Nylon 140A Dual Battery VSR Isolator Switch Voltage Sensitive Relay for Marine and RV 12V Systems

The MT003 is a voltage sensitive relay isolator designed for dual battery layouts running on 12V DC. Rated at 140A continuous with a 160A intermittent allowance, it handles the charge and load current of a typical start-plus-auxiliary arrangement without requiring the driver or skipper to remember a manual switch.

The relay monitors system voltage and links the two batteries once charging begins, then separates them again when the engine stops and voltage falls away. The result is a simple arrangement that tops up the auxiliary bank while driving or motoring, yet keeps the starting battery isolated so a fridge, winch or inverter cannot flatten it overnight.

The body is moulded in nylon — light, tough and naturally resistant to moisture, fuel splash and the constant vibration of an engine bay. With no moving parts to service and no manual knob to forget, the unit suits owners who want dual-battery management to look after itself.

• Charge linking — as system voltage climbs during charging, the relay closes and both batteries share the charge current.
• Automatic separation — when charging stops and voltage settles, the relay opens and the batteries are kept apart.
• Start battery protection — accessory loads draw only from the auxiliary bank, so cranking power stays in reserve.
• No manual step — nothing to switch, no procedure to memorise at the dock or trailhead.
• Nylon enclosure — moulded housing shrugs off moisture, fuel mist and vibration.
• Compact footprint — fits into an engine bay or battery locker alongside the batteries themselves.

Plan the layout before drilling anything — the relay sits between the two positive feeds and shares a common ground:

• Mount the unit on a dry, rigid surface close to both batteries, clear of exhaust heat and moving belts.
• Run the start battery positive to the main terminal and the auxiliary battery positive to the second terminal.
• Connect the ground lead to a clean chassis or engine block point, then check every lug for a firm seat.
• Keep cable gauge matched to the 140A continuous rating, and protect long runs with a fuse at the battery end.
• Before first use, confirm terminal torque by hand and verify the relay closes only once charging voltage is present.

• Boats — splitting charge between start and house banks on outboards, inboards and small yachts.
• RVs and campers — keeping the leisure battery charged while protecting the vehicle battery from fridge and lighting loads.
• Cars and 4x4s — dual-battery set-ups for fridges, compressors, lights and recovery gear.
• Workshops and plant — auxiliary power for trailers, compressors and mobile equipment.

• Minimum order — 1 piece, so single units and trial batches are both workable.
• Price — negotiable, quoted against quantity and packing needs.
• Capacity — 500 pieces per week.
• Lead time — 5 to 7 days for standard orders.
• Payment — T/T or Western Union.
• Packing — carton, with reinforced export packing for long-haul shipments.
• Support — application-based selection advice, batch inspection before dispatch, and follow-up on any field feedback.