Years ago, I started out with a Perkins 4-108 to replace the Chinese 20 HP engine in my sailboat. The engine had been under water, and I overhauled it, basically replacing the rings, mains, rod bearings, and gaskets. After cutting out and welding in new beds and installing the engine, I put a Mitsubishi 120 amp alternator on it. We used that for about five years. The belts would not last very long, and required frequent adjustment and replacement, but that was OK, as I was mechanically inclined to begin with. My point is, it came from a car, and worked well. I’ve been inside of some “marine” alternators, and while I won’t pretend to be able to tell what kind of metal they are made of, they sure look just like the ones from cars. Since car alternators are a huge market compared to marine engines, I suspect there is little difference, other than prices charged.
If you have a gasoline engine, you should use a marine alternator. It will be based on an automotive alternator, but with the addition of screens that (hopefully) prevent arcing at the brushes from igniting gasoline fumes.
Keep in mind that the higher output alternator will cause additional wear on the belt. 100 amps is about the limit for a single belt. Even then, you must use high quality belts, in order to get reasonable life. We have used Gates “Green Line” and NAPA “Gold” belt with good results. Industrial belt suppliers have available “aramid” fiber belts that will not stretch. They do wear, but at about twice the cost, might be a good investment.
Also, the battery wire attached to the alternator may be too small for the increased amperage. You can install a larger wire or add another wire to the original one. Typically, this wire will be routed all the way to the battery or a terminal strip. One way to reduce the voltage drop (which will be higher with the increase amperage), is to route the battery wire directly to the starter motor, which has a very large cable going to the battery. However, you will now be charging the start battery, not the house, unless a combiner or manual switch is used to connect them during charging, and you will loose the ampmeter on the engine instrument panel unless you attach the charging wire to the meter, and then to the starter battery terminal.
This would be a good time to install a fuse or fuse link in the battery charging circuit. Not many boats have this, and a short at the alternator can cause the wires to the battery to catch fire if shorted.
New Delco 90 amp. One year warranty. Solid 2 1/2 inch pulley for high output at low engine speed and low heat transfer to the front bearing. Two inch “foot” with adjusting ear 180 away from foot, fits most Perkins. Includes built in voltage regulator or set up for use with external voltage regulator (please specify). Note: your wire harness may not fit the terminals, and therfore might require that different wire terminals be placed on your original wire harness. Also, I’m calling this a “Perkins” in paretheses because many times the previous owner has changed the mount, so please check to see that the mounting base of your alternator has a two inch foot. Also, your original wire from the “B” terminal might be too small. Please call if you have any questions or concerns. $175 Call (727) 9430424
New 90 amp alternator. Fits most Japanese engines, including the marinized kubota. 3 1/8 inch between two mounting ears,
with adjusting ear 180 degrees away from foot. Uses same plug for wire harness as Yanmar and others. Solid 2 1/2 inch pulley to prevent heat on shaft from damaging the front bearing. $195 call (727) 943-0424
We have access to high output alternators that will fit many more types of engines. Please call.