BEP Marine 701-MD Motorised Battery Switch & 701-MDVS Voltage Sensitive Switch — Operation, Wiring & Fault Codes

Overview

Both units are built on BEP's proven 701 rotary switch mechanism with a motor drive added, so each battery bank can be switched from a remote panel while the switch itself lives right at the batteries. That keeps the heavy cable runs to starters, inverters, and thrusters short, minimizing voltage drop. Shared ratings: 275 A continuous, 455 A intermittent, 1250 A cranking, 32 Vdc maximum, ignition protected, twin 10 mm (3/8") tin-plated copper studs, surface or recessed mounting, and only 15 mA draw with the switch off. Recommended maximum cable is 50 mm² (larger cable up to 00/70 mm² must be strain-relieved).

701-MD — remote master disconnect

The 701-MD is a remotely operated on/off battery switch. A typical coach installation pairs it with a key switch at the dash (BEP 722-KS, or any standard on/off switch): turn the key on and the switch motors from Auto Off to Auto On; LEDs on both the switch body and the key switch show status. The knob can always be operated by hand — press the control knob in and turn clockwise to Manual On or counter-clockwise to Manual Off. Manual mode wins: while the knob is in a manual position, remote commands are ignored and an attempted auto operation just flashes the LED for 3 seconds. The knob must be returned to Auto Off before remote operation works again — the classic "remote switch stopped working" call is a knob someone left in manual.

Wiring rules that cause most faults: the INPUT stud must be wired to the battery side (output feeds the loads). The unit's black negative wire must come from the same battery that the switch is isolating, and each unit gets exactly one negative — taking the negative from another bank makes the switch behave erratically. The red/green/black control cable terminates in the supplied Wago plug to the remote on/off switch and LED.

701-MD LED codes (auto mode): off = switch off; on = switch on; flashing = motor travelling between states; rapid flash (0.1 s on / 0.1 s off) = supply voltage outside the 8–30 V auto operating range. In manual mode the LED is simply on or off with the switch position.

701-MDVS — voltage-sensing bank paralleling

The MDVS adds voltage-sensing logic so two banks (typically house and start) charge as one whenever a charging source is present — the same job as an ACR but implemented in a 275 A rotary switch with a manual knob and an emergency-parallel feature. Order the model matching system voltage: 701-MDVS (12 V, 8–15 V range) or 701-MDVS-24V (15–30 V range). Values below are 12 V / 24 V.

• Engages when the start battery exceeds 13.7 / 27.4 V for 5 seconds, or the house battery exceeds 13.7 / 27.4 V for 5 minutes — it senses which side the charge is on and applies the appropriate timing.
• Disengages (engine charging): if the paralleled banks sag below 12.2 / 24.4 V the LED mid-flashes (1 s on / 1 s off) for 5 minutes, then the switch opens.
• Disengages (non-engine or no charging source): below 13.0 / 26.0 V for 5 seconds the LED goes out and the switch opens 3 seconds later.

Emergency parallel: a remote momentary button forces the banks together (flat start bank scenario). Parallel holds for 10 minutes; if either bank has reached 13.0 / 26.0 V by then it stays engaged and keeps charging, otherwise it drops out. Holding the button 5 seconds disengages at any time. Manual override: push the knob in and rotate to Manual On or Manual Off; when the unit later tries an automatic action while overridden, the LED goes to rapid flash to tell you it is being blocked.

MDVS LED codes: auto mode — on = engaged, off = disengaged, 1 s/1 s flash = low-voltage disconnect countdown, rapid flash = voltage outside specification (below 8/15 V or above 15/30 V). Manual mode — rapid flash = manual override active. Emergency parallel — long flash (5 s on / 0.5 s off).

The MDVS carries the same negative-wire rule as the MD: black negative from the battery being isolated, one negative per unit, and the two control cables terminated in the Wago plug. In a typical BEP system drawing, each bank also has its own 701/701-MD isolator switch, with the MDVS bridging the two banks.

Service approach

These are sealed motorised switches — there is no field overhaul. Service consists of annual inspection (stud torque, corrosion, correct labels from the BEP 713 label set), a functional test of remote and manual operation, verifying LED behavior against the tables above, and replacing the unit if the motor, contacts, or sensing logic fail. Any erratic engagement pattern should send you to the negative wire and supply voltage before condemning the unit.