Big Alternator Power

Boat Repairs in Exotic Locations

Orriginal Delco 12si Layout

Some say that is the true definition of cruising. We heard that many times before leaving on this journey so we tried to keep our systems as simple as possible. Regardless, there is always something. We minimize power consumption as much as possible but we do enjoy a large dose of ice with our small (ahem) dose of rum in the evening. We have a minimum of solar/wind power which usually does fine, but when the engine runs, I want as much power out of it as I can get. I set the plant up with two 100 amp alternators—one for the engine bank and a second for the house bank. After arriving in the Caribbean heat the house bank was left wanting thus a conversion to a 200 amp for the house bank. The big alternator is built on a Delco 12si case and put out power as advertised. Unfortunately the builder had a smaller non-AGM battery bank and thus good success with the stock diodes. We proceeded to blow out sets of diodes regularly when we taxed the system. Not good.

Stock rectifier shown but with new
holes already in the case

210 Amp rectifier
Trial Fit

The fix: I found 210 amp bridge rectifiers specifically designed to “fit” the Delco 12si case and had a couple brought down with Hannah and Cameron. Well “fit” clearly means different things to different folks. Yes they would “fit” in the case and slightly (very slightly) clear the stator and rotor. But they really didn’t “fit” as in none of the holes or electrical connections lined up and lots of in-case mountings and ridges blocked the position. What’s to lose I thought and after some contemplation I busted out the dremel with cutting wheel and went to town. I removed all the pesky ridges and mounting studs, drilled and tapped new mounts, and reset the location of the main power connection. After a bit of aluminum fitting fastened down with JB Weld to provide additional support for the main power stud it all went together. Well almost. I also had to cut off the stock regulator connection so the brush and connections would clear the bridge rectifier.

Aluminum fitting being "welded" to
case for main power stud

Final Assembly, Close but Functional

With some trepidation I mounted it, wired it all up and it didn’t work! Aw crap. Bad news, I had to take it apart again, good news, the problem was simple. A small piece of the toothpick I used to retain the brushes during assembly had broken off when I removed it and was still keeping one of the brushes from making contact. Now loving the power it produces, quickly pushes the bank into absorption stage so the solar and wind can easily finish the job. Time to buckle down and build the backup with the new kit as well. The only problem has been the big stator as well as the electric refrigeration and watermaker clutches all spinning at once threw off the auto helm compass. Now repositioned, I'll report back on that some other time.