REDARC Smart Start SBI12D12V 100A dual-sensing smart battery isolator

Overview

The SBI12D is the dual-sensing version of the 12V, 100A Smart Start isolator. It watches both batteries and closes its solenoid when either exceeds 13.2V, so in addition to alternator charging of the auxiliary battery it lets a solar regulator or AC charger connected to the auxiliary battery top up the start battery. Size, 400A inrush rating, standby current below 5mA and LED fault indication match the SBI12. REDARC also documents start assist with a momentary push-button on the override wire.

• 12V and 24V models rated 100A or 200A continuous
• Connects at 13.2V (26.4V), separates below 12.6V (25.4V)
• D models sense both batteries for solar or AC top-up
• LED fault codes for over-voltage and contact voltage drop
• Standby current below 5mA, silver solenoid contacts
• Optional override wire for start assist and remote LED

How it works

The Smart Start SBI is a solenoid priority isolator for vehicles with two battery banks. A microprocessor watches the start battery: once the alternator has raised it to 13.2V (26.4V on 24V models) for five seconds, the solenoid closes and the auxiliary battery charges in parallel. When the start battery falls to the off threshold for ten seconds, the auxiliary battery and its loads are disconnected, so fridges and lights cannot flatten the battery needed to start the engine.

Dual-sensing D models monitor both terminals and close the solenoid when either battery exceeds 13.2V (26.4V). A solar regulator or mains charger on the auxiliary battery can then top up the start battery as well. Unlike a diode isolator, the solenoid path does not add a diode voltage drop to the charging circuit.

Key features

The 100A models (SBI12, SBI12D, SBI24, SBI24D) measure 75×70×80mm, weigh 200g and accept 400A inrush. The 200A models (SBI212, SBI212D, SBI224, SBI224D) measure 90×95×100mm, weigh 600g and accept 600A inrush, which suits heavy-duty and commercial vehicles or winching from both batteries. All draw under 5mA in standby, suppress solenoid voltage spikes and use silver contacts that REDARC rates as suitable for marine use. The SBI12KIT bundles an SBI12 with pre-terminated cables and fuses.

Installation and compatibility

Mount the isolator close to the start battery and away from direct engine heat, and fit fuses or circuit breakers at the battery end of both positive cables. REDARC's cable table for 0–3m runs gives 60A fuse and 8mm² cable without override or 100A and 21mm² with it on 100A models, and 125A with 21mm² or 200A with 35mm² on 200A models. The control terminals must never be connected, as this voids the warranty.

REDARC limits the SBI to lead-acid types (standard, calcium, gel, AGM, SLI and deep-cycle) and recommends start and auxiliary batteries of similar chemistry. The blue override wire can drive a dash LED or, through a momentary push-button, link the batteries manually to assist starting. Positive-earth vehicles are supported after contacting REDARC.

Monitoring and fault indication

A red LED shows when the solenoid is closed and both batteries are linked; it may stay lit for hours after the engine stops until the start battery drops to the off threshold. Two flashes signal over-voltage above 15.5V (31V), in which case the isolator opens to protect the other battery. Three flashes mean more than 1V has been measured across the contacts for over 30 seconds, typically excessive current or poor wiring, and the auxiliary battery is disconnected.

Questions and answers