I’m reviving an old thread, sorry.
This spring I had of the three stage alternator regulators fail. In my case it was a Xantrex 84-2006-01 XAR Digital Alternator Regulator that I bought in 2005. When it began to fail the reed switch first became inoperable although the regulator still functioned. Months later, the LEDs stopped lighting
and the alternator stopped charging, but when the large connector was wiggled, the LEDs lit and the alternator resumed charging. After several weeks of wiggling, wiggling no longer worked, and I replaced the regulator with a standard Ford external regulator to get us home from the Bahamas
I read this thread and the most common suspected
cause of failure of these three stage regulators was overheating
My regulator was mounted in the engine compartment of my Pacific Seacraft
34, forward and high on the port side. While it was warm there when the engine is operating, I have touched it and doubt that it exceeded 120°F. After removing the regulator, I could see a crack in the potting material at the Power Sense (red wire) terminal.
I heated the green potting material with a hot air gun until it was soft and leather-like, then while hot I broke it up and peeled it away from the circuit board with a small sharp screwdriver, a dental tool, and a pair of needle nose pliers. Surprisingly, I was able to remove almost all of it with little damage to the board. (I broke off the reed switch, cracked an electrolytic capacitor, pulled the top off a trimmer pot, and pulled off a component that I lost
in the pile of potting chips.)
It appears that the regulator failed due to corrosion
along the side of the circuit board where the reed switch was mounted and where four major terminals were connected. The potting material was a waxy substance. It was not adhesive
. It had separated from the aluminum
heat sink/mounting and from the Power Sense terminal. Water (?) had entered through the crack and corroded the copper traces along the edge of the board and attacked some of the components in that area including the reed switch, several resistors, an IC, and the copper traces.
The regulator was mounted with the corroded edge of the board down. If water was present, I would expect it to collect there. However, I have never seen water in this area of the engine compartment and would have thought it to be one of the driest places on the boat. Either the water got there unseen by me, or perhaps it was condensation
developed during temperature swings.
This is the regulator with the upper potting material removed. The circuit board of the Xantrex regulator was labeled “BALMAR MASTER LP REV K”.
The potting material on the bottom of the board enclosed a large bubble around the two power devices that were touching the heat sink. Although the inside of the bubble was stained, there was little corrosion
here. The staining was confined to the part of the bubble that would be the lowest when the regulator was mounted on the boat.
The bottom of the board was nearly corrosion free.
The corroded area on the top of the board extended from the rectangular pad on the left where the reed switch was mounted, past the four surface mount resistors, the IC, and the single
resistor. It then resumed near the four connectors on the right where it attacked the traces and several more resistors. The reed switch itself was also corroded.