by Collyn Rivers - Updated 2020

Electrical converters in RVs supply 12 volts dc from 230 volts ac in Australia/NZ, and most of Europe. These converters are intended for RV rental users, private owners for casual use, and those spending most nights in caravan parks. Their purpose, says one maker, is to ‘provide a dc power system, with optional battery backup’. Another maker describes that backup as 'emergency power'.

The ‘battery backup’ has limited capacity. It is likewise intended for limited or occasional use. Where 230 volts is available, lights and appliances are powered directly from the converter. The battery is used only when 230 volts ac is not there.

Typical up-market converter. Pic: setek.com

Electrical converters in RVs - unsuitable for free-camping

Electrical converters in RVs work well and reliably for their intended usage. That usage does not extend to free camping for more than one night. Nor do vendors suggest otherwise.

If the RV has LEDs, and uses only appliances originally installed, it should cope with one overnight stay. But rarely two. The vehicle must be driven for some hours the following day. And/or recharged every second night. This is best done from a 230 volt supply via a high output mains battery charger.

Free camping usage however requires a system run from the RV’s alternator, solar or a generator-charged battery. It uses 230 volts only to recharge batteries fast.

Limited charging

Most electrical converters in RVs charge batteries slowly. They do so because their output is typically only 13.65 volts. This is far too low for quick, let alone deep, charging. This is usually made clear in makers’ literature. One advises a deeply discharged 120 Ah battery so charged may ‘take 10 hours to attain 80% charge'. Plus 'a further 10 hours to fully charge.’

Another advises that charging that same size battery ‘requires up to 70 hours’. Overnight usage away from 230-volt power typically discharges such battery/s by 60%-70%. The inbuilt charging system precludes fully re-charging the following night (assuming 230-volt power). This, say, vendors, safeguards the battery from being overcharged. But no high-quality charging system overcharges batteries anyway.

The above is openly revealed in converter specifications. Only buyers with technical understanding are likely to understand the implications.

RV vendors may explain how to use the system. They rarely advise, however, that usage does not include extended free-camping. The converter instruction manual is not always given to the buyer anyway.

Voltage Drop Problems

The original electrical converter cannot be modified. Replacements that charge at higher voltage also charge faster. That, however, can only partially assist.

The limitation is that most converters produce 13.6-13.65 volts. Lighting and appliances, however, need 11.8 to 12.7 volts. Converters are intended for RV owners having 230 volts most of the time. That 13.6-13.65 volts thus enables makers to use cable far thinner than needed when running from a 12-volt battery. As a result, part or all of that RV’s related cable deliberately drops up to one volt. That's fine on 230 volts. But not when battery powered.

At least 80% of all RVs globally have these converters. In the USA it's a probable 95%. Most RVs using such converters have that lightweight cabling: it's much cheaper.

Replacing the converter

Electrical converters in RVs work well for their intended usage. They do not work well for extended free camping. If free camping is in mind there is little choice but to replace them.

Replacing the converter by a high-quality battery charger and dc-dc alternator charging assists. But if the RV has lightweight wiring, some needs upgrading. This includes all charging circuit and battery cabling, fridge cabling (essential), and the water pumps. If LEDs are not fitted, change whatever is. As LEDs draw far less current, the existing cable is fine.

Increasing battery capacity (alone) is pointless. The converter’s charging is inadequate for any purpose other than intended.

A high-quality battery charger charges the battery much faster. The appliances (particularly any compressor fridge), however, will not work as intended unless that cabling is upgraded.

With decent wiring in place a good solution is to install a battery management system. These include the 100% recommended dc-dc alternator charging, plus solar regulation. Many have also a 15-40 amp multi-phase charger. Plus energy monitoring.

You can alternatively use separate units. These may be a dc-dc alternator charger, and a serious multi-stage 110/2130 volts battery charger. Buy all from the same vendor to ensure they are 100% compatible.

LiFePO4 batteries assist

LifePO4 batteries in RVs produce from a typical 13.1 volts to about 12.9 volts. Whilst lightweight cabling imposes a voltage drop, that 13.1-12.9 volts is much higher than with other types of battery. These batteries also charge to at least 80% from 13.65 volts. They do so, however, very slowly. It's better by far to scrap the converter and install a high-quality charger.

For the technically minded

A typical converter works much as shown below. Most are 110/12 volt or 230/12 volt transformers. The have a full-wave bridge rectifier and possibly smoothing capacitance.

Some include a direct 12-volt input. As shown that ‘input’, however, is a few centimetres of wire plus a diode (to prevent reverse flow). That diode nevertheless introduces up to 0.6-volt drop. This reduces alternator charging to snail’s pace.

Typical basic converter. Pic: Copyright rvbooks.com.au

Most converters float the battery across that 13.60-13.65 volts output. They do so via a sensor, that typically limits float current to 0.8-1.5 amps. An override enables charging at higher current if the battery drops below a typical 10.5 volts). It so however at that unregulated 13.65 or so volts. This is not nearly enough for deep and rapid charging.

A few converters include multi-phase charging, but usually via fixed voltages for bulk, absorption and floating. They do not supply the constant current required for an effective bulk cycle.

Electrical converters in RVs - further information

See also Article Charge Batteries Faster and Deeper. It relates specifically to using converters for purposes for which they are not intended.

This subject is covered in depth in the author’s best selling book Caravan & Motorhome Electrics. It also covered (re solar) in Solar That Really Works (for cabins and RVs), and Solar Success (for home and property systems). My other books are the all-new Caravan & Motorhome Book and the Camper Trailer Book. For information about the author please Click on Bio.

These books have helped tens of thousands worldwide to make the right decisions. Any one of them will save you many times its cost.