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12v Relays

12v Relays

Regular price £49.99 GBP
Regular price Sale price £49.99 GBP
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Read about the relays and what they do....

Why use a relay for a campervan water pump-switch circuit?

Normally the tap switch contacts would carry the entire 12v current load at start-up. This often causes “arcing” which damages the small points to such a degree that the switch eventually ceases to function. So taps that are wired in line frequently have a short-lived lifetime.

By incorporating this relay into the circuit, helps the taps switch 70 milliamps switch to only energize the relay coil, not the pump directly. So the main current is carried by the much more substantial 40 amp rated contacts in the relay, giving you more power to the water pump. So again making your tap live longer.

Why use a VSR relay for a campervan split charge circuit?

This enables you to charge up your camper van's leisure battery using the starter battery/alternator of your vehicle. Included in the kit is a voltage-sensitive relay (VSR) that only draws power and charges your leisure battery when your starter battery is at a certain voltage. This ensures that you never end up with a flat battery in your vehicle... which is always handy.

Please note, VSR’s are only compatible with vehicles without a smart alternator, regenerative braking, or stop/start technology. If you're unsure please just drop us a message.


The Cyrix Battery Combiner is a microprocessor controlled heavy duty relay that automatically connects batteries in parallel when one of them has reached a pre-set voltage (indicating that the battery is being charged), and disconnects when the voltage decreases below float level (indicating that one or more batteries are being discharged). Cyrix Battery Combiners are an excellent replacement for diode isolators. The main feature is that there is virtually no voltage loss so that the output voltage of alternators or battery chargers does not need to be increased.

Why use an Intelligent Battery Combiner relay for a campervan split charge circuit?

Intelligent battery monitoring to prevent unwanted switching

Some battery combiners (also called voltage-controlled relays, or split charge relays) will disconnect a battery in case of a short but high amperage load. A battery combiner also may fail to connect a large but discharged battery bank because the DC voltage immediately drops below the disengage value once the batteries are connected. The software of the Cyrix-ct 12 does more than simply connect and disconnect based on battery voltage and with a fixed time delay. The Battery Combiner looks at the general trend (voltage increasing or decreasing) and reverses a previous action only if the trend has reversed during a certain period of time. The time delay depends on the voltage deviation from the trend.

Protection against overheating (due to a long duration overload e.g.)

The Battery Combiner will disengage in case of excessive contact temperature, and reengage again after it has cooled down.

No voltage loss

Battery combiners are an excellent replacement for diode isolators. The main feature is that there is virtually no voltage loss so the output voltage of alternators or battery chargers does not need to be increased.

Prioritising the starter battery

In a typical setup, the alternator is directly connected to the starter battery. The accessory battery, and possibly also a bow thruster and other batteries are each connected to the starter battery with battery combiners. When a Cyrix senses that the starter battery has reached the connect voltage it will engage, to allow for parallel charging of the other batteries.

Bidirectional voltage sensing and power supply from both batteries

The Battery Combiner senses the voltage of both connected batteries. It will therefore also engage if for example the accessory battery is being charged by a battery charger.

This has a dual power supply. It will therefore also close if the voltage on one battery is too low to operate the Battery Combiner.

In order to prevent unexpected operation during installation or when one battery has been disconnected, the Battery Combiner will not close if the voltage on one of the two battery connections is lower than 2 V.

Parallel connection in case of emergency (Start Assist)

The Battery Combiner can also be engaged with a push button (Battery Combiner remains engaged for 30 seconds) or a switch to connect batteries in parallel manually.

This is especially useful in case of emergency when the starter battery is discharged or damaged.

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