REDARC CE40S2 40A charge equaliser 24V to 12V40A charge equaliser for 24V two-battery systems with 12V centre tap

Overview

The CE40S2 is the 40A version of REDARC's Charge Equaliser for 24V negative-earth systems built from two 12V batteries in series. It balances the lower battery, which feeds 12V loads from the centre tap, against the upper battery with up to 40A of transfer current, in trucks, buses and service vehicles. Input is 20–32V, output 6–16V regulated to half the input, and both sides need 50A fuses. It shares the sealed 150×120×37mm, 680g housing of the CE25.

• 25A (CE25) or 40A (CE40S2) maximum output
• Input 20–32V from a 24V series battery bank
• Output regulated to half the input voltage
• Starts at 0.5V imbalance, stops below 1A transfer
• Input isolation, no extra relay or isolator needed
• Sealed 150×120×37mm, 680g, -20…+80°C

How it works

Many trucks and buses use two 12V batteries in series for a 24V system, and 12V equipment is often connected to the centre tap of that bank. Without correction, this load discharges only the lower battery and the two drift apart, shortening their life. The Charge Equaliser regulates its output to half of the 24V input and transfers energy from the upper battery to the lower one, so the voltage across the lower battery is held equal to that across the upper battery.

Because the 12V loads still draw from the lower battery itself rather than through a current-limited converter, peak currents are limited only by the battery. This suits loads that need a stable 12V supply with high inrush, while the equaliser's 25A or 40A rating defines the continuous balancing current.

Key features

The equaliser switches on when the two batteries differ by more than 0.5V and goes to sleep when the transfer current drops below 1A. It turns off after 20 seconds if the upper battery falls below 10.5V, instantly below 10V, and when the lower battery falls below 6V. Input isolation is built in, so no separate relay or isolator is needed. Both models are based on the BCDC platform, sealed for commercial use and rated for -20…+80°C.

Installation and compatibility

The equaliser is designed for two-battery 24V negative-earth systems. Fit it as close as practical to the lower battery, the one whose negative is earthed, and fuse both input and output wires: 40A for the CE25, for which REDARC recommends the FK40 kit, and 50A for the CE40S2. The red wire connects to the 24V positive, the brown wire to the centre tap and the black wire to chassis earth. Avoid direct steam or pressure cleaning of the unit.

Status indication

Two LEDs show charge status and faults. While equalising, the charge status LED blinks with a duty cycle proportional to current; a very short blink means the batteries are balanced. Flash codes on both LEDs identify over-temperature, under- or over-voltage of the lower or upper battery, and reverse polarity.

Questions and answers