While we're on the subject can someone enlighten me a bit for better understanding. My car has an automotive generator it has been running constantly well over the 100,000 miles that I've driven this PO car while it replaces the nonmarine electricity that has been used. Voiding the warranty doesn't make sense to me because Yanmar does not supply the prop or other attachments that might be connected to the diesel motor. That could be a whole new thread in small print but just asking.
So automotive alternators are fairly weak. Yes they produce 200+ amps now, but they are not designed for heavy lifting, so to speak. Any car with an alternator runs off the battery at all times. The alternator keeps the battery topped up at all times. This is in contrast to older vehicles with a generator, where the generator supplied the needed power, and the battery came in as a supplemental source of power. Automotive alternators have a light duty cycle. Marine alternators have a heavy duty cycle, which means they will be called upon to do more work. They will keep your starting battery topped up, just like in a car, but they will also charge the house bank. This creates a lot of heat and is hard on lightly built alternators like those found in cars usually (yes there are some exceptions but those are heavy/severe duty vehicles). So your alternator in your car will last you until the brushes are worn out, so long as you keep a healthy battery in the vehicle and avoid electrical surges from jump starting or battery removal while the engine is running.
Speaking of battery removal while the engine is running… this will kill an alternator in your car or truck, or boat. Now back in the 60’s when your early alternators were regulated by a pair of relays that cycled the field and stator on and off to produce power, you could get away with this. Those relay type regulators were robust and hard to kill. This was a carry over test from the days of generators, where the vehicle WAS powered by the generator, and pulling the battery was a valid test. Let’s fast forward to today. There are 2 main ways an alternator fails usually. The diode pack partially or fully fails, and the regulator fails. When the regulator fails, this is the easiest to test, you never get the normal 14v at the battery, it usually goes to battery voltage (open regulator). A shorted regulator will produce more than 14v and the average alternator can produce over 30v if not regulated. That will fry your electronics. The second most common type of alternator failure is diode failure. This is much harder to detect, as you need to observe the ripple current to determine failure. When the diodes fail the battery becomes the diode, by sacrificing some of its charge to keep the current to the rest of the vehicle DC. Now let’s say you decide to “test” your alternator by pulling the battery cable (or flipping the 12B switch) if your diodes have failed as soon as the circuit to the battery is lost (open) then you introduce AC current to the DC system. To save space and cost most electronics in your expensive car or boat are not hardened against this. You suddenly get -14v where +14v is expected. Basically the same as plugging the battery in backwards. Lastly if you remove the load from an alternator you suddenly get full current flow through the regulator which will cause it’s demise. This full current inrush doesn’t always kill the regulator the first time you do it (yes it can but not always), what it will do is damage the transistors that are working to keep everything happy. This damage makes them weak, unable to handle the rated loads and this will cause more heat, which will cause shorter lifespans. So don’t do it! Car, truck, boat, helicopter, airplane, or whatever you have that uses an alternator DON’T REMOVE THE BATTERY WHILE ITS WORKING.
Marine alternators also have spark arresters built in. It’s not so much of a big on a Diesel engine but critical for a gas engine. In the case of the alternator I removed, the brush area was sealed completely with a gasket preventing fumes from getting in and sparks from getting out. This is the easiest way to prevent sparks.
