# Planning a Camper Van Electrical System That Will Actually Hold Up

> Build the amp hour budget first, then choose chemistry, charge sources, inverter, wire gauge and protection that survive real vibration and heat.

Source: https://ocrv.info/resources/guides/planning-a-camper-van-electrical-system

A camper van electrical system is a small direct current power plant: a battery bank sized to a measured daily load, one or more charge sources feeding it, and distribution protected at every source. Planning it properly means building the amp hour budget first, then choosing chemistry, charging, conductors and protection to match.

Most van electrical builds fail in the same place: somebody picked a battery first because that was the exciting purchase, then worked backward and discovered the alternator could not refill it, the inverter could not start the induction cooktop, or the whole bank cycled to empty by two in the morning. The order matters. Loads determine bank size, bank size determines charge source capacity, and the combination of the two determines conductor size and overcurrent protection. Every step downstream inherits the errors made upstream.

The second common failure is not electrical at all. It is mechanical. A system that reads perfectly on a bench in a climate controlled garage begins to behave strangely after two thousand miles of washboard, expansion joints and cattle guards, because a lug worked loose, a crimp fatigued, or a conductor chafed through where it passed a bulkhead without a grommet. Vibration is the environment. Anybody designing for a van and not for a bench has to build terminations that assume constant low amplitude shaking for years.

The third factor here is local. An Inland Empire summer regularly pushes past 100 degrees, and the inside of a closed van parked on asphalt runs far hotter than the air outside. Lithium charge acceptance drops with temperature, battery management systems have high temperature cutoffs, and inverters fold back their output when the heatsink saturates. A layout that was fine in a mild coastal climate can become an intermittent nuisance here, so component placement and airflow deserve as much attention as the wiring diagram itself.

## Start at the loads, not at the battery

Write down every device, its current draw in amps at twelve volts, and the honest number of hours it runs on a normal day rather than a best case day. A twelve volt compressor refrigerator does not run continuously; it cycles, and in hot weather a typical unit consumes thirty to forty five amp hours per day. A roof fan on medium pulls around 1.5 amps, so eight hours is twelve amp hours. Interior lighting rarely exceeds three or four amp hours. The water pump is negligible on a per-day basis because it runs in short bursts.

The loads that break budgets are the ones people forget to convert. Anything running through the inverter has to be counted at the twelve volt side, so a sixty watt laptop for four hours is not sixty watt hours, it is roughly twenty amp hours once inverter efficiency and idle draw are included. A satellite internet terminal drawing fifty to seventy five watts continuously is the single largest consumer in most modern builds, easily one hundred amp hours per day on its own. A diesel heater is cheap while running and expensive during each glow plug start cycle.

Add the column, then add twenty five percent for the loads you have not thought of yet and for capacity fade over the years. Divide that total by the usable depth of discharge of the chemistry you are considering, not by its nameplate capacity. A one hundred amp hour flooded battery gives you perhaps thirty five usable amp hours in practice. The same nameplate in lithium iron phosphate gives you eighty five or more. That division step is where the real bank size finally appears, and it is often twice what the owner guessed.

- Twelve volt compressor refrigerator: thirty to forty five amp hours per day in hot weather
- Roof ventilation fan on medium: roughly 1.5 amps, twelve amp hours over eight hours
- Satellite internet terminal: fifty to seventy five watts continuous, often one hundred amp hours per day
- Laptop through an inverter: about twenty amp hours for four hours of use, including conversion losses
- Diesel air heater: about one amp while running, with a much larger draw during each glow plug start
- Add twenty five percent headroom, then divide by usable depth of discharge, not nameplate capacity

## Which chemistry earns its place in the bank?

Flooded lead acid is the cheapest per nameplate amp hour and the most expensive per usable amp hour. Depth of discharge below fifty percent shortens cycle count sharply, the practical working window is closer to thirty to forty percent, and the bank needs watering, ventilation and an upright orientation. Absorbed glass mat improves on that: it is sealed, tolerates vibration well, mounts in any position, and accepts a fifty percent working depth. Both share the same fundamental limit, which is charge acceptance around 0.1C to 0.2C, meaning a two hundred amp hour bank simply will not take more than twenty to forty amps no matter what you feed it.

Lithium iron phosphate changes the shape of the problem. Usable depth of discharge is eighty to ninety percent, charge acceptance is commonly 0.5C and sometimes 1C, and weight per usable amp hour is roughly a third of lead. That charge acceptance figure is the underrated one: a two hundred amp hour lithium bank can absorb one hundred amps from a DC to DC charger and a solar array simultaneously, which means a two hour drive genuinely refills the bank. Lead cannot do that regardless of how much charging hardware is bolted to the van.

The costs are real too. Lithium iron phosphate must not be charged below freezing, so the bank needs either a low temperature charge cutoff in the battery management system or internal self-heating. The management system is a protection device, not a charge controller, and when it opens under fault it disconnects the bank instantly. If that happens while an alternator is pushing current with no other load on the bus, the resulting voltage spike can destroy the alternator's regulator. That is one of several reasons a DC to DC charger belongs between the two.

## Three ways to put energy in, and how they share one bank

Alternator charging through a DC to DC charger is the workhorse. A voltage sensitive relay simply parallels the two banks, which was acceptable when both were lead and both wanted the same voltage. It is a poor match for lithium, because a lithium bank will pull whatever the alternator can deliver until something overheats, and because most modern vehicles use a variable voltage smart alternator that will not hold a charging voltage at all. A DC to DC charger fixes both problems by regulating current to a set limit, commonly thirty, forty or sixty amps, and by applying a lithium charge profile.

Shore power charging is the simplest of the three and the most frequently misconfigured. A converter or inverter-charger must be set to the correct profile for the chemistry, since a lead acid absorption voltage held on a lithium bank keeps the cells at full charge continuously and shortens their working life. Size the charger against the bank rather than against the outlet: a sixty amp charger into a two hundred amp hour lithium bank is a reasonable pairing, while the same charger into a lead bank is wasted money because the bank cannot accept it.

Solar completes the set. A maximum power point tracking controller beats pulse width modulation because it converts surplus panel voltage into additional charging current instead of throwing it away. Two two hundred watt panels wired in series produce roughly seventy volts open circuit and about eleven amps, and an MPPT controller turns that into around thirty amps at battery voltage on a good day. Watch the temperature coefficient: panel open circuit voltage rises as the cells get cold, so size the controller's input limit against a cold morning rather than a hot afternoon.

- DC to DC charger: required for lithium, mandatory with a variable voltage smart alternator
- Size the DC to DC unit against the alternator rating and the cable run, not against the battery alone
- Shore converter: set the correct chemistry profile, and size it to what the bank can actually accept
- MPPT over PWM: converts surplus panel voltage into current rather than discarding it
- Series strings raise voltage and suffer more from partial shading; parallel strings suffer less but need higher current wiring

## Conductors, fuses and the parts nobody photographs

Voltage drop is where twelve volt systems punish sloppy work. Target three percent, which at twelve volts is 0.36 volts. For a one hundred amp load ten feet away, the round trip conductor length is twenty feet, so the total resistance budget is 0.0036 ohm, or 0.00018 ohm per foot. Two AWG copper sits at roughly 0.000194 ohm per foot, which misses, so the correct conductor is 1 AWG or 1/0 for margin. A two thousand watt inverter is a different calculation entirely: it draws close to two hundred amps under full load, which means 4/0 cable kept as short as physically possible.

Protect at the source, always. A fuse exists to protect the conductor from the energy behind it, so it belongs within a few inches of the battery positive terminal, at the busbar, and at every branch. Lithium iron phosphate deserves special attention because a shorted lithium bank can deliver several thousand amps, well beyond the interrupt rating of a common ANL or bolt-down fuse. A Class T fuse carries an interrupt rating in the twenty thousand amp range and is the correct choice on the main positive lead of any lithium installation. This is not a preference; it is the difference between a blown fuse and a fire.

Build the distribution around a single positive busbar and a single negative busbar, and make that negative bar the one star point for the whole system. Multiple chassis bonds create parallel return paths that circulate current through the body and accelerate corrosion, so bond once and only once. On the alternating current side, the inlet feeds a transfer switch, the neutral to ground bond is established in exactly one place depending on whether shore or inverter is the source, and ground fault protection sits at the inlet or the first receptacle. Label every conductor at both ends.

- Three percent drop target at twelve volts is 0.36 volts total, round trip
- One hundred amps at ten feet one way needs 1 AWG or 1/0, not 2 AWG
- A two thousand watt inverter needs 4/0 on a short run and a fuse in the two hundred fifty to three hundred amp range
- Class T fuse on the lithium main positive, within a few inches of the terminal
- One negative star point, one chassis bond, one neutral to ground bond at a time
- Pure sine inverter for anything with a motor, a compressor or a medical device; modified sine runs them hot

## Why bench-tested systems fail on washboard roads

Terminations decide the service life of a van system. Solder has no place on stranded conductors in a vibrating vehicle, because it wicks up into the strands and creates a hard stress riser exactly where the wire needs to flex. Use a proper hex die crimper sized to the lug, adhesive lined heat shrink over every crimp, and ferrules on anything entering a screw terminal. Support conductors every eighteen inches, add a grommet or a split loom at every bulkhead pass, and apply a thread locking compound to busbar studs. Re-torque every terminal after the first hundred miles and again at the first service.

Heat is the second silent problem here. A closed van on asphalt in Eastvale or Mira Loma can reach interior air temperatures far above the outside reading, and the battery compartment is usually the least ventilated space in the build. Lithium charge acceptance derates as cell temperature climbs, and most battery management systems open a high temperature charge cutoff somewhere around 130 to 140 degrees. Inverters fold back output when their heatsinks saturate. Mount electronics on an interior bulkhead with air movement across the fins, not against a sun-facing sheet metal wall, and never above an exhaust component.

The shop performs this work in house at the posted mechanical and electrical rate of $260 per hour, with in depth diagnostics billed at $285 per hour with a one hour minimum that is credited toward an authorized repair. A load budget, a wiring diagram and a parts list typically take two to four hours. A complete bank, charge source and distribution installation with a shore inlet and a transfer switch commonly runs twenty four to forty hours depending on how much cabinetry has to come out. Sales tax of 7.75 percent applies to parts and materials only.

## Frequently asked questions

### How many amp hours do I actually need?

Nobody can answer that without your load list. Build it honestly, convert every alternating current device to its twelve volt equivalent including conversion losses, add twenty five percent, then divide by the usable depth of discharge for the chemistry you are considering. A build with a compressor refrigerator, lights, a fan and occasional laptop use often lands near sixty amp hours per day, which one hundred amp hours of lithium covers comfortably. Add a satellite internet terminal running all day and that same build needs two hundred to three hundred amp hours.

### Is lithium worth the price difference over absorbed glass mat?

Compare per usable amp hour rather than per nameplate amp hour, and include cycle count. A hundred amp hour absorbed glass mat battery gives about fifty usable amp hours; lithium iron phosphate gives eighty five or more from the same nameplate, at roughly a third of the weight, with several times the cycle life. The charge acceptance difference matters even more if you drive frequently, because lithium will absorb a full DC to DC charger output while lead simply will not.

### Can I charge from the alternator without a DC to DC charger?

With an older fixed voltage alternator and a lead acid bank, a voltage sensitive relay works acceptably. With lithium, or with any recent vehicle running a variable voltage smart alternator, it does not. Lithium accepts current until something in the path overheats, and a smart alternator drops its output voltage under conditions the relay cannot anticipate. A DC to DC charger regulates current to a fixed limit, applies the right charge profile, and isolates the alternator from a sudden battery management system disconnect.

### Why a Class T fuse instead of the one that came in the kit?

Interrupt rating. A lithium iron phosphate bank can deliver several thousand amps into a dead short, and many common bolt-down or ANL fuses cannot break that level of current cleanly. Instead of opening, the fuse can arc and sustain the fault. A Class T fuse carries an interrupt rating around twenty thousand amps at direct current voltages and clears very fast. It costs more than the fuse in the kit, sits within a few inches of the battery positive terminal, and is the single cheapest safety item in the build.

### What does a complete system cost to have installed here?

Labor is billed at the posted mechanical and electrical rate of $260 per hour. Design work, meaning a load budget, a wiring diagram and a specified parts list, usually takes two to four hours. A full installation with bank, DC to DC charger, solar controller, inverter, distribution, shore inlet and transfer switch commonly falls in the twenty four to forty hour range, driven mostly by how much cabinetry must be removed and reinstalled. Parts carry the posted markup and 7.75 percent sales tax applies to parts and materials only.

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OCRV Center. 23281 La Palma Ave, Yorba Linda, CA 92887. (949) 799-3387. info@ocrvcenter.com. Serving Eastvale, California in Riverside County, about 20 miles from the shop. All work is performed in shop at the Yorba Linda facility. No mobile, roadside or on-site service is offered. Scope is body, paint, structural, fiberglass, interior and vehicle systems work. Engine rebuilds, transmission rebuilds, drivetrain work, DOT inspections and emission testing are not performed.