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The regulator you use will be important. A fixed voltage regulator is likely to load that alternator heavily as the fixed charging voltage does not really take into account the battery charge state.
The so-called 3-step regulators are a better product, but they can be expensive.
Also, be wary exactly what they mean by a 55 A alternator. Is that continuous rated load? If so, at what cooling air temperature?
16 years ago I bought a small frame 100 A alternator from Ample Power and a 3 step regulator. The alternator, though expensive (then perhaps $300, and the 3-step regulator perhaps $100?) was rated 100A CONTINUOUS at a max cooling air temperature of 91 degC ( 196 degF !!!). I was sceptical at the time, but it is still running. I have seen it hold 60-80A for perhaps 15 minutes and manage it. The alternator output steadily drops as the charge of the batteries recovers, so I can't state a single figure. As a rule, I let this alternator breathe when it is working hard.... I leave the engine cover off the front of the motor and don the ear defenders.
I had experience of another manufacturer's alternator, seemingly rated to 100 A, and it blew in less than an hour, pulling perhaps 1/3 of that.
I have no interest in Ample Power other than saying that the alternator worked for me, and it still works.
Last edited by Rockter; 02-18-2009 at 08:38 AM.