Collection: Contactors, solenoids & disconnectors

Contactors, solenoids and disconnectors: ordering high-current battery circuits on board

This collection groups components that control or interrupt a high-current battery circuit: power solenoids, magnetically latched contactors, low-voltage disconnectors and timed relays. Their role is not to automatically split the load between two battery banks, but to cleanly open or close a DC circuit based on a command, a delay or a voltage threshold.

For automatic load splitting between engine battery and service bank, see the Battery Chargers collection instead. Here we focus on power interruption, remote control, protection against deep discharge and starter circuits.

L-Series Solenoids: simple 12/24 V control

The Blue Sea L-Series 150 A and Blue Sea L-Series 250 A solenoids are used to switch a DC circuit remotely without routing high current to the control panel. They suit permanent or intermittent high-current circuits: powering a secondary panel, controlling high-draw equipment, starter circuits or centralized power interruption.

• 150 A: compact solution for 12/24 V circuits with moderate current draw, featuring low coil consumption.
• 250 A: heavier-duty model for larger cable cross-sections, battery banks and main circuits.
• IP67 on L-Series models: useful in damp compartments or areas exposed to spray.

ML Solenoids: high current without hold current

The ML (Magnetic Latch) models such as the Blue Sea ML 7701 12 V, the Blue Sea ML 7718 12 V and the Blue Sea ML 7719 24 V are bistable contactors. They change state on a pulse and remain open or closed without consuming hold current. This is useful on a boat where a continuously powered coil eventually overheats and wastes power.

These models target very high-current circuits: 500 A continuous depending on wiring configuration, higher intermittent current, and strong starting capacity. They require proper wiring: cable cross-section, terminals, fuses, busbars and battery isolators must be sized with the same care as the contactor itself.

m-LVD and ATD Disconnectors: protect the battery or time a power cut

• Blue Sea m-LVD 7635: 12 V, 65 A continuous low-voltage disconnect that cuts non-essential loads when battery voltage drops below an adjustable threshold. Useful to preserve starting reserve or prevent deep discharge.
• Blue Sea ATD 7615: 120 A timed disconnect that can cut a circuit after a delay or act as a management relay depending on the configured mode. Suitable for equipment that must not remain powered indefinitely after engine shutdown or loss of a control signal.
• BEP 12 V 100 A solenoid: starter motor solenoid rated for intermittent service and high current peaks.

Selection criteria

• Intended function: remote control, safety cut-off, low-voltage disconnection, timing, or engine starting.
• Continuous and intermittent current: nominal rating is not enough; also check starting current, permissible duration and associated cable cross-section.
• Control voltage: 12 V, 24 V or multi-voltage control circuit depending on model.
• Coil consumption: a standard solenoid can draw power as long as it remains closed; an ML bistable model avoids this hold current.
• Environment: IP66 or IP67, ignition protection, gasoline engine compartment, proximity to batteries, ventilation and maintenance accessibility.
• Overall architecture: the contactor does not replace a fuse, a serviceable battery isolator, or a clear distribution diagram.

Skysat advice

Before selecting a contactor or solenoid, sketch the circuit: power source, load, upstream fuse, cable cross-section, control method and expected fault behavior. An m-LVD protects a battery from deep discharge; an ATD prevents a load from remaining powered after use; an L-Series solenoid switches a circuit; an ML serves very high currents with minimal hold current. These are not interchangeable products.

Pair with fuses, battery isolators, busbars, electrical cables and battery monitors to build a maintainable and safe installation.