Updated March 2016
Electrical converters in RVs supply 12 volts from 230 volt power. They work well from 230 volts, but not for long-term camping. Here’s how to fix the problem.
Electrical converters in RVs such as camper trailers, caravans and motor homes, supply 12 volts dc from 110/220 volts ac (USA) and 230 volts ac in Australia/NZ and most of Europe. These converters are intended for RV rental users, private owners for casual use, and for those spending most nights on 230 volts (or 110 volts) in caravan parks. Their purpose, to quote one maker, is to ‘provide a [110/230 volt run] dc power system, with optional battery backup’. Another maker describes it as ’emergency power’.
The ‘battery backup’ supplied usually has limited capacity. It is intended for limited and occasional use. Whilst 110/230 volts is available, lights and appliances are powered (at about 13.65 volts dc) directly from the converter. Energy is only drawn from the battery if/when a 110/230 volts ac supply is not there.
Typical up-market converter. Pic: setek.com
Electrical converters in Rvs such as camper trailers, caravans and motor homes work well and reliably for their intended usage. That usage does not extend to providing power for free camping for more than one night. Nor do their vendors suggest they do.
Most cope with one overnight stay if the vehicle has LED lights and (only) with the appliances originally installed. The vehicle must then be driven for some hours the following day, and/or recharged every second night. This is best done from a 230 volt supply via separate high output battery charger.
Free camping usage however requires a system that runs normally from the RV’s alternator, solar or a generator charged battery. It preferably uses mains (grid) 110/230 volt only as ‘emergency power’ to recharge batteries fast.
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 and a further 10 hours to fully charge.’ Another advises that charging that same size battery ‘requires up to 70 hours’. Overnight usage away from 110/230 volt power typically discharges such RVs’ battery/s by 60%-70%. The inbuilt charging system thus precludes fully 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, but only buyers with technical understanding are likely to understand the implications. RV vendors may explain how to use the system. They rarely advise that usage does not include extended free-camping. (The converter instruction manual is not always given by the RV vendor to the buyer anyway).
Voltage Drop Problems
The original electrical converters in RVs cannot be modified. There are replacement converters that charge at higher voltage. These may only partly assist. This is because most converters produce 13.6-13.65 volts (not the 12.6 or so volts that equipment typically requires). This enables boat, camper trailer, caravan and motor home makers to use cable that may be only a quarter or so of the gauge otherwise needed when a 12 volt battery powers the system. As a result, part or all of that RV’s related cable may lose up to one volt when run at a battery’s typical 12.6-12.0 volts.
At least 70% of all RVs made and/or sold in Australia/New Zealand have these converters. In the USA it is a probable 99%. It is unclear how many of these electrical converters in RVs have associated lightweight cabling, but many do.
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.
It is often suggested to replace by a high quality battery charger and or dc-dc alternator charging. Either or both assist but, if the vehicle has been wired using the converter makers’ typical recommendations, some cabling will need upgrading. These are those associated with charging. They include the main battery cabling, fridge cabling (essential), and the water pump’s. Lighting cable will be fine for LEDs. If not change whatever is there to LED (they draw far less current so the existing cable will be fine).
Increasing battery capacity (alone) is pointless. Apart from the huge voltage drop, the converter’s charging is inadequate for any purpose other than that which its maker intended. A high quality battery charger will charge the battery much faster, but the appliances (particularly any compressor fridge) will not work remotely as intended unless that cabling is upgraded.
With decent wiring in place (or in the unlikely event if will be adequate as is), the ideal solution is to install a BMS (Battery Management System) that includes the 100% recommended dc-dc alternator charging, plus solar regulation, and often a 15-35 amp multi-phase charger, plus energy monitoring.
It can alternatively be done using separate units such as a dc-dc alternator charger, and a serious multi- stage 110/2130 volts battery charger. If so, buy all from the same maker (or vendor) to ensure that they are 100% compatible.
For the technically minded
A typical converter works much as shown below. Most are 110/12 volt or 230/12 volt transformers with a full- wave bridge rectifier and possibly smoothing capacitance. Some include a direct 12 volt input. As shown that ‘input’ is simply a few centimetres of wire plus possibly a diode (to prevent possible reverse flow). That diode however introduces up to 0.6 volt drop – so reduces alternator charging to snail’s pace.
Typical basic converter. Pic: Copyright caravanandmotorhomebooks.com
In most, the battery floats across the 13.60-13.65 volts output via a sensor that typically limits float current to 0.8-1.5 amps. An override usually enables charging at higher current if the battery drops below a certain level of charge (typically 10.5 volts), but at a fixed 13.6 or so volts – not nearly sufficient for deep and reasonably rapid charging.
A few converters include multi-phase charging, but usually via fixed voltages for bulk, absorption and floating – not the constant current required for effective initial bulk cycle (typically 80% of the entire charge time).\
See also Article Charge Batteries Faster and Deeper.
This article relates specifically to the use of converters when used for a purpose for which they are not intended. No part is intended to imply or suggest that they are deficient in any way if used for the purpose for which they are 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 will save you many times its cost.