Caravan and motorhome transformers do two jobs at once: they step mains 230V AC down to 12V DC so your habitation electrics keep running when you're on an EHU pitch, and they manage the charging of your leisure battery at the same time. This collection covers 230V-to-12V power unit transformers, combined transformer/charger units, battery management systems, solar battery maintainers, replacement PCBs and control boards, and the connecting kits you need to wire it all in. Whether you're replacing a dead unit in a Bailey, Elddis, Coachman or Swift van, or building out a new campervan conversion from scratch, getting this component right is the foundation of a reliable onboard electrical system.What amperage transformer or charger do I need for my caravan or motorhome?
The answer depends on your 12V load and leisure battery capacity. A 10A unit suits lighter-use caravans running a few lights and a water pump. Most touring caravans and motorhomes with a full complement of 12V appliances need a 20A unit, which delivers 240W of continuous DC output. High-demand motorhomes or vans with large battery banks are better served by a 25A or 30A unit.
Brands in this range include BCA (whose power units are OEM-fitted across a wide spread of UK-manufactured caravans), Sargent (whose PX310 is a direct replacement for many factory-fitted Nordelettronica units), Dometic PerfectCharge (the MCA1215 15A and MCA1225 25A intelligent chargers), Waeco, and Oxford (whose Oximiser 3X and Solariser solar maintainer sit at the standalone battery management end of the range). The BCA range spans 10A, 20A and 30A output units, with the 13.8V DC output designed to power 12V appliances and deliver a float charge simultaneously. The Sargent PX310 is a 300W 3-stage intelligent unit with an LCD display showing charging status, configurable battery chemistry settings, and a silent fan mode for overnight use. The Dometic MCA1225 steps up to 25A output with compact, lightweight construction suited to motorhomes running larger leisure battery banks.
Campervan converters working through a BCA relay system will also find the PCB184MD relay control board and the EC115/EC155 connecting kit in this collection, alongside the PSU 2005 power supply unit, which protects both mains and 12V equipment while supplying a regulated 12V output. This collection sits within the broader 230V Equipment range, and pairs naturally with 230V plugs and sockets, EHU hookup leads, inverters, and if you're building off-grid capability, with solar panels and lithium power supply components elsewhere on the site.
This range is used by three main groups. Existing caravan and motorhome owners replacing a failed OEM unit need to identify the correct amperage and connector type before buying: many factory-fitted units from brands like Lunar, Bailey, Coachman, Elddis and Swift use BCA or Nordelettronica chargers, and the Sargent PX310 comes with an adaptor harness precisely because its connector differs from the PX300 it replaces. Campervan converters building from scratch on a VW Transporter, Ford Transit Custom, Mercedes Sprinter or Fiat Ducato typically specify a 20A or 30A BCA unit wired into a relay housing, giving a clean plug-and-play installation for the entire 12V habitation circuit. And battery maintenance users, who store their leisure vehicle for winter or extended periods, look to standalone chargers and solar maintainers to keep batteries in condition without cycling them down completely.
The most common mistake is undersizing the charger relative to the total 12V demand. A 10A unit running heated blankets, a fridge, a water pump, internal lighting and a TV simultaneously will be overwhelmed. A rule of thumb: your charger should comfortably cover the peak 12V draw of your appliances plus have headroom to service the battery. A second, less obvious issue is battery chemistry compatibility. Standard transformer/charger units deliver a lead-acid or AGM charge profile, and most BCA and Sargent units are specified for lead-acid and AGM batteries. If you've upgraded to a LiFePO4 lithium battery, check that the charger has a dedicated lithium mode or lithium wakeup function: the PX310 includes a lithium wakeup mode, but standard float charging can degrade lithium cells over time. For replacement jobs, always check the connector type before ordering, as the PX310 uses different connectors to the PX300 it supersedes and requires the conversion harness if plugging into the existing loom.
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Frequently Asked Questions
What's the difference between a caravan transformer and a battery charger?A transformer (also called a power unit) converts 230V AC mains into 12V DC to power your caravan's 12V habitation electrics directly. A battery charger takes the same 230V supply and uses it to recharge your leisure battery. Most modern units combine both functions: they power your 12V appliances and charge the battery simultaneously, distributing current between the two based on demand.What amperage transformer do I need for my caravan?A 10A unit suits caravans with modest 12V loads such as lighting and a water pump. A 20A unit (240W output at 13.8V DC) covers most touring caravans and motorhomes running a fridge, pump, lights, TV and heating fan simultaneously. A 25A or 30A unit is suited to motorhomes with larger battery banks or higher appliance loads. Always size the charger to comfortably exceed your peak 12V draw rather than match it exactly.What is the Sargent PX310 and what does it replace?The Sargent PX310 is a 300W 3-stage intelligent battery charger and power supply designed for caravans and motorhomes. It replaces the earlier PX300 and is also a compatible replacement for many Nordelettronica (NE143) units fitted as standard in factory-built leisure vehicles. It features an LCD display showing charging status, configurable profiles for different battery chemistries, a silent fan mode for overnight charging, and a lithium wakeup mode. Note that the PX310 uses different connectors to the PX300, so a conversion harness is required when fitting it into an existing PX300 loom.Which caravan brands use BCA transformers as standard?BCA (Powerpart) power unit transformers are fitted as OEM components across a wide range of UK-manufactured leisure vehicles. The 20A dual-stage unit (PS306) is used in Coachman Pastiche, VIP and Laser models (up to 2015), Elddis Encore motorhomes and Equi-Trek Evolution, among others. The 20A float-charge power supply (PS276) covers most Elddis and Compass models. If you're unsure which unit you have, check the part number on the label of the existing unit and match it to the BCA reference before ordering.Can I use a standard caravan transformer to charge a lithium (LiFePO4) leisure battery?Most standard caravan transformer/charger units use a lead-acid or AGM charge profile, which includes a float stage that lithium batteries don't need and can find harmful over time. If your charger has a dedicated lithium mode or configurable charge profile (like the Sargent PX310's lithium wakeup mode), it can be set up for LiFePO4 batteries. Without a lithium-specific mode, AGM is the next-best setting, but for best results and battery longevity, a charger with a proper lithium charge algorithm is the correct choice when using LiFePO4 cells.Can a caravan run on EHU without a leisure battery fitted?Some transformer units, including the Sargent PX310 and BCA units, can operate in PSU mode without a battery fitted, outputting a constant regulated 13.6V to power 12V appliances directly from the mains. However, fitting and running a leisure battery alongside the transformer is always recommended: the battery acts as a voltage buffer, stabilising the 12V supply and protecting sensitive 12V components from voltage spikes. It also provides power for habitation electrics if the EHU supply trips.What is the difference between a 2-stage and 3-stage caravan battery charger?A 2-stage charger moves through a bulk charge phase and then a float maintenance phase. A 3-stage charger adds an absorption phase between the two: once the battery reaches approximately 80% charge, the charger holds at maximum voltage and reduces current progressively until the battery is fully charged before moving to float. The 3-stage process is gentler on the battery, reduces charge time at the top end, and is better suited to AGM batteries. Most quality transformer/charger units in this range, including the Sargent PX310 and Dometic PerfectCharge, use 3-stage charging.What does the PCB184MD relay control board do in a BCA system?The BCA PCB184MD (which supersedes the earlier PCB147 and PCB164MD) is the control board for BCA relay control systems used in many caravan and campervan 12V wiring installations. It manages the switching of 12V circuits when mains power is present, and allows the BCA power unit transformer to distribute current correctly between the habitation load and the leisure battery. It's a direct replacement component for failed boards in existing BCA-wired installations.Is a solar battery maintainer the same as a mains transformer charger?No. A solar battery maintainer, such as the Oxford Solariser in this range, uses a small photovoltaic panel to trickle-charge a 12V battery from daylight, preventing self-discharge during storage. It's not designed to provide power to habitation appliances or to charge a deeply discharged battery quickly. A mains transformer/charger unit requires a 230V EHU connection to operate and delivers significantly higher output currents (10A to 30A). The two serve different purposes: the solar maintainer is a storage tool, the mains transformer is a site-use power supply and active battery charger.What voltage does a caravan transformer output?Most caravan power unit transformers output 13.8V DC under normal operating conditions, which is slightly above the nominal 12V of a leisure battery. This higher voltage is needed to push charge current into the battery rather than simply matching its resting voltage. During the absorption stage of a 3-stage charger, voltage may rise briefly to 14.4V to 14.7V depending on the battery chemistry setting selected. In PSU mode (no battery fitted), units like the Sargent PX310 output a constant 13.6V to run 12V appliances safely from mains power alone.
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