Battery disconnect relay: a must for your motorhome.

The battery disconnect relay is a standard part of the electrical system in any motorhome. With a starter battery and a supply battery on board, the component is essential. This is because the battery disconnect relay connects both energy storage devices while driving so that they are charged. If the engine and alternator stop running when the vehicle is stationary, the relay kicks in and cuts the connection. This prevents the loads from drawing power not only from the on-board battery, but also....

access the starter battery. If this did not happen, the starter battery would probably be so empty after a long night of watching TV that the engine would no longer start.

What is the function of the relay?

A relay is an electrical switch that has two positions. The battery disconnect relay in a vehicle such as a motorhome is used to disconnect the starter battery and the on-board battery when the vehicle is stationary (position 1) and reconnect them for charging (position 2). The two batteries are thus not directly connected in parallel, because that would have too many disadvantages: For one thing, the batteries would discharge each other when the vehicle is stationary for a long time. For another, the battery disconnect relay prevents defective consumers from damaging the starter battery. Compared to normal automotive relays, the battery disconnect relay for RVs is equipped with special contacts that can switch higher currents.

Simple or electronic - these are the differences

In terms of design and operation, there are two types of battery disconnect relays: simple and electronic. The simple models are located in the circuit between the two batteries and are connected to the alternator via the D+ line. If a vehicle has a starting and supply battery, the simple battery disconnect relay is usually already installed at the factory. The electronic version is equipped with voltage monitoring and does not require a D+ switching signal. It connects the batteries - when 13.7 volts are reached on one battery - fully automatically and disconnects them as soon as one of the two batteries has dropped below 12.8 volts. Not only is this more convenient, but it also makes installation easier by eliminating the need to search for D+.

Which is better: charge booster or battery disconnect relay?

Anyone who is concerned with battery management quickly comes up against the question of whether a battery disconnect relay is sufficient for their own requirements or whether it would be better to install a charge booster. Basically, the charge booster performs the same function as a relay: it couples the starter battery and the on-board battery so that both are charged while driving. At the same time, the charge booster optimally charges the body battery to be charged, guided by the characteristic curve. The respective battery type can be set on the booster. Connected via sense lines, it increases the charging voltage so that differences due to losses from cables that are too thin are compensated. A battery disconnect relay is already present in most new motorhomes, but a charge converter is not.

The charge booster is useful if you are ...

want to be self-sufficient and independent of the power outlet,
want to charge the body battery quickly and efficiently while driving,
have a high energy demand on board
or have problems charging the supply battery with your Euro 6 motorhome.

A battery disconnect relay is all you need if you ...

spend a lot of time on pitches and use shore power there,
start the journey to the next campsite with already fully charged batteries,
generally consume little power
or do not need a self-sufficient power supply for longer stays.

The right battery disconnect relay for your motorhome

In FraRon's online store, you can get various battery disconnect relays from Victron Energy for 120 to 400 amps. For modern lithium battery systems are specially matched disconnect relays available. With these components, you benefit from the fact that both the on-board battery and the starter battery are available to the consumers as total capacity as long as the voltage range of the starter is good. We will be happy to answer your questions and help you find the right isolating relay for your motorhome. Simply call us at +49 (0)6024 6341 560 and take advantage of our expert advice! In addition, our experts will be happy to take care of the installation for you with the competent installation service.