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Charging a camper van: solar, alternator and shore power
Most camper vans rely not on one, but three charging sources: solar panels, the alternator via a B2B charger, and shore power via a 230V charger. Each system has its strengths and limitations. Each source has its own weakness: solar in winter, the alternator when you sit still, shore power when there is no post.
Calculate your charging strategy
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Solar panels: free but unpredictable
Solar panels provide free energy without noise or fuel. On a good summer day in Southern Europe, a 200Wp panel produces around 800-1000 Wh. In winter or with cloud cover, this can drop to 100-200 Wh.
Advantages: no cost after purchase, silent, works when stationary. Disadvantages: heavily dependent on weather and season, takes up roof space, not enough as a sole source with high consumption.
Tip: solar panels are ideal as a base charge. They slowly top up your battery during the day, reducing your dependence on other sources.
Alternator (B2B charger): charging while driving
A B2B charger (battery-to-battery) converts your alternator's 12V into the correct charge profile for your battery bank. While driving, this typically provides 20 to 50 amps, depending on your B2B charger and alternator.
One hour of driving with a 30A B2B charger on a 12V system charges approximately 324 Wh, because its efficiency of around 90 percent counts too. That is often enough to supplement daily use if you drive regularly.
Important: a B2B charger is essential for lithium batteries. You cannot connect a lithium battery directly to the alternator for two reasons: the charge profile differs from lead-acid, and lithium batteries have very low internal resistance which can force the alternator to deliver maximum output. At idle or low speeds this can cause the alternator to overheat and fail. A B2B charger protects both the battery and the alternator.
Shore power (230V charger): fast and reliable
On a campsite with a power hook-up, a 230V battery charger can fully charge your battery bank. A good 30-50A charger fills a 200Ah lithium battery in 4-7 hours.
Shore power is also needed for heavy consumers you don't want to run from your battery: air conditioning, hair dryer or a washing machine.
Note: many campsites in Europe have limited amperage at the power post (6A or 10A). A 50A battery charger at 12V draws about 700-800 Watts from the post. With a 6A campsite connection (1380W) this usually works, but if the fridge and boiler also run on 230V the campsite breaker may trip.
Downside: you depend on infrastructure. When wild camping or on small campsites, shore power is not always available.
Charge stages: what a charger actually does
A battery charger does not simply put voltage on the battery; it works through stages. First the bulk stage, in which it gives all the current it can while battery voltage slowly climbs. Then absorption, where voltage is held constant and current tapers off by itself while the last few percent go in. Then float, a lower voltage that keeps the battery full without stressing it.
How long those stages take depends on the battery type. A lead battery genuinely needs the absorption stage and can spend hours in it; that is also why a lead battery on solar rarely gets truly full in winter. Lithium iron phosphate accepts the same current until nearly full and is therefore done much sooner.
So setting up your charger is not a detail. A charger left on lead settings with lithium installed charges too high or too long; the other way round, a lead battery stays permanently half full. Every charger in your camper, from solar to shore power, has to be set to the same battery type.
How fast may you charge?
Every battery has a limit on the current it can take, expressed in C. 1C means the capacity in one hour; on a 100 Ah battery that is 100 amps.
Rough guidance, always check the sheet for your own battery:
- Flooded lead and AGM (absorbent glass mat, a sealed lead battery): charge at 0.2C, so 20 amps on 100 Ah; some datasheets allow more, this is the safe side
- Lithium iron phosphate: often 0.5C allowed, sometimes 1C, so 50 to 100 amps on 100 Ah
Charging harder than allowed costs lifespan, and on lithium it is the battery management system that steps in, throttling or cutting off the charger. Charging gentler is always fine, it just takes longer.
This decides how useful a heavy charger is. A 60 amp shore charger on a single 100 Ah lead battery is waste; on 200 Ah of lithium it is exactly right. Work it out before buying: the battery sets the charger, not the other way round.
Cold: the limit people forget
A lithium iron phosphate battery must not be charged when the cells are below freezing. Discharging is fine well below zero, charging is not: metallic lithium plates onto the anode and that damage is permanent. Almost every battery with a built-in management system therefore blocks charging below roughly 0 degrees.
In practice you notice it on a winter morning: the sun is out, the controller reports power, and nothing goes in. That is protection, not a fault.
Three ways to deal with it. Put the battery inside the living space rather than in an outside locker or under the floor, because that is where it stays above freezing longest. Choose a battery with heating, which warms itself before it charges. Or accept that in winter you only charge once it is above freezing inside, and plan your consumption around that.
Lead batteries do not have this limit, but they do deliver less capacity in the cold. That belongs in your winter planning too.
Combining all three sources
A robust strategy combines all three:
Solar panels cover basic daytime needs (lighting, fridge, phone charging).
The B2B charger supplements on driving days. One hour of driving often compensates for half a day's consumption.
Shore power is used to fully charge when available, especially after several cloudy days.
The Super Wiring Wizard automatically estimates how much you need from each source based on your consumption profile and travel pattern.
Common mistakes
Relying solely on solar: even in Southern Europe there are consecutive cloudy days. Always plan a second source.
Not installing a B2B charger: you are driving anyway, so why not use that energy? A B2B charger is one of the most cost-effective investments.
Undersized shore power charger: if you only stay at a campsite for a few hours, you want to charge quickly. A 10A charger takes 20 hours to fill a 200Ah battery.
No coordination between chargers: when multiple sources charge simultaneously, one charger can raise the voltage causing the other to stop charging before the battery is full. Prevent this by choosing chargers that communicate with each other via a shared protocol (for example, linked charge controllers from the same manufacturer). This synchronises their charge phases and ensures optimal use of each source.
Calculate your charging strategy
Use our free tools to calculate your charging times and simulate your energy balance.
Frequently asked questions
- Can I go without solar panels?
Yes, if you drive regularly (B2B charger) and/or frequently stay at campsites with shore power. But solar panels give you more freedom when wild camping and cost nothing after purchase.
- Can I use all three sources simultaneously?
Yes, most modern charging systems (e.g. Victron) support this. The battery bank accepts current from all active sources until the maximum charge rate is reached. Just ensure the total charge current does not exceed your battery's rating (usually max 0.5C for lithium).
- How many solar panels do I need?
That depends on your daily consumption and travel area. As a rule of thumb: 150Wp per 500 Wh daily consumption in Southern Europe (summer). The extra 50% margin ensures you not only cover daily use but also replenish your battery. In Northern Europe or winter you need double. Use the Super Wiring Wizard for a calculation with your own figures.
- Can I charge my lithium battery in frost?
Not while the cells themselves are below freezing. The battery management system usually blocks it, but do not assume every battery does. Look at cell temperature rather than outside temperature: a battery inside a heated van can be perfectly warm while it freezes outside. Batteries with built-in heating solve this by warming themselves first.
- How long does alternator charging take?
That depends on your B2B charger's rating and on how empty the battery is. A 30 amp charger puts in roughly 30 Ah per hour of driving, so a half-empty 100 Ah battery is full after barely two hours on the road. Drive twenty minute hops and you add 10 Ah each time, which is less than a fridge uses on a warm day.
- Does my battery need to be full every day?
With lead: yes, as much as possible, because a lead battery left half full for days sulphates and loses capacity. With lithium iron phosphate: no. That battery is happy cycling between roughly 20 and 90 percent, and sitting at 100 percent constantly is not better for it. Full charging on lithium mainly serves to let the management system balance the cells, and that need not happen daily.
- Is a generator worth having in a camper?
Rarely. It is heavy, noisy, needs fuel and storage space, and in most places where you park up free a running generator is unwelcome or not allowed. For someone staying put for long winter periods with high consumption it can help, but in most campers the same money pays back better in extra battery capacity or an extra solar panel.