Although I have some prior experience with both residential wiring and sailboat wiring, it probably took me 40 to 50 hours of research to put together my electrical plan.
If you don’t want to put the time into this area of your build, I highly recommend https://amsolar.com. This company has developed kits for every size of installation for DIY conversion vans, their pricing is actually quite reasonable (i.e. they don’t really mark up all of the components they assemble for you in a kit), they have detailed schematics for each kit, and they can totally customize the kit to your specific needs. They also support what they sell, so if you are relatively inexperienced they can walk you through the installation of the kit. I spent a number of hours adding up the costs of an AM Solar kit if I purchased all of the parts myself, and only saved about 10%. The majority of their markup over the discount suppliers is on highly complex equipment, like the invertors and charge controllers. That’s exactly where I might need their support, so I’m purchasing most of what I need from them.
And even if you do want to put the time in, AM Solar is a thought leader in this field with great published resources for your learning pleasure. Their components and designs are all high-quality and suitable for van use.
Calculating electrical use
Planning an electrical system starts with listing all of the devices you wish to use, and figuring out how much DC energy they use in terms of “amp hours.” Here’s how I did this:
Made a list of each of our devices that use electricity, and track down the “DC Amp Hours” consumption rate for each device. In some cases I had to contact the manufacturer.
If it is an AC device that is powered through the inverter, I converted the AC amps or watts to DC amps. For example, a 1000 W microwave runs on AC current. I need to turn on the inverter, which will convert battery current from DC to AC and then power the microwave. This is somewhat of a simplification, but if I multiply the AC watts by .092, I will get the DC amp hours required. Using the microwave example, a 1000 watt microwave will consume 92 DC amps every hour it is on.
Estimate how many hours per day that device would be in use.
Multiply the DC amp hours times the hours in use to get the total daily DC amps consumed by that device.
Add up all of the devices to get the total DC amps for the day.
The total is the number of amp hours you will be drawing out of your battery bank each day. On an average day where Sharon is working, we will consume about 193 amp hours. On a minimal day where we are out and about or conserving, we will consume about 122ah. Here is a table showing my calculations.
|Electrical loads||DC Amps per hour||Hours per day||DC Amps per day - average||DC Amps per day - rationing||Comments|
|Vitrifrigo 130L||1.7||24.0||40.8||40.8||Assuming 1.7 avg draw|
|Water pump||4.0||0.5||2.0||2.0||30 minutes/day|
|6 12-LED interior lights, .2a each||1.2||7.0||8.4||5.0||Evenings only|
|30' LED light strips, .067a/foot||2.0||7.0||7.0||3.0||Evenings only, dimmed 50%|
|MaxxAir Deluxe Vent fan||2.0||14.0||28.0||14.0||Running 14 hrs/day at speed 9 for sleeping, working, cooking in hot climates|
|Espar or Webasto Heater fan||2.0||0.0||0.0||0.0||Won't run heater if vent fan is running and vice versa|
|Stereo||2.0||4.0||8.0||0.0||4 hours of use per day|
|Composting Toilet||0.1||24.0||1.7||1.7||24x7 vent fan|
|Fire/smoke detector||0.2||24.0||5.0||5.0||Unknown power draw|
|Bed fans - 2x||1.2||8.0||9.3||9.3||Necessary in hot weather|
|Invertor||0.7||3.0||2.0||2.0||Very little use|
|Cell phone 2x (using DC charger)||2.8||1.0||2.8||2.8||Assuming using phone completely each day|
|Cell booster (using DC convertor)||0.7||8.0||5.8||5.8|
|Sharon Mac (using DC charger)||3.9||8.0||30.9||30.9||Assuming total 8 hours of laptop use per day|
|Dave laptop (using DC charger)||4.2||8.0||33.8||Assuming total 8 hours of laptop use per day, if power is low, Dave don't work|
|CruisenComfort A/C||20.0||8.0||160.0||Assumes a 50% duty cycle. Exclude from daily calculations. Use only when at Rv campground, or batteries are topped off|
|Tank monitors||0.2||24.0||4.8||0.0||Garnet 709 SeeLevel II Tank Monitoring System. Only turn on to check levels, then turn off.|
|Total amps per day||193.4||122.4|
I did omit one huge load from the total that we will be building into the van, but don’t expect to be able to run off of the batteries, and therefore are not factoring into our daily consumption. That is the Cruise N Comfort DC air-conditioner. This unit consumes between 38 and 50AH when it’s running. If we’re well insulated, and we have the sleeping area closed off with a curtain, it would probably run about 50% of the time at night, or a total of 4 hours @ 40 amps per hour. If we end up having surplus electricity while off grid, this is where we’ll put it.
Note that running ANY kind of AC at all off-grid is pretty difficult without a generator running at the same time. People have tried residential window mount units, swamp coolers, rooftop units and massive solar banks, but they all take a lot of energy.
Calculating energy sources
The next step is to figure out how to put energy into the battery bank to match what you take out. There are four possible sources:
Solar panels. Solar panels are quiet, the energy is free, and the maintenance costs are low. There’s really no reason not to have some at least some solar. However, for heavier users solar may not provide enough energy. In sunny climates plan on getting 25 to 30 amp hours per day per hundred watts of solar. In cloudy climates, or in the north, or parked in the shade, expect anywhere from 0 to 10ah per day.
Running the car engine and charging the batteries via the alternator. An average van alternator has at best perhaps 80ah available for charging the battery each hour. If you have a heavy duty alternator, or install one, you can get 120ah or better.
Plugging in to shore power. With a typical van sized 30 amp service and a 3000 W inverter/charger unit, I can get up to 120ah.
Generator. With a typical van sized 2000 W portable generator, I can get about 180ah. We prefer not to use a generator because of the noise and pollution.
Putting your loads and your sources together
Once you know your loads and your potential sources, you can create a plan to meet your needs. Here’s our approach to meeting our energy needs:
Max out on solar. We will have between 560 and 600 watts of solar on the roof depending on whether I believe the manufacturers specs. We will also have 200 watts on flexible panels that we can set up on the ground near the van. On a sunny day while boondocking, our total solar production will be about 240ah. And of course there will be days with no production at all here in the Pacific Northwest.
Max out on battery capacity - use a 400ah lithium battery bank, of which we are allowed to consume 80%, or 320ah. By maxing out on battery capacity, we can go longer before we have to take some steps supplement the solar with some other source. If we have underestimated our battery capacity, I am leaving space for another 200ah battery. I’ve also sized all of the wiring for that capacity.
Use our heavy duty alternator and run the van engine at high idle, or take a long drive somewhere. Our heavy duty alternator puts out about 120ah, so to recharge a fully depleted battery bank would take about 3 hours of running the engine.
Finally, stop at an RV park for the night, do laundry, take long warm showers, charge the batteries, empty the gray water tank, dispose of the trash, and top off the water tanks. We hope to limit this to once per week.
We think that between solar, driving, and weekly RV campground stops, we will meet our electricity needs without needing to run the van motor at idle.
Selecting solar panels
This is actually not too complex. Look at the area on the roof you have, and figure out what will fit there. There are some constraints though.
Ideally all of the panels are of the same brand and size. The reason for this is different panels charge at different voltages and currents, and if you wire the panels up in parallel, the voltage of all the panels will be dragged down to the voltage of the lowest panel, so you lose some of the available juice from the higher performance panels. But you can find panels of different sizes that have roughly equivalent voltages and make it work.
You cannot have anything shading the panel. Even a radio antenna casting a partial shade on one cell out of 96 cells on a panel can cause a dramatic drop in performance for that entire panel. Don’t expect to put kayaks, bikes, fans, or other equipment on the roof adjacent to panels and get decent performance out of the panel with that stuff up there.
Plan on mounting only on the flat area of your roof, working around the other stuff you plan to put up there. At least on the Ford transit 148” wheel base, after installing the fan at the front, there’s only about 78” of length available, which barely fits three panels.
I don’t recommend flexible panels on roofs. When you glue them to your roof, they become a big black blob that soaks up heat, transfers it into your van, and prematurely ages the panel so that it lasts only a few years instead of the 25 years of a rigid panel. But in certain cases you may not have any option.
If you plan on extended boondocking, consider making your panels tiltable. Panels will produce up to 30% more electricity when they are directly facing the sun. Most people find this to be a hassle, but if you’re going to park more than two days it’s probably worth the effort. You won’t have other charging sources, and the tilting will pay off.
Here is a table of popular standard size panels for RV use.
|Solar Panel Cell comparisons||Price||Watts||Length||Width||Height||Weight||Cells||Vmpp|
|Canadian Solar Monocrystalline PERC 300W Panel - Black Frame||183||300||65||39.1||1.57||40.1||60||32.5|
|Canadian Solar 325W BLACK/WHITE Module CS1K-325MS||239||325||67.3||39.1||1.57||41.7||60||30.2|
|Solarworld 300W BLK/WHT Mono Module||222||300||65.95||39.4||1.3||39.7||32.6|
|Zamp ZS90 90W Solar Panel||343||90||58.3||13.5||1.38||14.3||18||19.1|
|Zamp 90W Short Solar Panel||343||90||39.56||19.88||1.38||14||18||18|
|SP100 Solar Panel||255||100||41.45||21.3||1.38||14.5||32||17.7|
|Zamp 170W Solar Panel||538||170||58.3||26.4||1.38||25||36||18|
We went with two of the Grape Solar 180w panels, and one Hightec 200w panel. The hightec doesn’t have the same reputation as Grape Solar, so I’m testing one of their 200w panels on the roof to see how it compares to the Grape solar. If I am truly getting an additional 10% of production out of that panel, I would consider swapping out the other two panels and selling them.
I knew we needed about 320 usable amp hours of battery storage. There are two different types of batteries typically used in RV’s, each with their own storage capacity. No battery allows you to completely discharge it and get all the juice out of it without damaging it. So you can’t just buy one 320AH battery to meet your needs. You need excess capacity so you can pull 320ah out of the batteries without damaging them. Here’s a table showing a comparison of the battery capacities, costs, sizes and weights for our needs.
|Battery Type||Usable capacity||Weight||Size||Cost||Cost per usable ah||Energy lost during charging||Typical number of charge cycles||Min time to recharge when empty|
|400AH LifeBlue Lithium (2 batteries)||320||113.2||19w x 13l x 9.5h||$3790||$11.80||<2%||2000||1.5 hours|
|600AH Lifeline AGM (4 batteries)||300||372||28w x13l x 12h||$1816||$6.05||10%?||1000||5 hours|
Note that the energy lost, the number of charge cycles, and the minimum time to recharge numbers are just rough estimates for comparison purposes.
Here’s what each of these items mean:
Battery type: the two most popular types of batteries for RVs are AGM and Lithium.
AGM is an improvement on the traditional lead acid battery found in cars for the last hundred years. They are sealed, you don’t have to regularly top them off with distilled water, and they don’t dump out acidic water vapor.
Lithium Iron Phosphate (LiFePo) is a newer technology that has been slowly moving into the Marine and RV world for the last 10 years. Note that this is not the same technology as a laptop or phone battery – LiFePo batteries do not explode when overcharged.
Usable capacity: Only about half of the total capacity of an AGM should be taken out of the battery at any time. Taking more than 50% out will reduce the battery life and should be avoided if possible. For Lithium batteries, up to 80% of the capacity can be taken out without damaging the battery. This means you need fewer total amp hours of battery capacity for lithium batteries than for AGM or Lead Acid.
Weight: AGM batteries weigh about 3 1/2 times more than Lithium for the same capacity - or in my case an additional 250 pounds. Weight in a small van affects van handling and fuel efficiency.
Size: AGM batteries will take up about 50% more space in your van for the same amount of capacity.
Cost and cost per usable amp hour: This is where lithium is painful. They cost more than twice as much for the same amount of capacity. If you are on a budget, stop here. Make AGM work for you – many people use them, they work great, it’s well understood technology. But if you have the cash, go lithium. They last at least twice as long as AGM’s as well, so in the end they are cheaper.
Energy lost during charging: lithium batteries can accept a ton of energy without losing any of it to heat until they are nearly full. This means all of your precious solar power goes right into the battery. AGM batteries lose some of their energy to heat during the charging cycle, so you need more solar or generator time to replace the energy you use.
Minimum time to recharge: see above – if you are running a big alternator on your engine while parked, you don’t have to run it as long to fully recharge your lithium battery bank. AGM batteries can charge at a high rate for a while, but then you have to slow down in the absorption phase for hours.
We decided on Lithium for our battery bank.
We looked at a number of different Lithium battery sources:
Victron is perhaps the most advanced. The batteries are part of a larger, networked electrical management system including chargers, inverters, solar charge controllers, and monitoring panels. Awesome system, but too expensive. The batteries themselves should not be installed without a separate BMS (battery management system), which monitors and controls charging and discharging, preventing them from being destroyed by too much of either.
Lithionics is a step down in sophistication, but they pride themselves on absolutely bullet proof lithium installation, and again, too expensive.
LifeBlue was recommend by AMSolar. One key differentiator from Battleborn is their integrated BlueTooth based BMS. I can monitor battery state of charge and individual cell health from any smartphone.
Battleborn is also a solid contender, but there’s no way to interface with the battery BMS and assess what’s going on.
Finally, there’s the “assemble your own” batteries from Electric Car Parts. There are a number of companies in the US selling individual Lithium cells, which you assemble into a full size battery bank, as well as install a separate BMS. I was attracted by the thought of saving $1800 in battery costs, but by about page 16 of the Orion BMS install manual I realized my punch list was already 2 miles long and growing. I will gladly pay the $1800 to have somebody else implement the BMS.
We selected two of the 200 amp hour LifeBlue lithium batteries for our battery bank. We have space and wiring for a third battery if needed.
Charging from the engine
There are number of different options for charging the house batteries from the alternator. All of these approaches require that your house bank and your starter battery be connected via a device and some really large gauge wire.
We went with the Victron Cyrix Li-CT 230A battery combiner (aka VSR).
We don't have a European alternator, which would require a B2B charger
The high amperage capacity will hopefully reduce our charging times if we need to run the engine while boondocking.
Lithium batteries can handle all of the current the heavy-duty alternator can throw at them, so we didn't need the current limiting function of a B2B charger.
It was cheaper than the B2B charger.
We are getting the Alternator Charging Kit from AM Solar.
This was a confusing area for me to research. I was trying to nail down these questions:
What prevents the alternator from overcharging the lithium batteries? Answer: alternator charging current will scale back as the combined battery voltage rises. In fact, because I have a factory installed AGM battery, my alternator voltage will never be high enough to fully charge the lithium battery house bank.
What prevents the lithium batteries from overcharging the starter battery when they are combined? Answer: the batteries are only combined when a charging level voltage is detected on either the house or starter side. So at rest when not charging, there will be no combining and overcharging of the starter battery.
What prevents the starter battery from being drained if the lithium battery resting voltage is high enough to trigger combining? Answer: the lithium battery resting voltage is below the combining threshold.
I finally decided to stop trying to cram more battery charging data into my head, trust that the AM Solar kit will function correctly, but I will install and monitor charging current and voltage the first few months.
Charging from shore power and using an inverter
We selected the Victron Multiplus 12/3000 Inverter Kit from AM Solar. This is an inverter/charger kit which includes all necessary wiring, lugs, heat shrink, switches, etc. to tie it into my power center.
30 amp shore power connection reduces our charging time
We don't need the 2400 W sustained power of the inverter, but the box is actually smaller than the 2000 W version and fits better in our power center.
The control panel allows me to dial back the current the charger will accept, which keeps me from blowing the fuses when I'm parked in the driveway of a friends house and hooked up to their electricity with a standard extension cord.
The kit is handy, as their markup on the parts is minimal and they package it all up for me. The main item they markup is the inverter itself, but I don't mind paying a few extra dollars for support on this complex piece of equipment.
Creating a circuit diagram
With all of the main components selected, it’s time to create a circuit diagram to show how everything connects, uncover missing components, and create a plan for wiring it all up. I used Microsoft Visio for this – it’s great at drawing lines that connect electrical components to other components. Here is the circuit diagram:
The Power Center contains the batteries and bulky piece of equipment that don't need any visibility or regular attention. All high current/high power devices (other than the alternator charging circuit) are located here to minimize long runs of heavy cable. The power center will be located behind the right rear wheel well.
The Control Center includes the DC circuit breaker/switches, inverter control panel, solar charge monitor, tank monitors, and any other switches and displays for monitoring and controlling the electrical system. The control center will be located on the forward face of the upper right cabinet by the sliding door. I will probably need to put a couple of items above the sliding door itself.
It's critical to properly fuse and protect all wires from shorts. If you don't put a fuse on a wire and it shorts out, it can melt, burst into flame, and set fire to your van. The idea is to put the fuse on the upstream side of the wire – where the energy is coming from – which is usually closest to the battery, alternator, charger, or solar panel. The size of the fuse can be based on either the maximum current the wire can safely support, or the maximum current the device or devices can safely consume. Generally, I size fuses based on the wire. I prefer using circuit breakers over fuses, as they can be easily reset when tripped, and don't require me to stock any spares. They are more expensive though.
The negative side of the power center is grounded directly to the vehicle chassis. Having a common ground for both the vehicle/starter electrical system and the house electrical system reduces potential for ground loops and electrical interference.
The negative side also has a shunt between the batteries and the negative busbar, which is used by the Victron battery monitor to measure all current going into and out of the battery bank.
Wire sizes were calculated using the Blue Sea Circuit Wizard. I never want more than a 3% drop in voltage on any of my circuits, and for critical charging circuits where I want to capture every bit of energy, I might size the wire to a one or 2% drop.
The positive side of the power center has a battery cut off switch, allowing me to completely disconnect the battery bank from the electrical system for system maintenance and storage. The one exception to this is the battery monitor circuit – if I switch off the batteries, I still want the battery monitor circuit functioning to show voltage. However, for long-term storage, this circuit also has a switch to eliminate this parasitic drain on the battery.
A Victron BP65 discharge protection device protects the lithium batteries from being over discharged. All DC devices are downstream of this unit, and if the battery voltage drops below a certain threshold, the unit will cut off power. There is also a separate switch mounted in the Control Center hooking up to this device that allows me to cut off all DC power consumption with a single switch. The only devices not routed through this circuit are the inverter, solar charge controller, and VCR. Each of these devices has its own circuit to detect when battery voltage has dropped too low.
All DC loads go from the BP65 to a Blue Sea distribution circuit panel in the Control center, and from there are distributed throughout the van. Each distribution wiring run carries both positive and negative wires to eliminate issues with poor grounds and ground loops.
The one exception to this distribution scheme is the air-conditioner. It didn't make sense to run such heavy wire for the 38 amp appliance in the back of the van to the circuit panel and back.
Not shown are wiring runs the individual appliances and devices. Some miscellaneous details on those:
The LED lights will be on two circuits, each with a buck boost converter. Without this, LED lights are prone to premature burnout due to the higher voltages coming from the alternator and other charging sources. The voltage needs to be stabilized to 12 V.
I may need to add the same buck boost converter for the MaxxAir fan. It's unclear to me whether MaxxAir has fixed the design flaw with their circuit boards that cause premature failure with higher voltages.
Wrapping it up
With the diagram done, I have a solid plan in place for where to place the larger electrical components, whee to place the conduits in the walls and ceiling, and how big each conduit run needs to be.