about 23mpg for any Americans out there. In comparison, our Subaru gets 7.0l/100km with the hitch-mounted bike rack loaded, but no ski box.
6) We will need to put a curtain behind the front seats on hot days. The air con was just barely keeping up on a sunny 30C day.
7) TrailForks may show trails at your destination, but that doesn’t mean those trails are going to be fun to ride. Drumheller has 8km listed, but it is all paved. Sigh.
8) Our tiny carpet on the step isn’t enough to keep the floor free of mud. During rain or mozzie attacks, we need a second carpet, large enough for two people.

Next up, the electrical system. I am really, really looking forward to fans, refrigeration, and recharging mobile devices.


New member
Thanks for the posts! Any progress on electrical? Also, what are you planning for heat? Do you have a drawing of your layout?


It has been a while since I updated our progress.

I got a private question about 4x4 and skiing in BC. I decided it would make more sense to share why we didn’t choose the 4x4 option.

We aren’t skiing with the van this winter, but will do so next year after getting the heat and plumbing done.

Most serious skiers will tell you that good tires are the most important part of winter driving.

4x4 does help with getting up hills at low speed. The problem comes when you turn around to go home and you now have to get back down the same sketchy roads.

We have a subaru as our daily (ski) driver, and while the all wheel drive is very helpful in getting out of parking lots, all the real challenges come in driving downhill.

The Mercedes 4x4 doesn’t perform at anything like the level of the Subaru all wheel drive, and the Subaru AWD only helps when you have your foot on the gas.

Most of our driving will always be on paved roads, and the fuel economy and lower centre of gravity of the RWD make a big difference there.

And yes, someday soon I am going to write up the electrical system, which is 80% done now.


Okay, ski season ended very early this year and I have taken a few days to sulk and whine about that.

It is time to move forward on the van, even though there isn’t anywhere it is currently allowed to go. All things will pass, presumably including my whining.

The core of the electrical system went in last fall, but didn’t get written up as we were busy chasing snow by the end of September.

The basic plan is stolen from the sailing world, because that is what I know. There is no AC system, as we didn’t have anything that needs AC power.

The two Blue Seas mini switches beside the fridge are the source control. The red one is the main switch, turn it off and everything on the house electrical system goes dark. The black switch is the engine charging system, switched on only when charging is needed. As these are marine grade (non-sparking, salt water immersion protected), they also have reflective labels so it is easy to see the settings while driving. Both switches are off in the photo.

The Blue Seas circuit breaker board has six circuits. This is both circuit protection and the on/off switch for electrical systems. The top switch is the fridge, the bottom switch is lights and device charging, second from bottom is the ventilation fans. The heater and blowers will get a switch, as will the water system, leaving one unused at this time.

Because the circuit breaker will have a sink beside it some day, this time it makes sense to use marine grade components. Hot, soapy water is less dangerous than salt water, but it could still ruin your night.

The wiring is all wrapped for abrasion protection and will be zip tied in place, but right now there isn’t much to tie to.

The circuit breaker panel feeds to connector blocks. This makes it easy to add to an existing circuit and share grounds. There will be five connector blocks in the finished van. The wires are colour coded by circuit: this is a pain during the build but I know from experience that I will glad before five years pass. The fan wiring (factory black and red) has blue electrical tape marking it as part of the blue circuit.

Near the bottom of the photo you can see the fuse block for the house battery which is hidden under the shelf on the right. The house battery ground is very accessible behind the vertical plywood divider. Always disconnect the ground before doing anything with the battery.

And finally, electrical 101: The fuse block and circuit breaker protect the wiring. Each electrical component (fridge, pumps, heater) gets its own fuse to protect the component.

Next up, the house battery and charging system.


House battery and charging.

This is a challenging topic, almost as prone to holy wars as insulation. There are a LOT of good approaches, and even more good-enough approaches.

My approach should work for me. If you want a microwave or a TV, well, this is not your answer. For us, the only thing that needed AC power was an old laptop, and it is definitely cheaper to replace the laptop with a USB C-era laptop than buy an inverter.

This is ONE solution to the problem. If your needs are different, your solution may also be different.

Decision one is battery chemistry.
Standard lead acid batteries are cheap, and not safe inside the passenger compartment. Forget about it.
AGM batteries are safe enough, cheap, and easy to work with. They are also extremely heavy, take 5.5 hours to fully charge from 50%, and have to be stored full. You can use solar for your trickle charging, but you must have some form of trickle charging to get reasonable battery life.
Lithium batteries come in many chemistries: LiFePO4 is the most commonly available in appropriate sizes because it is the safest.
LiFePO4 (called lithium for the rest of this post) is almost perfect for house battery use: it charges from 50% to full in one hour (or half an hour with a 10% reduction of battery lifetime), it has a consistent voltage for the entire usable storage, you can use 80% of the rated capacity every day, it weighs a third of AGM for the same use case, the smart charger can be pretty dumb, batteries prefer to be stored partially charged, and it can deliver much higher currents.
So lithium is a slam dunk winner, right?
Well, maybe. The cost is astronomical, batteries can’t charge below freezing, and damage can occur in hot weather if you can’t keep the battery coolish.

The cost of lithium is not quite as bad as it looks at first. As no trickle charging is needed, I could leave out the solar panels and solar charge controller. It looks like a dumb charger will be enough to protect the alternator for engine charging, so more money saved. With the high charging rates, I probably won’t ever need to charge from mains power, so I can leave out that AC smart charger too. Inverter users need to upsize the AGM bank to deliver high output current, but that didn’t apply for me.

Given my loads (fridge, diesel heater, pressure water), it looks like we will max out at 50AH/day in a 12 volt system. Three days on the hook requires 150AH usable power. Four days would be nicer, but not that common in my life.

For AGM, that is a 300Ah battery bank. Think two 4D cases in size and 180lbs to restrain.

For lithium, that is a 170AH to 190AH bank. Lifeblue sells a 200AH battery weighing 57 lbs in a 4D case. The LT version adds a heater so you can charge below freezing. This battery has an internal monitor, which may be accurate enough to run the house system.

For my needs, the lithium came in at about 15% higher cost for the whole system, possibly 20% if the dumb charger plan fails in real life. Yes, it has to be put somewhere where I can quickly remove it for storage in summer, but it is MUCH easier to restrain one light box.

Final answer, lithium, as the build simplicity is worth the cost to me. Again, this is LiFePO4. Tesla and phone batteries are a very different beast.

Battery chosen, location selected, now I just need to charge it.

The most basic charging system is to simply connect the house battery to the alternator and steal current. This almost never a good idea. But almost never is not never....

After a few email chats with Larry at Lifeblue, I went with the brute force approach. My van has switched power from the alternator (the base wiring for the second battery, option ?) which uses a solenoid and fuse to supply a direct alternator connection after the engine has run for a few seconds.

Wiring size is chosen by calculating the voltage drop based on planned current (E=IR). You can use this in reverse to deliberately create a voltage drop. Based on a 28’ circuit of 4 gauge wire, I estimated I would get about 50A charging rate, which should be in bounds for the alternator and about 50% of the safe charging speed for the battery. The wire would get slightly warm, about 10C above ambient at most, well within safe limits. Mercedes advertises a limit of 40A, but that allows for charging the engine battery and running accessories we don’t have. With my charging switch off when the van has real loads of its own, 50A should work fine. Worst case, I replace the alternator and controller.
Larry had experience doing this install with real sprinters and had very similar numbers. Our calculations give the same numbers, which isn’t a surprise, but actual experience beats theory.

The first test went moderately well, with an immediate surprise. The charge voltage was slightly higher than estimated and the charge rate is typically 57A to 60A.

It turns out that the VS30 sprinter charges at 14.6V, not the 14.2V Larry and I both used in calculations. Oops, there goes my factor of safety.

Still, it seems to work, and is well inside limits for everything except the alternator.

So this very simple system is almost never a good idea. Did I get into the rare exception? Maybe.

The first use the of the battery requires a full charge to set the capacity counter. When charging and the house battery is over 90% full, there is an interesting current slosh effect. The alternator can drop the voltage to 13.2 when the throttle is released. When this happens, the house battery is now charging the engine battery at about 10A, which trips the alternator controller into going back to 14.6V. Reaching 100% charge to calibrate is not working well.

That said, the 90-10 rule applies to liFePO4 batteries: try not to leave the battery above 90% or below 10% for any length of time. It is okay to visit, but you don’t want to live there.

We will only go above 90% for long weekends on the hook and when we need to recalibrate the ‘fuel gauge’ in the battery monitor, so this problem won’t come up often.

We may need to add a short section of 6 gauge wire to reduce the charging current. More testing will happen once once I install enough stuff to run down the battery.

For any non-sailors out there, ‘on the hook’ means at anchor without running the engine. There is probably an RV equivalent, but I won’t even start learning the lingo until I finish converting this cargo van.


For the final instalment of 2019 progress, there was a fridge in some of those pictures.

We chose a Dometic CRX65, which has about 57l capacity. It is pretty small, but with a need for bikes, kayaks, skis, and a shower in a 144, you have to give up something.

This model is 12V only, no propane and no AC power. The heat is vented at the back, which is convenient for our installation. Basically, the ‘chimney’ for waste heat is also a wiring channel.

The loaded fridge will weigh about 100lbs, which is something I don’t want to have hit the back of my head in an accident.

The fridge goes into the space just forward and below the bed platform. The space below will be plumbing and storage. The small box forward is the head/shower, which will mostly consist of a curtain. There will be storage above the fridge too.

The frame is mostly made of 1030 alu (1”x3”), chosen for stiffness to keep the structure from twisting. The frame is attached to the tracks both on the floor and the wall. Those attachment points should each fail at about 500lbs impact load per fitting. At this point in the collision, the fridge is suspended from that 1030 crossbar. When that fails (500lbs per side), the four sewn slings (red) will gently catch the now twisted frame while stretching about 4”. This is basically a crumple zone turned inside out.

The frame for the shower is also built of oversized aluminum. This stabilizes the fridge frame and keeps the fridge from spinning free in an angled collision.

The whole thing would be very strong if built in 1” square alu. The point of the 1”x3” is to get stiffness which dramatically simplifies the failure calculations.

Once the fridge frame was built, a storage box was added to stiffen the frame. This is also the step up into the bed, a seat, and the access point for some future plumbing.

If you look closely, you can see the entire aluminum frame is raised above the floor. I used laminated PU tile chunks for a thermal break. This air gap means that plumbing leaks will be easy to spot as the water will run everywhere. This design allows the van to flex without bending the interior frames. The tiny remnant of bare floor will get a covering eventually, hiding the gap.
Last edited:

Top Bottom