Electrical converter problems in caravans – problems when used for free camping

by Collyn Rivers

Electrical converter problems in caravans – nominal battery capacity

These converters run 12-volt appliances directly from 230-volt power. They do have a battery back-up but that battery’s capacity is only nominal. Few such converters can supply 12-volt power for more than one night away from 230 volts. One maker states that they ‘provide a 230-volt run 12-volt system, with optional battery backup’. In the USA a converter is often called an ’emergency’ supply.

Electrical converter problems in caravans – too low voltage

Apart from typically-limited capacity, there are two further electrical converter problems (when free camping). In particular, most converters produce about 13.65 volts. This is too low to speedily charge the batteries typically used. This is often made clear in the technical specifications, but not in the promotional literature.

One maker reveals that a deeply discharged 120 amp-hour battery is likely ‘to take 10 hours to attain 80% charge. And a further ten hours to fully charge’. Another advises that ‘charging requires 70 hours’. Vendors may explain how to use these systems. They may not, however, reveal this usually precludes extended free-camping.

Converters cannot be modified. The only solution is to replace it with a multi-stage battery charger. If frequently driving, it’s worth adding a dc-dc alternator charger. But this only partially assists.

The 13.6-13.65 volts converter output is a volt higher than needed by lights and appliances. RV makers realise this. Many accordingly use thin cabling. This drops the better part of one volt. That one-volt drop is acceptable when running from 13.6-13.65 volts. It is not, however, when powered by conventional batteries as these fall from 12.7 to about 11.8 volts as they discharge. Thin cable thus drops this to 12.3-12.4 volts whilst battery fed. And to 11.8 volts or so when still 50% charged.

Replacing that converter assists converter problems. But necessary also is upgrading charging, water pumping and fridge cabling. (Voltage drop is rarely an issue with LEDs.)

As explained below, however, there is now a new approach that partially assists.

Electrical converter problems in caravans – a new approach

The voltage drop problem is partially overcome by using lithium batteries. The (LiFePO4) versions used in RVs supply a constant 13.1-13.0 volts from 90% to 20% charge. They can be charged very much faster. They can also be safely discharged – to 20% remaining. All can be used in deep-cycle applications. Too light interconnecting cable, however, still introduces undesirable voltage drop but this is less of an issue with their virtually constant voltage.

LiFePO4 batteries require a management system. This system ensures equal cell voltage. It is built into some such batteries, but nevertheless, not all. They also require a specific charging regime.

Given that management system, it’s feasible to charge (to about 98% full) from a converter. LiFePO4s can be routinely discharged to 20% or less. Their usable output is thus greater than of lead-acid batteries similarly charged. LiFEPO4s charge well from alternators of 13.8-14.2 volts. Specialised DC-DC LiFePO4 alternator chargers are now available.

Redarc LiFePO4 dc-dc alternator charger. It is available in 25 amp and 40 amp versions. It also accepts solar input.

Lithium batteries are very different from lead-acid batteries. Seek expert advice before buying. See also Lithium-ion Batteries in Caravans and Motorhomes. 

See also (Charge Batteries Faster and Deeper).

Temperature effects

LiFePO4 batteries can be charged in ambient temperatures as low as -18º C. If below that, as long as they contain some charge by first being warmed by switching on a heavy load for a minute or two. (Vehicle headlights are fine for that.) If that is not feasible, see what can be done to warm them thermally.

Charge absorption is highest in ambient temperatures around 25º C (77º F), to 40º C (104º degrees F). Perfect for Australia. Less so in an Alaskan winter.

How a converter works

Most converters have an inbuilt 230/12 volt (or 110/12 volt) transformer, plus a bridge rectifier. Some have smoothing capacitors. There is usually a direct 12-volt input – but that is typically via a diode that introduces up to 0.6-volt drop. That diode is there to preclude the converter accidentally discharging the battery. It is better to have an optionally-used bypass switch. Anyone who knows their way around basic electrics can do this for you.

The RV battery floats across that 13.60-13.65 volts output. It normally charges at a mere 0.8-1.5 amps, but that charge typically increases if the battery drops below 10.5 volts. But it still only charges at 13.6 or so volts. This is far too low for adequately charging lead-acid or AGM batteries.

A few converters include multi-phase charging, but most have fixed voltages. They lack the constant current essential for deep rapid charging.

This article relates specifically to converters used for purposes other than intended. They work fine for that intended.

If considering the lithium battery approach, first read my article lithium batteries in caravans and motorhomes.

Electrical converter problems in camper trailers

Converter systems are less used in camper trailers. Where encountered however, this article equally applies.

If you find this article of interest or value you are likely to enjoy my books. They are the Caravan & Motorhome Book, the Camper Trailer Book, Caravan & Motorhome Electrics. Also, Solar That Really Works (for RVs and cabins) and Solar Success (for homes and properties. For info about the author – Click on Bio