PREVIOUS: RV Electrical System: Design
Central to the system and most visible are the batteries, which have to supply the electricity during the days when a hookup is not available. Two basic types are currently used in RV’s:
- Lead-Acid Batteries
- Starting Battery – Use only to start the vehicle; its plates are too thin.
- RV/Marine Deep Cycle Battery – Used as start and house battery. Don’t use.
- True Deep Cycle Battery – Has thick plates made to store and hold your power.
Flooded or AGM (Absorbed Glass Mat)
Flooded batteries, need regular maintenance, but their price make it the most affordable solution.
AGM’s are sealed, can be charged faster but are quite expensive.
Lead-Acid batteries cannot handle overcharging, partial recharging, nor discharging more than 50%. Though a periodic overcharge (equalization) is needed to prevent lead sulfate to accumulate.
- Lithium Batteries:
The new guy on the block. Not fully tested yet (as of 2015) for RV use, the LiFePO4 (Lithium Iron Phosphate) version is promising to change the RV lifestyle. Its major benefits are:
- Lifespan – 2000 to 5000 cycles (vs. AGM’s 500 to 1000 – vs. Flooded 300).
- Maintenance Free – like AGM’s, unlike Flooded.
- Better Charging Profile – fast, no phased charging, no equalization, accepts partial charging without harm, make better use of solar power, 100% efficiency (vs. Lead-Acid at 85%), low voltage sag.
- Higher Discharge – up to 85% (vs. 50% Lead-Acid).
- High Current Loads – better suited for induction cooktops and microwaves.
- Size & Weight – one third the weight and one half the size of Lead-Acid batteries.
These batteries have so many advantages over the current lead-acid technology, but also a few drawbacks. Cost is the major issue, an integrated BMS (Battery Management System) is needed and the batteries are still somewhat untested for RV use (the main question that remains is the longevity or the maximum number of cycles).
Lithium seems to have only major advantages in exchange for a much higher upfront payment and the risk of being one of the first in applying this new technology!
The other main component for boondockers. They will produce electricity for many years, without interruption and virtually no maintenance. Their efficiency can increase dramatically by aligning them with the sun, but most of us will compensate by installing more panels.
- Rigid Panels:
The rigid panels have been around longest and are well tested for RV use. They often come in large sizes and can supply large amounts of electricity. Its solar cells are protected with a glass pane.
- Amorphous Thin Film:
Flexible peel & stick. A decade ago Unisolar came with amorphous thin film solar that was fairly light, easy to apply and had great low-light properties. Efficiency was low and consequently needed much roof space.
- Semi-Flexible Panels:
Have a high efficiency like rigid panels, but are still about twice as expensive. Flexible (up to 30°), thin (3/32 in. – 3/16 in.) and light weight. No roof penetration is needed. The weight issue is always quite important for van conversions, but their thickness and flexibility make them ideal for a stealthy appearance. These panels seem to have some heat issues, what may reduce their efficiency, but that can be easily remedied with one or more extra ‘mobile’ panels that store under your mattress.
The importance of correct wiring is undervalued, yet critical for the electrical system. A complete system has many components, each with their own efficiency losses (solar panels, combiner box, MPPT controller, monitor and batteries). Correct wire thickness will ideally limit voltage drop to less than 2%. Always use voltage drop charts to calculate the appropriate wire size.
UPCOMING: RV Electrical System: Sizing