Pentair 471571 40-Volt Transformer Replacement MiniMax and PowerMax Commercial Pool/Spa Heater 40-Volt transformer replacement Fits Pentair MiniMax with CSD-1 Control and PowerMax commercial pool and spa heater models 525, 750, 900 Also fits Pentair MiniMax and MiniMax Low Nox commercial pool and spa heater models 525, 750, 900