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Split Charge Relays

Split Charge Relays switch current to the caravan’s leisure battery and/or fridge during towing, but in order to protect the car’s battery, become open circuit when the engine is switched off. They may be ignition controlled, requiring a separate signal wire connected from the ignition switch to the device, or they may switch automatically, with an electronic circuit within the device remotely sensing the state of the car’s alternator/battery, and only switching when sufficient current is available.

These Split Charge Relays are able to cope with high output fridges found in modern caravans, which because it has such a high output in such a small package has become the preferred format.

Bypass Relays


Bypass relays are used where the cars own lamp circuits cannot support their shadow circuits on the trailer or caravan. This may be because the circuit may not be rated to take the extra load of the trailer, or because the cars own bulb failure monitoring system might become confused with the extra load from the trailer lamps. In their simplest form, bypass relays operate by taking a signal current from the car’s lamp circuit, which then switches a relay and with it current to the equivalent circuit on the trailer from a supply derived directly from the car’s battery.

Monitors or BuzzersMonitors

Monitors are devices that sense the flow of current to the trailer or caravan flashers, and fulfil a legal requirement to warn of a bulb failure on the trailer flashers.

The simplest device is the audible monitor which is boot fitting, and which interrupts the individual flasher circuits at the point at which the 12N cable attaches to the car’s flasher circuits.

Feedback to the driver is via an internal 2khz electromagnetic buzzer, which is sweeter sounding than the old style 500hz buzzer that it replaces, is at a pitch that is more responsive to the ear, and is much more reliable.