Mastervolt Charge Mate Pro 90 Electronic Charge Relay

The Mastervolt Charge Mate Pro 90 is an electronic charging relay limiting secondary-bank current to 90A, with reverse current blocking.

Current limiting to the secondary bank is what separates a Charge Mate from an ordinary charging relay, and it solves a specific problem. A large flat house bank connected across an alternator will pull everything the alternator can produce, leaving the starter battery last in line. Limiting the secondary side means the primary charges first.

Reverse current is blocked even when the secondary battery voltage is higher, so a charged house bank cannot feed back toward the primary. A mechanical relay cannot do that. It conducts in both directions once closed, so mechanical relays combine and separate on voltage rather than controlling direction.

The electronic design has very low voltage drop, unlike a diode-based arrangement that gets one-way flow at the cost of charging voltage. An optional bypass switch adds emergency-start capability, and it works with alternators or battery chargers as the source. Explore more battery charging accessories.

• Limits secondary current so the starter charges first
• A flat house bank otherwise takes everything
• Blocks reverse current, which a mechanical relay cannot
• Low voltage drop, unlike a diode arrangement