Balmar Alternator Protection Module APM12 12V [APM 12] Fish Magnet It requires a flat section Marine Hardware Accessories It requires a flat section in the hull to be mounted and is excellent for boats traveling at high speeds that want to maintain accurate depth readings Circumference 84 Balmar has introduced a robust Alternator Protection Module which helps to protect the alternator’s diodes and internal voltage regulator against spikes (clamping up to 60V) and sustained over voltage conditions (beginning around 20V for the 12V version) Balmar APM devices meet ISO 16750 2 for Load Dump Protection and ISO 7637 2 for Surge Protection