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Power mix

Having a mix of power generation approaches will usually be more dependable and less expensive than relying on only one. For example, it is expensive (and maybe impossible) get Big Current with solar alone and difficult (or even impossible) to complete charging on alternator alone. But small amounts of both combine to make a workable and inexpensive charging system.

For this reason the solar + alternator combination is the most common and effective charging approach for vehicle dwellers. But there are times when one of these (or some other source) might do the majority of heavy lifting, or other forms of charging might be best suited to your particular use case.

Note: charging concurrently from multiple sources is normal and generally beneficial.


Alternator charging is usually the biggest bang-for-buck charging offgrid.1) It is automatic2) and will charge whenever you are driving. Consider the alternator as the backbone of your charging if you drive daily or near-daily.

For many people a plain combiner (relay, solenoid, VSR, “isolator”) will be cheap and highly effective for Bulk charging. Direct charging like this will often be most efficient in early morning when bank voltage is the lowest.

However, some cases suggest a more expensive DC-DC charger setup:

  • mandatory if you have a “smart” (variable voltage) alternator, common in Europe on recent models
  • mandatory if you have a large house bank (of any chemistry) compared to your alternator's output rating
  • suggested if you want a more predictable charge rate; DC-DC charge rates are typically consistent all the way through Bulk stage, no matter what the bank voltage is.
  • suggested if you want more of a hands-off approach

Alternator-only charging can work with lithium banks but for technical reasons solar or shore-power charging is usually required with lead batteries.


Some solar should probably be included in every build with few exceptions; it is a silent, long-lived charging source that can output whatever voltage your batteries need.

mounted solar

Having panel permanently mounted on the vehicle can be a quality of life upgrade; it is charging anytime the sun is falling on them.

Consider mounted solar as a backbone of your charging if you spend a lot of time emplaced in open areas with good insolation. Camping in non-forested areas, for example.

  • makes power whether or not you get up to set out the panels – they are already set up
  • can be very cheap if you source used panels (larger systems) or use simple PWM controllers with alternator-augmented systems.
  • works well - in open areas
  • works poorly - in partial shade

portable solar

Portable solar can work alone, can augment the mounted panel3), can be placed in sun, and can usually be angled for maximal harvest.

Consider portable solar as a backbone of your charging if you spend a lot of time emplaced in areas of shade adjacent to areas with clear sun. In a forest with canopy openings, for example.

  • must be set out to work
  • works well - when set out in the sun, especially when tilted toward the sun.
  • works poorly - when not deployed, like for people who move a lot or who do not diligently set up / take down the portables.

One way to predict if you will reliably set up the portables: how full is your vehicle's gas tank and your phone battery right now? If you are a “never let it get low” type you will likely set out portables consistently. If you are a “always running on [E]mpty” type you are less likely to set out the portables. This is a not a moral judgement, but rather a way to help assess whether or not portables would be a good source of power for your use case.

shore power

Having access to shore power (grid power) is like winning the vandweller lottery. It is cheap and practically unlimited. As long as you can keep your demand under ~1500w you can do practically whatever you want. Run a space heater? Microwave? Induction cooktop? Charge your batteries? Sure (just not all at the same time).

Consider shore power charging to be the backbone of your charging system if you regularly have access to shore power. E.g. you live in a house, rent RV spots with pedestal power, can use power at school/work, “moochdock” in driveways with access to an outdoor outlet. Even if you have to pay for the use of the power it will still be cheaper than off-grid approaches.

You can get away with a very simple, low-power, single-stage shore power charging setup

  • with lithium
  • with lead-chemistry batteries, if
    • you will be on the shore power for many hours a day; or
    • if you have solar helping out

You will need to spend money on a more powerful charger if your time is limited (only a couple hours each day). A multistage charger will be important for charging lead banks without solar.

More information in this article.


A generator can provide steady power regardless of ambient weather or other conditions. Generators are uncommon in vandwelling scenarios because most are charging by other means. But when they are present they are, effectively, a form of portable shore power.

Consider generator charging to be the backbone of your charging system if you already own the genny and solar is not able to meet needs due to weather or other conditions. In general, generator charging is most effective in the morning. Not only does morning charging work when the sun is low, but it will boost battery voltage up to where PWM controllers can find their feet.

bulk stage charging, at least
unless you are using a manual switch, not recommended
separate controllers
electrical/12v/power_mix.txt · Last modified: 2024/04/13 18:17 by frater_secessus