Si to AD Series Alternator High Output Alternator Conversion


If you have an earlier GM 6/12 mount alternator, our AD230 series GM-based alternator can meet your high output charging needs.

First a little alternator history on GM small case alternators. GM started using alternators in the early 60's. Their first alternator was the 10DN series externally regulated alternator. This alternator has what we refer to as the 6/12 mounting configuration, where the two main mounting points are 180 degrees straight across from each other, like clock hands at 6:00 and 12:00.

The distance between the center point of the 2 mounting holes on the 10DN alternator is 6-5/8 inches. GM used the 10DN externally regulator alternator until about 1969 when GM, through its Delco-Remy alternator division, introduced the 10Si series internally regulated alternator. The "SI" in 10SI stands for "systems integrated", meaning the voltage regulator is contained inside the alternator. The earlier 10DN series alternator had an external regulator mounted separate from the alternator. Corvette was the first production vehicle to use the 10SI in 1969. By 1972 all GM vehicles used the 10SI series alternator. They were available in several amperage ratings, from 37 to 61 amps. As power demands rose, GM (with Delco-Remy) made improvements to the 10SI. This new model became the 12SI series. Not only did it have a wider stator and rotor, it also featured larger openings in the back of the alternator, an improved Bridge Rectifier, and a better axial fan to improve cooling. The 12SI series has the same mounting as the 10DN and the 10SI at 6-5/8 inch center to center mounting hole spread. GM Delco Remy used the 12SI series alternator until about 1986.

Then in 1987 came the small case CS series alternators designated CS121 and CS130. The 121 and 130 in their designations refer to the outside diameter of the stator in millimeters. Both the CS121 and CS130 were available in the 6-5/8 inch spread 6/12 mounting configuration. The CS series in the small case was a considerable departure from the earlier 10 and 12 SI series alternator design. The CS units were considered "throw away" alternators in that it was never designed to be rebuilt. The change in design lead to many issues for the CS121 & CS130. The main problems with these alternators center around the bridge rectifier and the rear bearing. Earlier SI series used a finned bridge rectifier to dissipate the heat generated in the diodes during the process of converting the AC current the alternator generates to DC current. The earlier alternator designs used large fins and a powerful fan to dissipate heat. The CS series used a heat sink type bridge rectifier where the heat from the diodes AC to DC conversion process was dumped into the rear housing using a flat surface and heat sink compound. This heat sink area was right next to the rear bearing. The excessive heat would cause the rear bearing to fail prematurely. Coupled with the fact that the new bridge rectifier design stacked the positive diodes right on top of the negative diodes caused so much heat concentration in the rectifier that the rectifier would fail.

Then, in about 1996, they attempted to overcome the problems with the CS130 alternator with the next generation labeled the CS130D series. With numbering the just added the "D" to CS130, but they made a world of improvements, such as larger bearings, opening up the housing, and incorporating dual internal fans for much better cooling. The biggest problem with the CS130D alternator is the fact that they retained the same, in my opinion, junky bridge rectifier design as used in the CS130 alternator. Also the CS130D does not come in the 6/12 mounting configuration so you cannot retrofit the CS130D to earlier GM alternator with 6/12 mount with the later CS130D.

Next in about 2003 they came up with the AD230 alternator. The AD230 alternator is almost the same as the CS130D, they didn't make many changes. They improved the brush holder and rear bearing tolerance ring. They used a slightly wider stator which improved low end output. The biggest and most important change was scrapping of the problematic "stacked" type bridge rectifier. The AD bridge rectifier has both a positive and negative diode heat sinks. These two heat sinks completely separate but with the AD series they separated the negative diodes from the positive diodes and spread the two rectifier halves over a wider area of the alternator's rear housing.