Bruce asked: > Chas says on his Moore 2 Life blog that he has just had his third > alternator fail in five years and has been told "an average of between > 1 and 2 years is about right for an alternator being used every day > charging five domestic batteries". We're still on our first one after > nearly six years of charging four batteries. > > I've never heard that alternators should have such a short life - am I > just lucky?
Alternators on vehicles last much longer than this. In fact, modern vehicle alternators are a very reliable product. I suspect, but have no proof, that most alternators on boats are rather under-specced. On vehicles they are specced to deliver replacement current into a briefly discharged 90 - 100 Ah battery after the start up or to replace the charge during heated screen and lighting use for example. On boats, a similar sized alternator, is usually required to replace overnight use of lights, heating, fridges, water pumps etc into 400 plus, fairly well discharged, Amphours(and judging by some of the boats round here they seem to leave the lights on like people do in their houses on mains supply). If you couple this with a charge controller then you are driving a moderate alternator very hard for far longer than it would normally be required to do normally. My feeling is that the alternators are too small for the requirements placed upon them by modern boats with all mod cons. My first boat, where I marinised my own engine, had only a 60A alternator. That same alternator did a minimum of seven years and may still be on the boat for all I know. However, it was a simple, 12V boat with gas fridge, no Mikuni type heating, and no other power hungry mod cons. My two pennorth anyway. Roger
