Sterling Power APD24 24V Alternator Protection Device

Sterling Power APD24 — 24V Alternator Protection Device

The Sterling Power APD24 is a simple, inexpensive insurance policy for your 24V alternator. When a battery cable comes loose, a fuse blows, or an engine is electrically switched off while running, the alternator is momentarily disconnected from its load. That disconnection causes a dangerous voltage spike — on a 24V system, the spike back voltage can shoot above 33V and potentially much higher — that can instantly destroy the alternator's regulator and any other sensitive electronics on the circuit. Repairs can easily run into the hundreds of dollars.

The APD24 solves this by providing a safe discharge route for that spike. Wired directly to the alternator output, it absorbs the back-EMF event and routes it safely to ground — protecting the regulator and any downstream electronics without interfering with normal alternator operation. Installation requires only light wiring and no modification to the alternator itself. It's compatible with any 24V alternator or splitting device.

This is a particularly important addition to any 24V system running a Sterling BB DC-DC charger, an alternator-to-battery charger, or an advanced alternator regulator alongside a lithium battery bank. Lithium batteries can disconnect abruptly via BMS, and when that happens without alternator protection in place, the resulting spike is a common cause of regulator failure.

Key Specs:

• System voltage: 24V
• Dimensions: 90mm × 90mm × 60mm
• Weight: 0.25 kg
• Certifications: CE, UKCA

The APD24 is not a standalone solution for direct lithium battery connections. For lithium systems, a properly rated DC-DC charger is still recommended.